01 - Instrumentation and Experimental Techniques
02 - Methods For Structure Determination
03 - Computing in Modelling, Analysis and Design
04 - Crystallography of Biological Macromolecules
05 - Biological Small Molecules
06 - Organic Compounds
07 - Organometallic and Coordination Compounds
08 - Inorganic and Mineral Compounds
09 - Charge, Spin and Momentum Density
10 - Material Science
11 - Structure/Property Relationships
12 - Surfaces, Interfaces, Thin Films
13 - Fiber Diffraction
14 - Small Angle Scattering
15 - Diffraction Physics and Optics
16 - Crystal Growth
17 - Characterization of Defects, Microstructure and Texture
18 - High Pressure Crystallography
19 - High/Low Temperature Crystallography
21 - Topology
23 - Teaching Crystallography
24 - History of Crystallography
OC- Open Commission Meetings
As of September 16, 75 of a possible 128 reports had been received. More will be added as they arrive. Some have been edited by the program chairman. If no report appears for a session of interest to you, you may wish to urge the session chair to action or provide a report yourself.
A drastically abbreviated version of these reports will appear in the next issue of the IUCr Newsletter.
The results of the opinion poll gathered on the last two days of the Congress is currently being transcribed and tabulated and will be posted to the website soon.
01 - Instrumentation & Experimental Techniques
New Opportunities In X-ray Crystallography At Third Generation Synchrotron Sources.(01)
Keynote Lecturer: Carl-Ivar Branden
In his keynote lecture, C. Branden reviewed highlights of the first two years of the X-ray program at the European Synchrotron Radiation Facility (ESRF) in Grenoble where with cryocooling macromolecular structures are routinely solved to 2.5Å resolution from small crystals (10X10X100 to 20X20X20 µm). Energy dispersive diffraction to 120 Kev is used to follow in situ chemistry - for example cement hydration where short lived intermediate phases have been found to have strong influence on the final state. CO release by photolysis from myoglobin has been followed on the nanosecond timescale with Laue diffraction. MAD experiments include Se in E. Coli thioredoxin and Pb + Hg in agglutin on bending magnet beamlines equipped with CCD image intensified detectors. In the latter case the unit cell is 58.5X120X155Å, space group is C2221, resolution is to 2.9Å with Rsym in the 1.5 - 2.5 % range. Returning to the microfocus theme, beams 20µmX20µm in size were used to obtain fibre patterns from 5µm diameter spidersilk. Capillary optics reduces the beamsize to 2µm for diffraction and flourescence mapping of small particles and high pressure diffraction. In diamond anvil cells at pressures up to 100GPa in 10µm3 volumes, pressures equivalent to that at the centre of the earth or deep inside the major planets will be achievable in diffraction experiments. Submicro beam sizes have been demonstrated with Bragg-Fresnel optics. A wide ranging set of examples provided interesting science for all attendees - in physics, chemistry, macromolecular biology and materials science.
Session: Synchrotron Radiation I: Instrumentation & Techniques. 01.02
This symposium was organized around emerging areas of synchrotron radiation research that are heavily dependent on developments in x-ray instrumentation and techniques. X-ray scattering with 100 keV x-rays was compared to neutron diffraction by J. Schneider. The synchrotron x-rays have up to 3 orders of magnitude more intensity available and thus it is possible to work at higher resolution or, in the case of one example, to study surface rather than bulk scattering. H. Ullrich showed how the diffraction of x-ray fluorescence produced by the atoms themselves in a single crystal (Kossel technique) could be used to determine the lattice constants in microvolumes to one part in 100,000, a valuable method when trying to measure strain or residual stress in polycrystalline samples. Per Engstrom described how a combination x-ray diffraction/fluorescence study of a an inhomogenous fly ash particle could reveal chemical as well as structural information on a micron resolved scale with a monocapillary x-ray optic. Z. Barnea presented lysozyme protein diffraction data taken 70 to 100 times faster with a paraboloidally shaped focusing glass capillary producing a 40 micron diameter beam 40 mm from the optic. This holds promise for intensifying beams from x-ray tubes as well as synchrotron sources. S. Lagomarsino reported that a submicrometer line-focus beam of 150 nm width has been recently achieved with a hard x-ray waveguide based on a resonance effect in thin films. And finally, A. Bienenstock closed out the session by describing the scientific opportunity of building the next generation of synchrotron radiation source around the principle of a free electron laser (FEL) that at 8 keV could have a 150 fsec pulse width and a peak brightness of nine order of magnitude more than current synchrotron sources.
Donald H. Bilderback
Session: Detectors & Data Processing I: Macromolecular. 01.04
The evolution of area detectors and data processing techniques for crystallography data acquisition in the last 20 years has been considerable. Film densitometry, gas detectors, TV systems, image plates (IPs) and CCDs have been exploited. All these devices have strengths and weaknesses. Multi-wire proportional counters, for example, have true counting accuracy and
sensitivity but diminishing absorption and spatial resolution (parallax effects) at short wavelengths (although increased gas pressure certainly improves the capability). Due to interests in particular absorption edges of commonly occurring metal atoms in protein crystals, either introduced by soaking (e.g. Hg) or biotech (i.e. Se), for phasing and/or for very high resolution protein data collection, short wavelengths (e.g. 0.7 to 1.0Å) are needed. In particular then, solid state detectors have been a principal focus of development, matched by higher energy synchrotron machines. The strengths of CCDs and IPs include good sensitivity and preserved imaging capability with short wavelengths. Very impressive results have been obtained with on-line IP, very large IP (Weissenberg and Laue) off-line and on-line CCD devices. It has become possible, using intense, tunable synchrotron radiation, to readily measure multiple wavelength data (e.g. at 2 or 3 wavelengths, although at present users usually measure more wavelengths), to reach atomic resolution (i.e. 0.95Å resolution up to a molecular weight 'ceiling' so far of ~ 25-30 kDa) and record time-slicing dynamical protein crystallographic data. In chemical crystallography, area detectors (and associated data processing software) in the home laboratory are beginning to make a major impact improving the precision and/or throughput of structures. At SR sources the combination of the 'Princeton' CCD (S Gruner) and a high photon energy beam is a powerful combination as demonstrated by M Helliwell at CHESS with nickel octahexylphthalocyanine (Acta Cryst B in press). Helliwell also used a fast-slicing CCD (N Allinson) and IP to follow a temperature pathway towards the liquid crystal phase. In neutron crystallography the use of IP's has started in Japan (N Niimura et al.) and at the ILL (C Wilkinson, M Lehmann et al.). Further evolution of detectors is important; the combination of the large aperture of IPs with the better duty cycle of CCDs is required. Tiling of CCDs' into a 3x3 mosaic (E Westbrook, APS) has recently been exploited. Increased count rate capability and a move away from full frame readout should be possible with the 'pixel detector', a silicon based device with independent pixel counting chains. N H Xuong presented first results in the microsymposium of a prototype device involving the recording of the direct beam, as a test, into one of the counting chains. Ultimately a 1000 X 1000 pixels device (each pixel is around 150 µm square in size) will offer a major leap forward in detector performance. There are strong efforts and expertise with pixel detectors, as well at San Diego/Berkeley (Xuong/T Earnest), in Princeton (S Gruner) and Imperial College (G Hall). Pixel detectors can have a major impact in time-resolved experiments (count rate capability), MAD (faster data sets from brighter sources to tackle e.g. a 3-D structural molecular biology project for the human genome) and in atomic resolution data collection in raising the molecular weight ceiling above 25-30 kDa, referred to above, (fine phi-slicing for optimal peak to background of reflections without the need for full frame readout). In another application area, the ability to use smaller protein crystals, it is worth noting that since absorption is not a problem due to the small sample size, that longer wavelengths can be used (e.g. ~ 1.5 Å) quite readily for native and 'regular' derivative data collection, where MWPCs can image without parallax problems, and with the detector noise contribution being zero and where count rates are manageable (small sample volume). Detector investment, as well as data acquisition and processing software, at SR sources is vital. This is vital so as to take advantage of commercial developments and for the pixel detector development.
J. R. Helliwell
Session:Sychrotron Radiation III: Applications Time Resolved Micro-Crystal High Energy. 01.05
Symposium talks covered both powder and single crystal diffraction as well as newer areas, the use of diffraction anomalous fine structure/(J.L. Hodeau) and a device to give circularly polarized SR of either helicity (J.C. Lang). Time resolved powder diffraction (angle dispersive) has allowed Rietveld refinement of the geometrical parameters of atoms in an alumino phosphate structure, so that the time course of thermal dehydration could be followed on a video. (J.C.
Hauson). Third generation synchrotrons, together with new detectors (CCD or image plate) and new small or micro collimation systems have allowed diffraction patterns for samples 1 micrometer or smaller in dimensions, to be recorded and processed to give useful structure data. R. Neder described the use of a micro-manipulator and scanning electron microscope to mount these tiny crystals.
Session: Electron Diffraction From Surface LEED, RMEED, PED, etc. 01.08
The Minisymposium on Electron Diffraction from Surfaces emphasized the diversity of approaches to surface structure analysis using various forms of electron diffraction. Some of the techniques resemble x-ray diffraction in the sense that the source of diffracting electrons is located far from the sample, giving rise to incident plane waves. This applies to low-energy electron diffraction (LEED), which is the oldest and most productive technique for surface structure determination and which was described by K.A.R. Mitchell. It also applies to reflection high- energy electron diffraction (RHEED), which is rapidly developing into a powerful competing technique, described by A. Ichimiya. An exciting novel approach is the point reflection microscope, presented by J. Spence. Here the source of electrons, a field-emitter tip, is located within hundreds of Angstroms of the surface: it produces a diverging electron beam, multiplied into several divergent diffracted beams which produce images carrying three-dimensional structural information that remains to be interpreted. Other techniques use point sources of electrons that are located at atomic sites of the surface itself. Thus, photo- and Auger-electron diffraction, discussed by S.A. Chambers, both utilize the diffraction of electrons by atoms surrounding the emitting atoms to collect structural information. These two techniques in addition allow the energy discrimination of electrons coming from different elements, or even from the same element in different chemical environments. Another point source technique, which however lacks chemical discrimination, is Kikuchi electron diffraction, described by C.-M. Wei. These last three techniques were also presented in their "holographic" form: the diffraction patterns can be viewed as holograms, which often can be inverted by suitable Fourier transformation to produce real-space three-dimensional images of local surface structures. These images are invaluable as starting points for more refined structural determination using trial-and error searches. The effects of multiple scattering and the twin image problem on inversion schemes were discussed by several speakers, and emerged as crucial theoretical issues.
Michel Van Hove
Session: Neutron Scattering II: Instrumentation & Techniques. 01.09
This was the first ever microsymposium at an IUCr meeting for this rapidly growing technique capable of determining the perpendicular structures (and possibly the lateral structures) of monolayer magnetic, surfactant and polymer films. New reflutaneters at most major neutron scattering centers have expanded the range of problems that can be studied with this technique. The meeting had excellently presented papers over most of the range. One highlight was the paper by Hamilton, Hayter and colleagues from Oak Ridge Natl. Lab. which showed beautiful hexagonal diffraction patterns from aligned surfactant micelles under Poiseuille shear flow. The "crystallites" ordered at the quartz surface have mosaic widths of only a few degrees but the order does not extend for more than a few microns from the surface.
John W. White 02 - Methods For Structure Determination
Mad Phasing Theory And Practice.(02)
Keynote Lecturer: Wayne Hendrickson
In his keynote address, Prof. Wayne A. Hendrickson, Dept. of Biochemistry and Molecular Biophysics, Columbia University, summarized the development and current status of multiwavelength anomalous diffraction (MAD) phasing of x-ray data from macromolecular crystals. The potential of anomalous scattering has long been recognized, but it is the availability of readily tunable synchrotron sources that has led to the explosive growth in the number of macromolecular structures solved by the MAD procedure in recent years. Choice of suitable wave lengths for collecting data enables the investigator to exploit the relatively large changes in both the real and imaginary components of the atomic scattering factors at energies near the binding energy of the inner electrons of the heavier atoms (Z greater than 20). Such elements are present in some proteins, and in any case they can be introduced into proteins by various methods. For example, Se can replace S in methionine which can then be incorporated during protein synthesis, and brominated nucleic acids can often be complexed with proteins. Atoms in the lanthanide series of elements exhibit particularly strong anomalous scattering and substituted for Ca in a protein have proved very effective in MAD phasing, and in general the heavy atom derivatives used for MIR phasing can also be used in the MAD procedure. Cryogenic techniques for collecting x-ray data, and careful attention to equalize absorption effects have greatly improved x ray diffraction data from crystals of macromolecules in recent years. Although anomalous scattering is anisotropic the effect has not limited the use of the MAD procedure. Indeed, the method is becoming in many cases the method of choice for ab initio phasing of x-ray data from macromolecular crystals.
Direct Methods in Real and Reciprocal Space. (02)
Keynote Lecturer: George Sheldrick
Professor Sheldrick presented an overview of the historical development of direct methods of structure solution, work which set the stage for the recent advances that have allowed the extension of direct methods to larger and larger structures. In reviewing the early tangent-formula based approaches, he emphasized that what made techniques work in the hands of users was often a combination of methodological advances with the implementation of those advances in robust and user-friendly computer programs. The recent excitement in the field centers on the Shake and Bake technique developed in Buffalo, which Professor Sheldrick reviewed in detail. This technique, in which the process of phase refinement cycles between real and reciprocal space, has now successfully determined phases for small proteins, but it is limited to structures for which data can be measured to atomic resolution. Extension to structures for which atomic resolution data are not available will require the inclusion of some other form of phase information, such as anomalous scattering or location of heavy atoms by Patterson techniques. Professor Sheldrick presented a brief introduction to his own implementation of this methodology, a new computer program with the charming name of Half Baked. This fine overview of the history and current status of the field of direct methods left the audience with a real feeling that there is reason to hope that the solution to the macromolecular phase problem is in sight.
Session: Difficult Crystals: Data Collection, Reduction & Refinement. 02.01
World wide, diffraction systems are being used by newcomers to crystallography with only limited experience, and it was clear at Seattle that if the small molecule community frenzy to purchase CCD diffractometers is sucessful, the rate of structure determination will rise by an order of magnitude in the next few years. Against this background it seemed timely to re-air old experiences of the difficulties that can befall the small molecule crystallographer, and show how modern techniques can help cope with them. It was clear from all the talks that modern hardware and software is up to the task, but that the problem is knowing how to get the best out of them. Dietmar Stalke made the low temperature handling of sensitive crystals seem quite practical as a routine operation. Larry Falvello warned of the dangers involved in lowering symmetry, and the importance of treating solvent of crystallisation. Carolyn Brock talked about the problems with structures having Z'>2 (i.e. more than two molecules in the asymmetric unit). Often the crystals are of poor quality, and the motifs related by pseudo-symmetry. When she asked for a show of hands, more than 60 people have unpublished structures with Z'>1, presumably because they don't conform to Acta minimum requirements. Since the Journals Commission is looking for ways to reduce the size of Acta C, this leads me to speculate that perhaps they should only publish structures with R greater than 7%, or having at least one weird bond length. After all, other structures can be regarded as 'normal', and so safely be deposited electronically. Geof Jameson tried to de-mystify the treatment of twinning, and explained that only in extremis was it necessary to 'loose' the crystal. Merohedral and pseudo merohedral twinning can often be dealt with quite routinely from serial diffractometer data. Curt Haltiwanger addressed the problem of what to do when TREF 5000 failed to solve a structure, and came up with the answers SIR92 or Shake&Bake, showing yet again that amicable competition between software developers was good for the whole community (its also good to see effective competition about to enter into the hardware market). Nigam Rath showed that with modern area detectors it is possible to work under ordinary laboratory conditions with very small or very poor quality crystals, thus providing the service crystallographers with yet more sticks with which to beat their own backs.
Session: Direct Methods of Phase Determination. 02.03
The focus of the Microsymposium was well summarized by Dr. Fan Hai-fu, the transition of direct methods to problems outside of their traditional areas of application. These include transitions from small to large molecules, from single to powder crystals, from periodic to incommensurate structures and from X-ray to electron diffraction data. Dr. Isabella Karle opened the session with a very interesting presentation on her peptide structure determination work, sharing much useful advice. Other highlights in the session included the description by Dr. W. Lasocha of several successful applications of direct methods to powder diffraction data and the talk by Dr. R. Miller on the Shake-and-Bake approach, which has now been successfully used in the determination of several large small molecules and proteins. Most striking was the large number of talks related to new direct methods approaches and new applications that were presented in Microsymposia other than the Direct Methods one. This clearly shows that the goal of extending direct methods beyond their traditional small molecule applications has now been realized and acknowledged.
Session: MAD & MIR Macromolecular Phasing. 02.04
Phase determination in macromolecular crystallography remains an intellectual and experimental challenge. For new structures the phase problem is generally solved by reducing the size of structure to that of a small number of strong scatterers introduced into the macromolecule. Multiwavelength anomalous diffraction (MAD) is being used more and more often now that appropriate synchrotron facilities are available. MAD eliminates the lack of isomorphism problem that is often the biggest impediment to isomorphous replacement (MIR). The mathematical similarity of MAD and MIR is being exploited in new sophisticated phasing programs by Axel
Brunger and Eric DeLaFortelle and Gerard Bricogne for refinement of heavy atom parameters and computation of macromolecule phases. Brunger further showed how accurate high resolution electron density from MAD phasing can be used to evaluate the success of model refinement.
Session: Structure Determination Using Powder Data. 02.05
This session highlights the tremendous progress made in solving crystal structures from powder data and the diverse methods utilized to obtain the results. These included straight forward application of Patterson functions and 'direct methods' as for single crystals, Monte Carlo methods and use of specialized chemical knowledge. Specialized software for use in all stages of powder work is now available and their application to solution of drug structures zeolites and extended solids was demonstrated. Of particular importance was the fact that many structures can be solved using data obtained with regular x-ray powder diffractometers even with a limited amount of data. Interest in this topic exceeded expectations as a standing room crowd with every seat filled remained almost to the last talk.
Session: Macromolecular ab initio Phasing. 02.06
Peter Main opened the session on ab initio phasing of macromolecules with an overview of progress and challenges in the field. He believes that the low resolution phasing problem is effectively solved to a resolution of 12A (which was supported by results presented by Vladimir Lunin), and that density modification methods are effective starting from about 5A resolution. So the challenge is in the medium resolution range, which he is approaching through histogram matching of wavelet transforms. Gerard Bricogne argued that, if we cannot even refine a protein model without stereochemical information, we cannot hope to solve protein structures ab initio without that information, which he is working to include in structure factor statistics. Masao Fujinaga and Piet Gros each presented an alternative way to use stereochemistry by adding appropriate energy terms to random atom models, refined either by genetic algorithms or molecular dynamics. Chris Gilmore showed us that maximum entropy/likelihood techniques applied even to electron diffraction data. Finally, two speakers gave us reason for optimism by reminding us that current techniques, imperfect as they are, will already solve structures with a favorable parameter/observation ratio: non-crystallographic symmetry averaging can solve virus structures (Michael Chapman), and traditional direct methods can solve protein structures with atomic resolution data (David Smith).
03 - Computing In Modelling, Analysis And Design
Session: I: The Internet. 03.01
The Internet increasingly pervades all aspects of one's everyday professional and private life. The net's killer application, the World Wide Web, has fundamentally altered many aspects of information delivery since the 1993 IUCr Congress in Beijing. The microsymposium thus highlighted the expectations and difficulties that crystallographers can have from using Internet technology and overviewed recent technical developments significant to crystallography. The IUCr has considerable commitment to scientific publishing and the chairperson of its Electronic Publishing Committee went through advantages, disadvantages and cost factors of electronic information compared to the conventional print on paper and use of libraries. In particular the difficulties with electronic publishing were detailed in relation to the requirements for IUCr Journals. A strategy for scientific publishing was outlined where the active participation by relevant IUCr Commissions was considered essential, and one practical scenario was detailed. It is always interesting to observe how technology revolutions influence the working styles of other scientists and consequently the overview of the role of the World Wide Web in computational and pharmaceutical chemistry provided food for thought. In particular the trials in running scientific conferences entirely electronically over the Internet indicate one way to diversify in the future leading to savings in cost. But for the present one needs to know what resources and tools are currently available, and particularly appropriate for the professional crystallographer. So we were treated to a tour of databases, information and teaching sources, trials in electronic publishing, a brand new Crystallographer's Guide to Internet Tools and Resources, searching, mail servers, etc. Two technology developments certain to have considerable impact on Web use by crystallographers were presented. One is the Java programming language and the other VRML, the Virtual Reality Modelling Language. Both were demonstrated in applications of interactive graphical representations of molecules and crystals distributed over the Web, and the advantages and disadvantages of these general purpose (net based) tools over dedicated local implementations were made particularly clear. The session chairman was H.D. Flack, the vice-chairman, Y. Epelboin and the speakers were E. N. Maslen, G.D. Purvis, Y. Epelboin, J.C. Huffman and A. LeBail.
Session: Internet Workshop
As a follow-up to the microsymposium on the Internet, a Workshop was run to allow hands-on familiarity with many types of Internet applications to be obtained. The workshop chairman had gathered together a group of enthusiastic tutors who each gave brief (5min) presentations of their area of Internet knowledge and experience. This was followed by hands-on demonstrations using UNIX workshations, pcs and mac. The organizer and tutors had also put together a comprehensive hypertext documentation in the form of a series of World-Wide Web files called 'A Crystallographer's Guide to Internet Tools and Resources' complete with a Table of contents and indexes. A printed version of this Guide was distributed to participants and will soon be available to the general public. The topics treated ranged from the simple and commonplace to those with high interactivity and advanced graphics. The World Wide Web was given a prominent place in which search engines, addressing modes, browsers, authoring tools, markup language (HTML), writing styles for hypertext and the treatment of non-Latin alphabets (e.g. Kanji and Cyrillic) were treated. The advanced interactive and graphic W3 applications generated by the use of the Java and VRML languages attracted considerable attention and this was also the case for the Perl scripting language so frequently used in server-side applications. It is a general observation that especially in the database area that the W3 is being increasingly used as a convenient graphics and distributed front end to existingand new programs installed on a server. The accessdoes not necessarily need to be world wide but can be limited to in-house applications by the use of passwords and access control. The Internet has been used in the organization of crystallographic conferences, for the distribution of information on Crystallographic associations, for access to the World Directory of Crystallogaphers, IUCr Journal submission and consultation, and by use of the News-group (sci.technique.xtallography and bionet.xtallography). A further important development has been the extension of Internet e-mail to allow the transmission of documents other than simple text messages. This is achieved by the MIME protocol allowing true and simple platform-independent multi-media e-mail. A Crystallographer's Guide to Internet Tools and Resources is freely available over the World Wide Web at URL: http://www.unige.ch/crystal/w3vlc/int.index.html and in thenear future in printed form.
Session: II: General Advances & Application: 03.02
The Microsymposium, an Open Commission Meeting of the IUCr Commission on Crystallographic Computing, provided a general overview of new developments in the field. New softwares (SIRWARE by G. Cascarano) and algorithms (G. Zanotti) for the direct solution and the refinement of small and macro-molecules from single-crystal data and of small molecules from powder and electron diffraction data, were presented. The most outstanding development reported is the possibility of extending automatic direct-methods techniques from the traditional small-molecule field to more difficult problems, including single isomorphous protein data. The second general topic was that of databases and data exchange. The lively presentation of B. McMahon on the usefulness and versatility of the CIF files, as a standard means for exchanging crystallographic data was followed with great interest. The two last communications were on highly innovative topics, software for charge density studies (T. Richter), which are becoming more and more popular with the increased availability of accurate low temperature data, and techniques for deriving force-field parameters (S.J. Maginn) for the modeling of weak interactions which are essential for crystal engineering and structure prediction.
Session: III: Macromolecular Map Fitting & Modification. 03.03
The session was opened by K. Cowtan with a brief overview describing the current status of density modification methods, their successes and limitations, and the convergence between the map modification and map fitting disciplines. K. Das then gave an example of electron density averaging between crystal forms in the structure determination of HIV1-RT. His innovations included local scaling of the related densities, averaging omit maps to reduce bias, and the use of a reciprocal space convergence criterion. These techniques combine to reduce the problems of bias to an initial structural model. D. Turk described his 'Main' package, which combines model building, refinement, and density modification in an integrated manner. The continuous consultation of the experimental observations allowed by this method facilitates structure building and reduces errors. C. Carter reported a difficult structure solution using the molecular replacement in which bias to the starting model was a serious problem. His approach combined non-crystallographic symmetry averaging using maximum entropy maps, and phase permutation using likelihood ranking, in a system where conventional density modifications failed to remove the model bias. A. Szoke described a new method of combining real and reciprocal space information through a wavelet-related technique which he describes as a holographic method. Some test calculations using his program, 'Eden', demonstrate the power of this method to solve a structure from a very small known fragment. This was widely commented on as the most exciting talk of the session. D. McRee described the latest facilities for map fitting in XtalView, including automated fitting of main chain and side chain residues. T. Oldfield went on to talk about his work towards the semi-automation of the map fitting process, including methods for automatically identifying secondary structure features in the map, connecting these features, fitting the sequence, and then fitting and refining the main and side chains. His knowledge based approach, implemented in Quanta, builds on all the information available from solved structures in the PDB. The session was very well attended, with only standing room available for much of the time, and generated a good deal of interest.
Session: VI: Materials Research. 03.06
This session illustrated how effectively molecular simulation can now contribute to crystal structure determination. Simulated annealing was presented as a means of circumventing the phase problem in structure solution by allowing direct refinement of initially random models. C. M. Freeman's overview described compelling applications of this direct space structure solution route to both inorganic and molecular systems. To accelerate model-building approaches or as an aid in rationalizing structures yielded by simulation, both Y. Le Page and C. M. Kölmel presented methods to determine space group symmetry from an initially triclinic description; the latter demonstrated an essentially fully-automatic way to derive unit cells and then full space group symmetries and asymmetric unit descriptions from discrete models. Significant progress in the prediction of molecular crystal structures was described by M. U. Schmidt. N. Harrison illustrated how periodic Hartree-Fock calculations can rationalize the complex behavior of ostensibly simple oxides and yield a range of computed properties. Simulation of the geometries and energetics of point defects in oxides was addressed by R. A. Jackson. Molecular simulation, as evidenced in the variety of techniques mentioned in the session, clearly has an important place, not only in optimizing the benefits that can be extracted from crystallographic results, but also as a major aid in crystal structure solution and refinement.
04 - Crystallography of Biological Macromolecules
The Structure of Bovine Mitochondrial F1-Atpase- An Example of Rotational Catalysis. (04)
Keynote Lecturer: A.G.W. Leslie
Andrew Leslie presented the Monday Keynote Lecture, " The structure of bovine mitochondrial F1-ATPase- An example of rotational catalysis?" The F1-ATPase, a 350 kD assembly responsible for the synthesis of ATP consists of 3 a/ß dimers, and a single T subunit at the center of the assembly. The F1-ATPase is complexed in cells to a transmembrane gated proton channel (Fo) that provides the driving force for the synthesis of ATP. The structure of ATPase is the first crystallographic analysis to reveal how chemical and mechanical transformations are coupled in proteins. Dr. Leslie showed us that the different three a/ß pairs of subunits, although identical in sequence, assume three different conformations in the assembly. At one active site ADP + Pi is bound, at one ATP is bound, and the third active site is empty. Apparently, the active sites of the F1-ATPase alternatively assume a conformation 1) complementary to substrates, 2) complementary to product, and 3) open, as a function of the position of the T subunit. It is clear from the analysis that the synthesis of ATP is promoted by local complementary to ATP. The structure beautifully validates the conclusions about the action of the F1-ATPase based on biochemical studies. The rotation of the T subunit, which causes the subunit holding ADP + Pi to change into a conformation complementary to ATP, is thought to occur through the action of the proton pump, by a mechanism yet to be elucidated. Reference: Abrahams, J.P., Leslie, A.G.W., Lutter, R. & Walker, J.E. (1994). Structure at 2.8 resolution of F1-ATPase from bovine heart mitochondria. Nature 370:621-628.
The Intergration of Structure-Based Drug Design and Combinatorial Chemistry For Efficient Drug Design. (04)
Keynote Lecturer: Ray Salemme
Ray Salemme described some of the major challenges and problems encountered in structure-based drug design, and ways that combinatorial chemistry can expedite the discovery of lead compounds that are candidates for iterative improvement. Ray reviewed a series of thermodynamic and structural studies of ligand binding to strepavidin, which binds biotin and analogs of biotin with extremely high affinities. These studies clearly show the challenging difficulties of rationalizing and predicting binding constants. Since the free energy of binding includes both enthalpic and entropic components, subtle variations in interactions between ligands and the protein, coupled with charges in solvent structure and conformational freedom, can produce large and unpredictable changes in binding constants. The predictive power of current modeling approaches is quite limited, even when detailed structural data are available. Consequently, structure-based drug design proves to be most powerful when used in an iterative manner to improve the properties of lead compounds. One method now being used for identifying leads involves automated screening of compound libraries produced by combinatorial chemistry. Ray described a novel combinatorial approach for developing libraries of lead compounds to block the active site of thrombin, a serine protease involved in blood clotting. Thrombin has three major subsites within the active site of the enzyme. By combining multiple chemical groupings that might interact with one or more of these three subsites, he has produced lead candidates that were then optimized by structure-based techniques to produce potent and selective inhibitors of thrombin. One of these thrombin inhibitors will soon be advanced into clinical trials.
Protein Conformational Analysis. (04)
Keynote Lecturer: Janet Thornton
Janet Thornton of Birkbeck College London focussed on developing approaches and software tools that facilitate automated validation of protein structures and aid in the analysis and classification of macromolecular structures. Methods for validating structures that are based on knowledge derived from known structures were discussed as was the effect of including information from recently solved, atomic-resolution protein structures. A hierarchical system, CATH, was presented that describes protein structures in terms of class, architecture, topology, and homologous superfamilies. It was clear that as the number of known protein structures grows, our need to analyze properly these structures will increase dramatically if we are to succeed in mining the wealth of information to be found in our structural databases.
Session: Enzymes. 04.01
The microsymposium on enzymes can be summed up under the themes of unity and diversity. Unity in the strategic importance of structure for understanding mechanism, first exemplified 30 years ago with lysozyme, as Greg Petsko reminded us, and diversity in the vast number of enzymes and substrates available for study. David Barford's talk on protein phosphatase demonstrated beautifully the advances in understanding the mechanisms of both the tyrosine phosphatase and the serine/threonine phosphatases through structure determinations of three principal players. Betsy Goldsmith followed with an account of the regulatory properties on MAP kinase. Moving from proteins to DNA as substrate, Xiaodong Cheng's talk on DNA methyl transferase provided an example of substrate modification before catalysis. In a base flipping mechanism, the enzyme takes the base to be modified into the catalytic site and replaces the vacant site on the DNA with a loop from the protein. Bauke Dijkstra completed the analysis of proteins that act on macromolecules with a description of muramidase, the extraordinary all helical doughnut shaped protein that catalyses the hydrolysis/transglycosylation reaction. This chemically attractive mechanism had been considered for lysozyme but ruled out on structural and chemical evidence. It is interesting to see that other enzymes can exploit it.
Turning to enzymes that act on small substrates, Charles Hasemann described the recently determined structure of the bifunctional enzyme, 6-phosphofructo-2-kinase/fructose 2,6 bisphosphatase which showed that the kinase domain resembled adenylate kinase and the phosphatase domain phosphoglycerate mutase and that the catalytic sites on the two domains were well separated. The final two talks illustrated some unexpected themes. The structure of urate oxidase, described by Natalie Colloc'h, exhibits a 16 strand M barrel in which each of the four subunits contributes four strands. The catalytic site, identified from inhibitor binding studies, shows no metals, no cofactor and no functional amino acids. The enzyme appears to act by correctly locating the two substrates, urate and oxygen. Lynne Howell ended the session with a demonstration of the significance of structure for mechanism in the studies on arginosuccinate lyase/p crystallin. Genetic studies had shown that residues important for catalysis are located on parts of the chain far apart in sequence. In the structure these are far apart in space on the subunit but brought together in the tetrameric assembly, thus providing an explanation for intragenic complementarity, a mechanism in which an active multimeric protein can be assembled from monomers produced by two different inactive mutant alleles of the same gene.
Session: Metalloenzymes. 04.02
Metalloproteins have had a historic place in the development of macromolecular crystallography. This meeting showed the remarkable diversity of metalloenzyme structures. The past few years have seen a flowering of this field, with the first structures of vanadium, nickel, cobalt and tungsten-dependent enzymes; the spectacular detail of the multi-metal cytochrome oxidase structure; and the strange twists of metalloenzymes obtained from archaebacteria. Evelyn Jabri opened the Metalloenzymes microsymposium appropriately with the nickel enzyme urease- appropriately because this was the first enzyme ever to be crystallized, even though it was not known to contain nickel until many years later. She showed that this is a beautiful example of a metalloenzyme in which an unusual metal geometry is exquisitely defined by its protein surrounds. Other presentations ranged through enzymes dependent on iron (sulfite reductase, by Brian Crane and a PCB degrading dioxygenase by Yukio Mitsui), copper (nitrate reductase, by Elinor Adman) and zinc (glyoxalase I, by Alex Cameron). Perhaps the highlight, however, were the molybdenum-dependent enzymes of the two final presentations, by Jeffrey Boyington and Herman Schindelin. It is not long since molybdoenzymes seemed intractable. These two examples however, formate dehydrogenase and DMSO reductase, illustrated several special properties of the metal, including unusual chemistry, and unique ligands. Here they include molybdopterin guanosine dinucleotides and (in formate dehydrogenase) a selenocysteine residue. Most spectacular of all, Herman Schindelin finished the session with the first view of the complete nitrogenase complex, comprising both the Fe/Mo and Fe proteins. The trick to obtaining a stable, crystallizable complex seemed to be the use of ADP and AlF-4 as a non-hydrolyzable transition state analogue.
Session: Hot Macromolecular Structures I. 04.07a
There was a wealth of new structures described in the submitted abstracts. Selection of 10 topics for oral presentation was not easy. The programme included 3 intracellular regulatory molecules, 3 extracellular recognition molecules, 2 molecules of medical importance in response pathways and 2 new enzymes. Each of these structures revealed some new information but within a framework of established knowledge of structural principles.
The structure of the 26 nucleotide RNA pseudoknot nanomolar inhibitor of reverse transcriptase described by Craig Kundrot showed that nucleic acids as well as proteins have an ability for domain swapping which may or may not be significant for biological activity. The two following structures of intracellular regulatory proteins both exhibited all helical topologies. Cyclin H, the component of the cell cycle activating kinase (CAK) and described by Kyeong Kim, has a similar structure to Cyclin A, despite only 12% sequence identity, but there are sufficient differences to indicate that its interactions with CDK7 should show different features to those of cyclin A with CDK2. Bcl-XL, described by Steven Muchmore, is a component of a family of proteins that modulate apoptosis. The structure has been solved using a combination of NMR and X-ray diffraction. The helical fold is similar to the structures of diphtheria toxin and the globular domain of colicin, suggestive of a role for this protein in transmembrane events, but the structure also contains a long (about 43 amino acids) disordered loop with possible involvement in control by phosphorylation. The programme then moved to the cell membrane with a description of the T cell receptor by Christopher Garcia. The structure has the familiar immunoglobulin fold for the 2 variable and the 2 constant domains but there are with sufficient differences from the standard fold and the structure could only be solved by MIR.
The next structure, colicin A, by Michael Wiener provided one of the highlights of the session and showed how we can still be delighted and surprised by new structures. The channel forming bacterial toxin has 3 distinct domains involved in receptor binding, translocation and pore formation linked by an extraordinary long (160 Å) helical coiled coil. The crystals were 80% solvent and the structure had been solved by engineering cysteine residues. It seemed remarkable that such a non-globular structure had crystallized. The next structure also showed equal surprises and biological significance. Vladimir Malashkevich's structure of the pentameric glycoprotein heptad repeat domain (45 amino acids) from the cartilage oligomeric matrix protein showed 5 helices 73 Å in length wrapped around each other to form a superhelix with a hydrophobic channel in the centre and a polar exterior. A chloride ion was located in the centre of the core. On exposure to xenon gas, 8 xenon atoms were located at defined sites in the channel. This is the first example of a 5 helix bundle at atomic resolution and the structure has significant implications for the structures of ion channel proteins such as the nicotinic acetylcholine receptor. Trevor Greenough described the 5 fold symmetric C reactive protein involved in acute phase response, a challenging molecular replacement solution. This speaker remained remarkably cool despite problems with the projector that resulted in his last 6 slides being placed in random order. Vivienne Lee described the structure of a 30K C-terminal fragment of T fibrinogen. Both these last 2 structures provide definite clues for function with medical relevance.
The session ended with 2 enzyme structures. The human lysosomal sulphatase described by Charles Bond, is an enzyme involved in processing N-galactosamine-4-sulphate. The structure, the first example of this class of enzymes, showed 2 domains one of which with 10 strands of M sheet resembled unexpectedly the structure of alkaline phosphatase, especially in the region of the catalytic site. The final structure of apopain, a cysteine proteinase involved in apoptosis and described by Jennifer Rotonda, showed, as expected, similarities to ICE but with sufficient differences in certain inhibitor peptide binding subsites that will certainly be of interest to the pharmaceutical industry intent on manipulating this biological pathway.
Session: Macromolecular Assemblies. 04.08
The session started with a brief description by the chairman of the pyruvate dehydrogenase complex of which the icosahedral core - of the Bacillus stearothermophilus enzyme - had just been solved at 5 Å resolution by Tina Izard. The outer diameter of the 60-meric particle is 230 Å, the inner diameter 140 Å while there are large pores of ~55 Å cross section which allow CoA to diffuse inside and find the acetyl group bound to lipoyl domains which swing around the core in a very dynamic fashion.
The next speaker was Stephen Burley who described the fascinating complex of the "TATA Box" bound to the TATA Box binding protein (TBP) and the Transcription factor TFIIB. In the complex, crucial for the initiation of transcription in all living organisms, the TBP-TATA binary complex has virtually the same structure as in the TBP-TATA-TFIIA ternary complex. With the knowledge of the TBP-TATA-TFIIA complex solved in other laboratories, the quaternary TATA TBP-TFIIA-TFIIB could be depicted and a framework for future experiments and discussions was obtained, including the role of TATA box-binding protein associated factors (TAFs) of which two structures were reported.
Next, Ada Yonath described the heroic efforts to reveal the structure of the ribosome in atomic detail. A whole series of poly-heavy atom derivatives had been tried and yielded new electron density maps at low resolution. The goal of obtaining better ribosome crystals via new purification methods was for a moment rewarded by crystals diffracting to 1.9 Å. These turned out, however, to be of a "degradosome" multi-protein complexes of 250,000 dalton associated with ribosomes. Although not the real goal still a most remarkable achievement.
Steve Sprang described the intricate structure of the trimeric G protein Gi ßT. The structure was solved by a combination of MR, MAD and MIR. The -component had been studied in various complexes and its catalytic mechanism as well as regions responsible for important conformational changes were identified. The ß subunit contained seven propeller motifs plus a number of important helices. The ß subunit is much smaller and only interacts with ß, not with . The ß subunit has numerous interactions with ß in such a manner that it stabilizes the GDP form of Gi . Numerous questions still need to be unraveled but mapping the wealth of biochemical data onto the structure is providing a rapidly increasing degree of insight.
The next speaker was Pedro Alzari who described the organization of the wonderful cellusome. This arrangement provides "up to nine hydrolytic enzymes on a string" outside the cell - all attacking cellulose. The scaffolding protein is CipA which has a "dockerin domain" which allows it to bind to the outer membrane. It contains nine dockerin receptor domains which each can bind a hydrolytic enzyme which all have a dockerin domain at the C-terminus. The set of enzymes on a string has no constant stoichiometry yet has apparently an evolutionary advantage.
John Tainer described the structure of a pilin dimer in which two subunits are interacting via an anti-parallel coiled coil, burying 1100 Å2 of surface. Yet, as a result of an extensive search for a model of the pilin fiber, this interaction is probably a crystallization artifact and the organization of the pilin in the fiber is a quite different organization with five subunits per turn, a pitch of 41 Å and carbohydrates and hyper-variable regions on the outside. A video illustrated dramatically the wonder of the assembly process.
Paul Sigler described the structure and action of GroEL, a machinery which, alone or in complex with GroES, somehow prevents other proteins from going on the wrong folding path. The mechanism of action is still not completely settled so Paul refrained from using typical sexy Southern California style slides but, instead, showed schematic transparencies since otherwise the audience might believe that the proposed mechanism was true. The structure determination of the double ring of seven subunits in the tetradecameric GroEL cylinder was truly a remarkable feat as well as its refinement by the Brunger group using torsional molecular dynamics procedures. The complex with the co-chaperonin GroES was described in the session on Friday.
Session: Protein-Carbohydrate Structures. 04.11
Despite the fact that carbohydrates constitute the single largest component of the biosphere, widespread and comprehensive structural research on carbohydrates and the proteins that act on them are of comparatively recent origin. Nevertheless it turns out that the first enzyme and the third protein to be X-ray analysed namely, lysozyme, had to do with carbohydrates. The structure of lysozyme was determined as early as in 1964. The structures of several other enzymes were determined in the late sixties and early seventies, but none of them act on carbohydrates. Through the middle and the late seventies and the eighties, the number of structure determinations on enzymes which act on carbohydrates steadily increased. The nineties witnessed an explosive growth in the structure determination of such enzymes. Indeed, among the proteins with known structure which act on carbohydrates, enzymes now constitute the largest group. This was rightly reflected in the programme of the session. Two of the five invited talks, those by Gideon Davies and Patrick Van Roey, and as many as three of the four contributed presentations were concerned with enzymes. Another large group of carbohydrate binding proteins belong to the immune system. It was not included in the programme of the session as there was a separate session on the immune system at the Congress. However, there was a contributed presentation on a sialoadhesin which was there in the guise of a lectin. In popular imagination, the class of proteins most closely associated with carbohydrates is perhaps the lectin family. Until recently, most of the action in this area has been concerned with plant lectins. While novel results with considerable general interest continue to emanate from struc- tural work on the plant proteins, exciting results on animal lectins have emerged in recent years. This excitement was conveyed by Jim Rini in his talk on an animal lectin family. Toxins constitute another set of lectin-like molecules which has received considerable attention. The current interest in this area is primarily on bacterial toxins, the so called AB5 toxins. They formed the subject matter of the talk by Wim Hol. Another group of proteins which act on carbohydrates is made up of periplasmic sugar binding proteins, the work on which was pioneered by Florente Quiocho and his colleagues. The analysis of the structures of these and other carbohy- drate binding proteins has provided a wealth of information on the atomic details of protein-carbohydrate interactions. The first talk in the session, after the overview by M. Vijayan, was concerned with these interactions and was given quite appropriately, by Quiocho. The quality and the breadth of the presentations at the session and the large attendance in it reflected the growing importance of protein-carbohydrate structures in structural biology.
Session: Drug Design II: Macromolecule Based. 04.12
This symposium was planned as a forum to take a new look at how structure-based design is actually done in industry, to review the spectrum of solutions found to the problems of siting and support, and to call attention to some of the remaining challenges and opportunities of structure-based design. The commonly recognized first structure-based drug is the angiotensin-converting enzyme (ACE) inhibitor Captopril, which was designed in about 1975 by a team of Squibb scientists led by Miguel Ondetti. The pioneering structure of carboxypeptidase A, a zinc-dependent exopeptidase, provided the structural underpinnings for the design process based on the hypothesis that ACE, a zinc-dependent exodipeptidase, worked like carboxypeptidase A. That hypothesis appears to have been correct, although to date no structure of an ACE has been determined. In the subsequent decade, the concepts of structure-based drug design were developed, refined, and popularized in a number of visionary laboratories around the world. This decade marked the birth of the biotechnology industry and a growing realization of the potential of structure-based design by the pharmaceutical industry. It saw the beginning of the first wave of additions of crystallographic groups to pharmaceutical research organizations, which continued into the late 80's. Beginning in about 1985, structure-based drug design underwent its trial by fire. It was tough going at first: overly rosy appraisals of technological capabilities, poor siting and support of crystallography groups, misunderstandings of how best to do this kind of design. But, by 1995, many of these problems had found solutions of a sort and the first modern structure-based designs were available to patients or soon to be so.
While there may be some discussion as to which is the first of the modern designs to become a full-fledged drug, a leading candidate was the subject of the first presentation: the drug Trusopt, a carbonic anhydrase inhibitor used to treat glaucoma. Presentations on two of the most competitive of recent design efforts, HIV protease and thrombin, illustrated the evolution of structure-based drug design in the last decade as the presentors for these were given the task to (1) give a reasonable review of the overall effort, where available, (2) present the results that reflect their own contribution, and (3) to provide some analysis of the design process and the role of structure. These discussions were augmented by presentations in several additional design areas of current interest: HIV reverse transcriptase, influenza virus neuraminidase, human renin and plasmepsin, an aspartic protease and new target to fight the parasite Plasmodium falciparum, the causative agent for malaria. Finally, one talk was designed to open discussion in a new area of design for small-molecule antagonists of protein-protein interactions. This is a matter of some discussion in drug design circles in industry and there is a significant prejudice against the idea that one could design a small molecule that would act to prevent, attenuate, or alter (1) the binding of macromolecular ligand to receptor, as in the case of interleukin-1, for example, or (2) the formation of hetero-oligomeric complexes of macromolecules into active assemblies, as is found in the cell-cycle regulatory or signal transduction complexes. However, examples such as HSV ribonucleotide reductase, where a peptidomimetic of the C-terminus of one subunit inhibits subunit association, and FGF, where di- and tri-saccharide mimics of heparin enhance the binding of ligand to receptor. The example of the calcineurin-FKBP12-FK506 complex presented in the symposium illustrated how the drug FK5 06 facilitates protein-protein interaction between calcineurin and its binding protein FKBP12. Such structural findings suggest new strategies for novel analogues altering this protein-protein interaction. One testament to the success of structure-based design was the large number of papers and posters related to it scattered throughout this conference.
From the discussions and presentations, one can draw a concensus picture of how current drug design in industry is practiced for efficiency, which includes the following conclusions: Siting and Support - Proper. Integration of the structure determination group that provides ready access to useful protein samples is crucial to productivity in drug design. Role of Chemistry. Due to the allocation of many chemists in a given project, chemistry programs move at a momentum of their own and create many more relevant compounds than can actually be examined crystallographically as complexes with target within a useful time period. The key to structure-based design in these circumstances is to determine which compounds NOT to study and here computational chemists are of great help. Two kinds of compounds are of special interest: the new chemical leads and those molecules that inexplicably violate current structure-activity relationships (SAR). Structure-Based Drug Development. Other properties besides biological activity, such as solubility and ease of uptake, ability to reach the appropriate site of action in vivo, resistance to degradation and avoidance of rapid excretion are desirable. Some of these properties can now be understood and manipulated at the molecular level and can thus be the subjects of structure-based design, too.
M. Grütter & H. Einspahr
Session: Muscle & Motor Proteins. 04.13
In the past year great advances have been made in our understanding of the molecular motor, myosin. Clyde Smith reported on the recently published structure of a fragment of myosin cross bridge crystallized with ADP vanadate as an analogue of the transition state complex. This form would be expected to show the beginning of the power stroke in muscle and indeed it does. Equally exciting was the report from Ron Milligan on high resolution cryo electron microscopy of actin decoated with myosin cross bridges, where on addition of ADP he was able to see the distal lever arm of the myosin cross bridge rotate through 35. The crystal structures of two forms of a second molecule motor, kinesin, were reported by Jon Kull and Elana Sablin. These demonstrated an unexpected similarity with myosin and showed evidence of a common mechanism, a mechanism similar to that of the G-proteins. Burtnik described the structure of gelsolin, an actin severing protein, which has six similar sub domains and is capable of a rich polymorphism. The session was a high point in our understanding of molecular motors.
R. Fletterick Session: Protein Design & Engineering. 04.14
The design and characterization of protein sequences, intended to fold into specific 3D structures, is becoming a powerful tool for elucidating rules of protein folding. At the session, designs and subsequent characterizations by x-ray and solution methods were presented: -helical
coiled-coils (by R. Hodges and N. Ogihara) -helical bundles (by L. Regan, C. Schafmeister and D. Eisenberg), and ß-sheet proteins (by L. Regand and J. Kelly). At present, sequence-structure relationships are best understood for the coiled-coils. It appears possible to design sequences that fold into two- or into three-stranded coiled-coils, and a proposal was put forward by N. Ogihara for coiled-coils that are designed to crystallize. Designs for hetero-coiled-coils (in which two different helices form a molecule) were presented by R. Hodges. These find numerous applications in medicine, when it is necessary to bring two molecules into proximity.
Session: Immune System. 04.15
The immune system session covered the structures and functions of immune system proteins. After a summary by Graham Bentley, the session started with a discussion of immunoglobulin superfamily (IgSF) members, with an overview of IgSF structures by Yvonne Jones, followed by the presentation of the new structure of ICAM-2 by Jia-Huai Wang. We also heard about structural studies of antibody fragments, including both catalytic (Marcel Knossow) and therapeutic (Anne Bloomer and Steve Sheriff) Fab fragments, and the new structure of the Fab portion of a human IgM rheumatoid auto-antibody binding to its autoantigen, IgG Fc (Adam Corper). The structures of two MHC-like molecules were discussed: the neonatal Fc receptor (Pamela Bjorkman) and the non-classical class I MHC molecule murine CD1D1 (Ian Wilson). The structure of CD1 does not include bound peptide, and it showed significant changes in its peptide binding groove compared to classical class I MHC molecules. The next talk by William Stallings covered the structure of a new class II MHC/peptide/superantigen complex. The final talk by David Garboczi was the presentation of progress towards the structure of a complex between a T cell receptor and its class I MHC/peptide ligand. Although all of the density in the T cell receptor portion of the electron density maps had not yet been interpreted, it was clear that the T cell receptor bound to the expected place on the MHC/peptide complex, with contacts to the peptide and MHC helices.
05 - Biological Small Molecules
Session: Drug Design I: Small Molecule Based. 5.01
The role of ligands in drug design was emphasized in a variety of talks. We heard about ligands used to show whether the x-ray or the NMR structure of human endothelin is more relevant to G-protein-coupled binding, ligand inhibitors of glycogen phosphorylase, conformational analyses of ligands, and a ligand-receptor database. The session highlight was Jon Clardy's description of the crystal structure of a fascinating complex between the immunosuppressive drug rapamycin, FKBP12 (FK506 binding protein), and the FRB (FKBP12 rapamycin binding) domain of human FRAP (FKBP-rapamycin associated protein). The ligand rapamycin manages to occupy hydrophobic binding pockets in both proteins at the same time. Since the proteins have few interactions with each other, it is essentially the rapamycin molecule that holds them together. This observation of rapamycin's "matchmaker" function has exciting implications for gene therapy because the induced dimerization of proteins that would not otherwise interact could be used to regulate gene transcription and other cellular processes. When rapamycin complexed with FKBP12 binds to human FRAP, it can interrupt the signal from the interleukin-2 receptor and thereby suppress immune response. Human FRAP is a very large protein involved in cell cycle progression which belongs to the ataxia-telangiectasia mutant (ATM) family. No structural information was previously available for any member of this family, so the rapamycin-FRB domain-of-FRAP portion of the complex is of particular interest, especially since it may correspond to a regulatory domain.
06 - Organic Compounds
07 - Organometallic And Coordination Compounds
Session: Organometallic Chem. & Coordination Compounds. 07.00
Half of the presentations in the microsymposium featured structures whose data sets were collected on SMART systems, which provided many of the highlights of the session. Strict adherence to the schedule precluded what would have undoubtedly been a highly controversial discussion of the presentation made by Dr. Carl Krüger. Dr. Krüger's talk focussed on electron deformation density studies that demonstrated errors in published structures. The most stunning results were those of disordered metal atoms in simple phosphine structures. While many of the errors discussed affected only immediate geometric parameters, the distortions that arose as a result of not considering the errors were often non-trivial. Dr Krüger astonished the audience with the claim that up to 10% of published structures could be in error. Of potentially equal controversy was a demonstration that SMART data was of little use when applied to electron density calculations. Dr. Krüger presented a phosphine structure in which experiment, calculation and CAD-4 data led to the assignment of a partial negative charge on the phosphorous; using SMART data results in a partial positive charge! The value of SMART data, however, was emphasized in the first and last talks by elegant studies of hydrogen-bonding in organometallic chemistry (L. Brammer), and some beautiful clusters containing up to 40 metal atoms (C. Campana).
08 - Inorganic And Mineral Compounds
Session: Inorganic & Mineral Compound. 08.00
The analysis of inorganic crystal structures was the topic of the first three lectures of this microsymposium. The compact representation of space group symmetry by orbifolds presented by Carroll Johnson led naturally into David Brown's attempt to match the chemical properties of atoms with those of Wyckoff positions , and to the demonstration by Stanislav Borisov (whose paper was given in his absence by Leonid Aslanov) that the heavy ions in inorganic crystals often lie on cubic face- or body-centered lattices with a spacing of around 5 Angstroms. The problem of finding similar structures in the databases was addressed by the next two speakers. Hans Burzlaff approached the problem algebraicly, using similarity matrices, while Emil Makovicky preferred a geometric approach, simplifying structures by replacing coordination polyhedra by spheres. Boris Zvyagin then showed that many structures could be generated out of smaller modular units such as those found in spinel and pyroxene, and Leanne Cook explored the relationship between perchlorate ions and the volumes of the cavities they occupy. The session concluded with a panel discussion.
09 - Charge, Spin And Momentum Density
Session: Multipole and Maximum Entropy Refinement. 09.01
The chairman, Claude Lecomte assisted by Bob Blessing, organized his session in time. A number of people were invited to present a lecture, while some time was reserved for contributions. The organisation went smooth and no problems occurred. The topics were measurement, multipole analysis and Maximum Entropy. A nice number of abstracts were submitted: 32, witnessing the good health of the field. Execution. The number of participants was estimated to be about 150. In particular Maximum Entropy drew many interested people.
Session: Comparison of Theory with Experiment. 09.02
Comparison between theoretical calculations and the outcome of experimental studies was the focus of this session, with some emphasis on the complementary role of the two approaches. Following a thought-provoking introductory lecture (Spackman) combined theory/experiment results were presented for an inorganic system, organometallic and bio-organic crystals. For Al2O3, recent LAPW and Hartree-Fock calculations on p (r) (Schwarz) were compared with preliminary results obtained from a very recent synchrotron x-ray study of corundum (VanBeek). A more definitive comparison is eagerly awaited. A detailed joint exp./theory study of chromium fischer carbene complexes (Wang) focused on the deformation density, atomic charges and d orbital populations, and was representative of many similar demanding studies in this area. Lecomte discussed the application of topological analysis to H-bond interactions in a variety of biologically important organic systems, and convincingly demonstrated that consistent and meaningful results are now being obtained. In an excellent conclusion to the session, the chairman invited presenters of related papers to speak briefly on their work, and this provided everyone with the ideal opportunity to familiarize themselves with the variety of work in the area, and also to get to know the presenter.
Session: New Information on Crystals From Electron Diffraction. 09.03
The original title, High Resolution Microscopy, persisted for a long time, although it was pointed out that it did not represent the field intended. It took the chairman, John Spence, quite some time to get a program together: he needed several persons that were speaking somewhere else. The rule that each person was allowed to perform only once, made this impossible. No posters were submitted. In April it became clear that the session coincided considerably with a session on the related field Materials III, strain measurements. since a similar clash occurred with session 9.04, it was decided to ask for a swop between the two. The request was not answered, not withstanding several follow ups. Only a few weeks before the conference it became clear that the organizers did change the schedule but had not informed anybody. The late change had some unpleasant travel consequences for some speakers. Execution. The number of participants amounted to about 30. It is clear that the field is not in the centre of crystallography. It is a pity since the results are highly relevant and the field is very alive.
Session: Magnetization and Momentum Density. 09.04
The chairman, Bruce Forsyth, had to select speakers from a very small number of participants in the field. Only a program that filled just over half the allotted time could be made. This allowed to meet the request from the Momentum community of the Commission on Charge, Spin and Momentum Density to have some time to report on their progress. Arun Bansil made this part of the program. As stated above, this session suffered from a clash of interest as well and asked for a swop. The result is reported above. No posters were submitted. Execution. The program drew up to 50 persons.
10 - Material Science
Sensors and Actuators: Smart Crystals. (10)
Keynote Lecturer: R.E. Newnham
R.E. Newnham from Penn State University gave a very interesting and enlightening lecture on 'smart' crystals. These materials are both sensors and actuators and are used in a hugh variety of applications including cars and household appliances as well as in space and military technology. R. E. Newnham compared the possibility offered by the different types of materials, electrostrictive, magnetostrictive and shape memory sensitive and showed, starting from their crystallographic properties, how far one can go in the engineering of new devices. The trend is toward minitiarizing and mimicking biological functions. The very lively lecture, full of striking examples, was followed by a very large audience which practically filled the room.
Applied Physics of Quasi Crystals and Applications. (10.01)
Keynote Lecturer: Jean Marie DuBois
Starting with the first publication of Shechtman and his collaborators (1984), DuBois presented a short history of quasi-crystals, followed by a description of the current state of the art of material preparation and structure determination using Al-Mg alloys as an illustration. He described spectroscopic experiments, the theoretical background concerning electronic structure, and the physical (electric and thermal conductivity) mechanical (unusual hardness, small frictional coefficient) and chemical (resistance to corrosion) properties of quasi crystals that make them of great potential interest to industry.
Modern Power Diffraction In Materials Science. (10.08)
Keynote Lecturer: Daniel Louer
In the first 20 minutes of his lecture D. Louer reviewed powder diffraction beginning with the 1916 Debye-Hull papers to the First International Powder Diffraction conference at Oxford in 1995. Thereafter, he discussed his research at the University at Rennes and illustrated the topics with specific examples. The high x-ray intensity and tuneability of synchrotron sources were used, e. g., in a study of InSb at 5.1 GPa using In K radiation. Time resolution studies by neutron diffraction can now be done as illustrated by the 10 minute per pattern in situ study of -MnO2 during electrochemical reduction. Traditional uses of the powder diffraction method continue to improve. A most important innovation is the 3rd generation Search-Match routine that uses the completely digitized diffraction pattern instead of just d's and I's. The application of the Rietveld method to quantitative analysis represents a significant advance to a long standing problem. The most noteworthy advances were the progress in ab initio structure determination from powder data using direct methods, Patterson and Fourier maps, the maximum entropy principle, simulated annealing, Monte Carlo method, and the atom-atom potential method. Each of these methods was illustrated by specific examples. The complexity of the structures that have been solved are rapidly increasing and, Professor Louer felt, may eventually rival those from single crystal data.
Session: III: Strain & Stress Measurements. 10.03
Stress levels and strain measurement are very important issues in the growth of thin films. Whether introduced by design, or unwanted artefacts, it has become of considerable current interest to establish reliable methods for their evaluation. There is a great variety of techniques that can be used such as Raman or luminescence spectroscopy, curvature measurement, computer modelling, or diffraction techniques based on neutron, X-ray or electron crystallography. This microsymposium concentrated on the two last mentioned techniques and brought together a distinguished set of speakers who are authorities in the field. Convergent beam electron diffraction techniques offer more modest strain sensitivities at very high spatial resolution whereas X-ray diffraction gives very high strain sensitivity with more modest resolution. The X-ray strain measurements of Dr. Fewster (Philips Research), using a high resolution multiple-crystal multiple
reflection diffractometer on GaAs, gave absolute values of the lattice parameter, accurate to better than 1 in 105. At this level of sensitivity even reference crystals were found to be potentially unreliable standards because the lattice parameters varies with the scattering depth of the measurement. It becomes necessary to make careful choice of the Bragg reflections used in the measurements. When strained layers were grown on the substrate it was found that substrate distortions also occur and had to be taken into account. Dr. Zuo (Arizona State University) showed that in order to achieve the highest spatial resolutions in electron diffraction careful choice of zone axis is required. High symmetry axes give rise to channelling effects that actually reduce the size of an existing beam relative to that of the incident focused probe and allow measurements to be made with 1 nm spatial resolution. Dr. Mayer (Max Planck Institut, Stuttgart) gave an impressive demonstration of measurement of strains in aluminum on silicon substrates at the 1 in 104 level using electron diffraction. He introduced Hough transforms and stressed the need for full dynamical theory calculations for work at this level of accuracy. Dr. Armigliato (CNR, Bologna) gave a beautiful demonstration of the utility of more routine sensitivities (5 in 104) and spatial resolutions (10 nm) in studying strains introduced into silicon by LOPOS technology. His results showed impressive agreement with model calculations based on the SUPREM IV modelling program.
Session: IV: Aperiodic Structures & Incommensurate Phases. 10.04
The domain of aperiodic structures includes quasicrystals, incommensurate and misfit or composite structures and some polytypes. The microsymposium and the poster session dedicated to aperiodic structures covered all these topics and revealed lively interest in the field. Many cases of disorder revealed by diffuse scattering patterns have been studied in icosahedral and decagonal crystals. The presentations of F. Denoyer and P. Gibbons included discussion of some interesting arcs of diffuse scattering and their interpretation and modeling. In an attempt to obtain absolute values of structure factors, R. Colella described a carefully designed dynamical scattering experiment. The problem of structural resolution of decagonal phases was solved by T. Haibach by successful combination of maximum entropy and 3+d-dimensional Patterson methods. M. Onoda presented a study of a series of structures based on a remarkable exploitation of the powder method. In the same field, S. Schmid revealed the consistent appearance of similar modulation functions despite the variability of the chemical compositions. Molecular dynamical techniques used to understand the origin of incommensurate structures of inorganic compounds presented by V. B. Gaillard seems very promising and will certainly be generalised in the future.
Session: VII: Optic/Electronic Materials. 10.07
Sidney Abrahams (USA) began the proceedings with a discussion on how to search for new ferroelectric and ferroelastic materials. He showed that approximately 8% of all inorganic structures are polar and thus a look through the inorganic database reveals at least another 200 potential ferroelectric crystals to be studied. Pam Thomas (UK) then gave a spirited talk on periodic domain inverted crystals (PDI). The formation of PDI crystals is an important recent development in the field of optical second harmonic generation. These structures have the capability of virtually eliminating the phase mismatching that normally limits the use of optical crystals in SHG applications. Pam showed that crystallography has an important role to play in both developing PDI and in studying what happens when domains are inverted. Elena Belokoneva (Russia) discussed the family of non-linear optical crystals based on KTiOPO4, with illustrations of many related structures of germanates and silicates. Douglas Keszler followed the non-linear optical theme by showing that aluminum borate crystals had high non-linearites which could even be predicted by simple theory. Finally, Ladislav Bohaty demonstrated the occurrence of a truly huge number of potential electroptic crystals simply by studying the known space groups of many hundreds of chemical species.
Session: VIII: Powder Diffraction. 10.08
This microsymposium spanned topics from limits on precision and accuracy, to data collection protocols, uses of magnetic neutron diffraction and anomalous X-ray dispersion, characterization of multilayers, depth profiling, and the determinations of polymer electrolyte structures. A highlight was the presentation by Bill David of the RAL, UK, who described the achievement of markedly superior fits of observed and calculated diffraction profiles in Rietveld refinement through the use of independent peak shape and width parameters. The method very effectively deals with the issue of anisotropic peak characteristics and allows the determination of structural results that are independent of (and therefore unbiased by) the peak shape model. Evidence for the 'saturation' of esd's at long counting times was provided, along with a strong recommendation for the use of variable step counting time protocols during data collection. A method of decoupling the structure and peak contributions was described by Dave Cox of BNL, USA, this time through the fixing of peak parameters at the values determined during a pre
Rietveld LeBail-type refinement. Mikhail Kovalchuk of the Russian Academy of Sciences, Moscow, presented a comprehensive description of the use of X-ray standing waves as a sensitive probe for the characterization of multilayers on single crystal surfaces, while Francoise Bouree of CEA-CNRS Saclay gave a comprehensive description of the key steps in the determination of magnetic structures from powder neutron diffraction data. Philip Lightfoot of St. Andrews, UK, presented an elegant and visually stunning description of the ab initio determination of the crystal structures of polymeric materials through the use of Monte Carlo and constrained Rietveld refinement methods.
Session: Materials XI, Fullerenes. 10.11
The selection of six talks in the fullerene microsymposium illustrated that the field of
fullerene research continues to be extremely broad and interesting. One is reminded about the tale of several blind men and an elephant; each one described the elephant as something vastly different, depending upon whether they touched its leg, trunk, ear, tail, etc. The first view came from Masaki Takata, who described powder x-ray experiments using image plates at Photon Factory, in conjunction with maximum entropy analysis of the data. His group has been able to locate Y and Sc atoms inside the fullerene cages, as well as to resolve the atomic structure of the carbon cage. Roger Moret spoke on diffuse x-ray scattering from orientational flucturations in C60 crystals. Humberto Terrones discussed a model for the nearly spherical graphitic onions which have been observed, explaining a mechanism of shell growth that would suppress the expected faceting of successive layers. Alan Balch described the work in his laboratory on chemical modifications; while everybody seems to like fullerenes, it takes a synthetic chemist to find molecules that can hug and kiss them. Gyula Faigel spoke about some alkali fullerides, comparing the conducting polymer and insulating dimer phases of [K, Rb, Cs]C60. Finally, Kosmas Prassides discussed the crystallographic properties of heterofullerenes C59N and their fullerides. The general interest in this topic is evinced by the fact that the audience remained in full strength past 6:00 on Friday. The related posters, and other talks scattered around the Congress also showed that fullerenes continue to excite the imagination and stimulate creative research.
Session: XII: Local Order & Defect Scattering in Crystals. 10.12
A good deal of attention was devoted to the detailed description, via diffuse scattering of local order and atomic displacements in alloys and oxide crystals. The talks were truly at the experimental and theoretical forefronts of the field and one could see quite clearly how diffuse scattering will play an increasingly important role in defining critical aspects of "local crystallography" in complex materials. It is certainly envisioned to become more important in macromolecular studies as well, especially as synchrotron-based image plates are used for x-rays and multidetectors are employed in time-of flight neutron studies.
Session: XIII: Advanced Battery & Fuel Cell Materials. 10.13
The microsymposium on battery and fuel cell materials focused predominantly on the structures of transition metal oxide insertion electrodes for rechargeable lithium batteries which are finding increasing application as power sources for laptop computers, cellular phones and camcorders. Structures of oxygen-ion conductors for high temperature fuel cells also featured prominently in the program. The presentations highlighted the importance of understanding structure-property relationships on a fundamental level; such knowledge is being successfully used to tailor the structures of electroactive materials to improve their performance in electrochemical cells. Michael Mansuetto of Argonne National Lab. demonstrated with neutron diffraction data how the framework structure of alpha-manganese dioxide could be stabilized by reaction with lithium oxide (rather than a cation, such as Ba2+ or K+) to provide an electrode with significantly improved electrochemical stability over conventional alpha-MnO2 materials. Other highlights of the conference included the husband and wife contributions from Per and Kia Onnerud, both formerly of MIT. Per gave an elegant description of cation and anion disorder in pyrochlore structures, such as Y2(ZryTi1-y)O7 and discussed relationship between these structures (which can also be considered as non-stoichiometric fluorite-type) and high oxygen-ion conductivity at elevated temperature (1000oC). Kia, a PhD graduate from Josh Thomas' laboratory at Uppsala University, Sweden, gave detailed accounts of lithiated V6O13 structures and the development of a very rapid processing method to produce crystalline LiMn2O4 (spinel) electrode structures. Ryoji Kanno of Kobe University, Japan, extended the discussion of spinel electrode materials to spinel solid electrolytes Li2MX4 (X-halogen) that showed high Li-ion conductivity at elevated temperatures. A highlight of the poster session was Gary Burr's presentation (Argonne National Laboratory) of an in situ structure analysis of deuterated LaNi5Dx and Al-substituted LaNi5-yAlyDx electrodes that were obtained during the discharge of nickel-metal hydride cells, the first time that such experiments on metal hydride electrodes have been successfully undertaken. The data showed a remarkable agreement between the amount of deuterium within the electrode determined electrochemically during discharge and structurally by profile refinement of the neutron data. With the increasing interest in batteries and fuel cells, the IUCr can look forward to further sessions on the structural characteristics of these exciting types of ionically conducting materials.
11 - Structure/Property Relationships
Session: Molecular Recognition. 11.01
An overview of some of the most interesting results concerning supramolecular recognition of molecules (fullerenes- J.L. Atwood, chiral moieties - F. Toda), anions (c. Pascard) and varieties of molecules and/or ions (I. Goldberg, Candeloro de Sanetis) was made and was supplemented by some recent data on selective uptake of isomers from mixtures (K. Tomita). Most impressive is to see to what extent common images of supramolecular structures differ from experimentally determined ones, as is the example of helical rather than spherical micelles. Interdisciplinary charater of the topics was clearly seen when a non-crystallographer (F. Toda) attracted attention of crystallographers when demonstrating enantioselectivity or even specifically of reactions in chiral solids. Crystallography for inclusion-type compounds is of that crucial importance as it has been for silicate chemistry. Relating structure to thermodynamic and kinetic characteristics becomes a new area for exploration by crystallographers (L. Nassimbeni). Supramolecular crystallography seems to be doing very well.
Session: Chemical Crystallography of the Future: Open Commission. 11.02
That part of crystallography which provides valuable information to all fields of chemistry is often identified as service crystallography. The reduced appreciation crystallographers receive who are overworked producing crystal structures creates problems related to academic careers and often leads to misunderstandings between the service crystallographers and the community they serve. Because the connectivity of atoms is often confirmed faster, cheaper and more reliably by diffraction techniques than with spectroscopic methods service crystallography has become a very important part of chemical crystallography. However, chemical crystallography is a much broader field so that it is impossible to address all topics in a single session and the microsymposium addressed a few of the most interesting and timely topics in a structure determination, the rate determining step is often the availability of suitable crystals. R. Boese talked about two crystallization techniques, his an in situ IR-laser technique for low melting samples (actually a miniature zone refining procedure) and a cooling device, equipped with a video system, which controls the seeding/growth process. The first technique was used to successfully grow crystals of norbornadiene in its low temperature, non-plastic, ordered form. In a fabulous, multi-media moving-picture lecture, A. Pinkerton gave examples of the grandiose perspectives of CCD area detector systems with their ability to collect data from very small (20-50 micron) organic crystals with sufficient accuracy that comparative electrostatic potential studies should be readily possible. His presentation continued with the structures of photo-exited states and super-modulated twins - some aspects of his talk sounded like science fiction. The same was true with Y. Ohashi's talk, he described a collection of full data sets in 2 hours using a double-imaging-plate diffractometer allowing him to trace time-resolved solid state reactions. Even faster data sets will be possible when a new CCD system, currently under construction, is completed. Single crystal diffractometry will no longer be a static method! The dyeing of crystals by Kahr was not a misprint as anticipated by some participants who were then fascinated by the colors of crystals and the questions related to the mechanisms of the dyeing process and the structures of the "dyed" crystals. Clearly this is an intriguing field, still in its infancy, with many challenges that will need the interplay of a great diversity of techniques to understand. Antipin said that there is much more information in a high-resolution data set than usually exploited. The charge density maps which he presented gave some examples of 'inverted bent bond': even ammonia has bent bonds! Using a closo-carbaborane, he presented electron density maps which prove that both non-classical three- center-two-electron bonds and classical two-electron-two-center bonds exist simultaneously. Finally, Motherwell discussed perspectives on future data retrieval from the Cambridge Database and techniques being used to check crystal structures for errors, especially worrisome if plans to store 'private communication structures' are put into practice.
Session: Dynamic Properties in Molecular Crystals. 11.03
Molecular motion of atoms in the crystal phase has been discussed from a general point of view on the ground of number of experimental findings obtained by low-temperature X-ray and neutron crystallography integrated by a variety of non-traditional techniques such as: X-ray diffuse scattering and energy dispersive diffuse scattering, neutron and far-infrared spectroscopy, and solid-state nuclear magnetic resonance.Physical systems treated ranged from molecular to biomacromolecular crystals with particular regard to: calculated motions and side-chain dynamics in protein crystals, n-fold reorientational dynamics in substituted cubane crystals, rigid and non rigid motion in highly flexible nitrogen compounds, rotational disorder in adamantane, order disorder phenomena in cyclodextrine and calixarene inclusion compounds, thermal motion in crystals displaying antiferroelectric-paraelectric transitions.In spite of the rather highly specialistic nature of the microsymposium, the treatment of the different subjects as well as the following discussion have been of general interest and able to identify a number of common aspects in the dynamical behaviour of molecules in crystals.
Session: Solid State Reactions: Structural Therm. & Kinetics Aspects. 11.04
This symposium covered studies of a wide range of reactions within organic, inorganic and metallic crystals. The first lecture was concerned with problems of methyl transfer, which occur sometimes in the solid state but more usually in the melt. Experiment showed that the methyl groups were transferred in an intermolecular fashion, and that sometimes a particular overall reaction occurred by more than one mechanism. Photochemical reactions initiated by light at absorption maxima generally take place on the surface of the crystals of the parent species but can be induced to occur within the bulk of the crystal if the initiating light comes from the tail of the absorption band. This gives many advantages in the study of photochemical reactions in crystals. A unifying factor for the solid state reactions of inorganic crystals was found to be provided by the strain induced in a crystal as a result of reaction. This determines the kinetics and spatial pattern of the reaction as well as the structure and morphology of the solid state products. Phase equilibria in metallic systems have recently been predicted to be composition dependent if the precipitated phase is coherent, and high-temperature in situ experiments have demonstrated this effect for a Ni-24 atomic % V alloy. Finally, the thermal decomposition of alkali metal salts of halogenocarboxylic acids has been shown to give the metal salt and a polymeric product, and experiments have shown how the detailed structure and composition of the polymer depends on the decomposition conditions.
Session: Analysis of Atomic Displacement Parameters. 11.06
Two major topics discussed in the microsymposium were recommedations concerning nomenclature for atomic displacement parameters Aka temperature factors Aka thermal parameters and the appropriate interpretation of these parameters. K. Trueblood, chair of subcommittee on temperature factor nomenclature, of the IUCr Commission on nomenclature reported on the sub committee. With respect to the question of interpretation, a model can be simply fit into the crystallographic data or the ADP's may be modified using lattice dynamics. Applications to crystallographic data on proteins were illustrated by T. Schneider (serine protease) and M. Teeter (Crambin). The successful development of lattice-dynamical models to ionic compounds (mainly oxides and silicates) was illustrated by C.M. Gramaccioli, R.T. Downs showed a generalized model to deal with freely rotating molecules, and B.J. Wuensch discussed anharmonic vibration of metal atoms and the displacement distribution in fast-ion conductors. Posters on display included an interesting analysis of the flexibility of the P-O-C ester link in phosphoenolpyruvates by T.P. O'Connor and R.H. Blessing, and a theoretical study on the Pa3 phase of anthracene (Einstein versus Debye modelling) by A.T.H. Lenstra, K. Verlust and C. Van Alsenoy.
Session: Chiral Compounds of Industrial Interest. 11.08
The microsymposium was comprised of a short general introduction and five talks, concerning biologically active and drug-related compounds, problems connected with resolution processes, and organic/inorganic materials with interesting optical and/or electric properties. Brian Patrick, a PhD student from Vancouver (Canada), offered a remarkably mature presentation at his first international conference. In general, questions, comments and, when the time-schedule allowed, discussion showed that the lectures were well received.
12 - Surface, Interfaces, Thin Films
Structures of Surface Studied By X-ray Diffraction. (12)
Keynote Lecturer: Robert Feidenhaus'l
Dr. Feidenhaus'l presented general principals of x-ray diffraction from crystal surface and then described the techniques used to measure and analys the spectrum. He next described several interesting examples of crystal surface structures analyzed by the method and entertained questions from the audience. This keynote lecture illustrated the power and potential of the technique.
Session: I: Surface & Interface Crystallography. 12.01
Several new surface structures were reported, mainly of semiconductors. S. Ferrer described the low-temperature structure of Ge(001) in which dimers were found to interact laterally. K. Akimoto showed the formation of ordered structures at the Ag-Si (111) interface. H. Schultz had convincing evidence of vacancy and interstitial defects in the InSb(111) surface. The application of maximum-entropy analysis methods was pursued for the Si (111) 7 x 7 surface by C. Cavartho, with a comparison of Fourier and ME maps. C. Lucas reported a study of coabsorption structures of Cu and Br electrochemically deposited on Pt (111), including an interesting CuBr monolayer phase. Finally, D. Walko analyzed diffuse scattering around truncation rods of Cu (110) in terms of island distributions arising from deposition of Cu at low temperatures.
13 - Fiber Diffraction
Session: II: Methods of Structure Determination. 13.02
In the second session on fiber diffraction, methods for structure analysis were discussed. M. Tsuji described how 'lattice images' from high resolution electron microscopy of drawn fibers could be used to characterize the local variations of crystallinity within a specimen. Not only were relatively radiation-resistant aromatic polymers considered, but also aliphatic chains gave useful data when held in a liquid helium-cooled sample holder. High resolution images and fiber diffraction data were also used by I.G. Voight-Martin to characterize liquid crystalline polymers. In her work, she also demonstrated that electron crystallographic structure analyses (energy minimization and use of maximum enthopy and likelihood for phase determination) of monomers could provide new insights into the nature of the mesogenic polymers solids. Crystal structures of polymers based on single crystal electron or fiber x-ray diffraction data were discussed by S.V. Meille, D.L. Dorset and M.P. McCourt. In the first talk in the series, polymorphs of poly (pivalolactone) and isotactic polypropylene were described, their quantitative crystal structures analyzed mainly by conformational search procedures. The second talk dealt with the applicability of direct phasing methods for determining structures without the use of molecular models. The last talk showed how model fitting could be used to resolve the atomic structure after direct phase determination, when data sampling was incomplete. In the two fiber diffraction talks, N.S. Murthy described how two dimensional profile fitting could be used to determine the distribution of crystallites in a drawn sample. A complete description of the types of disorder in fiber samples and their effect on experimental diffraction data was given by R. P. Millane, with the aim of extracting more accurate data for structure analysis.
14 - Small Angle Scattering
Session: II: Applications. 14.02
In the first of two SAS microsymposia (MS14.01), we were treated to a tantalizing treatise on the tools and techniques of small-angle scattering. The application of these tools and techniques was the focus of the second microsymposium (MS14.02) held on the morning of Monday, August 12, 1996, which drew a large, attentive, and participatory audience. Here we were introduced to an array of SAS applications with material subjects ranging from ribosomes, eye lens cataract and muscle to mesogens, alkanes, micelles, peptides and proteins. Heinrich Stuhrmann lead the charge with a masterfully gesticulated discussion of polarized neutron scattering and its use in deciphering ribosome structure. Hot on Heinrich's heels was Anne-Marie Levelut with her announcement and colorful description of a novel class of mesophases composed of "crystals of defects" observed in chiral thermotropic mesogens. Next up was Steve Perkins, who delighted the crowd with a most convincing protocol for automated SAS curve modeling as applied to a variety of multidomain proteins. It works! Annette Tardieu, the next speaker, spell-bound the audience when she introduced her topic with a rather graphic photograph of eye lenses. At one point in the presentation, I could have sworn I saw one of them wink. But I must admit that my new bifocals are taking some getting used to. Undaunted, Annette went on to describe how SAS is being used to understand the nature of the interactions of the crystallins, proteins responsible for transparency in the healthy eye lens and for opacity in cold cataracts. The mechanism of muscle contraction and how this is being investigated at a structural level using state-of-the-art synchrotron x-ray sources was addressed by Tom Irving. Tom presented a convincing case for undulation based beam lines at third generation synchrotron facilities. Now, all we have to hope for is that radiation damage does not compromise these measurements. Phase separation at a microscopic level in binary long chain alkanes was reported on by Elliot Gilbert. This fascinating process, referred to as microphase separation, involves the slippage of molecules along their long axis to form interleaved lamellae of distinct compositions in bulk alkanes. Next on the mat was Jan Pedersen who introduced us to his pet giant worm-like micelles, composed of lecithin, organic solvent, and water. Jan showed how SAS and Monte Carlo simulations have been used to characterize the structure of these polymer-like micelles at the level of cylindrical cross-sectional profile, size distribution and persistence length. The session ended with a tour-de-force examination of the structures that the anti-microbial peptides, alamethicin and magainin, form in solid substrate supported lipidic bilayers. In this study, the power of in-plane neutron scattering as a tool for investigating membrane structure was demonstrated convincingly by David Worcester, co-chair of the microsymposium. The session closed with a photo opportunity for speakers and chair alike. There was unanimous agreement among the subjects and the photographer that Professor Stuhrmann not display his infamous, signature hand-wave (see, for example, photo of Professor Stuhrmann on Page 12 of IUCr Newsletter Vol. 3. No. 3) during this very serious occasion.
15 - Diffraction Physics And Optics
Neutron Diffraction Studies of Coordination & Organometallic. (15)
Keynote Lecturer: Thomas F. Koetzle
Dr. Koetzle started his interesting lecture making a brief comparison of the similarities and differences between the scattering of x-rays and neutrons by solid samples. He emphasized the peculiar potential uses of neutron radiation toward the discrimination of different isotopes, the analysis of magnetic structures or the precise positioning of light atoms, trying to point out how neutrons and x rays can be complementary in crystallographic research. Most of the examples presented involved elastic scattering measurements on single crystals of organometallic and coordination complexes. Dr. Koetzle showed how the neutron diffraction experiments have been crucial in discovering new types of bonding systems, for example, those interactions involving metals and two atoms linked by a s-bond. In particular, he commented on the neutron diffraction studies carried out on the characterization of classical and non-classical transition metal polyhydrides (dihydrogen complexes), and on the discrimination between both types of complexes. The relevance of these studies toward the understanding of reaction and/or catalytic mechanisms was also subject of Dr. Koetzle's talk. Examples displayed included the hydride dihydrogen interconverting iridium complex IrIH2(H2)(PPiPr3)2 or the catalytic precursor pentahydride [OsH5(PMe2Ph)3]+. It was, without any doubt, an exciting keynote lecture on the use of an alternative radiation type useful for improving our knowledge of the structure of matter.
Session: Diffraction Physics I: Neutron & X-Ray Optics. 15.01
This session focussed primarily on new developments in instrumentation, including monochromators, neutron polarizers, and the use of image plates in the Laue diffraction method. A total of six lectures were presented. Mihai Popovici of the University of Missouri Research Reactor spoke on the intensity and resolution characteristics of bent crystal monochromators whereas Tom Vogt of Brookhaven National Laboratory described a composite Ge crystal monochromator, with an anisotropic mosaic, which has proven to be highly successful in neutron powder diffraction applications. David Mildner of NIST told us about the current state of polycapillary optics and reported focussing gains approaching a factor of one hundred. Clive Wilkinson showed how neutron Laue diffraction could be efficiently performed using cylindrical image plates read by a laser. Although unable to attend, a talk by Valerie Nunez of Oxford on recent advances in super- mirror transmission polarizers for neutrons was given on her behalf by the chairman. Finally, Professor Hua-Chen Hu of the China Institute of Atomic Energy discussed her recent investigations concerning secondary extinction of x-rays and neutrons in mosaic crystals. All told, the session was interesting and informative as evidenced by the many questions asked of the speakers by the audience.
Session:Diffraction Physics II: Magnetic Structures with Neutron & Synchrotron Radiation. 15.02
M. Salamon (University of Illinois) began the lively and diverse microsymposium on determining magnetic structures with neutron and x-ray scattering by illustrating the species
sensitivity of resonant x-ray magnetic scattering, and describing the direct observation of the 5d moment induced on non-magnetic Lu atoms when they are dispersed in a magnetic Dy host lattice. A. Goldman (Iowa State University) then demonstrated how the polarization dependence of the resonant and nonresonant x-ray cross-sections can be used to deduce the moment-directions of unknown magnetic structures in a variety of rare earth nicklate superconductors. R. Robinson (Los Alamos National Laboratory) reminded the audience of the power of traditional neutron scattering methods, describing subtle and impressive magnetic crystallography studies of several uranium intermetallics. K. Hirota (Tohoku University) then followed with an elegant discussion of recent neutron scattering studies of 1-D spin-Peierls systems, which were complemented by high resolution x-ray studies. A highlight of the session was Thomas Brueckel's (HASYLAB) demonstration of how the increased penetration depth possible with high energy magnetic scattering (50-100 keV) offers a new direction for characterizing magnetic structures, particularly transition element magnetism. Finally, G. Gruebel (ESRF) discussed the use of resonant and nonresonant x-ray scattering for separating the orbital and spin magnetization densities in materials, illustrating with fascinating new results on rare earth metals.
16 - Crystal Growth
Morphology of Crystals Based on the Theory of Hartman & Predok, and on the Roughening Transition. (16)
Keynote Lecturer: Pieter Bennema
In introducing the lecture, the chairman remarked on the distinguished place of morphology in the history of crystallography - it having been the originator of our science, although now, since 1913, almost completely forsaken in favour of structural studies of crystal interiors. Introducing Professor Benemma, he drew attention to his academic lineage, especially to his early contact with Hartman and Perdok in Groningen, and to his having won, just last year, the prestigious Frank award.The lecture itself was an enthusiastic, excited and detailed exposition of Professor Benemma's theory of Crystal Graphs - connected nets of bonding contacts for every hkl plane, summarizing the crystal-growth behaviour in every direction. The theory is based on Hartman's original concept of Periodic Bond Chains, but is much further developed now, by the consideration of surface roughening phenomena (and calculation of surface interaction energies) and by the application of computer analysis. A variety of applications were shown, many of which exhibited pleasing agreement with the theory.
J. H. Robertson
Session: I: Macromolecular Crystallization Workshop. 16.01
Session chair A. McPherson introduced the audience to some of the current approaches to characterizing macromolecular crystal growth, focusing principally on the use of atomic force microscopy to elucidate the mechanisms of protein and virus crystal growth, visualize defects, and observe some unexpected phenomena such as the incorporation of microcrystals into larger, growing crystals. R. Cudney then reviewed many of the current practices and approaches to optimizing protein crystal growth conditions. He emphasized, particularly, the use of data bases for developing new screening approaches to specific problems, and discussed some of the pitfalls associated with the process. G. DeTitta discussed the use of temperature control to promote crystallization, and the design of new apparatus. That allowed the screening of conditions over a continuum of temperatures under very carefully regulated conditions. A. Ducruix used lysozyme as a model system, to illustrate the effects of both anions and cations on protein solubility, and suggested how they might be used to manipulate and control crystal growth. J. Ng, from Giegé's laboratory in Strasbourg presented a series of crystallization studies, on a variety of small RNA molecules, including tRNA's. He described how specific tRNA's could be selectively crystallized for a tRNA mixture by manipulation of conditions. He also presented results from investigations of RNA crystallization using a variety of novel polyamines. The final talk of the session was by A. Edwards of Canada. In what was probably the most unique approach to crystallization, he illustrated with three different proteins how molecular biology could provide a valuable tool. By selectively forming abbreviated, yet active domains of a protein, coupled with standard crystal growth screening methods, crystals of proteins could be obtained in an expeditious manner. His examples provided impressive evidence for the increasing impact of genetic engineering on structural analysis.
Session: II: Fundamentals. 16.02
The highlight of the session was molecular dynamic simulation (Dr. Huitema et al., NL) of the generation of stacking faults, and healing of these defects, depending on time available and distance to the interface. Rough and smooth interfaces act differently. Outcrop to the surface of stacking fault, twin lamellae producing either reentrant angle or rough interface and screw dislocation dipoles were shown to be competitive with conventional 2D nucleation and dislocations in generation of steps on a growth interface in various supersaturation ranges (N.B. Ming, China). At supersaturation (~20%) used for fast growth of ADP-KDP crystals there is little dependence of vicinal hillock on supersaturation while step rate shows an atypical decrease on ADP. Impurities produce not only well pronounced S-shape n(s) dependence of the step rate (n) vs supersaturation(s) but a slight sublinear dependence. Content of Fe, Cr, Al and organic impurities changes the n(s) dependence. A hollow core around the dislocation step source in KDP crystals was revealed by atomic force microscopy (L.N. Rashkovich, Russia, DeYoreo, USA et al). Ga atoms diffuse from (111)A to the (100) face of GaAs during MBE to the distances up to 1 micron though the steps are present on the (100) face. The distance depends on the arsenic flux to the surface. This effect changes the temperature of transition between the 2D nucleation and step flow modes (T. Nishinaga, Japan). A spectral sensitive optical interferometric technique developed by K. Bachmann (USA) allows not only measurement of the growth rate from dense gases, but also observation of oscillations corresponding to deposition of one atomic layer. Nucleation and spread of epitaxial monolayers of Ge on Si were observed by STM at temperatures up to 900K and captured on video tape. Nucleation on mismatched Si(111)-7x7 was demonstrated along with 7x7 kinks at steps (B. Voigtlander, Germany). X-ray topography revealed traditional striations in solution grown KDP crystal and striations due to macrosteps induced by morphological instability (I.L. Smolsky et al., Russia). Periodic roughing and facetting was found, probably due to the variations of impurities (X-Y. Liu et al., China). Transition from folded to unfolded chain crystallization and a corresponding self poisoning effect may be responsible for the existence of an unusual minimum on the dependence of the growth rate on temperature for the ultra-long chain n alkanes (E. Boda et al., UK).
Session: III: Methods/Materials. 16.03
The most outstanding contribution of the session was presented by J. Hulliger, U. of Berne, Switzerland, on the growth and characterization of nonlinear-optically (NLO) active organic inclusion compounds. The class of compounds consists of a non-polar molecular host crystal with parallel structural channels (e.g. Perhydrotriphenylen, PHTP) in which linearly shaped molecules with acceptor-donor groups can be placed (A-¼-D inclusions, ¼: thiophene, stilbene, etc.). The inclusion compounds synthesized by the authors are polar, compared with only 25% of the corresponding single-component systems. These inclusion compounds can be tailor made for NLO applications. Crystals of PHTP-(A-¼-D) were grown from 2-butanone or paraldehyde solution and by sublimation. K. Kojima (Japan) reported good quality crystals of C60 and C70 of several millimeters diameter from the vapor phase and the characterization of the fcc C60 crystals by synchrotron radiation topography, etching and microhardness tests. Individual dislocations were observed and dislocation densities, and glide systems determined.
Session: IV: Controlling & Predicting Crystal Morphology. 16.04
F. Leusen described several algorithms for the prediction of crystal habit as a function of solvent, particularly Cerius. J.H. Ter Horst then described the successful application of Cerius to predicting the habits of the explosive RDX, in T-Butyrolactone and Cyclohexanone. D. Gidalevitz described the use of atomic force microscopy to establish the biomolecular step size of B-acanine & glycine, followed by the use of grazing incidence x-ray diffraction to phase which molecular layers form the step boundaries. I. Kuzmanko used grazing incidence XRD to demonstrate the formation of tri-layers at the air-water interface. M. Zawdrotko described the correlation of metalloorganic molecular layers and grids to crystal form, and the development of organically based clays. Ned Seeman described a rigid DNA motif that should permit controlled habit control on a DNA N
17 - Charaterization of Defects, Microstructure And Texture
18 - High Pressure Crystallography
Novel Crystal Physics Under Pressure. (18)
Keynote Lecturer: Yasuhiko Fuji
Prof. Fujii pointed out that developements are taking place on two frontiers, one that extends the maximum pressure, the other increasing precision at more modest conditions. In the first case, he presented results of studies on halogen systems. Although metallization of H2 has been a long-term goal of high pressure science, the required pressure is extremely high. His group has, therefore, concentrated on molecules up higher molecular weight namely I2,Br2 and IBr. I2 undergoes a series of phase transitions from Cmca to Immm (21GPa), to I4/mmm (43GPa), and finally to Fm3m (55GPa). In the insulator-metallic transition (21GPa), a molecular form is retained, although intermolecular bonds are formed. To show results of higher resolution he studied [N(CH3)4]2 MCl4 (M=Mn,Fe,Zn), phases that have frustrated spin systems that can be described in the Axial Next Nearest Neighbor Ising System. With pressure temperature and Q resolution of 10Mpa, 0.05oC and 1.2 X 10-4Å-1, respectively they have shown that this system demonstrates a series of commensurate phases, not the incommensurate system inferred from lower resolution experiments.
Session: I: Elements & Simple Compounds. 18.01
Crystal structure analysis under high pressure reveals chemistry of elements and new properties of matter that are often drastically different from those observed at ambient pressure. Some of the most remarkable applications of high pressure crystallography were presented in the microsymposium. N. Hamaya described a pressure-induced phase transition in the crystal of SnI4 at 7GPe (ca 7 x 104 atm), followed by its amorphisation at 20 GPe, and then at 55 GPe its recrystallization into a new metallic phase with the molecules dissociated. S.P. Besedin reported isotope effects of AlH3 and AlD3 compression, and theoretical predictions of transformations of these analogues into metal. A general review of recent neutron diffraction studies on superionic conductivity in cubic hallides by S. Hull provided new insight into the structures of superionic phases. Pressure-induced change of Ga hybridization in rare-earth gallides, at the phase transition transforming Ga-layers into 3-D networks, was investigated both experimentally and theoretically, and vividly presented by U. Schwarz. M.L. Medarde reported the insulator-metal phase transitions in (rare-earth) NiO3 perovskites, and explained unusual observations of the octahedra tilts decreasing with pressure. M.I. McMahon has rewrittten a chapter on the phase diagrams of lanthanides: the previous results are revised and new transformations and phases added. Finally, K. Takemura discussed his powder diffraction analysis of another group of metals, Cs, Ba, Zn and Cd, which yielded anomalous compression difficult to reconcile with the absence of phase transitions at these pressures. The poster communications described difficult to measure results, and general conclusions concerning whole groups of substances. For example, the poster by R.J. Nelmes on a new systematics of structural phases of the II-VI, III-V and group IV semiconductors, based on their experimental results, is of exceptional importance for the technological applications of these materials. Their results were reproduced theoretically, as described in the lecture by A. Mujica. Other excellent results in the poster session were structural systematics of the phases of P, As, Sb and Bi presented by H. Iwasaki et al, systematic of groups V elemental group IV-VI compounds, and the phase transitions both in molten and solid KCl and KBr by S. Urakawa et al. The session clearly showed that high pressures are a very efficient means of modifying crystal structures and investigating the properties of matter.
Session: III: Molecules, Ices and Minerals. 18.03
Microsymposium 18.03, part of the series on high pressure crystallography, concentrated on recent experiments on a wide range of materials from molecular solids, through ices to minerals. An over-riding theme that emerged from both the oral and poster presentations was the improvement that has been made in both precision of experimental measurements at high pressures, and in the range of pressures and temperatures at which such measurements can now be performed. As a result of these developments, the majority of oral presentations concerned previously undetected or unsuspected complex phenomena that occur in relatively simple systems. For example, M.S. Somayazula reported the discovery and characterization of a large number of intermediate compounds in the methane-hydrogen systems. Similarly, high pressure diffraction studies on H-bonded ices (J. Loveday et al.) including methane and ammonia suggest that structural complexity is a common feature even in mono-molecular solids at high pressure. High pressure neutron diffraction studies by W. Kuhs of nitrogen and oxygen clathrates (framework structures built of water molecular with guest molecules in cages) show that these also show complex structural and phase transition behavior unsuspected by theoreticians. Relatively simple mineral structures such as cristobalite (SiO2) has also been shown (by K. Kingma et al.) to undergo sequences of phase transitions at high pressure while R.J. Angel presented a review of more complex mineral structures that undergo either phase transitions without symmetry change, or changes in compression mechanisms at high pressures. It was clear from this microsymposium that the continued application of high precision diffraction techniques at high pressures will continue to reveal a rich variety of previously unsuspected solid state behavior.
Session: V: New Frontiers. 18.05
This MS entitled "New Frontiers" was organized to introduce new scientific and technical ideas to high pressure crystallography to extend its scientific opportunity and potentiality. Three talks were related to the new instrumentation, three to new sample systems ranging from nanocrystals to biomolecules, and two to new theoretical calculations and graphic displays: Goncharenko reported a neutron magnetic scattering study of heavy fermion systems such as uranium monopnictides and europium monochalcogenides up to 6GPa by a sapphire anvil cell (SAC) and to 25GPa by a diamond anvil cell (DAC), and successfully observed a systematic magnetic transition. A pressure-induced antiferro-to-ferromagnetic phase transition of SrFeO3 was clearly observed as a spectral change of hyperfine magnetic field of Fe nucleus which was monitored with a completely new SR-excited Mossbauer technique up to 80GPa by DAC (S. Nasu). A Compton scattering technique with 60KeV x-rays from a synchrotron source was introduced to survey electronic property under pressure. Oomi et al. Reported a preliminary result on Li metal in which as appreciable change of the Compton profile is observed at 2 GPa. Tolbert and Alivisatos carried out both x-ray diffraction and optical absorption on nanocrystals of CdSe, InP, and Si ranging 2-50 nm in size and observed systematic elevation of transition pressure due to the nature of quantum confinement. Olsen et al. Reported an enhanced bulk modulus of Fe2O3 nanocrystal 7nm in size based on their x-ray diffraction data up to 50 GPa. The pressure effect on biological systems was reported by Gruner who observed unusual lattice expansion of the structure of membrane lipid due to an inherent hydration mechanism. The pressure 0.2 GPa is a significantly large purturbation to the biological systems with the carefully balanced competition of interactions. The combination of classical and first principles molecular dynamics can lead to a very powerful procedure in identification of crystal structures. Tse and Klug calculated and predicted a high-pressure structure of several silica systems. A new interactive graphics for systematic crystal chemistry of high pressure silicates was introduced by Hazen and Downs. The pattern of polyhedral linkages is systematically classified and demonstrated.These new instrumentational/computational techniques and new scientific fields inspired audiences with new direction of high pressure crystallography.
Session: VI: Data Collection & Analysis. 18.06
This was the last session of the high pressure microsymposia. Careful selection of topics and close cooperation of all speakers, session chairman and program committee made this event a very good compliment to the previous 5 high pressure microsymposia. The first 3 contributions gave the state-of-the-art of image plate high pressure work which attracted also many non-high pressure people. The second part showed where the limits of high pressure work are in single crystal, powder and amorphous diffraction. Ample time was given to discussion after each part. John Parise had accepted to summarize the whole high pressure event at the end of the session and presented a very tasty "high pressure menu" to both insiders and the curious crowd.
W. F. Kuhs
19 - High/Low Temperature Crystallography
21 - Topology
22 - Databases
Session: Database III: 25 Years of PDB. 22.03
A microsymposium entitled "25 Years of PDB" was held at the IUCr XVII Congress and General Assembly in Seattle on August 11th, in order to celebrate the 25th anniversary of the PDB. The symposium began with a brief overview by Joel L. Sussman (BNL/Weizmann Institute of Science) of the current status of the PDB and the plans, which are well underway, to convert the PDB into a much richer 'Three- Dimensional Database of Biological Macromolecules (3DB)', based on an object-oriented approach. A status report on AutoDep, a user friendly deposition procedure, that has been developed at the PDB and uses a WWW based interface, was also briefly presented. Edgar Meyer (Texas A. & M. Univ.) described the activity at Brookhaven in the years just before and leading up to the establishment of the PDB, at Brookhaven National Laboratory. He stressed how even in those early days, the concepts of networking and molecular graphics were key components in the creation and development of the PDB. Helen Berman (Rutgers Univ.) discussed the early history of the PDB, focusing on the scientists who played key roles in its establishment, with slides showing how some of us looked, way back in the early '70s. The lecture went on to discuss the establishment of the Nucleic Acid Database (NDB) and its relationship to the PDB. David R. Davies (NIH) gave a fascinating lecture describing the particular impact that the PDB has had in the area of research relating the structure and function of molecules involved in the immune system. It focused on how the structural information in the PDB has played a key role in determination of new structures via molecular replacement, and how the wealth of structural information in the PDB has made in possible to do comparative structural analyses of these molecules. Frank Allen (Cambridge Structural Data Centre) discussed the inter-relationship of the PDB & the Cambridge Structural Database. He showed the parallel increase in the size of the two databases and predicted that by the year ca. 2010, there could be well over 600,000 protein structures in the PDB. G. Marius Clore (NIH) gave a lecture on 'Improving the Quality of NMR & Crystallographic Protein Structures by Means of a Conformational Database Potential Derived from Structure Databases'. He showed the impact that high-resolution X-ray structures were having on developing new conformational potentials for use in NMR structure determination and refinement. It was also very exciting to see that this approach is likely to have an enormous impact in X-ray structure determination; in particular, when only low resolution X-ray data are available. In such cases the orientations of the side chains are often uncertain, and the new potentials will likely lead to a much better approach than what is used currently. It could also lead to greatly improved techniques for constructing theoretical models. Wolfram Saenger (Free University, Berlin) began the final lecture of the microsymposium with a gift of flowers for the occasion, or at least 'virtual flowers' in the form of a beautiful slide, and then went on to discuss what happened to fiber diffraction studies in the PDB. His talk was not just wonderfully suited to the occasion, but full of humor, focusing on how accurate fiber diffraction studies have been and still are in relation to comparable single-crystal studies, as well as on the enormous impact these studies have had on structural biology. It was announced by the chair that on November 17-21, 1996, there will be a second special celebration in honor of the 25th Anniversary of the PDB and the 10th Anniversary of the Swiss-Prot Database at the 24th Katzir Conference, entitled 'Bioinformatics<--->Structure'. To be held in Jerusalem, Israel. The meeting will focus on the relationship of sequence, structure, function, and databases. Sessions will include talks, poster presentations and computer demonstrations with access to the Internet. Details of the meeting, including the full list of invited speakers and the ca. 200 submitted abstracts, are available on the WWW at URL: http://www.pdb.bnl.gov/pdb25sw10 or at the mirror sites listed on that page, or via the PDB¼s Web home page.
23 - Teaching Crystallography
Session: Teaching Crystallography. 23.01
Teaching Crystallography: The microsymposium, which was attended by 100-150 persons, was divided into three parts. The first three speakers concentrated on crystallographic teaching in various parts of the world. Dr. Phavanantha presented a very thought provoking talk about the situation in Thailand and neighbouring countries. The number of trained crystallographers in relation to the population is small compared to many other countries and the availability of equipment is scarce. The next two speakers demonstrated computer aided instructional materials both for PC and Mac platforms. The last two speakers dealt with the problems of what to include in the crystallographic curriculum at the undergraduate as well as the graduate level for "non-crystallographers" (chemistry, physics, materials science, etc.) which started a very lively discussion in the audience. It was concluded that these questions are very important and a continuing discussion must go on. The number of people attending this microsymposium as well as the discussion part of the session clearly shows a need for a session of this type and it would probably be beneficial if the microsymposium on teaching crystallography is arranged somewhat earlier in the meeting and not in the end. Seven posters on teaching crystallography were on display. Two contributions (K.M. Crenell; R.B. Neder & Th. Proffen) displaying instructional materials are available on internet.
24 - History of Crystallography
OC - Open Commission Meetings
Session: Open Commission Meeting.
The meeting was organized to discuss a number of projects of the Commission: Multipole refinement and Maximum Entropy. Thirty to forty people were expected, but the attendance rose to about sixty. The informal character allowed free and extensive discussion.The minutes of the meeting can be obtained from the chairman, Karlheinz Schwarz, or the secretary, Mark Spackman. Some comments: The whole conference was organized in such a way that it was easy for the community of Charge, Spin and Momentum Density to reach one another!! It is advisable to make clear in an early stage what the duties and responsibilities are of the session chairs and the concerned members of the program committee . It seems that the organization of the program started off rather centralized and became more and more decentralized in its organization. I liked the decentralization, but I do not know whether it resulted in negligences.