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On the Cover: Contributors |
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The IUCr Newsletter is distributed to 587 libraries and 15,000 crystallographers and other interested individuals in 39 countries. Feature articles, meeting announcements and reports, information on research or other items of potential interest to crystallographers should be submitted to the editor at any time. Submission of text by electronic mail and graphics, slides or photographs by express mail is requested. Items will be selected for publication on the basis of suitability, content, style, timeliness and appeal. The editor reserves the right to edit. Cost of distribution in Australia, Czech Republic, France, Italy, Japan, Poland, South Africa, Switzerland, and The Netherlands is borne by crystallographic associations or institutions or by individual crystallographers in these countries. Address changes or corrections and requests to be added to the mailing list should be addressed to the editorial office. If you would like to see a copy of the IUCr Newsletter in your college or university library, send the address to the Newsletter office so that we can add it to our mailing list. IUCr Executive Secretary:
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Editor Newsletter Design & Production Assistant Editor Copy Production Hauptman-Woodward Med. Research Inst. 73 High St., Buffalo, NY 14203, USA Tel.: 716-856-9600 FAX: 716 852-4846 e-mail: patti@hwi.buffalo.edu
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Over the past 50 years, crystallography has transformed our understanding of crystal and molecular structure. This prospect was a driving force for early crystallographers; Dorothy Hodgkin saw crystallography as liberating chemists from the difficult and ultimately unsatisfactory task of determining molecular structure by the classical chemical approaches. The success of crystallography has made it a uniquely indispensible tool for chemistry, biology and physics. In this respect I feel incredibly lucky to be working in such a dynamic and exciting field. Success, and the urgent demand for structural data, has brought constant innovation in both methods and technology. Small molecule structures can be solved within hours, and the time required to solve a 2000-atom protein structure is now often less than was required to solve a 20-atom structure when I was a graduate student! This very success brings problems, however. The very real skills of crystallographers can be undervalued when many (but not all) structures can be solved routinely, with little training. It also brings increased risk of errors, ranging from minor to very serious, even wrong structures.
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As Greg Petsko reminded us at last year's ACA meeting, macromolecular crystallography is rapidly heading in the same direction as chemical crystallography, and many macromolecular structures will soon be solved more or less automatically. With the help of synchrotrons, MAD phasing and automated software, several have already been solved in a day or two! The emerging structural genomics programmes will accelerate this trend. What should we do to prevent our science from being seen as "routine" in future? Should we do anything? I believe that we need to reintroduce and revitalise the teaching of crystallography at undergraduate and graduate levels (from which it has all but disappeared in many institutions). I would also advise graduate students to develop multiple skills, so that as well as being crystallographers they are also biologists, chemists and physicists, who can bring a unique structural perspective to the other things they do. We have to be vigilant for error in our journals and structural databases, and constantly develop (and apply) better validation criteria. And we have to constantly remind administrators (sometimes even colleagues) of the importance of crystallography, its interdisciplinary place in science, and its manifest success. Edward N. Baker |
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Are You Still Undecided About the IUCr Meeting in Glasgow? This is being written on February 12th, nearly 2,000 abstracts have been submitted, and they are still arriving; registrations are beginning to flow; the satellites are now taking registrations; the social programme is attracting a lot of bookings; the exhibition has only a few small stands left; more sponsors are getting involved; the computer fair is nearly ready everything is coming together for a truly spectacular scientific meeting in August in Glasgow. Are you still undecided? Some people are complaining about the cost. Actually on a per day rate it is as cheap as any international meeting and certainly cheaper than some! For students, accommodation with ensuite facilities in excellent student housing at Strathclyde University right in the middle of town the cost is £370 including breakfast and evening meals. Add to this the £200 registration fee, £10 for 10 days of bussing and it works out at £58 per day for almost everything. For those of us for whom student days are just a memory, it is only £10 a day more than this. It is the 10 days of course that makes it relatively expensive, but it is these ten days that make it so special and so exciting: the sheer concentration of crystallography in all its marvellous diversity over such a period. For industrialists the strong programme in industrial crystallography is concentrated in the first 5 days (which also span a weekend). So submit your abstract (with modest late fee!), fill in your registration form, and book your accommodation all of which is in the 2nd announcement or on the web at: http://www.chem.gla.ac.uk/iucr99/ or e-mail: iucr99@chem.gla.ac.uk for a copy (or any other problems). And have a holiday afterwards. The abstracts will begin to be posted on a web site soon, which will give you the flavour of the science. A brief survey of the abstracts is quite mouth-watering. Or else you could spend the rest of your life at subsequent conferences hearing the words 'Do you remember at Glasgow when...?' and not being able to join in! Be there! Chris Gilmore, Judith Howard, Northern Networking and the IUCr99 Team
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Highlighted Articles from IUCr Journals John Helliwell, Editor-in-Chief of Acta Cryst and Chairman
of the IUCr's Commission on Journals has arranged for reviews
of articles in current issues of IUCr journals to appear in this
and future issues of the IUCr Newsletter. Improved X-ray Optics at HomeEven with new synchrotron radiation beamlines in operation or under construction worldwide, there is still continued need for increasing the capability of equipment operating in the home laboratory from sealed-tube or rotating-anode sources. New developments in x-ray optics will have a significant impact on the power of laboratory x-ray sources. These developments come from steady improvement of the performance of x-ray optical components based on total reflection (mirrors, capillaries, & waveguides), refraction (refractive lenses), and diffraction (crystals & multilayers, Bragg-Fresnel lenses, zone-plates, etc.). The successful fabrication of a replica ellipsoidal mirror ["Focusing Mirrors for Use with Microfocus X-ray Tubes", U. W. Arndt, P. Duncumb, J.V.P. Long, L. Pina, & A. Inneman, J. Appl. Cryst. 31 (1998), 733-741] and the development of polycapillary optics ["Applications of Polycapillary X-ray Optics in Protein Crystallography", P-W Li & R-C Bi, J. Appl. Cryst. 31 (1998), 806-811] are described in a recent issue of the Journal of Applied Crystallography. In conjunction with a new microfocus x-ray tube, a hollow needle-like ellipsoidal mirror can produce an intensity through a 0.5 mm**2 aperture that is comparable to that produced with rotating anodes and Franks mirrors at 1/100th of the power dissipation. This suggests that much more compact and energy efficient instrumentation can be created for the home laboratory. The replica mirror technology has been developed by Hudec and his collaborators in the Czech Republic (and is similar to the replica mirror work of Ulmer and of de Korte). A mirror is made by coating a shaped mandrel with a gold reflecting surface followed by a thick electroplated nickel shell to retain the elliptical figure when released from the mold. There are also prospects for another 10-fold intensity gain if the smoothness and shape of the reflecting surface can be further perfected. Crystallographers go to a synchrotron radiation source to collect a higher-resolution data set on protein single crystals because of the higher intensities available. With a 20-fold increase in intensity from a monolithic polycapillary x-ray optic, a higher resolution structure for acidic phospholipase A2 (2.2 Å, Rsym=8.6%, 83 Å unit cell) was observed when the Supper mirrors on a rotating anode were replaced by a polycapillary optic. Monolithic polycapillary optics are fabricated by pulling bundles of monocapillaries to various shapes and have been under active development by other groups including those of Kumakhov, Gibson, etc. These optics may well enhance the quality of work that can be done with laboratory sources when used with single crystals of modest-size unit cells. Don Bilderback, Cornell U., Ithaca, NY, USA Quantifying Similarity of Coordination "What compounds have structures similar to the compound that I am currently studying?" is a question often asked by people working in the field of inorganic crystals. They are often surprised to find that there is no simple answer. The problem lies in what one means by "similar". Isostructural examples of simple binary compounds that crystallize with the NaCl or calcium fluoride structure can be easily found because all NaCl-type structures are identical, but this is not true of more complex compounds. The coordination environments of "similar" compounds are rarely identical. But how does one quantify the difference? Two recent papers in Acta Cryst. B provide partial answers to this question. The purpose of the paper by Makovicky & Balic-Zunic ["A New Measure of Distortion for Coordination Polyhedra", Acta Cryst. B54 (1998), 766-773] is to quantify the degree of distortion of a coordination polyhedron from regularity. By plotting the volume of the coordination polyhedron against the volume of the circumscribed sphere for a number of isostructural compounds, the structures can be quickly classified by their degree of polyhedral distortion. The paper by Bergerhoff, Berndt, Brandenburg & Degen ["Concerning Inorganic Structure Types", Acta Cryst. B55 (1999), in proof] proposes a more direct way of finding similar structures by scanning the databases for isopointal compounds that crystallize in the same space group and have atoms occupying the same Wyckoff positions. They have constructed a database of Standard Inorganic Crystal Structures (SICS) selecting the best structure determination for each compound reported in the Inorganic Crystal Structure Database and transforming it to a standard setting. Numerical descriptors stored in SICS measure the degree of difference between each pair of isopointal compounds. We may not yet have found the perfect measure of similarity, but these two papers point the way. I.D. Brown, McMaster U., Hamilton, Canada Something for Everyone in Acta CIssues of Acta C have a broad spectrum of structures for all tastes and disciplines; inorganic to organic structures, X-rays and neutrons diffraction studies at low-temperature and high from powders and crystals, some with disorder but most without. The large December 1998 issue of Section C contained the following interesting examples. The characterization of a mixed valence (MnIII, MnIV) manganese complex [(bpy)2Mn(u-O)2Mn(bpy)2] (ClO4)3.CbH5NO2. 0.5H2O] by Lashgari et al. (pp. 1797-9), using crystallographic and IR spectroscopy methods, shows quite different and unusual manganese environments. Rabinovich et al. (pp. 1740-2) show that in the hydrated uranium (IV) bromide structure [UBr(H2O)8]Br3.H2O, the uranium atom is coordinated in a novel tricapped trigonal prismatic arrangement. Among the many organic studies, commercial paracetamol is shown by Clegg et al. (pp. 1881-2) to yield on crystallization diparacetomol as an oxidatively coupled dimer. Bromine aficionados will enjoy a very interesting and detailed study of a hydrogen-bonded anhydrous theobromine structure reported by Ford, Ebisuzaki and Boyle (pp. 1980-3). The definitive power of our "non-sporting method" is demonstrated yet again in the ellucidation of the structure of epiclusianone (Santos et al., pp. 1990-2). A brave effort by Bemm and Oestmark (pp. 1997-9) defines precisely the nature of the explosive 1,1-diamino-2,2-dinitroethylene and assists in explaining its properties. The rationalization of the blue luminescence of tetracyano-p-xylene is given by Arena et al. (pp 2003-5) in terms of its crystal stacking interaction. Sydney R Hall, Crystallography Centre, U. of Western Australia |
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All ten crystallographic nomenclature reports by the Commission published in Acta Crystallographica are now online at: http://www.iucr.ac.uk/iucr-top/comm/cnom/index.html. Nomenclature of Polytype Structures. Acta Cryst. A40 (1984), 399-404, Nomenclature for Crystal Families, Bravais-Lattice Types and Arithmetic Classes. Acta Cryst. A41 (1985), 278-280, Nomenclature of Inorganic Structure Types. Acta Cryst. A46 (1990), 1-11, Statistical Descriptors in Crystallography. Acta Cryst. A45 (1989), 63-75 and Acta Cryst. A51 (1995), 565-569, Definition of Symmetry Elements in Space Groups and Point Groups. Acta Cryst. A45 (1989), 494-499, Symbols for Symmetry Elements and Symmetry Operations. Acta Cryst. A48 (1992), 727-732, Nomenclature, Symbols and Classification of the Subperiodic Groups. Acta Cryst. A49 (1993), 594, Atomic Displacement Parameter Nomenclature Acta Cryst. (1996), A52, 770-781, Structural Phase Transition Nomenclature. Acta Cryst. A54 (1998), 1028-1033 Online availability of the nomenclature reports of the IUCr and its sister organizations is expected to ease the difficulty many working scientists have in accessing recommended nomenclature that previously was available only in print. This Webpage also provides hotlinks to the nomenclature resources of the Bureau International des Poids et Mesures (Home of the SI system of units), IUPAC (International Union of Pure & Applied Chemistry), ISO (International Organization for Standardization) Technical Committee 12: Quantities, units, symbols, conversion factors, and IUPAP (International Union of Pure & Applied Physics) Commission on Symbols, Units, Nomenclature, Atomic Masses and Fundamental Constants (SUNAMCO) among others. S. C. Abrahams, USA |
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IUCr President, Ted Baker, presided over the session commemorating the formation of the International Union of Crystallography at the 1998 annual meetings of the three regional affiliates of the IUCr. At the first of these sessions at the ACA meeting in Washington, D.W.J. Cruickshank presented a historical review of the formation of the Union in 1946, the first General Assembly and Congress of the IUCr held at Harvard in 1948, the publication efforts of the Union, and the roles of figures such as Paul Ewald and Robert Evans in founding the Union. Cruickshank provided statistics showing how Acta Crystallographica has grown over the years. G.R. Desiraju then gave a talk on crystal engineering and stressed the parallels between it and inorganic chemistry. Both fields require a combination of analysis and synthesis. Observing and understanding the intermolecular interactions giving rise to crystals constitutes the analytical component of crystal engineering, while the techniques used to design new solids and materials makes up the synthetic part. I.K. Robinson showed several examples of diffraction techniques applied to the study of surfaces. He presented the problems and nomenclature associated with surfaces science very effectively for members of the audience more accustomed to working with three-dimensional crystal structures. L.N. Johnson summarized crystallography's impact on biology and biochemistry. She presented several examples ranging from early studies of protein crystals to the large number of contemporary structures that have made X-ray crystallography a major component of structural biology. The second 50th anniversary session took place at ECM 18 in the Czech Republic where H.B. Bürgi's elegant talk illustrated the power of X-ray crystallography to determine the transitional, rotational and vibrational movement of molecules with high resolution, precision and accuracy and provided reliable data with which to test and extend theories of molecular structure and dynamics. J. White combined the use of neutrons and X-ray powder diffraction, optical microscopy and small angle surface diffraction techniques to obtain stunning images and detailed information concerning growing surfaces, thin films and liquid crystals. White provided examples of simple forms of life having highly reproducible extremely varied structure of complex symmetry. W. Hendrickson gave a brilliant guided tour of the short but spectacular history of macromolecular crystallography. He noted that as of 1997 there are 8,800 known protein structures and he gave a thumb nail sketch of some of the most recent, most complex and most exciting additions to the protein data bank including the nucleasome core particle, a membrane ion channel, a yeast 20S protesasome having 50,000 non hydrogen atoms, and his own study of a protein that the AIDS virus uses to attach to blood cells it infects. Finally, Hendrickson described emerging technical developments that will turn the promise of the genome project into the reality of understanding the structure and function of the thousands of unknown proteins encoded in the human, animal, insect, plant, and bacterial genomes. He predicted advances in undulator sources, CCD detectors, cryo-crystallography, MAD phasing analysis and selenomethionyl protein production. At the anniversary session at the AsCa meeting in Malasia, A. Jenner, co-recipient of the 1998 Azimov Prize, presented a remarkable analysis of the complex, multi-dimensional, mathematical and geometric symmentry patterns that he finds in the forms we see in nature ranging from snow flakes and ice crystals to viruses and membrane proteins. Everything from stain glass windows to the logo from the Atlanta ACA Meeting is seen through new eyes when you witness a lecture by Jenner. C. Brock gave a superb presentation, describing the conformational complexity of the deceptively simple biphenyl molecule. The review covered history, interdisciplinary science, theory, solid, solution, and gas state experiment and the future. X-ray results on various polymorphs and analogues of bipheyl reveal twist angles between the rings, varying from 0° to 68°. Electron diffraction studies of the twist angle in unsubstituted biphenyl consistently give an angle of 42°. Carol ended her talk with a summary of some of the latest technological advances including simultaneous refinement of multiple temperature data sets, analysis of non Bragg scattering data, ab initio structure determination for powder data, and characterization and prediction of packing patterns that should permit further analysis, interpretation and understanding of the biphenyl conundrum over the next 60 years. T. Tsukihara gave an insightful description and analysis of the extraordinary complex and exquisitely beautiful structure of a cytochome oxidase. He sorted out the pieces of the enzyme and then assembled them like a master architect explaining in detail the two protein pathways through the enzymes that are consistent with mutation studies and function of the enzyme. Tsukihara's talent for eloquently describing the assembly of two copies of the 13 different proteins in the enzyme is as awe inpiring as the self assembly process mastered by nature over a few million years. R. Stenkamp and W.L. Duax |
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Highlights of the 1998 meeting of the American Crystallographic Association (July 18-23, Arlington, Virginia) include the session marking the 50th anniversary of the IUCr, the transaction symposium on Crystal Engineering, a lively press conference, and a vist to the Hall of Geology, Gems and Minerals at the National Museum of Natural History. Transactions Symposium: Crystal EngineeringCrystal Engineering is a cross-disciplinary field that concerns the development of protocols for predicting and controlling the structure and functional properties of solids. Such properties include color and melting point, polarity, porosity and conductivity and are relevant to areas as diverse as nonlinear optics, high Tc superconductors and polymorphism in pharmaceuticals. The session on Analysis, Prediction and Crystal Growth included talks on graph set notation in hydrogen bonded systems (R. Davis), prediction of entire crystal structures (S. Price), imaging crystals during growth using atomic force microscopy and self-assembly of higher density materials using organic/inorganic interfaces (T. Palmore). A session on Applications of Crystal Engineering described formation of inorganic coordination polymers as ion exchange or absorptive materials (R. Rogers), inorganic ion exchange in nuclear waste clean-up (A. Clearfield), the solid state reactivity of tailored stereoselective materials (B. Foxman) and a supermolecular synthon (K. Birdha). Hybrid Structures described organic/inorganic synthons with charge assisted hydrogen bonding and metal ion coordination (C. Aakeroy), nicotinamide lamellar organic sheets separated by rigid pillars with Ag(I) coordination, ligand coordinated polymers stabilized by large inorganic anions (J. Zubieta), the use of aggregates rather than molecules as building blocks (J. MacDonald), and multicomponents architectures (L. McGillavary). Discriptions of Weak Interactions included many that were stronger than conventional hydrogen bonds, including donor/acceptor bonding combined with CH-O hydrogen bonding in heterocyclic N-oxides (S. Blackstock), N-I interactions forming extended chains, dimers, or simple adducts (B. Pennington), and the six-fold phenyl embrace ubiquitous in the CSD and quite capable of directing overall structure (T. Steiner). G. Desiraju challenged the audience to devise new methods to compare, analyze and codify structures. He warned that unless such methods are developed, we will simply drown in a sea of crystal structures. The symposium was organized by R. Rogers (U. of Alabama) and M. Zaworotko (U. of Winnipeg). The Transaction Proceedings will be published in the Spring of 1999. [R. Rogers] Small Angle Scattering from Complex MaterialsSmall-angle scattering of neutrons and X-rays can help integrate structural data from other methods (high resolution crystallographic, NMR, electron microscopy, etc) to the study of complex materials. The use of small-angle scattering techniques is driven by advances in chemical synthesis, deuterium labeling, computational power, algorithm development and modeling capabilities. Applications described included studies of the regulation of kinase activity (J. Zhao and J. Trewhella), proteins that aid in protein folding (R. May), ab initio protein folding, protein compaction and changes in hydration (S. Doniach), prion association implicated in neurodegenerative diseases (S. Doniach), aggregation of b-amyloid peptides linked to Alzheimer's disease (T. Thiyagaran) and the hydrothermal synthesis of zeolite NaA (S. Han). New developments in micro-synchrotron beams and lithographically fabricated mixing cells currently are being explored at CHESS and Princeton. A session on modeling small-angle scattering data addressed biological structures, materials and dislocations. Speakers described a suite of programs for biological structures and polydisperse systems (D. Svergun, svergun@embl-hamburg.de), analysis of membrane mimetic, self-assembled lipid layers and Langmuir-Blodgett films using reflectivity data (N. Berk), Monte Carlo simulation of micellar and polymer systems (J. Skov Pedersen), reverse Monte Carlo algorithms to model glass structure (J. Zwanziger), randomly oriented non-crystalline systems of interacting scatterers with structure on length scales from 10-20,000 Å (P. Schmidt), multiple small-angle neutron scattering from plasma-sprayed ceramic deposit microstructures with correlation to electron microscope images (A. Allen), and ultra-small-angle X-ray scattering by dislocation in single-crystal aluminum as a function of plastic deformation (G. Long). Small-angle scattering is ideal for monitoring conformational transitions and dynamic processes in non-crystalline states. Neutron contrast variation, and more sophisticated sample environments continue to expand the potential for materials research with these tools. [J. Trewhella] The session on Electronic Materials, organized by D. Cox and W. Wong-Ng, highlighted state-of-the-art X-ray and neutron diffraction studies of materials having useful electric and magnetic properties. Presentations included studies of the variation in the Tc of HgBa2CuO4+d (E. Antipov, Moscow), complex phase diagrams of mixed metal oxides (D.J. Buttrey, Delaware), magnetic ordering (G. Bottger), bond valence calculations for metal oxides (T. Santoro, NIST); magnetic phase transitions in systems with colossal magnetoresistance (P. Woodward, New York), ferromagnetic ordering in layered Mn(ReO4)2 where hydrogen bonding paths between layers play a role in the ordering (C. Torardi, DuPont), crystal engineering based on heterocycle radicals (W. Cordes, Arkansas), promising candidates for the next generation of hard magnets (H.Luo, Missouri-Columbia), and ternary BaO:TiO2:Fe2O3 phases having structural features corresponding to natural magnetic multilayers (L.A. Bendersky, Maryland). B. Sales (Tennessee) discussed filled skutterudites (LnFe3CoSb12) in which a "rattling" lanthanide atom results in low thermal conductivity. Other topics were a space charge model explaining the perovskite relaxor ferroelectrics (P. Davies, Pennsylvania), electrochemical expansion and contraction of AB5-type alloys and design of lower-cost non-Co alloys for use in nickel-metal-hydride batteries (T. Vogt, New York), experiments to determine the polarization charge density in GaAs requiring repeated measurement of several thousand intensities to obtain adequate statistics (U. Pietsch, Postdam), and characterization of three new high-temperature polymorphs of potassium dihydrogen phosphate determined by studying single-crystal islands within polycrystalline fragments. (A. Subramony, Washington). [J. Kaduk] The Computational Methods session focused on user-friendly computational tools to better determine, visualize, and understand macromolecular structures. The wide range of topics covered included direct methods (I. Uson, Gottingen) density modification (G. Perrakis, EMBL Grenoble), structure completion (G. Bricogne, MRC-LMB Cambridge), six-dimensional Molecular Replacement (S. Sheriff, BMS; C. Kissinger, Agouron Pharm.), and 'Multi-MAD' strategies (A. Brunger, Yale). Small signals are increasingly used to learn more about the behavior of proteins at very high resolution (D. Brodersen, Aarhus) and very low resolution (B. Yu, Tallahassee). The anomalous signal of sulfur atoms at only ONE wavelength (SAD method) has even been used to solve a structure ab initio by classical heavy-atom phasing (Z. Dauter, Brookhaven) with direct methods being used only to detect the position of the anomalous scatterers! [E. de La Fortelle] With respect to Direct Phasing of Macromolecules, structures containing as many as 2,000 non-hydrogen atoms are being solved routinely by Shake-and -Bake and SHELX "half baked" methods by Hauptman, Sheldrick, Weeks and Schafer. Gilmore described results from the maximum entropy-likelihood method focused on expanding the viability of the direct methods to lower resolution data. Direct methods procedures have proven to be extremely useful in tackling large proteins with substructures containing as many as 30 Se atoms (Smith and Howell). Low resolution data studies included the application of the Few Atoms Model (FAM) to the 50S Ribosomal Particles (Podjarny), using "glob" scattering factors with projected electron diffraction data (Dorset), and a procedure based on the genetic algorithm paradigm (Miller) for icosahedral viruses. [S. Fortier] H. Einspahr (New Jersey), chairman of the symposium on Structure Based Drug Design, noted that structural information impacts the drug-design process at the lead-finding and lead optimization phases. Speakers discussed the design of inhibitors of tropical disease targets, cholera toxin and glyceraldehyde-3-phosphate dehydrogenase (W. Hol, Washington), HIV-1 protease inhibitors that combine potency, solubility, oral bioavailability, serum lifetime and safety (P. Fitzgerald, New Jersey), influenza virus neuraminidase inhibitors with nanomolar potencies (M. Luo, Alabama), dipeptide mimetics that preserved the essential backbone structure of a compound while disguising it from proteases (A. Swain, New Jersey), and ribosome-inhibiting proteins including ricin, shiga toxin and versatile pterin compounds (J. Robertus, Texas). Other protease targets described included Ras farnesyl transferase (C. Strickland, UK), integrase (J. Alexandratos, Maryland), and aldose and aldehyde reductases associated with the complications of diabetes (O. El-Kabbani, Australia). S. Abdel-Meguid (Pennsylvania) emphasized the importance to structure base drug design of experience, synthetic accessibility, water molecules, solubility of ligands, electrostatics, iterative design, maximizing interactions, starting the design from liganded structures and having dedicated molecular biology and protein purification teams. [H. Einspahr] Amorphous Materials pose a challenge to structural characterization techniques. A workshop on the topic concerned numerical modeling of disordered materials based on diffraction data and reliable representations of atomic interactions. P.H. Gaskell (UK) demonstrated how chemical bonding constraints can be used to help interpret low-Q diffraction data. R. McGreevy (Sweden) presented his reverse Monte Carlo method and D. Drabold (Ohio) and P. Vashishta (Louisiana) illustrated atomic scale simulation methods combining first-principle electronic orbital calculations with multi-million atom dynamic simulations to uncover extended-range structural characteristics. The full program included a Symposium on Non Oxide Gases (organized by J. Zwanziger, Indiana), Surfaces, Interfaces and Films (organized by W. Dmowski, Pennsylvania) and Colloids and Gels (organized by J. Kieffer, Illinois). The symposium on surfaces focused on the characterization of structural disorder in narrow interfacial regions and applications of state-of-the-art techniques ranging from small-angle and synchrotron X-ray scattering, to neutron reflection. B. Aiken (New York) illustrated potential photonic applications of some non-oxide glasses and R. Bush (California) described recently discovered five component bulk metallic glasses that remain amorphous and have outstanding mechanical properties without requiring the extreme quench rates typically associated with metallic glasses.[J. Kieffer] In a symposium on Neutron Scattering in Structural Biology, organized by B. Schoenborn and B. Von Dreele (New Mexico), speakers described locating solvent and hydrogen positions in crystals of tetragonal lysozyme (N. Niimura, Japan), concanavalin A (J. Helliwell, UK) and coenzyme cob (II)alamin (P. Langan, France). LADI uses a cold quasi-Laue beam in combination with a large neutron image plate (IP) detector to improve data collection efficiently. Comparisons of neutron and X-ray scattering density maps of myoglobin show that hydrogen can be located in atomic resolution X-ray maps. P. Langan described the structural biology station at LANL. With spallation neutrons and their time-dependent wavelength structure, diffraction data are collected as wavelength resolved spectra. B. VonDreele uses neutron powder diffraction to screen heavy atom derivatives and follow changes in protein conformation and packing. Other speakers discussed the use of low resolution (~12Å) neutron diffraction to locate detergent in crystal forms of porins (P. Timmins, France), phasing using a buried reference layer (C. Majkrzak, Maryland) and supermirror coated guides to maximize neutron flux (D. Clemens, Switzerland). Improvements in fiber data collection technology were described for studies of the coat protein of filamentous bacteriophage M13 (M. Ivanova, Florida), and DNA hydration using data collected with a large array of microstrip detectors was described (T. Forsyth, UK). The closing round table session chaired by J. Sacchettini (Texas), G. Bunick (Tennessee) and P. Langan addressed coordination of software development for new instruments, advantages of medium resolution neutron studies over high-resolution X-ray studies for locating hydrogen and the need for larger crystals and perdeuterated proteins. [P. Langan] In the General Interest Group Session, Ways of Thinking about Structures, M. Spackman (Australia) described a new way of defining boundary surfaces around molecules in a crystal structure. Y. Abramov (New York) reported experimental and theoretical studies of the charge density in crystal structures of four D,L amino acids, emphasizing the bond critical points for the hydrogen bonds, and E. Bruton( Missouri) described a Cambridge Structural Database search for hydrogen bonds of the type D-HX-M in (M, a transition metal; X,F,Cl or Br; and D,C,N or O). Bruton's results are consistent with an electrostatic theory for hydrogen bonding. W. Ojala (Minnesota) presented a class of benzylidineanilines with a nitrile at one end and a halogen at the other that are acutely sensitive to the switching of the two substituents. Other topics included highly complex tiling patterns in the crystal structures of aluminum rich intermetallic compounds that contain pentagons which share edges connected by quadrilaterals and triangles (E. Ryba, Pennsylvania), a new way to look at familiar space group diagrams(C. Johnson, Tennessee), and the modelling of molecular features observed on the (110) face of a lysozyme crystal using an atomic force microscope (J. Konnert, Washington, D.C.). [Carol Brock] A session on Publication and Presentation of Crystallographic Results focused on tools, techniques, and philosophy. K. Duffy of ACS Journals discussed preparation of graphics for publication (http://www.pubs.acs.org/instruct/illus.html). The key advice is to use high quality originals directly from a laser printer and make the original 3.25 inches wide in order to identify potential surprises when reduced. G. Petsko spoke on the craft of lecturing and advised 1) Tell a story; 2) Tell only one story, 3) Tell the audience what you're going to tell them, tell them, and tell them what you told them; 4) Give a maximum of 24-33% background material; 5) Vary the pace of the talk, use no more than 1 slide/minute and at least 1 slide/2 minutes; 6) Be sure that all your slides/overheads can be clearly seen from the back of a large room that is not very dark so that you can still make eye contact with your audience. The minimum font size is 28 point, bold or even extra bold; 7) For complex subjects, try to find the right metaphor; 8) Be yourself, and use humor only if it's natural to you; 9) Don't read your slides, summarize them in different words; 10) Be gracious, give lots of credit; 11) Use colorful language and try to blend in analogies with every day life; 12) Don't use gimmicks like two projectors that might get in the way of clarity. [M. Olmstead] Over 1,100 crystallographers attended to hear 225 oral presentations, view the 350 posters and visit the exhibition where over 20 industrial companies displayed the latest in equipment, apparatus, books, software and services. Reporters and science writers attending a press conference heard presentations of highlights of the meeting. Subsequent media coverage included editorials highlighting the macromolecular program in Science and Nature Structural Biology and commentary in Physics Today. The banquet featured a presentation of the Elizabeth Wood Writing Award for 1998 to Robert Hazen. A full report of the oral presentations appeared in the Fall 1998 issue of the ACA Newsletter and can be viewed at http://www.hwi.buffalo.edu/ACA. The Local Chair was W. Wong-Ng and the Program Chair Louie Delbaere.
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Sixty microsymposia and over 592 posters covered 46 different topics of crystallography at the Eighteenth European Crystallographic Meeting (Aug. 16-20, Prague, Czech Republic). Highlights of twenty-two of the sessions reported by session chairs are included here. Microsymposia topics are in bold print. The session on Phase Transitions (A2) included an excellent review of theoretical methods and sophisticated computer programs to study phase transitions (K. Schwarz, Vienna). Analysis of structural pathways relating different modifications of polymorphic compounds using Periodic Nodal Surfaces (S. Leoni, Zurich), powerful crystallographic methods for the study of Spin-Peierls phase transitions (M. Braden, Karlsruhe), and unusual first-order phase transitions without change of space group symmetry and isosymmetrical phase transitions in alkali borates (S. Filatov, St. Petersburg) were also described. T. Hahn (Aachen), V. Janovec (Prague) and H. Klapper (Bonn), who are collaborating on a review article about twins and domains, all gave insights into the current state of the topic. [L.Bohaty] The Microsymposium on Mineralogical Crystallography (B1) began with a review lecture by R. Allmann (Germany) concerning the minerals in the Inorganic Structure Database. Other talks concerned the P-V-T equation of state of phengite-3T (G. Ferraris, Italy), deviations from ideal symmetry in wollastonite-like structures (J. Hybler, Czech Republic), and in alums and garnets (O. Frank-Kamenetskaya, Russia), and determination of the position and orientation of guest species in intercalating clay minerals (D. Janeba, Czech Republic). Finally, D. Gubareva (Russia) demonstrated that the water state in various vein quartz samples, as revealed and characterized by TEM and IRS, can be indicative of their ore-bearing capacity. [S. Durovic] S. Hovmöller described the solution of unknown crystal structures from high resolution Electron Microscopy and Electron Diffraction (B2) patterns using direct methods. Both EM and ED data permit structure refinements to an accuracy of about 0.01 Å in atomic positions for inorganic crystals. W. Neumann and the Oslo group (Gjønnes, Hansen and Li) described characterising new advanced materials, including quantum wires, quantum dots and clusters and precipitates in alloys. G.N. Kryukova (Novosibirsk) characterized metal oxides used for catalysis in detail. [S. Hovmoller] H. Gleiter (Germany), a pioneer in the field of Nanocrystalline Materials (B3) reviewed theoretical and experimental information concerning the structure of interfaces, grain sizes of crystallites, conventional grain boundaries and applications to nanocrystalline materials. C.E. Krill (Germany) discussed structural analysis of grain sizes, strains and atomic displacements in nanoscaled solids. The effects of particle size on ferromagnetism and magnetoresistivity (C. Vazquez- Vazquez, Spain), the study of grain boundaries and orientation correlationship by atomic resolution electron microscopy (W.M. Straub, Germany) and the preparation of materials having severe plastic deformation properties (I.V. Alexandrov) were discussed. [H. Schaefer] P. Laggner (Australia) opened the symposium on Small Angle Scattering (B6) with a survey of highly-promising SAX applications in synchrotron radiation and related research and analytical laboratory routines, and chemical industry production controls. This was followed by a discussion of the particle chord-length distribution function and the interpretation of particle scattering (W. Gille, Germany) and an account of SANS studies on "onion-type", three-layer block-copolymer micelles with promise for waste removal recovery (J. Plestil, Prague). The microstructure of Ni-based superalloys was the focus of the talk by P. Strunz (Prague). Talks on a new design for moderate pressure studies of liquid crystal phase transitions (M. Steinhart, Prague), and the influence of salts on serum albumin solution structure and aggregation (S. Mokeeva, Russia) rounded out the session. [P. Laggner] Presentations in the symposium on Aperiodic Crystals (B7) included a new theoretical approach for structure factor calculation of aperiodic structures based on the reference lattice concept (J. Wolny, Krakow), a unified description of the crystal chemistry of a family of oxide pyroborates based on superspace group symmetry analysis (S. Schmid, Canberra), the advantages of the super space group approach to the description of complex layer structures (S. van Smaalen, Bayreuth), an electron diffraction study of intermetallic compounds (S. Lidin, Stockholm), and use of antiphase boundaries to describe structure with displacement waves propagating along specific crystallographic directions (A. Ustinov, Kiev). S.B. Abraham, (Beer-Scheba) used the cluster approach to redetermine the structure of quasicrystals of Mn80Si15Al5, previously studied in terms of the Amman-Beenker cluster. T. Janssen discussed the mission and objectives of the special interest group on aperiodic crystals of the European Crystallography Assn (http://www-xray.fzu.cz/sgip/aphome.html) .[G. Chapuis] Topics in the symposium on Low-ordered Structures/Fibre Diffraction (B8) included time-resolved SAXS/WAXS experiments on phase-transition of non-crystalline samples (W. Bras, France), correlation of fibre diffraction data and molecular dynamics (MD) simulations on cellulose II fibres (L.M.J. Kroon-Batenburg, The Netherlands), studies of the dynamic structure of water in a biological polyelectrolyte (A. Deriu, Italy), a new procedure to retrieve partial radial distribution functions in amorphous materials using anomalous scattering (A. Burian, Poland), studies of fibrillin rich microfibrils and their three-dimensional arrays in vivo (T.J. Wess, UK), localization of deuterium labels in purple membranes by neutron diffraction (M. Weik, France) and the influence of hydrogen bonds on gel formation in peptide-based molecules (B. Kojic-Prodic, Croatia). [J. Kroon] The microsymposium on Systematics and Structure-Function Relationship in Organic Chemistry (C2) covered polymorphism, hydration, inclusion phenomena, and weak intra- and intermolecular interactions in condensed media. 200 years after Klaproth's discovery of two polymorphic forms of calcium carbonate (calcite and aragonite), F. Herbstein (Israel) presented examples of different forms of polymorphism, introduced a physical chemical scale for polymorphism and suggested a new nomenclature. F. J. J. Dijksma's (Scotland) studies of anhydrous brucine and its two hydrates, using DSC, TGA and X-ray powder diffraction, indicate that dehydration of the tetrahydrate proceeds via a dihydrate, that mediates the reversal of layers between tetrahydrate and anhydrous forms. Brucine is used to separate racemic mixtures by co-crystallization, and the hexapedal host compounds discussed by S.A. Bourne (South Africa) show molecular recognition properties with practical applications. A provocative opinion about the forces responsible for holding the organic world together, was presented by J.D. Dunitz (Switzerland). A crystal structure corresponds to an equilibrium at which attractive and repulsive forces must balance. Dunitz contends that at normal contact distances the dominant force is invariably repulsive and crystals are held together mainly by repulsions that oppose the disentanglement of interlocking molecules rather than by attractive forces. T. Borowiak (Poland) used data from the Cambridge Structural Database to demonstrate the importance of weak 1,4 - non-bonded interactions of the S...O and S...S type in stabilizing the geometry of 3,4'-diquinolinyl sulfides and M. Nieger (Germany) discussed the merit of using CCD detectors for collecting X-ray data for small molecules. [U. Rychlewska] The symposium on Inorganic Compounds (C5) included a review lecture (V. Kaucic, Ljubljana), analysis of structures of cobalt/nickel containing aluminides with filled pentagonal clusters (M. Ellner), phase stability and physical properties of the YbCu5-related intermetallics (K. Kosuge), analysis of intercalates (P. Èapková), non-linear pseudohalides in copper(II) complexes (M. Dunaj-Jurèo) anion-centred tetrahedra (S. Filatov), physical properties of compounds in the phase-system Ln2O3-ReO2-Re2O7 (H. Ehrenberg), and use of the bond-valence concept in inorganic crystallography (A. Santoro). [R. Cerny and Z. Weiss] The scope of Supramolecular Assemblies and Inclusion Compounds (C7) has expanded from molecular recognition involving cyclodextrins, calixarenes, or crown ethers to using non covalent forces (hydrogen bonds, Van der Waals forces, P-P interactions and coordination bonds) to design super molecular (SM) assemblies with specific architecture and properties including components with predesigned chemical functions and the ability to self assemble. Supramolecular chemistry relies on 3D structural information provided by X-ray crystallographic analysis to design new compounds and characterize final products. Several novel crystalline SM families are based on the synergy between two different types of building blocks and synthons endowed with directional linking functions. A section on natural or semi-natural compounds included talks on isolation and crystallization of cyclodextrins with 9,10,14,16 and 26 rings having saccharide conformations related to glycoproteins (K. Gessler, Germany), total chiral separation from a racemic mixture of a phermomone in the chiral cavity of a trimethylated cyclodextrin utilizing van der Waals forces and weak polar interactions (I. Mavridis, Greece), bile acids and salts as useful models of biliary stone formation (S. Candeloro, Italy) and complexation of aromatic glycosides and b-cyclodextrin (L. Malpezzi, Italy). Other new materials described included porphyrins used to control metal binding photosynthetic systems and nanoporous solids (I. Goldberg), a urea inclusion complex that undergoes continuous replacement of one hydrocarbon guest by another with enantiomeric discrimination, polyoxometallic (Mo, V and W) derivatives useful for catalysis (R.A. Coxallet, UK), calixarenes with metal chloride anions (A.T. Gubaidullin, Russia), cationic receptor complexes that alter cis-trans photoequilibrium of the guest (M. Cesario, France) and Cs-selective crown ethers with a cavity governed by a counter anion (J. A. Manskava, Ukraine). [G. Tsoucaris] The session on Transmission and Signaling Across Membranes (D1) began with a review of studies on the regulation of the oncogene ras by GAP proteins, resulting in an acceleration of its GTPase activity (A. Wittinghofer, Germany). The recent structure of the Ras-RasGAP complex shows how the "arginine finger" of GAP inserts into the switch II region of Ras and triggers a change which enhances GTP catalysis. S. Smerdon (UK) described complementary work on the regulation of the rho-family small G-proteins. The work of both groups has enhanced understanding on the activation mechanism of Ras and Ras related proteins, whose cancer causing forms are responsible for a significant fraction of human tumors. E. Baraldi (Germany) described a complex structure that causes X-linked immunodeficiency in humans. O. Mayans (Germany) described the autoinhibited form of the serine kinase of the giant muscle protein titin which revealed blockage of the catalytic aspartate, common to all known protein kinases, by a tyrosine not from the activation segment. The structure revealed a two-step activation mechanism with binding of Ca2+ and calmodulin and specific phosphorylation of the critical tyrosine. These molecules are important targets for the design of antiviral drugs. R. Engh (Germany) described inhibitors for cAMP dependent protein kinase, and H.J. Snijder (The Netherlands) presented the first structure of is an integrated membrane phospholipase. The 12 strand-b-barrel of this protein is reminiscent of porins which have 16 or more strands. The audience was fascinated to see how biology has transferred the same catalytic activity into a completely different protein context. [M. Wilmanns] The microsymposium on DNA/RNA Structure (D2) had contributions from the most active areas in this rapidly-growing field. Z. Shakked (Israel) described DNA sequences involved in protein recognition, including conserved and flanking sequences in the binding site of the E2 papillomavirus protein. She showed how knowledge of native DNAs is revealing information on their ability to be perturbed by protein binding. Other talks described the remarkable structure of the sequence d(GCGAAAGCT), which forms a duplex with the central run of adenines formed into a zipper-like stack of bases, flanked by GA mismatches (B. Shepard, France), progress on the structure of 5SRNA (C. Betzel, Germany), and major-groove complexes involving several intercalating agents in current clinical trial (C. Cardin, UK). G. Leonard (France) described the second DNA-RNA hybrid crystal structure, in which alternation of the backbone in the RNA strand is in striking contrast to a model proposed from NMR studies, emphasising the need for more structural information. B. Luisi (UK) presented a data-base approach to the analysis of amine-amine close contacts in the major groove of oligonucleotide structures with high base-pair propeller twists. [S. Neidle] Presentations in the Immune Recognition (D6) symposium concerned acquired immune response, innate immune responses and signal transduction in lymphocytes. The structure of the human Bactericidal/Permeability Increasing Protein that neutralises inflammatory response, revealed bound phosphatidylcholine, suggesting its mode of action (L. Beamer, USA). A Fab antibody complex explained the relative difference in hydrolysis rates of esteres (B. Gigant, France), and the antigenic determinants of birch tree pollen, showed the epitope to be one of three determinants found in homologous tree pollen allergens (M. Gajhede, Denmark). Camelid antibodies present a curiosity among immunoglobulin structures since they are composed of heavy chains only. In the structure of the complex formed between the VH domain of a camelid antibody and lysozyme, the unusual arrangement of CDR1 and CDR3 creates an antigen-binding site that could readily enter the substrate-binding site of lysozyme (L. Wyns, Brussel). The combined use of X-ray crystallography and electron microscopy was discussed by E. Hewat (France) and illustrations of how neutralising anti-viral antibodies can function either by blocking the host receptor-binding site (Foot and Mouth Disease Virus) or by impairment of dissociation of the virus (Rhinovirus) were presented. D. Housset (France) described a new fold for the Vb domain in the structure of a Fv fragment of a T cell receptor. K. Fütterer (USA) described how the conformational flexibility and structural independence of the two SH2 domains of a protein kinase could account for the activity of the enzyme in several different immune signal transduction pathways. [G. Bentley] P. Lindley (France) reviewed the importance of Metalloprotein (D8) photosynthesis, oxydative phosphorylation and nitrogen fixation and the power of diffraction and spectroscopic techniques to investigate the chemistry of these important metal centres. D. Garner (UK) also stressed the importance of high resolution macromolecular crystallography in studying metal centres essential for normal growth and development and introduced the concept of the Bond Valence Sum rule and a distortion theorem to assist in determining details of the metal coordination. Other presentations described the mechanism of action of a complex of dimethylsulphoxide (DMSO) with an oxotransferase containing a molybdopterin cofactor (S. Bailey, UK), hydrogen metabolising enzymes with [Ni-Fe] centres responsible for base-assisted heterolytic cleavage of hydrogen molecule (M. Frey, Grenoble), structures of a cytochrome c6 and a dimeric cytochrome c3 (C. Frazão, Portugal), a catalytic mechanism based on structural and kinetic data on vanadium halo-peroxidases (A. Messerschmidt, Munich), and calcium dependence of the complex formation between the S100 proteins and the annexins (S. Réty, France). [P. Lindley] The importance of Synchrotron Radiation (E1) was emphasized in two of the three opening plenary lectures. V. Kaucic reviewed the latest advances in inorganic crystallography fostered by the brightness, high energy and high resolution of the 4th generation sources (submicrometer line focus and sub picoseconed pulses). Kaucic discussed introducing specific changes into zeolites and the use of neutron capability to map magnetic moments. Z. Dauter gave a comprehensive review of macromolecular applications of synchrotron radiation to high resolution structures. Talks covered macromolecular applications (Z.Dauter), magnetic x-ray scattering (C.Vettier), powder diffraction (D.E. Cox), microfocussing optics (I.Snigireva) and studies of supramolecular chemistry (W.Clegg). [Ake Kvick] The Neutron Scattering (E2) symposium included a review of research opportunities in Europe at Grenoble, Oxford, Berlin and Dubna, (J. Kulda, ILL http://www.psi.ch/ensa) Other talks included a review of dynamical studies of microelectron volt excitations, hydrogen motions and magnetic excitations in calixarene inclusion compounds (R. Caciuffo, Ancona), evidence that composite curved monochromators of perfect crystals can outperform graphite (P. Mikula, Rez), a study of mercury superconductors at pressures up to 5GPa (B. Savenko, Dubna) and protein crystallographic studies using neutron sensitive image plates and quasi-Laue technique (D. Myles, Grenoble). [C J Carlile] S. Neidle (UK) began the session on Structure and Function in Molecular Biology (E3) with a review of DNA structures including quadruplexes with potential applications in cancer therapy. Other talks concerned the classification of DNA sequences according to curvature characteristics and the influence of DNA flexibility on gene regulation, packing and replication (S. Pongor, Trieste), studies of the solvation of DNA showing that water and cations that bind in well defined sites may contribute to specificity of DNA interactions with gene regulating proteins (B. Schneider, Prague), evidence of ligand induced conformational change in dihydrofolate reductase, useful for drug design (V. Cody, Buffalo), the coordination geometry of 38 internal water molecules in acetylcholinesterase conserved in four crystal structures of different inhibitor complexes (T. Steiner, Rehovolt), the use of the conjugate peak refinement method to look into calcium-induced conformational transition of domain III in annexin V (J. Sopkova, Orsay) and comparative conformational analysis and catalysis in a fumarase family of lyases (V. Zaitsev, Daresbury). The conference proceedings are available at http://krystal.karlov.mff.cuni.cz/ecm/. The full text of the principal contributions will be available in book form in 1999. [J. Hasek] The session on Ab-initio Methods for Structure Determination (E5) was focused on the macromolecular field. The programs Shake and Bake (Weeks, Xu, Miller and Hauptman, US) and Half Baked (Uson and Sheldrick, Germany) reveal the power of reciprocal space direct methods when combined with real space filtering to solve structures with as many as 1000 independent non-H atoms (provided that data to 1.1-1.2 Å resolution is available). The Automated Refinement Procedure (Lamzin, Morris and Perrakis, EMBL) is based on iterative interpretation and refinement using an atomic model and 2 Å resolution data where the original phase information is limited. C. Gilmore and W. Dong (UK) efficiently samples phase space using error-correcting codes and ranking manageable numbers of phase sets with maximum likelihood. At very low resolution, Lunin (Russia) models a small number of atoms to reduce the number of phase sets to be analyzed. Application of the Few Atoms Model algorithm to the T50S ribosomal particle, resulted in images which have a high map correlation with corresponding EM images. New theoretical approaches to the phase problem presented by C. Giacovazzo (Italy), were based upon phase relationships for structure factors with rational indices. [Alberto D. Podjarny] |
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AsCA '98 Macromolecules, Materials and Multiple Diffraction in Malaysia The Asian Crystallographic Association Meeting (Oct. 13-15, Malaysia) featured four plenary lectures, fifteen microsymposium in three simultaneous sessions and 164 poster presentations in a well balanced program covering all areas of crystallography. Plenary Lectures Y. Ohashi, president of the Japanese Crystallographic Society, gave a plenary lecture on Real-Time in situ Observation of Chemical Reactions including photoracemizations, reversible structural changes, transformations, and a description of a new online two-dimensional detector which can collect a three-dimensional dataset in less than 1 msec using synchrotron radiation allowing analysis of excited states of molecules. In his plenary lecture on Direct Determination of X-Ray Reflection Phases Using Multiple Diffraction: Theory & Experiment, C.-L. Chang (Taiwan) presented the principles of n-beam diffraction and showed how triplet phases can be determined experimentally. At least one thousand triplets were measured in the examples he gave, indicating that the method can be successfully applied to macromolecular structures. Chang indicated that the method could be extended to mosaic crystals. [A. Authier] In a plenary lecture titled Drug Design Against a Shifting Target, P. Colman (Australia) described the structure based design of inhibitors of the influenza virus neuraminidase. A general strategy for drug design when the target has a high mutation frequency was proposed. [T. Tsukihara] The Microsymposim on Diffraction Theory and Technology included a presentation on "Dynamical Diffraction at Grazing Incidence" in which A. Authier (France) described a new derivation of the dispersion surface involved in dynamical diffraction and solution of third-degree equation. A.Y. Nikulin, (Australia) discussed "Uniqueness of the Complex Diffraction Amplitudes in X-ray Bragg Diffraction" and how physical considerations permit unique solutions for structure-factor profiles. Other presentations included "Computer Simulation as a Tool for the Analysis of Diffuse Scattering", (T.R. Welberry, Australia), "Correlated Interface Structures in Superlattices Determined by X-ray Scattering", (Y. Yamaguchi, Tokyo) and an optical microscope and X-ray powder phase diffraction phase analysis of niobium doped hexagonal potassium tungsten bronzes (A. Hussain, Bangladesh). [S.L. Chang] P. Reynolds (Australia) began the microsymposium on Neutron Diffraction with a lucid account of the application of high resolution powder diffraction (using IRIS at the ISIS facility) to the study of magnetic diffraction involving paramagnetic materials with and without applied magnetic field, and magnetically ordered materials above and below a magnetic phase transition. These measurements can provide information on structure and spin distribution comparable with that derived from polarised neutron measurements on single crystals. Y. Fujii (Japan) reported a study of a'-NaV2O5, a truly fascinating material that contains parallel linear chains of V4+ (S=1/2) and V5+ (S=0) ions in an alternating arrangement. There is a spin-Peierls transition at 35 K, below which there is a doubling of the lattice parameter along the V4+ chains. Inelastic neutron scattering was used to confirm that the direction of pairing is along the chains, and to estimate the binding energy of the pair as 10 meV. C. Wilson (UK), described neutron structural studies at several temperatures to gain insight into the librations of terminal methyl groups in paracetamol, the location and possible disorder of hydrogen in short hydrogen bonds, and proton disorder in substituted benzoic acids. He described the effect of temperature upon hydrogen atom geometry including libration of a methyl group and migration of a hydrogen atom in a short hydrogen bond. The latter showed evidence of reverse migration at higher temperatures. The C-H value extropated to a point without torsinal motion of the methyl (-50°K) was 1.186Å. Chick's overheads can be viewed at http://www.isis.rl.ac.uk/crystallography/wilson/asca.htm. Y. Karasawa-Haga (Japan) spoke on recent developments in the use of image plates in neutron diffraction including collection of a refinable data set from a hen egg-white lysozome collected at ILL in only ten days. Applications in powder diffraction, residual stress measurement and the evaluation of neutron beams were also described. C.J. Howard (Australia) illustrated the use of neutron powder diffraction for the accurate determination of oxygen positions in metal oxides with examples of phase transitions in zirconia and perovksites. In his concluding remarks, Chairman Fujii noted recent and planned development of neutron sources in the Asian region, including new reactors in Australia and China, and a powerful new spallation source in Japan. [C. Howard] A highlight of the microsymposium on Aperiodic Structures and Incommensurate Phases was a paper on "Structure Studies of Quasicrystals by Convergent-Beam Electron Diffraction and High-Angle Annular Dark-Fields (K. Saitoh, K. Tsuda, M. Tanaka and A.P. Tsai). The paper describes clearly revealed transition metal positions in decagonal quasicrystals. The resolution is nearly equal to that of the usual high-resolution transmission electron microscope but the interpretation of the image is much easier with this powerful new technique. [A. Yamamoto] The Macromolecular microsymposium included a review of recent results on proline specific peptidases. M. Geiss (Australia) described the remarkable degree of selectivity and specificity among distinctly different peptidases that depend upon the precise sequence surrounding the proline or prolines at the site of cleavage. M.R.N. Murthy (India) gave an illuminating discussion of the interplay between symmetry relationships and sterochemical features of the subunits of a mottle virus. He showed that N-terminal arms extended from a pentamer play an important role in the viral capsid assembly. Y. Kai (Japan) described the structure of phosphoenolpyruvate carboxylase from E. coli, a homotetramer consisting of 883-residue subunits. In addition to the (b/a)q barrel, each subunit has 33 more a-helices. T. Baker (New Zealand) described the structure of rabbit hemopeptin, a heme binding protein. The complex structure, composed of two homologeous domains each containing four sequences repeats, belongs to a growing family of b/a propellers having 6,7 and 8 blades and a narrow ion containing channel at the hub. The structure revealed a heme group bound at an unexpected location offering new insights and raising new questions about the mechanism by which the protein sequesters toxic heme groups. The structure of a complex between the DNA cleaving colicin E7 and its inhibitor IM7 revealed a new fold of the inhibitor and colin E7 folding undisturbed from the negative structure. The predicted DNA binding site of the colicin E7 is far from the extensive interface between the toxin and the inhibitor. This feature raises questions about previous predictions or the significance of the crystal complex (H.S. Yuan, Taiwan). B. Kobe (Australia) presented the structure of phenylalanine hydroxylase, mutations of which cause the disease phenylketonuria. The structures in both the dephosphorylated and phosphorylated states were determined to understand how the activity is regulated. Other symposium presentations included: structural studies of deoxycytidylate hydroxymethylase from bacteriophage T4 (S.W. Suh, Korea), a human immunoglobulin G receptor (K.F. Maxwell, Australia), a 20 S proteasome from bovine liver (M. Unno, Japan), conformational changes in methionine residues upon the electron and protron transfer processed by cytochrome c oxidase from bovine heart (M. Yao, Japan), and sheep liver class I aldehyde dehydrogenase, in which comparison with class II enzyme explains the substrate specificity differences (H.M. Baker, Australia). T. Hori (Japan) discussed the temperature jump-Laue method and described the denaturation studies on a chimeric 3-isopropylmalate dehydrogenase. W.L. Duax (USA) gave a talk on the structures of a Cs+ complex of gramicidin D and an NH4+ complex of a killer toxin KP6alpha. The coordination of the cesium ion is achieved by interaction with the p orbitals of the carbonyls in gramicidin D. [A. Hamid Othman] |
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Materials Characterization in Russia A national conference on applications of X-Ray, Synchrotron Radiation, Neutrons and Electrons for Material Characterization will be held at the Shubnikov Institute for Crystallography in Moscow, May 23-27, 1998. The program will cover protein crystallography, X-ray and neutron structure analysis, surface sensitive method and reflectometry, diffractometry and topography, inelastic scattering, dynamical diffraction, X-ray, neutron and electron optics, spectroscopic method and magnetic scattering. The proceedings will be published in the Journal of the Russian Academy of Science. The conference is supported by the Russian Academy of Sciences, the State Committee of the Russian Federation of Science and technology, and the Russian Fund of Fundamental Researches. Contact: Secretariat, L.G. Yanusova, RSNE99@ms.crys.ras.ru |
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Erice 2000: Crystallography of Molecular Biology Courses in the crystallography of Molecular Biology have been held in Erice every six years since 1976. The fifth course will be directed by L.N. Johnson, Oxford and divided in two parallel meetings, Methods in Macromolecular Crystallography and Prospectives in Crystallography of Molecular Biology, for which Louise has designated two co-directors, respectively D. Turk, Ljubljana and D.I. Stewart, Oxford. The meetings will run from May 25-June 4, 2000. For information, contact: Exec. Sec., P. Spadon, Dept. of Organic Chem., Via Marzolo 1, 35134 Padova, Italy, Fax: 39 049 8275 239, paola@chor.unipd.it or http://www.geomin.unibo.it/orgv/erice/johnson.htm. |
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The 1999 Denver X-Ray Conference will be held Aug. 2-6 at the Sheraton Steamboat Resort, Steamboat Springs, Colorado, USA. Detailed conference information and a tentative program is available at http://www.dxcicdd.com. For information, contact D. Flaherty, Conf. Coordinator, ICDD, 12 Campus Blvd., Newtown Square, PA 19073-3273, Tel: 610-325-9814, FAX: 610-325-9823, flaherty@icdd.com. |
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Surface X-Ray and Neutron Scattering Sixth Int'l Conference on Surface X-Ray and Neutron Scattering (6SXNS), Noordwijkerhout, The Netherlands, Sept. 12-17, 1999 will accept oral and poster contributions, proceedings will be published in a special issue of Physica B. Topics will include: *growth and structure of surfaces and interfaces, *surface and interface roughness, *magnetism of layered materials and surfaces, *surfaces and interfaces of ligands and soft condensed matter, *soft x-ray and EUV scattering, *techniques, instrumentation and theory, attendance is limited. Contact: 6SXNS Secretariat, Philips Res. Lab. WB33, Prof. Holstlaan 4, 5656 AA Eindhoven, The Netherlands, Tel: 31 40 2744551, FAX: 31 40 2745002, mfrankn@natlab.research.philips.com, http://www.research.philips.com/sxns/firs.html. |