Meeting report

ECM20 - Krakow

Amorphous materials

[ECM20]
David Sayre said in his Plenary Lecture, that 'non-periodic objects provide some of the most challenging subjects for crystallographers'. D Cockayne (UK) described the use of energy filtered electron diffraction to obtain structural parameters from small volumes of amorphous materials including samples as small as 2nm on a side. T Weber (Switzerland) discussed the analysis of disordered systems by Monte Carlo methods using algorithms that allow a more extensive search of parameter space compared with traditional approaches. J Cole (UK) showed the power of combining a range of analytical techniques to study the structures of glasses. She analyzed rare-earth phosphate glasses using neutron, X-ray and EXAFS data. A Le Bail (France) stressed the importance of the choice of starting models in refinement algorithms. He compared results from the RDM (Rietveld for Disordered Materials) and the RMC (Reverse Monte Carlo) methods, and raised questions about the optimum approach to take. Y Golubev (Russia) considered supermolecular ordering in some naturally occurring substances, in which globular clusters were detected. An underlying theme of the symposium was the importance of reliable techniques for refining models against structural data, and of obtaining data which can discriminate between alternative models of amorphous structures.

D Cockayne

Quasicrystals

[Speakers and chairs] Speakers and chairs in session on Molecular Basis of Disease and Rational Design of Drugs.
M. de Boissieu (France) reported evidence for phason fluctuations detected by high resolution synchrotron X-ray diffraction on single grains of quasicrystals. The I-Cd-Yb phase, the first stable binary icosahedral phase, opens the way for a deeper understanding of quasicrystal structure and formation. Optical conductivity of several intermetallic compounds of the Al-Cr-Fe system in a broad range of frequencies was described by J.M. Dubois (France).

Other topics addressed included stable icosahedral quasicrystals in binary Cd alloys (A.P. Tsai, Japan), a novel method for construction of four-coordinated structures from the Frank-Kasper dense packed systems (V. Dmitrienko, Russia), and the physical and electronic transport properties of quasicrystals determined by their electronic structure (Z. Stadnik, Canada).

Janusz Wolny

Structure determination from powder

[Authier, Giacovazzo] Andre Authier introduced Plenary speakerC. Giacovazzo
Two speakers presented the latest results of their work on the global optimisation method using a Genetic Algorithm (K.D.M. Harris, Birmingham) and Simulated Annealing (M.A. Neumann, Accelerys). A new direct space program optimised for non-molecular compounds using object-oriented programming (V. Favre-Nicolin, Geneva), the latest developments of the program EXPO (R. Rizzi, Bari) and a review of achievements of the grid search method in direct space (V.V. Chernyshev, Moscow State U.) were presented. Several oral presentations in other microsymposia and plenary lectures by C.J. Gilmore (Maximum Entropy and Structure Solution from Difficult Data) and by C. Giacovazzo (Direct Phasing in Crystallography: from Powder Data to Proteins) dealt with structure solution from powder diffraction.

R. Cerny, Switzerland

Minerals

[ECA officers] Officers of the ECA 2002: D. Viterbo, C. LeComte, M. Duarte, M. Jaskolski,G. Filippini, and P. Beurskens.
Presentations by representatives from Germany, Denmark, Italy, Switzerland, Russian and Australia described new approaches to the study of minerals including the use of synchrotron radiation and the Rietveld method which has opened a new era in physics and chemistry of minerals and their synthetic analogues. The application of modular theory and the polysomatic concept for the systematization and interpretation of large mineralogical families, namely zeolites, titanosilicates, minerals of heogbemite and eudialite groups, were discussed.

D. Pushcharovsky, Chairman

Physical properties and structural relationships

[Wlodawer] Alex Wlodawer at the exhibits
Studies of physical properties in organic and inorganic materials were combined with detailed structural investigations in order to identify correlations. J. Cole illustrated the balance between molecular and supramolecular attributes in organic non-linear optical materials designed for potential use in telecommunications. Her structural studies included charge-density experiments, hydrogen-bonding characterization, bond-length variation and thermal motion analysis. H. Ehrenberg described a type of Morin transition in (Co1-xMnx)4Nb2O9 dependant on the Co: Mn ratio using high-resolution synchroton powder and single crystal diffraction techniques. For x = 0 a co-linear magnetic structure is observed and for higher Mn content weak ferromagnetism occurs. This transition might find application in new sensor materials. B. Mihailova investigated spatial variation of atomic arrangements and the related strain in ferroelastic W domain walls of lead phosphates using micro-Raman spectroscopy. Using in situ high-pressure diffraction experiments, B. Palosz illustrated that the distinctive properties of nanocrystalline materials are critically dependant on the local atomic structure of the constituent crystallites. J. Schreuer demonstrated how resonant ultrasound spectroscopy permits detailed study of the elastic behavior of crystals and how elastic properties can be related to chemical composition.

Ulrich Bismayer and, Katarzyna Stadnicka

[ECA banner] Post closing ceremony pose on the steps of the Lecture Hall with the new ECA banner.
Structure prediction

Computational methods for predicting the crystal structures of organic molecules from their chemical diagrams were tested in spring 2001 by the Cambridge Crystallographic Data Centre. Eighteen participants sent predictions for the unpublished crystal structure of each of three organic molecules. Sam Motherwell (CCDC) presented an overview of the results of this test, which enabled nonparticipants to appreciate both the progress and problems in organic crystal structure prediction.

Most successful predictions had been based on searches for the global minimum in the lattice energy. W. Mooij (Accelrys, ex-Utrecht) described how increasingly accurate models for the lattice energy, including atomic multipolar electrostatics and ab initio calculation of the intramolecular distortion energy, improved the relative lattice energies of small alcohols and sugars. J. Novoa (Barcelona) demonstrated that dispersion corrected Density Functional calculations predicted that the experimental structure of acetic acid was the global minimum.

This is a significant improvement of the relative energies compared with the GROMOS forcefield. He also described pioneering ab initio molecular dynamics simulations, in which crystal structures involving collective proton transfer were seen, emphasizing the limitations of the usual rigid molecular model approximation. J. Breu (Regensburg) emphasized the sensitivity of relative lattice energies to the molecular model, describing calculations on polymorphs in a series of organo-metallic salts. Correcting for the apparent bond shrinkage due to librational motion made a significant difference to the relative lattice energies. Despite the accuracy demanded of lattice energy minimization methods, J. van de Streek (CCDC, ex- Nijmegen), presented the first extensions of such methods to zwitterion and molecular salts, suggesting that the methods may be more widely applicable than previously thought. Although all this work showed that improvements in the computational model increased the reliability with which the known polymorphs would be found at or very close to the global minimum in lattice energy, there often remained rather more energetically feasible crystal structures than known polymorphs. G. Desiraju (Hyderabad) discussed a new approach designed to determine which of the thermodynamically feasible structures were also kinetically favored. He illustrated a method that had successfully re-ranked the low energy structures of one of the molecules in the CCDC test. This was based on identifying crystal structures in the CSD with the supramolecular synthons appropriate to the target molecule, and replacing the parts of the molecular structures which differed.

The microsymposium demonstrated that some organic crystal structures have been successfully predicted, considerable development in the thermodynamic basis of crystal structure prediction is in progress, and fundamental questions about kinetic control of crystallization need to be incorporated into the prediction process.

Sally Price (UCL) Chairperson

[Shmueli] U. Shmueli
Motion and change in crystals

The dynamics of crystals are usually ignored in diffraction studies, probably because the determination of the static aspects of crystal structures is so sophisticated. Such disregard is not justified! The speakers in this microsymposium illustrated the power of combining diffraction and NMR-methods to reveal motion in deoxycholic acid clathrates (C.K. Prout), to interpret variable-temperature diffraction experiments (C.C. Wilson), to elucidate complex changes in molecular packing within a few degrees of phase transition temperatures (F. Iwasaki), and to distinguish topochemically controlled, organic solid-state reactions from alternative transformation mechanisms, (M. Kaftory), and to classify and understand the phase transitions observed in ionic cyano-elpasolite compounds (D. Chernyshov). A better understanding of the dynamics of phase transitions is relevant to a better understanding of polymorphism. The complex potentials of hydrogen bond dynamics revealed by the atomic displacement parameters of protons may be important for the prediction of structures of biologically relevant molecules.

H.B. Bürgi, Chair

Supramolecular materials

[Becker] Pierre Becker
Supramolecular systems include discrete complexes, nano-structures, crystal-engineered polymers, and polar molecular crystals. In introductory remarks I. Goldberg (Tel Aviv U.), co-chair of the session, demonstrated successful application of molecular recognition algorithms in the construction of supramolecular porphyrin domains in solution as well as in the solid state. M. Zaworotko (U. of South Florida) discussed the design of hybrid nanoporous solids and discrete infinite structures of nanoscale faceted polyhedra. V. Langer (Göteborg U.) presented a colorful report on efforts to engineer supramolecular hydrogen bonded arrays using organic phosphoricacids as building blocks consisting of layered motifs with architectures that are tunable by chemical modification of the basic unit. S. Bourne (U. of Cape Town) described self-assembly of polynuclear complexes between substituted thioureas and metal ions, showed that the metallomacrocyclic moieties formed in this manner may further combine into polymeric networks, some of which can be useful as chemical sensors for volatile solvents.

T. Bartczak (Technical U. of Lódz) addressed the host-guest chemistry of lariat ethers, their conformational flexibility and ability to form supramolecular structures. J. Hulliger (U. of Berne) described polar domain formation in molecular crystals and growth of bipolar macroscopic crystals with an inhomogeneous spatial distribution of polarity by controlled seeding. The phenomenon was studied theoretically and by scanning pyrroelectric- and phase-sensitive second harmonic- microscopy.

I. Goldberg

Cryo electron microscopy

[Oleskyn] Barbara Oleskyn
The Cryo-EM symposium focused on structural analysis of biological objects that are difficult or impossible to crystallize. Following the plenary lecture by D. Sayre (SUNY, USA) concerning X-ray analysis of a whole cell, E. Orlova (Birkbeck college, UK) began the symposium with a review of the principals of single particle structural analysis and its application on symmetrical (viruses) and non-symmetrical (ribosomes) objects. The resolution alone may not tell much about system functioning since structural fragments could undergo significant conformational changes within the complex. For big complexes, like ribosomes, there is no need to obtain the structure at atomic resolution to confirm that tRNAs have different positions in pre- and post-translocational states. D. Nicastro (MPI fur Biochemie, Martinsried) presented applications of tomography for analysis of cryo-electron images of whole cells and organelles. 3D structures obtained by this technique from a single-axis tilt series of supramolecular assemblies provide new insight into their organization in situ. H. Stuhrman (Inst. de Biologoe Structurale, Grenoble) described how variation of proton spin polarization can be used for structure determination in a way similar to neutron scattering with various concentrations of D2O in crystals. E. Chabriere (U. Henri Poincare, Nancy) demonstrated a direct phasing method, based on topological properties of connectivity of electron density maps, for identification of elements of the protein’s secondary structure. J. Bosch (MPI fur Biochemie) combining EM data and X-ray crystallography for structure determination of the Tricorn protease forming hexamers. Finally, A. Urzhumtsev (U. Henri Poincare) discussed modeling bulk solvent in macromolecular crystals.

Elena Orlova

Enzymes

[Schenk] Henk Schenk
The microsymposium on Enzyme Mechanism and Intermediates included reports on the reaction mechanism of urease, a nickel metalloenzyme (S. Ciurli, Bologna), molybdenum and tungsten enzymes (M. Ramao, Lisbon), dehaloperoxidase, a probable descendant of an ancient oxygen carrier (L. Lebioda, South Carolina), ondothiapepsin (J. Cooper, Southampton), intermediate states of thymidilate kinase (E. Fioravanti, ESRF), a novel serine-carboxyl proteinase (A. Wlodawer, NCI Frederick), a bifunctional IMPase/FBPase enzyme (B. Stec, Rice U.), hyperthermophilic amylase (A. Linden (EMBL Hamburg), an outer membrane protease OmpT (L. Vandeputte-Rutten, Utrecht), and a complex multi-threaded investigation of the mechanism and specificity of L-asparaginase. (J. Lubkowski, NCI Frederick).

Wojciech Rypniewski

Crystallogenesis

[Souhassou] M. Souhassou
R. Hilgenfeld (Jena) discussed developments in crystallization in 13 European groups, the synergy between biology and physics in macromolecular crystal growth, and new crystal kits and methods. Other topics addressed included over expression of proteins in E. coli and eukariotic systems (Zou, EMBL), crystallization of membrane proteins, and a semi-rational approach to handing multi-parameter space (J. Zeelen, Frankfurt), control of pH to promote crystallization and act as a cryoprotectant (M. Brzozovski, York), and the importance of the purity in samples of membrane proteins (J. Abramson, Imperial College).

Naomi Chayen

Theory and experiment

[Gies, Fuess] H. Gies and H. Fuess
The 'Wavefunctions and Properties from Experiment' Microsymposium was designed to encompass interactions between theory and experiment, densities other than charge densities and applications of diffraction experiments to theory and chemical properties. D. Jayatilaka reviewed the philosophy behind the extraction of wavefunctions from experimental measurements, described a method for constraining variational quantum mechanical wavefunctions in order to reproduce experimental measurements and outlined applications to three systems from X-ray and polarised neutron diffraction experiments using his TONTO software.

[Krakow] In the central court of the Royal Castle before the banquet at ECM 2001 in Krakow.

B. Dittrich (FU-Berlin) described a straightforward method of space partitioning in the context of transferability of electron density fragments from amino acids and oligopeptides in modelling the electron density of proteins. Hirshfeld surfaces, based on spherical atomic densities for molecules in a crystal, are easy to calculate compared with surfaces obtained from topological analysis of density distribution.

P. Becker (CNRS, Paris) introduced a new approach for computing charge and momentum densities which uses an ab initio model in the form of cluster-based calculations and adopts a 1-particle reduced density matrix partitioning scheme to eliminate cluster surface effects. For LiH and MgO crystals the resulting Compton profiles and structure factors compare well with experimental data. The use of Hartree-Fock and correlated wavefunctions for the clusters enables one to estimate the local correlation effects in ionic crystals. P. Macchi (Milan) showed that the bonding in a series of octahedral metal carbonyl clusters can be characterised according to molecular charges and environments.

This is done in terms of the topology of the electron density, electrostatic properties, and intermolecular interaction energies. Intra- and inter-molecular effects can be distinguished by analysing differences between solid state (experimental) and in vacuo (theoretical) properties. J. M. Raulot (CNRS, Paris) presented an ab initio study of two lead-containing perovskite minerals and their ferroelastic and ferroelectric phase transitions. P. Starynowicz (U. of Wroclaw) discussed charge densities in two salts of biologically important phosphate esters.

P. Mallinson

Prizes

[Zaworotko] Mike Zaworotko
The ECM 20 Cambridge Crystallographic Data Center (CCDC) Poster Prizes prizes were awarded to:

L. Dobrzycki, Warsaw (YAG Crystals Substituted with Erbium and Ytterbium);

G. Paliwoda, Jagiellonian, Krakow (Mutual Recognition Between Diastereoisomers, Quinine and Quinidine, in the Solid State);

M.U. Schmidt, Clariant GmbH (Ternary Mixed Crystal Structure Solved by Predictions and Powder Diffraction);

The Prizes (amethyst geodes and $250 checks) were presented at the Closing Ceremony by CCDC Scientific Director, Frank Allen.

Protein Crystallography Beyond 2000 (PCB2k) - Satellite meeting on macromolecules

[Dutheil] M. Dutheil
High throughput and high quality protein crystallography in the post genomics era brought 60 young scientists and experts together to Krynica, Poland, immediately after ECM20. The PCB2k conference, organized by the Jagiellonian U. (Krakow), the U. of York, and A. Mickiewicz U. (Poznan) with support from the MAX-INF network of European crystallography laboratories and synchrotron sites was divided into four sections. In a section on protein expression and crystallization, T. Wilkinson’s (York) introduction to protein production was followed by M. Brzozowski’s (York) lecture on crystallogenesis and P. Umbach’s presentation of the Protein Structure Factory in Berlin. A session on bioinformatics and structural genomics, included lectures on predicting protein interactions (R. Russell, Heildelberg), analysis of information flow in structural genomics (W. Minor, Charlottesville), crystallographic probing of enzymatic mechanisms (B. Stec, Huston), and presentations from structural genomics centers at Argonne (A. Joachimiak) and Orsay (A. Bentley). X-ray sources and data acquisition strategies were discussed by S. McSweeney (Grenoble) and S. Popov (Hamburg). The phasing and refinement session featured lectures on S/I/Br phasing (Z. Dauter, Brookhaven), automated molecular replacement(C. Kissinger, San Diego), multi crystal averaging (E. Dodson, York), NCS averaging(D. Turk, Ljubljana), maximum likelihood (G. Marshudow, York), and high resolution structure refinement (K. Wilson, York). The meeting ended with a lecture by G. Dodson (Mill Hill) who summarized the awesome past achievements of macromolecular crystallography and emerging challenges to understanding of the molecular clockwork of the living cell. There were tutorial sessions on HKL2000 (W. Minor), Main (D. Turk), and CCP4 (M. Winn). Discussions continued at a bonfire, with folk music and dancing, that lasted long into the night. The meeting was held concurrently with an ECM20 Satellite on synchrotron radiation organized by J. Grochowski (Krakow). Participants could attend the lectures of both programs, fostering exchange between the biological and physical worlds. We are indebted to the organizational skills of S. Krzywda (York and Poznan) and K. Lewinski (Krakow).

Mariusz Jaskolski, Poznan