Meeting report

XX Congress and general assembly

KEYNOTE LECTURES

Ion pumping by Ca2+-ATPase of sarcoplasmic reticulum

[Toyoshima]In the keynote lecture by Chikashi Toyoshima, he presented, using several movies, how the Ca2+-pump (ATPase) works based on their crystallographic and molecular dynamics studies. His group has been successful in determining 6 intermediate state structures, covering the whole reaction cycle. In this lecture, he presented a new 2.4 Å structure of the E2 state stabilized with two potent inhibitors that bind to the transmembrane region. He addressed why such large and complicated domain movements are necessary, what ATP and phosphorylation do, and why H+-countertransport is necessary. He stressed that ion pumps are vigorously fluctuating by thermal energy, which is utilized efficiently for structural changes. Large domain motions are necessary for the mechanism of the pump, and protonation of specific acidic residues is required for structural integrity. These proposals were sustained by molecular dynamics studies, which certainly provide a new dimension to the work of Toyoshima’s group.

Giuseppe Ines 

KN07 structure analysis of modulated crystals

[Petricek]Vaclav Petricek, through his development and continual improvement of the “industry standard” JANA suite of programs, has made an enormous contribution to the rapidly growing area of aperiodic crystallography. He gave a presentation of the application of the superspace approach introduced by de Wolff, Janssen and Janner to higher dimensional crystal structure determination, focussing on atomic modulation functions and their determination in conventional as well as composite modulated structures. The broad range of crystal structure types in which modulated structures have nowadays been found, including inorganic and organic protein crystals, was highlighted. The efficiency of methods used for the solution and refinement of such modulated structures were discussed along with more recent methods including maximum entropy and charge flipping methods. The introduction of discontinuous atomic modulation functions and the use of the superspace approach to systematize the structural characterization of whole families of closely related structure types were highlighted.

Ray Withers

High throughput technologies in structural biology

[Stevens]The explosive growth of biological macromolecular crystallography in the genomics era has necessitated many technological innovations to facilitate high throughput operations. The plenary lecture by Raymond Stevens dealt with these innovations. Recurring themes of the innovations introduced by Stevens and his collaborators have been miniaturization and automation. Miniaturation has been achieved in NMR, thermodynamic measurements, electron microscopy and high throughput crystallization. He described the application of the new technologies to structural genomics of enzyme pathways, studies of biophysical properties, structure-based drug discovery and structure-based enzyme replacement therapy. He provided glimpses of future technology developments including the crystallization of membrane proteins, total synthesis of genes, crystal engineering via surface mutagenesis, in situ X-ray diffraction data collection and the development of miniaturized, compact X-ray sources for intensity data collection.

M. Vijayan 

Protein kinase inhibition and substrate recognition

[Johnson]Louise Johnson brings incredible experience to the understanding of the structure and function of the human kinome. There are 518 protein kinases that make up the human kinome and which are key components of cell signalling pathways. Defects in these processes lead to diseases such as cancer, diabetes and arthritis and hence protein kinases have become targets for drug design and therapy. Louise’s research team in Oxford has concentrated on the structures of the cell cycle protein kinases and in particular CDK2/cyclin A, CDK2/cyclin E, CDK7 and polo-like kinase. In addition to these studies she and her colleagues recently published a high impact review in Science surveying progress in this field with special reference to kinase inhibitors that are in clinical trials or in the clinic, and for which structural information is available[1]. Louise has co-authored an excellent text on crystallography with Tom Blundell, is a Fellow of The Royal Society of London, and was made a Dame of the British Empire (‘DBE’) by The Queen for her services to biophysics. Louise is Sir David Phillips Professor of Molecular Biophysics at Oxford U. and she is also Life Sciences Director at the new UK Diamond Light Source being constructed at the Rutherford Appleton Laboratory at Chilton near Oxford.

John R. Hellliwell

Reference

[1] Noble M.E., Endicott J.A., Johnson L.N., Science, 2004, 303, 1800. 

[Audience]Audience at the Opening Ceremony

The importance of structure in the design of lithium battery materials

[Thackeray]Climate change is now recognized as the greatest threat facing humanity in the 21st Century. Transportation accounts for more than 30% of CO2 emissions. The solution for the next 20-40 years is likely to be the hybrid electric vehicle, combining an internal combustion engine, or later a fuel cell, with a rechargeable battery. The battery of choice is the rechargeable lithium-ion battery. Mike Thackeray demonstrated how crystallography has played a key role in the discovery and understanding of new electrode materials essential for the operation of the rechargeable lithium-ion battery.

[Gems]Figure 1
The positive electrode material used in the current generation of lithium-ion batteries is the lithium intercalation host LiCoO2 (R3m). The capacity to store lithium is limited by the stability range of the solid solution LixCoO2; 0.5 < x < 1. Crystallography has revealed that it is possible to insert Li2O into compounds such as α−MnO2 (hollandite structure). The presence of oxygen in the centre of the hollandite tunnels significantly enhances the ability to insert and remove lithium. Crystallography has also revealed a new concept in lithium intercalation materials, in which the compound consists of an intimate intergrowth between a stabilising compound, such as L2MnO3, and an electrochemically active component, such as LiNiO2. Such intergrowths open the way to a higher capacity to store lithium than conventional materials. Turning attention to the negative electrode, Thackeray has demonstrated, using crystallography, that it is possible to understand new and unusual mechanisms by which lithium reacts with intermetallic compounds. For example, one of the metal components may be extruded from the crystal structure but can then re-enter the structure on lithium extraction. The remarkable correspondence between compounds that are sufficiently stable to act as electrodes in lithium-ion batteries and those that exist in the world of gem stones was highlighted in the talk (Figure 1). Some of the most promising lithium battery materials are based on the structure of spinel, olivine and garnet, all of which are being actively pursued as electrodes for the batteries.

The demand for lithium ion batteries will grow substantially over the next 10 years and crystallography will continue to play a vital role in both the fundamental science needed to understand the materials and for their technological exploitation.

Peter G. Bruce, Chair

Molecular recognition principles in protein-ligand interactions

[Klebe][1000s of answers]More than 300 people gathered in the Michelangelo lecture hall to listen to Gerhard Klebe’s fascinating exposition on the design of bioactive compounds. He turned the approach to science of many of his listeners topsy-turvy by pointing out that the published literature has many answers ready to be discovered, if only we can find the appropriate questions! To achieve this goal the published information needs to be preprocessed into databases. Gerhard has met this challenge for protein-ligand complexes, structural water in biomolecules, the shapes of binding pockets with respect to the prediction of their functional properties and for the relationship between protein structure and ligand binding data, without overlooking, however, the problems of substrate promiscuity. He showed the importance of filling the pockets and subpockets of protein active sites for achieving selectivity. Virtual screening of ligands in the computer, synthesis of promising lead compounds and determination of their binding were demonstrated for aspartyl proteases. The chiral nature of proteins implies the disconcerting problem that one enantiomer of an active compound may have a beneficial effect while the other one damages the organism. In such cases knowing their binding characteristics is as important as determining their crystal structures. Interestingly enough, calorimetric experiments allow determination of the thermodynamic parameters without prior resolution of the racemate, as was demonstrated for some inhibitors of trypsin and thrombin. The talk displayed the rich toolbox available today to developers of new bioactive compounds.

Hans-Beat Bürgi

Structural studies of macromolecular complexes: cytochrome b6f

[Smith]Janet Smith’s lecture highlighted two aspects of her recent work. She opened her lecture with a dedication to two giants of macromolecular crystallography, Carl-Ivar Brändén and Muttaiya Sundaralingam, who had recently passed away. Janet then took us on a fascinating journey through the complex life of the cytochrome b6/f complex, which functions in the electron transfer chain between the two photosystems in the photosynthetic apparatus of plants, blue green algae and cyanobacteria. Despite years of previous biochemical work in other laboratories, the structure of the large complex which includes two copies of each of eight different polypeptides, unexpectedly revealed the presence of an additional haem cofactor, located close to the putative binding site for the electron donor, plastoquinone. Janet speculated that this haem may play a role in short-circuiting electron flow, which is known to occur in the complex. Janet concluded her presentation with a description of the new protein crystallography facility, GM/CA-CAT, being constructed on behalf of the NIH at the Advanced Photon Source at the Argonne National Labs near Chicago. The suite of three beamlines, two on novel canted undulators and the third on a bending magnet, promises to be one of the finest protein crystallography facilities in the world. The three lines are all completely independent and one offers an extraordinary energy range of 3 to 35 keV. Operations are intended to be fully automated with crystal-mounting robots at each station. The Blu-Ice software from SSRL has been adapted for use at GM/CA-CAT. Janet Smith provided the audience with a fascinating, beautifully told story of some of her recent work and a glimpse into facilities promised for the near future.

Mitchell Guss

CIMS SESSIONS AND OCM

The Commission on Inorganic and Mineral Structures (CIMS) sponsored two Keynote Lectures (Lynne Mc Cusker, “Elucidating the structures of nanoporous microcrystals” and Tim White, “Crystallographic basis of synthetic mineral immobilisation”), an Open Commission Meeting (OCM) and five microsymposia, as well as four other microsymposia co-sponsored with other Commissions. Attendance dealing with inorganic structures, particularly in materials science, was higher at IUCr-XX in comparison with previous IUCr congresses. 

Crystal chemistry of inorganic and mineral compounds

[Vegas]A. Vegas
[Ferraris]C. Ferraris
Angel Vegas’ (Spain) proposal to apply the Zintl-Klemm concept to the cation positions in some oxides, especially silicates, set the stage for a series of well-prepared lectures. Sergey Krivovichev (Russia, Austria) reported on his fascinating findings in the field of uranyl selenates. His most important finding is that these materials form various kinds of nano-structures which have the potential to open up new fields in both basic and applied research. Charles Geiger (Germany) emphasized the importance of vibrational spectroscopy for clarifying the nature of molecule – mineral inner-surface interactions in natural microporous silicates. Obviously, X-ray studies with their averaging effect in space and time are less suited for unravelling local phenomena and structures. Cristiano Ferraris (Singapore, France) clearly demonstrated the difficulties encountered in the investigation of Oxygen/Fluorine ordering in niobium oxyfluorides. By studying several rare minerals Natalia Zubkova (Russia) was able to derive a systematic of the topologies of arsenates. The microsymposium was attended by 80 – 100 delegates on average and was accompanied by lively discussions.

Wulf Depmeier, Herta Effenberger 

Modularity and modulation in inorganic and mineral structures

[Cario]L. Cario
[Ferraris]G. Ferraris
[Charkin]D. Charkin
This session took place in a hall with an auspicious name, the Donatello Hall, introducing perhaps a new renaissance of the subject. The topics selected covered practically the entire field of modular structures and modulation. Laurent Cario (France) presented a generalization of the modular approach to 2D-misfit layered chalcogenides. It leads to a design of new commensurate and noncommensurate 2D layered compounds using the 2D building blocs observed in known structures. Giovanni Ferraris (Italy) spoke about recurrent modules in modular structures. He described a plethora of modules observed in oxides and silicates and showed how they can be used in modelling hitherto unknown structures of polysomatic series, interpreting topotactic reactions and defects, as well as tuning the properties of new synthetic materials. Jirí Hybler (Czech Republic), discussed the problems of structure refinement of partially disordered OD structures. They demonstrated the importance of separate scaling of so-called “family reflections”, common to all polytypic sequences, and the “polytype reflections”, characteristic for a given polytype. Improper scaling produces “ghost peaks” in the Fourier syntheses. Luca Bindi (Italy), treated the incommensurately modulated structure of natural melilite (a disilicate of Ca, Al and Mg) by means of a five-dimensional refinement. It confirmed that the modulation is primarily related to the variation in the Ca coordination but demonstrated substantial differences between the natural and synthetic specimens. The last speaker of the session, Dmitri O. Charkin (Russia) demonstrated a modular approach to the tailoring of bismuth-containing layered perovskites. Instead of simple doping of various compounds of this type, they introduce additional 2D structural moduli, building in this way complicated mixed-layer structures. They prepared more than 20 new structure types and a range of new ferroelectrics.

Giovanni Ferraris

Structure/property relationships of technologically relevant inorganic and mineral compounds

[Taulelle]F. Taulelle
[Delgado]M. Delgado
[Moore]Moreton Moore
Although minerals have been investigated for many years, it has become increasingly evident that the study of their formation, crystal structure and reactivity is an endless source of inspiration for designing novel materials. The knowledge of the structure of a given material is an important step forward towards understanding its properties. It is at this point that much chemistry begins: new experiments, which may yield related materials with improved properties, may be proposed.

The session began with a talk by Bernard Grobety (Switzerland) on nanotubes of chrysotile, an asbestos (carcinogenic) material, the use of which deserves careful safety consideration. He reported research on the behavior of chrysotile fibers in the environment and suggested that new applications requiring only small amounts of chrysotile should be targeted.

Francis Taulelle (France) presented a stimulating talk on solidstate Nuclear Magnetic Resonance (NMR) crystallography of inorganic materials. He explained the principles of NMR crystallography on powders (giving special emphasis to the use of Wyckoff spectra) and summarized major recent advances towards that goal. NMR and X-ray crystallography are complementary techniques, extremely powerful when used in tandem.

Carlo Lamberti (Italy) showed the importance of combining synchrotron powder X-ray diffraction and spectroscopic methods in the study of guest molecules in microporous (zeolitic) hosts. Zeolites are heterogeneous catalysts and their active sites are located within the internal cavities of the structures. The reactivity of the active sites is analyzed via the adsorption of probe molecules monitored by infrared and Raman spectroscopies. Miguel Delgado (Venezuela) discussed semiconductor materials, with application in solar cells, based upon chalcopyrite using powder XRD.

The symposium was closed by Moreton Moore (UK) with a talk on the growth and morphology of diamonds. Some 80% of natural diamonds are used in industry because they contain defects or impurities that result in poor optical properties. However, industry uses mostly synthetic diamonds. Based on X-ray topography, he discussed the growth modes of natural and synthetic diamonds grown by high-pressure/high-temperature methods.

João Rocha, Alessandro Gualtieri 

MS35: polytypism and twinning

[Arakcheeva]A. Arakcheeva
[Viti]C. Viti
[Herbst-Irmer]R. Herbst-Irmer
This microsymposium attracted theoreticians studying crystal symmetry and users of software packages for automatic solution and refinement of crystal structures. Twinning or polytypism is less common in organic than in inorganic structures, but the statistics can be biased by different approaches taken to the problem. Typically, polytypes can coexist in the same crystal and often only an average structure is reported in these cases. A nice example was presented by Daniela Pinto (Italy) for the case of the new mineral vurroite, a complex sulfosalt whose structure has been solved by the application of modular theory of homologous series. Thanks to OD theory, it has been shown that vurroite includes two polytypes: thus, the new minerals are actually two and not just one! A relationship between the crystal structure of incommensurately modulated layer compounds and the family of polytypes according to which the layers can be stacked has been shown for the first time by Alla Arakcheeva (Switzerland) who illustrated the case of β-K5Yb(MoO4)4. Cecilia Viti (Italy) discussed the structure of polygonal serpentine. New HRTEM results provide an explanation of puzzling features of the XRPD pattern of this mineral. Massimo Nespolo (France) and Regine Herbst-Irmer (Germany) devoted their contributions to theoretical and experimental aspects of the twinning problem, respectively. Nespolo discussed the case of large-index twins and showed that often such twins actually have a lower effective twin index because, besides the subset of (quasi)overlapped lattice points accounted for by the classical twin cell, the contributions of other quasi-overlapped nodes must also be included; thus hybrid twins have been defined. Herbst-Irmer presented a strategy to measure the full contribution to the diffraction pattern from the different individuals of a twin when the diffracted spots do not exactly overlap because of non-zero obliquity twinning. The procedure has been implemented in SHELXL and also tested for structures of proteins.

Giovanni Ferraris

Inorganic and mineral structures solved and refined by powder diffraction data

[Gies]H. Gies
[Kaduk]J. Kaduk
[Argyriou]D. Argyriou
[Vidal]K. Vidal
[Ting]V. Ting
Most of the contributions in this session complemented powder diffraction with other techniques such as electron diffraction, electron microscopy or solid-state NMR spectrometry. Hermann Gies (Germany) described the characterisation of a new hydrous layer silicate, RUB-39 which condenses, when heated, to a framework silicate with zeolithic pores. One interesting feature of RUB-39 is that the layers are held together by extremely short inter-layer H bonds (2.4Å), also detected by solid- state 1H NMR data. This is in contrast to other layer silicates which only form short intra-layer H bonds. James Kaduk (USA) described the synthesis and characterization of the molecular solid insulator Pd(NO3) and the hygroscopic layered sulphate (Mg,V) O0.63 (SO4) (H2O)1.5. Particularly interesting was the description of the new compound NaGe4 possessing a zeolite-like Ge framework. This compound resulted from the systematic search for new more efficient thermoelectric materials. Here the Na atoms occupy ordered sites but some residual Na atoms can also be found in the large 24-ring channels. At the end of his talk he presented the new and rather complex silicate mineral ‘charoite’ The presentation by Dimitri Argyriou (Germany) concerned the superconducting layered cobaltate NaxCoO2·yD2O studied using electron and neutron powder diffraction data. One of the principal difficulties in the study of this material is the refinement of the water molecules which requires the location of the hydrogen atoms. Thanks to a convenient combination of H and D in the compound, only the O of the water molecule needed to be refined. This allowed determination of the Na arrangement and provided an explanation of why the water amount remains constant and the Na content can vary. In her talk, Karmele Vidal (Spain) summarized her results on new cathodes for solid oxide fuel cells using powder diffraction techniques which constitute part of her doctoral thesis work. These cathodes are based on a new family of iron oxide perovskites. The last contribution by Valeska Ting (Australia) was on the modelling of stacking faults in ordered perovskites by refining the amount of two stacking faulted variants in addition to the main variant.

Jordi Rius-Palleiro

Open commission meeting on inorganic and mineral structures (CIMS)

[Merlino]S. Merlino
[Makovicky]E. Makovicky
A short introduction by the chairperson on the activity of CIMS during its first triennium preceded six oral contributions that touched different fields of interest for CIMS: from modular aspects of inorganic crystal structures to databases of structures, single structures, graph theory and pressure calibration. A number of polytypes can coexist in the same crystal and often only an average structure is reported, as shown by Stefano Merlino (Italy) who illustrated basic examples of applying Object Discover (OD) theory. Even undiscovered new forms of a compound can be predicted after unravelling OD polytypes. Emil Makovicky (Denmark) reported on a series of crystal structures based on the same modules which incrementally increase their size. The problem of identifying structure type included in the Inorganic Crystal Structure Database (ICSD) was discussed by Rudolf Allmann (Germany). The crystal structures of iron-containing minerals recently characterized in collaboration with different European laboratories were efficaciously illustrated by Dmitry Pushcharovsky (Russia). In connection with his well known theory on bond-strength/bond-length correlations, David Brown (Canada) showed examples of graph theory application which provides better models for structures with deformed coordination polyhedra. Masanori Matsu (Japan) presented his results on T-P-V equations of state obtained by applying his breathing shell model to molecular dynamics methods in order to establish better pressure calibration standards at high T and P.

Giovanni Ferraris

MICROSYMPOSIA 

Chiral and non-centrosymmetric structures

[Metrangolo]P. Mentrangolo
[Persoons]A. Persoons
[Strumpel]M. Strumpel
[Bernstein]J. Bernstein
Presentations in this microsymposium ranged from organic materials to nonlinear optical (NLO) properties of polymers. P. Metrangolo (Italy) discussed ways to self- assemble perfluorocarbons (PFC’s). As these compounds are insoluble in H2O, it was shown that cocrystallizing these materials with hydrocarbons (HC’s) resulted in hybrid PFC-HC systems. The spontaneous self-assembly of these systems resulted in strongly directed hydrogen bonding in addition to chiral resolution. Continuing with the theme of chirality, A. Persoons (Belgium and USA) discussed nonlinear optical properties of chiral polymers. The NLO effects indicated connections between magnetic hypersusceptibilites and chirality. Thus it is possible to observe these types of NLO phenomena even in a centrosymmetric environment. Also, helical assemblies that exhibited NLO-CD (circular dichroism) effects were discussed. These crystalline liquid state assemblies could be switched by the application of an electric field. M. Strumpel (Germany) discussed invariom modeling, specifically how to determine the absolute configuration of a structure with light atoms. This model uses aspherical electron density and works well with structures in chiral space groups. Pioneering research on chiro-optical imaging using a circular extinction imaging microscope was discussed by W. Kaminsky (USA). With this technique it is possible to examine heterogeneously organized media via intrinsic CD and anomalous circular extinction. In the final talk, J. Bernstein (Israel) discussed organic non-centrosymmetric structures, by referring to Kitaigorodskii’s famous comment ‘centrosymmetric molecules are not expected to crystallize in non-centrosymmetric space groups.’ Bernstein discussed some examples of polymorphs that crystallize in both chiral and achiral space groups.

P. Shiv Halasyamani

Polymorphism

[Reutzel-Edens]S. Reutzel-Edens
[Sato]K. Sato
[Pulham]C. Pulham
The talks in the Polymorphism microsymposium ranged from theoretical to applied and well represented this highly charged field, including prediction, thermodynamics, control, and design of polymorphs. By far the most represented industry was the pharmaceutical industry, perhaps due to the high interest generated by recent patent cases which hinged on polymorphism. Susan Reutzel-Edens (USA) discussed the pharmaceutical industry’s need for total understanding and control of the solid state of active pharmaceutical ingredients (APIs). She highlighted the need to carefully evaluate the thermodynamics and stability relationships in development of crystallizing processes. 

Frank Leusen’s (UK) discussion moved from experimental realities and control to the state-of-the-art in predicting polymorphism. While much progress has been made, it was clear that rational control and design of polymorphs from first principles is not likely any time soon!

Kiyotaka Sato (Japan) and Colin Pulham (UK) provided insight into efforts to control and modify polymorphism via conditions of crystallization. Sato discussed emulsions which, despite their complexity, could be used to crystallize desired polymorphs. Pulham went to another extreme in the study of polymorphism at high pressure, where access to new polymorphs is possible.

Mike Zaworotko (USA) managed to meld crystal engineering with polymorph control with the innovative concept of forming co-crystals of polymorphic APIs with readily available, pharmaceutically acceptable, molecules with complimentary intermolecular interactions. Co-crystals provides a level of solid state control not available for pure compounds The field appears to have huge practical application and likely will lead to many new APIs with improved properties. As brought out in his talk, the field of co-crystals has long been known, but has been little studied, especially given the huge practical implications. It is also clear that the term ‘co-crystals’ will be the subject of continuing debate!

All in all, the message of the microsymposium was clear; the control and prediction of very high value crystalline solids remains an elusive, yet incredibly important field which should provide fundamental insight and practical application. Time will tell how soon the crystallographic community can rise to the challenge!

Elias Vlieg and Robin D. Rogers

Controlled building of crystals from non-covalent interactions

[Davey]R. Davey
[Hossein]W. Hossein
[Ruiz-Perez]C. Ruiz-Pérez
[Comotti]A. Comotti
[Gorbitz]C.-H. Görbitz
Presentations in this microsymposia covered three complementary aspects of supramolecular solid-state chemistry; nucleation, crystal building, and structureproperty correlations. 

Roger Davey (UK) presented a thoughtful and instructive lecture on the use of UV/vis spectroscopy; vibrational spectroscopies; NMR; and neutron scattering in understanding the key interactions in highly concentrated solutions of five different organic molecular compounds. In many cases a clear link between solvent mediated self-assembly and the resulting crystal structures could be determined.

Wais Hossein (France) described the use of molecular tectonics for the rational design and formation of molecular networks with predefined connectivity. The precise metrics and dimensionality of many 1-D and 2-D networks can be controlled by careful design of the nature and position of recognition sites within each tecton.

Catalina Ruiz-Pérez (Spain) focused on the design and assembly of extended transition-metal containing networks. The syntheses, crystal structures and magnetic properties of a range of malonate-based copper(II) complexes were described in detail.

Angiolina Comotti (Italy) discussed weak interactions at the gassolid interface and was able to provide considerable insight into the nature of specific CH···π and π···π interactions that were present between hexagonal porous hosts and a variety of guests, such as carbon dioxide and methane, using NMR spectroscopy.

Finally, Carl-Henrik Görbitz (Norway) demonstrated how small peptides can act as building blocks for the deliberate assembly of tubular porous structures. Through suitable, and very deliberate, covalent modifications to the hydrogen-bonding capacity of individual peptides, 2-D assemblies can be replaced with microporous architectures with considerable strength.

Christer Aakeroy

Packing of organic molecular compounds

The speakers in this session reflected the dynamic and diverse nature of research in organic solid state crystallography in academic and industrial laboratories. Symposium sponsorship from the RSC journal CrystEngComm allowed for extended discussions among the speakers over dinner.

[Barbour] L. Barbour
[Nitrobenzene guest] Figure 1: The replacement of enclathrated air with nitrobenzene guest in a non-porous calixarene.
The Symposium was kicked off by Len Barbour (South Africa), who showed how well known calixarenes can be made to perform new tricks. By subliming p-t-butylcalix[4]arene, empty cavity-containing materials are obtained that are capable of absorbing small guest molecules such as vinyl bromide and gases such as CO2 even though there is no pore or channel in the structure to admit them. The work poses difficult to address questions about the nature of diffusion through close packed organic solids. The phenomenon was delightfully illustrated by a video sequence showing the replacement of calixarene-included air with a more favoured guest, nitrobenzene. When a drop of nitrobenzene is placed on the crystal, bubbles of included air are rapidly evolved as oxygen and nitrogen molecules in the cavities are replaced by the aromatic guest (Figure 1). The integrity of the single crystal is preserved throughout. Exciting discussion was provided by Stan Nyburg concerning the pressures of H2 gas required to put hydrogen as a guest in related systems.

[Gervais] C. Gervais
Claire Gervais (Switzerland) outlined her new approach to polymorph prediction based on a ‘derived crystal packing model’. Taking layers or slices of known polymorphs, Claire derives a series of daughter phases based on common packing motifs and symmetry operations. Comparison with the powder patterns of unknown polymorphs, particularly patterns of poor quality that do not admit ab initio structure solution and Rietveldt refinement, can yield the structure of inaccessible polymorphs. To illustrate, she derived a model for an unsolved phase of the pharmaceutical Modenafinil. Vigorous discussion was led by Luigi Nassimbeni.

[Gillon]A. Gillon
The pharmaceutical polymorphism theme was continued by Amy Gillon (UK). Amy showed how a very wide range of techniques are applied to screening and characterizing drug polymorphic forms. A key question she addressed concerned when is it appropriate to stop looking for polymorphs with reasonable confidence that no new forms will subsequently be identified – a formulation and intellectual property nightmare.

[Kubicki]M. Kubicki
Maciej Kubicki (Poland) provided a thoughtful look at the poorly understood world of compounds with Z’ > 1, i.e. crystals with more than one molecule (however we might define it) in the crystallographic asymmetric unit, including crystals where there are two independent half molecules using examples from his own work on nitroimidazole derivatives.

[MacGillivray]L. MacGillivray
The final speaker, Len MacGillivray (USA), illustrated the profound control over solid state reactivity that can be gained through the use of 1,3-dihydroxy benzene as a template to position reactive double bonds. The work has resulted in the highly efficient synthesis of exotic structures such as ladderanes. What was particularly pleasing about Len’s talk was the systematic use of increasingly bulky substitutents on the diol template in order to bring about the desired, convergent crystal packing arrangements, representing a clear case of crystal structure design and control with immediate application.

Given the tender age profile of the researchers, many more interesting results can be expected in IUCr meetings to come.

Jonathan W. Steed and Carolyn P. Brock

Crystallography and forensic science

[Kugler]W. Kugler
[Fitzpatrick]R. Fitzpatrick
[Heijinen]W. Heijinen
[Shovel]
[Pistol barrel][Pistol barrel]Contact traces at the muzzle of the barrel of a Police Officer's pistol
[Terada]Y. Terada
[Nakai]I. Nakai
The advent of DNA profiling evolutionized forensic science. In the absence of material leading to the recovery of DNA, however, the forensic scientist has to rely upon chemical analysis of classical trace materials in order to establish or eliminate links between suspect and crime scene. X-ray powder diffraction (XRD) and X-ray fluorescence (XRF) are two valuable non-destructive analytical methods available for this purpose, and recent developments of these methods were illustrated by the speakers through practical applications at interesting crime scenes. Werner Kugler (Germany) described a case in which the analysis, by in situ powder diffractometry, of traces of material on the barrel of a police officer’s hand gun exonerated the officer of the murder of a suspected bank robber. The gun had discharged accidentally after having been dropped on the sidewalk and traces of quartz and calcite on the barrel confirmed the officer’s account of the incident. Soil is potentially one of the most useful evidence types, and Rob Fitzpatrick (Australia) outlined the systematic sequence used in its analysis. In a double murder case, XRD was used to identify and compare clay minerals in soils on a shovel belonging to the suspect, with those in the soil of a quarry where the bodies were buried. Paper used to write threatening letters was analysed by Wim Heijnen (The Netherlands). XRD identified the fillers (talc, chlorite and kaolinite) present and also provided a measure of the cellulose crystallinity. The use of synchrotron radiation in forensic analysis has been pioneered by Yasuko Terada (Japan). She described cases in which the light source was used for XRD and XRF analysis of trace amounts of material including fluorescent powders used as markers when thrown at robbers. Use of portable XRD/XRF equipment for in situ analyses at crime scenes may become routine in the future, and in the final presentation, Izumi Nakai (Japan) illustrated his talk with pictures of a compact, portable diffractometer currently used at archaeological sites for mineral identification.

David Rendle and Izumi Nakai

Crystallography and environmental science

Multiple connections between environmental science and crystallography were highlighted by this microsymposium, with topics ranging from geomicrobiology to materials research, from basic science to industrial applications.

[Gualtieri]A. Gualtieri
In the opening lecture, Alessandro Gualtieri (Italy) documented that structural differences among zeolites (NH4-substituted chabazite and phillipsite) affect their potential as „slow-release” fertilizers.

[Guyot]F. Guyot
François Guyot (France) showed some exotic cases of carbonate biomineralization. Spatial distributions of various carbonaceous species, including proteins, carbonates, and polysacharides can be mapped using scanning transmission Xray microscopy; energy-filtered images reveal how microorganisms induce the precipitation of calcite, aragonite, or amorphous calcium carbonate.

[Jordan]G. Jordan
The environmental importance of mineral dissolution was emphasized by Guntram Jordan (Germany), who presented results of atomic force microscopy studies on mineral/water interface processes. A variety of dissolution mechanisms were illustrated by the examples of carbonates, plagioclase feldspars, and apophyllite.

The final two lectures focused on crystallographic problems related to the production and properties of materials that are used in environmentally friendly industrial applications. K. Byrappa (India) discussed the methods and results of the hydrothermal synthesis of nanocrystalline TiO2 on an amorphous carbon substrate, a composite that is used as a photocatalyst. Katsuhito Mori (Japan) presented a study on polyhydroxybutyrate thin films. Film thickness, surface roughness, and crystallographic orientation were characterized using X-ray reflectivity; the environmental significance of the study comes from the fact that such films are biodegradable.

Mihaly Posfai

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