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International Union of Crystallography

The IUCr is an International Scientific Union. Its objectives are to promote international cooperation in crystallography and to contribute to all aspects of crystallography, to promote international publication of crystallographic research, to facilitate standardization of methods, units, nomenclatures and symbols, and to form a focus for the relations of crystallography to other sciences.

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Charge density and optical properties of multicomponent crystals

APIs in the design of multicomponent functional solidsOptical materials serve a major role in modern sciences and technology. Many of the devices we use feature technology resulting from material discoveries in this fast moving area of research. Nowadays, the need for more efficient devices and minimisation in optoelectronics requires a novel approach towards crystal engineering of functional solids. A solution can be multicomponent materials built from either organic or mixed organic and inorganic components selected in a specific way, to combine molecular and structural properties to form a 3D architecture. Optical properties of a crystal strongly depend on two factors, i.e. the spatial distribution of molecules in the crystal structure and the electronic properties of molecular building blocks. The latter are easy to predict whereas the former are not. Crystal symmetry is often a key to obtaining a desired property. Noncentrosymmetric crystal structure (chiral/polar) is a necessary (limiting) condition for such properties as nonlinear properties of even order and linear properties like optical activity, piezoelectricity, pyroelectricity and ferroelectricity. However, fulfilling symmetry rules does not guarantee the existence of a physical effect. The choice of building blocks is crucial; in ideal cases, push–pull molecules should be linked with constituents enabling synthon formation flexibility.

Active pharmaceutical ingredients (APIs), through their favourable donor/acceptor spatial distribution and synthon formation flexibility, are attractive building blocks in modern materials crystallography. An API is a substance or a mixture of substances used in the manufacture of a drug product and which becomes an active ingredient in the drug product itself. Here, a Polish scientist (working in Professor Katarzyna Stadnicka’s group at the Jagiellonian University in Kraków) presents design strategies for optical materials based on selected pharmaceutical molecules [Gryl (2015). Acta Cryst. B71, 392-405; doi:10.1107/S2052520615013505]. Gryl successfully presents the factors that contribute to molecular recognition in the four selected polar/chiral crystal phases. Theoretically predicted optical properties of the molecular/ionic building blocks as well as bulk effects were all confirmed experimentally. This work shows that quantitative crystal engineering techniques combining structural analysis, charge density studies, prediction of properties and their measurements enable the full analysis of the obtained functional materials in terms of their usefulness in practical applications. The study is just a first step in the design of novel optical materials based on push–pull molecules and APIs.

This work presents an alternative application for pharmaceutical solids that are of major interest in the pharmaceutical industry. Dr Gryl’s journey with optical materials based on API started with three polymorphs of urea and barbituric acid adduct [Gryl, Krawczuk & Stadnicka (2008). Acta Cryst. B64, 623-632; doi:10.1107/S0108768108026645]. The co-crystals display synthon polymorphism (a possibility to use the same donor and acceptor sites in many ways) and hence enable the manipulation of the outcome of the engineering process. Why not use the same “flexible” molecules and incorporate them in a lattice containing components with high molecular (hyper)polarizability? This is a next step in Dr Gryl’s research. First, of course, as much as possible needs to be known about the selected building blocks and there is no better way than to study crystal structures containing those building blocks.

Posted 29 Jul 2015 

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Introduction to selected articles from the 15th ICCBM

The July 2015 issue of Acta Crystallographica Section F, Structural Biologyme0585 Communications features a special selection of papers that elaborate on presentations made at the 15th International Conference on the Crystallization of Biological Macromolecules (ICCBM15), which was held in Hamburg, Germany, 17-20 September 2014.

The first international meeting of this kind was held in 1985 at Stanford, California. ICCBM15, organized under the umbrella of the International Organization for Biological Crystallization (IOBCr), represents an unbroken span of 30 years of these biennial meetings. With 300 conference participants, the continuing and growing interest of crystallographers, chemists, physicists and engineers in crystal growth is confirmed, and this special section is a fine example of the range of research that these meetings continue to attract and support.

The articles are a useful addition to Acta Cryst. F and cover important structural biology topics related to crystallization. These include progress in nucleation studies, new techniques for detection of crystalline precipitates, production and scoring of nano- and micro-sized crystal suspensions in support of emerging applications of X-ray free-electron laser data collection procedures. These and more are examples of responses to the continued challenges to produce crystals for structural biology, featured at the Hamburg meeting.

We draw your attention to this special section of the issue, confident you will find much of interest you might not encounter elsewhere in your reading, and we hope that it whets your appetite for ICCBM16 which will be held on 2-7 July 2016 in Prague, Czech Republic.

Posted 23 Jul 2015 

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Journey into the crystal

[Touring exhibition]In our quest for the riches of the centre of the Earth, we have been discovering stones of varying shapes and substances since prehistoric times. Some stones have very unusual angular shapes with flat, fairly smooth sides, as if they had been manufactured. These natural angular shapes have long been a source of inspiration to learn more about the structure and composition of these fascinating objects.

Crystallography is little known to the public, even though it underpins much of the research into matter in physics, chemistry, new materials and life sciences. You could say crystallography originated with humanity’s exploration and interaction of these natural wonders. The study of matter continues apace today where we see crystallography is present in almost every field of science and technology.

The importance of crystallography provides a compelling argument to show as wide a community as possible, including children and junior students, the value of this scientific discipline [Hodeau and Guinebretière (2015). J. Appl. Cryst. 48, doi:10.1107/S160057671501064X].

With this goal in mind a travelling exhibition, Journey into the crystal, was launched to share with the general public the importance of the science and beauty of matter in the crystalline state. The exhibition takes visitors on a journey of discovery about matter, but also on a journey through time to the beginning of crystallography.

Through the journey into the crystal, the public discover why the crystal is intriguing, how it is so useful to science and how it plays such an important role in our daily lives. Visitors learn about the birth of crystallography and the multiple facets of crystals as objects of beauty, objects of science and contemporary objects with numerous applications.

The discoveries in crystallography of the 20th century have dispelled the mysteries about atomic structure and the physical properties of crystals, giving them a new place at the heart of modern civilisation. Crystals are now research tools used in investigations that cover an immense range, from the composition of our planet Earth to the microscopic structures of materials and the molecules of life.

The exhibition has already visited places such as Algeria, Ghana, India, Belgium, Argentina, and many other countries. The mission is to continue the road trip. If you would like to inquire about the exhibition visiting an institution near you please get in touch, med@iucr.org

You can find more details on our site Crystallography matters... more! http://www.iycr2014.org/resource-materials/voyage

Posted 20 Jul 2015 

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Advances in membrane protein crystallography

in situ data collectionMembrane protein structural biology has made tremendous advances over the last decade [Weyand & Tate (2015). Acta Cryst. D71, 1226-1227; doi:10.1107/S1399004715008317], as indicated by the exponential growth in the number of structures that have been published. These advances are a result of many factors including improvements in membrane protein overexpression, stabilization of proteins using antibodies or thermostabilizing mutations, and the enhancement of crystallization technologies such as crystallization in lipidic cubic phase (LCP).

However, there are still many challenges associated with membrane protein crystallization, data collection and structure determination. Major problems often arise because membrane proteins frequently form tiny crystals, which either cannot be improved in size or can be improved in size but, as a consequence, lose diffraction quality. In addition, crystal handling, such as mounting the crystals and soaking in cryoprotectants, is often the reason for the loss of diffraction quality through mechanical shear-induced microlesions. This is particularly true for membrane protein crystals, which are often very fragile because of their high solvent content and being very thin in one dimension. Two independent groups, Axford et al. and Huang et al., have published methods that make a major contribution to addressing these problems, which will facilitate high-resolution data collection from fragile crystals.

In the methodology demonstrated by Axford et al. [Acta Cryst. (2015). D71, 1228-1237; doi:10.1107/S139900471500423X], a standard in situ 96-well sitting-drop crystallization plate was used. The plate with the sample was left for several days until crystals grew to their maximum size. Instead of harvesting and mounting the crystals, the team mounted the entire plate on the beamline and standard procedures were then used for data collection from the membrane protein crystals. Results demonstrated that membrane protein structures can be determined at a synchrotron source using in situ room-temperature data-collection strategies.

Huang et al. [Acta Cryst. (2015). D71, 1238-1256; doi:10.1107/S1399004715005210] took the in situ approach one stage further and showed the applicability of room-temperature data collection for in meso/in situ crystallization and its use for high-throughput crystallography of membrane proteins crystallized in meso using LCP technology.

The two in situ high-throughput methodologies open up new perspectives in X-ray crystallography of membrane proteins and will provide a more rapid route to structure determination where the crystals are too small or fragile to mount, or where radiation sensitivity requires data collection from hundreds of crystals. In situ data collection therefore provides an excellent alternative to data collection at the X-ray free-electron laser, which cannot currently provide sufficient time for users.

Posted 09 Jul 2015 

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The silent partner in macromolecular crystals

jm5003The mother liquor from which a biomolecular crystal is grown will contain water, buffer molecules, native ligands and cofactors, crystallization precipitants and additives, various metal ions, and often small-molecule ligands or inhibitors. On average, about half the volume of a biomolecular crystal consists of this mother liquor, whose components form the disordered bulk solvent.

The solvent is therefore integral and also often an intrinsic part of almost any macromolecular crystal structure. Its disordered bulk components as well as its ordered constituents of varying nature need to be accounted for in modelling and refinement. The improvement of bulk-solvent description from a fundamental perspective is largely driven by methods development. In bulk-solvent refinement, users have limited choice beyond solvent-model selection and therefore not much opportunity for the introduction of bias or specific model errors, with the caveat that suboptimal masking sometimes can introduce density artefacts. In contrast, modelling of distinct solvent electron density almost always requires thoughtful interpretation, and using appropriate tools for (automated) building and validation can greatly improve the quality of structure models.

In a paper by [Weichenberger et al. (2015). Acta Cryst. D71, 1023-1038; doi:10.1107/S1399004715006045] a group of authors examine how to estimate the overall solvent content of a macromolecular crystal, how to account for and model disordered bulk solvent and how to properly identify and model distinct electron (or nuclear, in the case of neutron diffraction) density of ordered solvent molecules. The authors also emphasize that modelling of the biologically important interface region between the protein molecule and solvent is still incomplete, and advanced solvent models of these dynamic regions need to be developed.

Posted 25 Jun 2015 


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XXIV Congress & General Assembly of the International Union of Crystallography (IUCr 2017)

iucr2017logoIndia will host the 24th Congress & General Assembly of the International Union of Crystallography 2017 from August 21-28, 2017. We extend a warm welcome to all crystallographers from across the world!

A cutting edge program with plenaries, keynotes, microsymposia and posters, commercial exhibits, satellite meetings, workshops and official meetings of the IUCr is planned. This will be a state of the art international meeting set in the unique ambience of India.

Hyderabad is a modern city of 9 million people that has gained prominence as an important software and pharmaceutical centre. Its iconic symbol is the Charminar or four minarets, which draws its inspiration from the tetragonal crystal system. It is the central motif in our logo for IUCr 2017.

Hyderabad International Airport has a wide range of connections through hubs in the Gulf, South East Asia and Europe. Of course, one can also fly in through Delhi, Mumbai or just about any major airport in India. The Congress venue, Hyderabad International Convention Centre (HICC) is on par with the best Congress destinations around the world and equipped with the finest technological, communication, digital and audio-visual tools.

We are sure that IUCr 2017 will be an experience to remember for everyone. 

Gautam R. Desiraju
Immediate Past President, IUCr
Posted 23 Jun 2015