XXIV Congress and General Assembly

Hyderabad, India, August 2017

Reports from some of the 119 IUCr2017 microsymposia are included here. Other microsymposia reports will appear in the next issue of the IUCr Newsletter.

Biological Macromolecules

MS-028: Long-wavelength applications in macromolecular crystallography

This methodology-based microsymposium addressed several aspects both on the theoretical background and challenges as well as on the practical application of energies lower than or equivalent to 6 keV for de novo structure solution of biological macromolecules. Intrinsic challenges of this technique, including absorption from the sample, its holder and the environment (use of a He atmosphere or vacuum), radiation damage (use of kappa geometry), air scattering and large scattering angles (special detector setups), were discussed. Two presentations on specialised synchrotron beamlines were given, introducing BL-1A at the Photon Factory, Japan, and I23 at Diamond Light Source (DLS), UK. The former reaches wavelengths of 2.7 and 3.3 Å and is equipped with an automated sample changer delivering samples in an He atmosphere and a laser setup enabling the removal of liquid surrounding the crystals. The latter beamline at DLS has a dynamical wavelength range from 4 to 1.5 Å, thus easily reaching the absorption edges of Ca, P, S and other light elements, and is equipped with a large semi-cylindrical detector allowing reflections at a 90° geometry to be recorded.

MS-072: Solving the phase problem without experimental phasing

The microsymposium was organised first highlighting science cases in strong need of development for structure determination without experimental phasing, followed by the state of the art in new methods adopted at various places to tackle this common problem. M. R. Murthy (Indian Inst. Sci.) nicely introduced the encountered issues, taking as an example serendipitously crystallized proteins for which the structures were solved using a large-scale molecular replacement protocol. It was followed by two related presentations on biological crystal objects grown naturally in living organisms, where P. Montaville (Synchrotron SOLEIL) and L. Redecke (U. Luebeck) in turn highlighted the difficulties in adapting known experimental phasing techniques to their peculiar systems. S. Arold (KAUST) followed in describing the ContaMiner webserver, developed with the goal of quickly checking for known contaminants through fast MR-based screening of deposited crystallographic data. C. Millán Nebot (Inst. Biol. Mol. Barcelona) provided an introduction to the new implementations within the ARCIMBOLDO suite, where small and accurate fragment search complemented by full structure expansion via autotracing appears a potential solution for structure determination of unknown folding. Finally, F. Simkovic (U. Liverpool) concluded with the applicability of the AMPLE pipeline towards phasing trans-membrane protein structures, again through tentative MR model building.

MS-073: Minimizing radiation damage

MS-073: Minimizing radiation damage session chairs and speakers. (l-r) Richard Henderson, Yvonne Thielmann, Elspeth Garman, Mike Hough, Clement Blanchet, Go Ueno and Karol Nass.

Radiation damage is a phenomenon that presents challenges but also opportunities in many areas of structural biology. This microsymposium covered both the underlying principles and the practical implications of radiation damage in a range of different fields. The topic of radiation damage in macromolecular X-ray crystallography was introduced by the opening speaker, E. Garman (UK), who also described approaches to quantifying dose through the RADDOSE software and new methods to identify the location of specific damage caused by X-rays using the RIDL package. R. Henderson (UK) gave a perspective on radiation damage studies in structural biology and in particular, issues around radiation damage caused by electron bombardment in high-resolution cryoEM. This phenomenon is increasingly of concern with the current spectacular improvements in the resolution of cryoEM structures. K. Nass (Switzerland) described observations of radiation damage on very rapid timescales in certain XFEL experiments with longer X-ray pulse lengths, and work to characterise these by two-colour pump-probe approaches at the LCLS. C. Blanchet (Germany) presented studies of radiation damage in SAXS at the P12 BioSAXS beamline at PETRA3. This included discussion of strategies to minimize the effect of radiation-induced aggregation on SAXS data. G. Ueno (Japan) presented an interesting study of low-dose data collection with high-energy synchrotron X-rays to determine close-to-intact structures and compared these to XFEL results. Finally, an impressive new method of high-pressure cryoprotectant-free cooling of protein crystals with a very high success rate in freezing crystals grown in widely used commercial screens was presented by Y. Thielmann (Germany).

MS-081: Macromolecular machinery

'Diversity' is probably the word which best describes the microsymposium on macromolecular machinery covering secretion systems, transcription control, protein trafficking and signal transduction. Well balanced in all important respects, and particularly geographically, the session counted on speakers from both North and South America as well as Asia, Europe and Oceania. However, diversity was most importantly represented by the range of techniques and approaches taken by the speakers in order to understand the full complexity of the molecular machines themselves and the underlying biological phenomena to which they relate. There was an overall feeling that structural biology and cell biology are rapidly merging into a single unified discipline with seamless borders.

The careful dissection (and reconstruction) of the type III secretion system (Strynadka) and the transcription anti-termination complex (Wahl) were spectacular examples of the success of combining X-ray crystallography with cryoEM. Other speakers (Duff, Ghai and Nivaskumar) often resorted to other approaches, including experimentally validated modelling techniques and SAXS, in order to gain biological insight. Imelio, giving his first presentation in English, clearly highlighted structure-function relationships in phosphotransfer reactions.

The session left no doubt that studies of macromolecular machinery will become an increasingly important component of future IUCr meetings.

Crystal engineering

MS-003: Crystal engineering solutions to improve pharmaceutical tableting

The first presentation of this microsymposium focused on linking crystallographic features to tableting behavior of drugs. After introducing the bonding area-bonding strength (BABS) model for powder tableting, data of several polymorph pairs were presented to advance the idea that polymorphs with higher true density exhibit higher BS. This idea, if proven, can be adopted for qualitatively predicting tableting performance of polymorphs, which is useful for the pharmaceutical industry. The following lecture covered a recent attempt to explain different tableting behavior of several nitrofurantoin cocrystals by analyzing their structures, where the presence of active slip planes was shown to be an important criterion for exhibiting good tabletability. Consistent with this idea, an example was given in the third presentation where cocrystallization of griseofulvin with acesulfame deteriorated tabletability. In the fourth talk, a computational approach to qualitatively classifying or even predicting mechanical properties of crystals was presented, which considered slip planes and direction of Burgers * vector relative to the slip planes, both of which can be calculated from crystal structures. In the final talk, the BABS theory was applied to explain the tableting behavior of eutectic mixtures between aspirin and paracetamol.

MS-030: Crystallization mechanisms of small-molecule organic materials

MS-030 speakers and chairs. (l-r) Isaac Rodríguez Ruiz, Jaime Gómez Morales (Chairman), Abdul Ajees Abdul Salam, Ian Rosbottom, Ilia Guzei and Tonglei Li.

Five interesting lectures covered the main aspects of crystallization phenomena. Tonglei Li (Purdue U., USA) spoke about solution speciation and implication on nucleation mechanism. Ian Rosbottom (U. of Leeds, UK) discussed the control of crystal morphology and its importance in downstream processes and filtration. Isaac Rodríguez Ruiz (Commissionnât de l'Energie Atomique de France) spoke about small-angle X-ray scattering (SAXS) coupled either to micro-batch precipitation or to a microfluidic platform, to elucidate the initial stages in the precipitation. Abdul Ajees Abdul Salam (U. of Manipal, India) showed the potential of laser-assisted crystallization to crystallize amino acids and proteins. Finally, Ilia Guzei (U. of Wisconsin, USA) spoke about enantiotropic phase transitions in molecular solids involving Z' = 12. Besides these interesting talks, there was a high participation of communications as posters (22), many of them presented also as e-posters.

MS-057: Charge-density studies in crystal and cocrystal engineering

MS-057 speakers and chairs. (l-r) E. Espinosa, T. S. Thakur, J. Contreras-Garcia, M. Ernst, A. Krawczuk, S. J. Coles and K. K. Jha.

This microsymposium highlighted the applications of charge-density studies and the newly developed topological descriptors towards the understanding of structure and properties of single and multi-component crystals. Invited talks from C. Matta (Canada) and J. Contreras-Garcia (France) focused on the applications of topological descriptors for studying intermolecular interactions and physicochemical properties calculations. C. Matta presented work on the use of the localization-delocalization matrix for the development of QSAR/QSPR models and its applications in predicting the pK_a and aromaticity of molecules. J. Contreras-Garcia on the other hand highlighted the applications of newly developed NCI descriptors of electron density for the analysis of attractive and repulsive interaction regions that can be very helpful towards the understanding of single and multi-component crystal formation. E. Espinosa (France) presented an invited lecture on the understanding of the effect of crystal environment on the nature of intermolecular interactions in molecular complexes involving a halogen atom in the two extremes (a salt and cocrystal) studied through charge-density analysis. Besides these, there were three interesting talks by S. J. Coles, K. K. Jha and M. Ernst that emphasized charge-density applications to pharmaceuticals and materials.

MS-075: Tailored properties of molecular co-crystals

MS-075 speakers and chairs. (l-r) Delia Haynes, Srinivasulu Aitipamula, Richard Cooper, Jenna Skieneh, Anilkumar Gunnam, Susan Bourne, Anil Kumar, Sreenivas Reddy Lingireddy and Anuradha Pallipurath.

Co-crystals have gained immense popularity in academia and in industry for their ability to fine-tune material properties. The session was aimed at providing an opportunity to senior and young researchers to present their recent results in this area of research. A total of seven speakers presented talks on topics ranging from regulatory aspects and applications of co-crystals to optimization of co-crystal screening methodologies.

Co-crystals are currently in a stage of transition from lab to market and hence it is important to know how the regulatory bodies classify them. Sreenivas Reddy Lingireddy (Eli Lilly Company, USA) highlighted key aspects of the FDA's guidance on co-crystals and provided valuable information on regulatory pathways for the development of co-crystals as drug products. Streamlining co-crystal screening methodologies is valuable in understanding co-crystal formation. Richard Cooper (Oxford, UK) highlighted a data-driven approach to predicting co-crystal formation that reduces the number of experiments required to successfully produce new co-crystals. Delia Haynes (Stellenbosch, South Africa) highlighted guest exchanges in hydrogen-bonded frameworks; remarkably, stepwise and multiple guest exchanges occur within a given single crystal. Anil Kumar described the challenges in developing nutraceuticals for commercial use. The final three presentations were shorter talks by early career researchers. Jenna Skieneh described a co-amorphous phase with curcumin while Anuradha Pallipurath described a series of co-crystals that show irreversible thermochromism on converting to salts. Anilkumar Gunnam spoke about using co-crystallization to stabilize the neutral form in a series of zwitterionic molecules.

MS-092: Bio-compatible porous materials for drug delivery

MS-092 speakers and chairs. (l-r) M. Gemmi, P. Falcaro, A. Bacchi, K. Sarkar, M. Fantini and P. Horcajada.

This microsymposium presented the hottest news on design, engineering, characterization and biomedical applications of diverse and technologically relevant porous materials. Metal-organic frameworks (MOFs), ordered mesoporous silica and self-assembled metal-organic polyhedra (MOPs) were discussed and their functional drug-delivery properties illustrated. Speakers presented results on bio-stability, bio-compatibility and bio-accumulation as a function of the administration route of MOFs (P. Horcajada), the external surface functionalization of MOF nano-particles and their biological compatibility (S. Wuttke), efficiency of the encapsulation of diphtheria anatoxin (D-ANA) into ordered mesoporous silica (M. Fantini), and encapsulation of other therapeutics into MOP nanocages (K. Sarkar). An overview of cutting-edge electron microscopy techniques was also presented to show how progress of this characterization can benefit the investigation of porous material systems (M. Gemmi). The focus of the session conjugated the synthetic strategies and structural characterization of different families of ordered porous materials with the assessment of their efficiency in biomedical applications. Based on the outcomes proposed in this microsymposium, it is indisputable that this research is quickly moving towards the development of novel smart materials for medicine.

MS-102: Halogen bonding at the interface between small molecules and macromolecules

MS-102 speakers and chairs: (l-r) K. M. Sureshan (co-chair), Anssy Peuronen, J. A. Gavira (Chair), Kari Rissanen and Pierangelo Metrangolo.

Sunday was indeed the day of halogen bonding! The keynote address by G. Resnati set the platform for two microsymposia on halogen bonding. The afternoon microsymposium started with a talk by P. Metrangolo, who showed various examples of the use of halogen bonding as a decisive design element in various supramolecular systems. He demonstrated that a diblock copolymer substituted with terminal iodoalkyl chains showed organized assembly through halogen bonding. This is indeed an exemplification of the power of halogen bonding in organising an otherwise random polymer. Also he showed that halogenation of tyrosine residues in proteins leads to misfolding due to the halogen bonding. With systematic chemical mutation of a small amyloidogenic peptide DFNKN, he demonstrated the efficacy of halogen bonding in aggregation of the peptide, which led to the gelation of the peptide. By incorporation of the modified peptide in full-length fiber-forming protein, Metrangolo showed that fibrillation can occur much faster than the native protein. Current momentum and relevance of halogen bonding in designing small hosts were nicely highlighted by Kari Rissanen and Anssy Peuronen. They illustrated the design and synthesis of molecular cages or capsules thanks to the intrinsic properties of halogen bonds, i.e. directionality, strength etc.

MS-110: Phase transitions in alloys and molecular solids

MS-110 speakers and chairs: (l-r) Palwinder Singh, Kinga Suwinska, M. Sabeena, Philippe Guionneau, Zeljko Skoko, Mois Aroyo and Tony Linden.

Five oral presentations took place in the microsymposium: (1) Materials studies by the Bilbao Crystallographic Server by M. I. Aroyo (Spain); (2) Competing b.c.c. β to h.c.p. α phase transformations in Ti-1Mo alloy by M. Sabeena (India); (3) Multiscale structural view of phase transitions in spin-crossover molecular solids by P. Guionneau (France); (4) Phase-transition study of Ag-doped Ge₂Sb₂Te₅ thin films by P. Singh (India) and (5) Mystique world of acrobatic molecular crystals by Z. Skoko (Croatia).

From the first presentation one could get extended knowledge about the possibilities offered by the Server, which is equipped with a set of structure-utility programs including basic tools for transformations between different structure descriptions or transformations compatible with a specific symmetry reduction. Phase-transition studies in composite materials of potential technological applications were presented by two young Indian researchers (Sabeena and Singh). The spin cross-over associated with structural modifications in iron(II) molecular complexes discussed by Guionneau was shown to start at the atomic level and then propagate from the coordination sphere to the crystal packing and to the sample scale. Finally, the negative thermal expansion in crystals known also as thermosalient crystals or, more colloquially, jumping crystals, was discussed in detail in an excellent presentation by Skoko.

MS-119: Interactions in solids under stress

MS-119 speakers and chairs: (l-r) Kamil Dziubek, António dos Santos, Shanti Deemyad, Anton Targonskiy, Arianna Lanza, Andrew Cairns, Ines Collings, Alla Arakcheeva and Boris Zakharov.

This microsymposium highlighted issues related to unusual phenomena arising in solids at non-ambient conditions, from high pressures to acoustic excitation and studied by various techniques including spectroscopy, X-ray and neutron diffraction. The symposium included three long talks and four short talks. A. Arakcheeva (EPFL, Switzerland) showed new experimental results indicating that noble gases Ne and Ar, which are commonly used as pressure-transmitting media, influence high-pressure behavior of CH₃NH₃PbI₃ perovskite. K. F. Dziubek (LENS, Italy) presented new results on the phase diagram of urea at high pressures and high temperatures to show that solid-state reactions under high pressure are directed by the structure of the molecular crystal precursor. A. M. dos Santos (ORNL, USA) reviewed the state of high-pressure neutron scattering experiments. He showed that novel neutron sources coupled with innovative neutron guide geometries enable the delivery of much greater fluxes to the small samples which are common for high-pressure studies. In parallel, new developments in high-pressure devices allowed experiments that were only dreamt of a decade ago.

After the meeting in Hyderabad, we, a group of 22 IUCr 2017 participants, travelled to Delhi, being thrilled to start our golden triangle tour. The starting city, Delhi, houses amongst others the impressive Qutub minar, Bangla Sahib Gurudwara Sikh temple and India gates. Afterwards we continued to Agra where we were fortunate to visit the Agra fort and the marvellous Taj Mahal. On our way to the pink city Jaipur, we visited the interesting Fatehpur Sikri. In Jaipur itself, we visited the beautiful Amer fort and the Astronomical Observatory. After this exciting journey, we travelled back to Delhi where we said goodbye to our new friends, bus driver and excellent tour guide. Front row (l-r): Florencia Di Salvo, Hanna Dabkowska, Anna Schenk, Marv Hackert, Irina Makarova. Back row (l-r): tour guide Mina, Eddie Arnold, Ellie Francis, Aicardo Roa-Espinosa, Sue Byram, Eduardo Villalobos, Elke De Zitter (contributor), Stuart Mills, Kerry Goodman, Sebastian Klinke, Laurens Vandebroek, Elena Selezneva, Leo Sazanov, Kiyoaki Tanaka, Alex Vasiliev, Anne Tuukkanen, Umut Ozugurel, tour guide Sunil.