ACA 2015

Philadelphia, PA, July 2015
www.amercrystalassn.org/

Excerpted from ACA RefleXions, Fall 2015, continued from Volume 24, Number 1

2.1.5: Structural dynamics

The session had a mixture of technique and application talks, and included work on metals, materials, small molecules and proteins. M. Schmidt (USA) gave a full kinetic description of the photocycle of photoactive yellow protein, including movies of transitions around the cycle. P. Coppens (USA) showed how to scale diffraction data properly to reveal transient electronic structure. G. Phillips (USA) described the work of his student Jonathan Clinger on a new photo-signaling system for time-resolved studies. M. Trigo (USA) discussed phonon dispersion as measured in real time with a pump-probe examination of Brillouin zone coverage between Bragg spots. T. Gallagher (USA) spoke about designed flexibility in antibodies. The construction of a special chamber that allows compounds to be exchanged in frameworks (MOFs) and viewed clearly was presented by J. Cox (USA). A. Dashti (USA) described the use of manifold embedding methods to reveal conformational landscapes of ribosomes and the ryanodine receptor.

2.2.1: Advances in multi-crystal approaches and serial crystallography

Advances in multi-crystal approaches and serial crystallography session speakers (l-r): back row: Danny Axford, Cornelius Gati, Nadia Zatsepin, Qun Liu; front row: John Spence, Jennifer Wierman, Gleb Bourenkov, James Holton.

Due to the design of novel X-ray light sources, X-ray beams with unique properties, femtosecond pulse duration and full spatial coherence, new techniques for data collection are needed. The session included topics ranging from merging data from a handful of incomplete data sets collected at a synchrotron to serial femtosecond crystallography (SFX) at hard X-ray free-electron lasers, where a single crystal only withstands the X-ray pulse for fractions of a second before it is completely destroyed. J. Spence (USA) introduced the broad spectrum of exciting SFX experiments, as well as methodological developments and limitations of the technique. J. Holton (USA) covered the problem of anisomorphism in multi-crystal data merging and its utilization to overcome the crystallographic phase problem. J. Wierman (USA) introduced a novel algorithm to overcome the problem of indexing diffraction patterns with extremely low photon counts. G. Bourenkov (Germany) and D. Axford (UK) described novel data-collection schemes for micron-sized crystals with the major advantage of using easily accessible synchrotron light sources. Q. Liu (USA) described experimental phasing using multi-crystal approaches at synchrotron light sources, and obtaining phase information from SFX data sets using native S-SAD.

2.2.2: Materials discovery and crystal growth

Materials discovery and crystal growth session speakers (l-r): Paul Forster, Jared Allred, Efrain Rodriguez, Patrick Woodward, Jennifer Aitken, Kirill Kovnir, Susan Latturner, Joshua Goldberger.

This session brought together some of the top materials and solid-state chemists in the field to demonstrate how crystallography is key towards promoting materials discovery. The focus of the session was on inorganic solids such as transition metal oxides, chalcogenides, and some new main group compounds as well. P. Woodward (USA) revealed how cation ordering in layered perovskite oxides can influence the octahedral tilting and change their functionality. K. Kovnir (USA) illustrated how heavy alkaline earth metals (such as Sr and Ba) 'rattling' around inside clathrate cages produce specific thermal conductivity properties that make them potential next-generation thermoelectrics. J. Goldberger (USA) has prepared Group IV analogues to graphane, such as germanane, an interesting semiconductor with a direct band gap. J. Aitken (USA) showed that compounds such as CdGeP₂ that have the diamond structure are semiconductors with photovoltaic and luminescent properties. S. Latturner (USA) is investigating magnetic ordering in a series of intermetallic phases prepared through exploratory synthesis. J. Allred (USA) reported on a new ternary iron chalcogenide with unconventional magnetic behaviour at higher temperatures. J. M. Mangan (USA) discussed the synthesis and crystal chemistry of a series of pnictides in which electronic structure calculations and ion size effects were key to understanding their properties and their non-stoichiometry.

2.2.3: How I spent my summer vacation: experiences derived from small-molecule summer schools

This session featured presentations from past ACA summer school students, including academic faculty, postdoctoral researchers and graduate students. Presentations covered small-molecule crystallography, crystal engineering, mineralogy and the diagnosis of a new disease, 'Adult Onset Crystallography' (AOC). S. Hurst (USA) discussed her efforts to secure funding for the purchase of a single-crystal X-ray diffractometer to serve a host of schools in the Colorado Plateau area and collaborative studies using the ALS Synchrotron. L. Mitchell, postdoctoral researcher at US Naval Academy, discussed work that she performed while a graduate student at U. Texas at Austin solving structures for 10 different synthetic groups, including luminescent iridium complexes to be utilized in OLEDs. C. Durr (USA) discussed utilizing crystallography to develop a new project within his research group. D. Johnston (USA) discussed the incorporation of his benchtop diffractometer into his department's undergraduate curriculum, research with undergraduates and collaborations with other institutions. J. Lee (USA) discussed his application of knowledge gained at the summer school to undergraduate research. As a new faculty member with no prior formal X-ray crystallography training, he used the ACA summer school experience to start an undergraduate research program in synthetic inorganic and organometallic chemistry using his department's benchtop diffractometer. N. Valdez (USA) is using X-ray crystallography to characterize minerals. Nichole showed several examples including how Olex2 could be used to observe both extended structures and polyhedra.

2.2.4: SAS with membranes and membrane proteins

SAS with membranes and membrane proteins session speakers (l-r): Marc Lensink, Frederick Heberle, Drew Marquardt, Volker Urban, Shuo Qian, Ryan Oliver.

V. Urban (USA) showed how a biocontinuous microemulsion system was used in a SANS study of the incorporated antimicrobial peptide melittin; the results were comparable to other studies of melittin in liposomes. R. Oliver (USA) presented his work on determining micelle and bicelle structure with SAS. Ryan's systematic studies on detergents and lipid-detergent mixtures provide important references to optimize membrane protein folding in solution for SAS experiments. M. Lensink (France) presented the latest developments in probing membrane protein structure with SAS and molecular modeling. Their strategy of combining explicit atomic detergent modeling with SANS measurements has significant potential for structural studies of other detergent-solubilized membrane proteins. D. Marquardt (Austria) focused on the methods and structures of asymmetric liposomes. The effort of developing well controlled asymmetric liposome bilayers constituted a significant step toward a more realistic model membrane system for biophysical and membrane protein studies. S. Qian (USA) reported that a membrane structure determined from SANS data is consistent with the previously determined X-ray structure and clearly revealed the water distribution in a membrane fusion intermediate structure.

2.2.5: Mechanistic and spectroscopic structural enzymology

The session focused on X-ray crystallographic studies of large complex enzyme families augmented by neutron diffraction, NMR and mutational analysis. The targets of the studies were a carbonic anhydrase surface variant that is a drug target for several aggressive cancers (B. Mahon, USA); mutation and cofactor analysis of a flavin trafficking protein from the syphilis spirochete (D. Tomchick, USA); the role of S-adenosyl-l-methionine (AdoMet)-dependent methyltransferases in metabolism and signal transduction (R. Trievel, USA); and GTPase and redox enzymes (F. Meilleur, USA).

2.3.1: Professional development: communicating your science

Professional development: communicating your science session speakers (l-r): back row: Jarrod French, Joseph Gindhart, Darcy Gentleman, Celeste MacElrevey, Andrew Torelli; front row: Amalia Issa, Katherine Sippel. (Photo courtesy of Andy Torelli.)

In this session, organized by the Young Scientists Special Interest Group, speakers offered advice on how to effectively communicate to specific audiences. D. Gentleman (Manager of Science Communications at the American Chemical Society) challenged the audience to describe their research in a simple way to diverse audiences including government officers and policymakers. A. Issa (Chair of the Dept. of Health Policy and Public Health at U. of the Sciences in Philadelphia) outlined the design of presentations for policymakers and the general public. Pharmacokineticist C. MacElrevey (Nuventra Pharma Sciences) discussed the challenges of maintaining good laboratory practices while working within the guidelines set by the FDA and EPA. J. Gindhart, a program director in the Division of Cell Biology and Biophysics at NIH, discussed the importance of communicating with your program officer throughout the NIH grant cycle. K. Sippel, a contract science writer and editor from BioScience Writers, offered specific tips to clarify writing, such as removing redundant and unnecessary text, choosing appropriate power words, and balancing adjectives and prepositions. Copies of the presentations have been posted in the Young Scientists Zone on the ACA website.

General interest posters

Three posters concerning solid-state reactions and two posters using data from small-molecule studies to inform protein crystallography fascinated poster session reviewer, C. Schwalbe (UK). The topics and authors of the posters were 'Doping effects on thymine monohydrate crystals' (E. Koch, USA); 'Dynamic reaction pathways in the single-crystal-to-single-crystal solid-state Diels-Alder reaction of N,N'-bis(cyclobutylimino)-1,4-dithiin with 9-vianyanthracene' (S. Khorasani, South Africa); 'Probing halogen photoelimination - how can photocrystallography help?' (S. L. Zheng, USA); 'Non-canonical hydrogen bonding to AdoMet is a common feature of AdoMet-dependent methyltransferases' (R. Fick, USA); and 'Protonation changes geometry of histidine rings' (Z. Dauter, USA). Carl's own poster concerned 'H...H clashes in published carboxylic acid structures'.

3.1.1: Etter Early Career symposium

Jessie Zhang

In her Etter Award Lecture, J. Zhang (USA) described her studies of the phosphorylation state of the C-terminal domain of RNA polymerase and its effect upon transcription. Eight other student and postdoctoral talks were selected for presentation in the symposium. M. Whitley (USA) combined small-angle X-ray scattering and NMR analysis of a mutant of human γD-crystallin. D. Mast (USA) described a powder diffraction study of technetium metal at high pressure and variable temperature. J. Gadient (USA) presented in situ high-pressure measurements for a number of negative thermal expansion materials. A. McGrath (USA) presented structural insights into ligand entry, malleable binding and induced helical movement in P-glycoprotein drug targets. K. Handing (USA) revealed how the binding of zinc to serum albumin sheds light on metal transport and distribution in mammals. L. Mueller (USA) discussed the structure and catalytic mechanism of a member of the acetoacetate decarboxylase-like superfamily. P. Janowski (USA) discussed how molecular dynamics can be utilized to improve the analysis of crystallographic data. P. Krotee (USA) described the use of electron diffraction to obtain crystal structures of Type II diabetes-related peptides from very small crystals.

3.1.2: Local structure and complex materials

O. Borkiewicz (USA) showcased in situ studies of energy storage materials found in batteries. Hard X-rays have elucidated failure and operational modes in new candidate materials. K. Jensen (USA) presented a relatively new experimental method: computed tomography pair distribution function (ctPDF) analysis. Jensen demonstrated the power of this technique for the spatial mapping of the internal crystalline and amorphous phases in a traditional AAA battery without even having to open up its case. She reported that ctPDF analysis was used to identify sources of sulfuric acid that are decomposing the hull of the Mary Rose, Henry VIII's warship that was sunk in 1545 and recovered in 1982. I. Levin (USA) discussed advances in reverse Monte Carlo modeling using multiple data types simultaneously, fitting one model to X-ray and neutron PDF, EXAFS and diffuse electron diffraction data. K. Page (USA) described recent advances in data reduction on the total scattering instruments at the Spallation Neutron Source. M. Donakowski (USA) presented data on a family of RuO₂-derived nanostructured composites that are enabling the development of ultracapacitor technology.

3.1.3: Hot structures I - intracellular protein regulons

(Left) The human COP9 signalosome (CSN) is a master regulator of intracellular protein degradation. CSN regulates the largest class of ubiquitin ligases of which humans have several hundred. Ubiquitin ligases confer substrate specificity to ubiquitination. Ubiquitinated proteins include crucial regulators of DNA repair, growth and development. (Photo courtesy of Richard Bunker.) (Right) Hot structures I - intracellular protein regulons session speakers (l-r): Christopher Colbert, Huanchen Wang, Kristina Djinovic-Carugo, Hyun-Joo Nam, Richard Bunker, Chelsy Prince, Oluwatoyin Asojo. (Photo courtesy of Hyun-Joo Nam.)

R. Bunker (Switzerland) described his studies of an elaborate ~350 kD eight-protein hetero-complex that is a master regulator of intracellular protein degradation. Richard analyzed crystallographic and electron microscopic data and discussed the functions of each subunit based on the mutational studies. C. Colbert (USA) described the cytoplasmic domain of PupR, a TonB-dependent transporter. K. Djinovic-Carugo (Austria) reported on the high-resolution structure of the 200 kDa α-actinin-2 dimer from striated muscles. O. Asojo (USA) described the high-resolution structure of an 11 kD protein from sand fly salivary gland homogenate, part of an effort to develop a vaccine to combat leishmaniasis, which is transmitted by the sand fly. H. Wang (USA) presented structural studies of two kinases involved in cellular signal transductions. C. Prince (Canada) presented the structure of LapB, a key regulator of lipopolysaccharide synthesis pathways in E. coli.

3.1.4 and 3.2.4: Standard practices in crystallography I and II: data-collection strategies and data reduction

(Left) Standard practices in crystallography I session speakers (l-r): back row: George Sheldrick, Dorothee Liebschner, Gerard Bricogne, Tobias Weinert, Mitchell Miller, Dominika Borek; front: Peter Müller. (Photo courtesy of Peter Müller.) (Right) Standard practices in crystallography II session speakers (l-r): back row: George Sheldrick, Zbigniew Dauter, Bruce Noll, Leo Straver; front row: Peter Müller, Dominika Borek, Chelsy Prince, Dorothee Liebschner. (Photo courtesy of Peter Müller.)

The session began with three talks on SAD phasing. D. Liebschner (Japan), T. Weinert (Switzerland) and C. Prince (Canada) spoke on 'The challenges of soft X-rays: data collection above 3 Å wavelength', 'Fast native SAD phasing for routine macromolecular structure determination', and 'Tricks for success using zinc SAD phasing', respectively. D. Borek (USA) discussed 'Theory and practice in X-ray diffraction data processing'. Data-collection strategies were addressed by M. Miller (USA), G. Bricogne (UK) and Z. Dauter (USA). B. Noll (USA) and L. Straver (Netherlands) gave examples of how the data-collection strategy influences the outcome of a diffraction experiment. G. Sheldrick (Germany) described how modern absorption correction and scaling are performed on the software level. Bruker AXS provided financial support for the session.

3.1.5: Structural modeling for SAS

Structural modeling for SAS session speakers (l-r): Thomas Weiss, Xiaolin Cheng, Farzaneh Tondnevis, Frederick Heberle, He Song. (Photo courtesy of Xiaolin Cheng.)

This session described combining solution small-angle scattering (SAS) data with computational modelling to uncover structure. X. Cheng (USA) combined molecular dynamics simulations with neutron contrast variation data to elucidate the lateral organization of lipid membranes. H. Zhang (USA) runs Monte Carlo calculations on highly parallel GPU architectures interfaced with a web-based GUI front end to interpret SAS data. F. Heberle (USA) focused on the spatial organization and raft formation in asymmetric lipid vesicles. H. Song (USA) described the solution structure of the full-length Saccharomyces cerevisiae RNase III with and without RNA. F. Tondnevis (USA) described her work in elucidating the structure of the E. coli clamp loader clamp complex with SAXS, in which the solution structure shows an opening of the sliding clamp sufficiently large for DNA loading not found in the crystal structure.

3.2.1 and 4.1.4: Important science from small-molecule structures

Important science from small-molecule structures session speakers (l-r): front row: Bruce Foxman, Marilyn Olmstead, Javier Campo, Matthew Wander, Larry Dahl, Larry Falvello; back row: Christine Beavers, Xiaoping Wang, Garry McIntyre, Feliu Maseras, Alberto Albinati.

The session combined physics and chemistry, theory and experimentation, graduate students and established scientists. Topics addressed included neutron diffraction studies of magnetic chirality (J. Campo, Spain), aperiodic crystals (G. McIntyre, Australia) and a single-crystal-to-single-crystal transformation relevant to catalysis in H₂ fuel cells (X. Wang, USA). Xiaoping showed a periodic table weighted by relative abundance at the earth's surface which explained why iron-based catalysts are particularly desirable. C. Beavers (USA) described a single-crystal-to-single-crystal transformation in a spin-crossover system, and B. Foxman (USA) discussed mother-daughter orientation relationships in phase transitions. Theory was addressed in talks on the bond-valence model (M. Wander, USA) and application of the AIM (atoms in molecules) approach to computational homogeneous catalysis (F. Maseras, Spain). M. Olmstead (USA) described ordered co-crystals of C₇₀ with bromobenzene derivatives. K. Knope (USA) focused on actinide-organic interactions, and S. Bart (USA) discussed the impact of size and reducing capability on the organometallic chemistry of uranium. In his lecture on the theme of multiferroics, with switchable electric and magnetic ordering, P. Stephens (USA) provided cautionary comments on the pitfalls of structure refinement using powder diffraction data. I. Đilović (Croatia) gave a talk on remarkable supramolecular chemistry involving host-guest complexes and a polyamine host that takes part in dynamic molecular recognition. The Cambridge Structural Database (CSD), now 50 years old, was the subject of two talks. C. Brock (USA) discussed the results of CSD-based studies of high-Z' organic structures, including translational modulation, an abnormal distribution of space group frequencies, and the common appearance of layered structures and polytypes. C. Groom (UK) gave a comprehensive review of science derived from the 787,912 structures in the CSD. An introduction to the philosophy and origins of the database led into a description of frontier knowledge-based studies, including an example of how the solubility of a compound can be improved by understanding its crystal structure. L. Dahl (USA) described Pd-based hetero- and homometallic clusters stabilized by CO and PR₃ that can be formed by up to 165 metal atoms.

3.2.2: Powder pair distribution function and pharmaceuticals

The session highlighted the use of the atomic pair distribution function (PDF) to study amorphous and nanocrystalline pharmaceutical drugs. X-ray powder patterns are used as fingerprints to characterize the presence of drugs in specific solid forms because the efficacy of the drug depends on its solid form. When some drug components are amorphous, or nanocrystalline, this approach breaks down and approaches such as PDF analysis are needed. Using synchrotron radiation, S. Billinge (USA) showed how extremely small signals from dilute nanocrystalline drug products in aqueous suspension could be extracted from solvent backgrounds, allowing the structure of an inhaler drug compound to be studied in dosage form. E. Cheung (USA) showed how small signals could yield critical information about recrystallization in the amorphous form of an excipient (packaging material). Understanding how drugs recrystallize from the amorphous state is a critical safety issue if drugs are brought to the market in the metastable amorphous form. Cheung highlighted the importance of gathering complementary experimental information such as NMR data, for a proper understanding of these complex problems. A. Sheikh (USA) showed that PDF could tell whether or not milling modified the structure of a drug. V. Petkov (USA) showed that rather high-quality PDFs useful for many applications might be obtained from in-house devices. P. Juhas (USA) described ab initio determination from PDF data of structures previously determined by conventional methods. This opens up the possibility of solving structures of nano-sized drug clusters that cannot be solved crystallographically. J. Kaduk (USA) used traditional powder diffraction to resolve troublesome issues with supposedly known structures of pharmaceuticals.

3.2.3: Hot structures from membrane systems

Hot structures from membrane systems session speakers (l-r): Jessica Thomaston, Elisabeth Lowe, Jason Moore, Elise Blankenship, David Lodowski, Yu-Chung Chang, Bil Clemons. Not shown: Martin Caffrey. (Photo courtesy of David Lodowski.)

Membrane protein structures reveal the mechanisms of transmembrane signaling, transport and secretion that are critical to understanding human health and disease and identifying key therapeutic targets. E. Lowe (UK) discussed the sensor domains from the Bacteroides hybrid two-component systems, which regulate expression of genes involved in polysaccharide breakdown. B. Clemons (USA) discussed the differences between tail-anchored membrane proteins in fungi and humans. M. Caffrey (Ireland) described using his lipidic cubic phase technique to determine the structure of an outer membrane porin that is involved in the transport of a component of biofilms produced by Pseudomonas aeruginosa - a pathogen that contributes to the death of cystic fibrosis patients. J. Thomaston (USA) highlighted a continuous network of ordered solvent extending from the gating histidine to the N-terminus of the influenza M2 proton channel. E. Blankenship (USA) presented the structure of native-source rhodopsin stabilized in an active-state conformation competent for G-protein binding. A water-mediated hydrogen-bonding network, not seen in the ground state, directly links the chromophore binding site to the site of G-protein binding over 30 Å away. J. Moore (USA) reported on the crystal structure, mutational experiments, dimerization characteristics and signaling of the membrane proximal domain of a family of tyrosine kinases that play a role in angiogenesis.

3.2.5: Evolving techniques for SAS

Evolving techniques for SAS session speakers (l-r): Hiroshi Okuda, David Green, Wim Bras (at rear), Kamila Wiaderek, Daniel Sunday (at rear), Brian Collins, Peter Mario Worsch (at rear), Tobias Madl (at rear), Cheng Wang. (Photo courtesy of Cheng Wang.)

Since the early attempts in the late 1930s, small-angle scattering (SAS) has evolved as a widely used high-resolution nondestructive structure probe for a broad range of applications in materials science, structural biology and environmental research. Over the past decade, with the development of third-generation synchrotron sources, spallation neutron sources and free-electron lasers, as well as advanced detectors, there have been many exciting new developments; for example, the application of resonant X-rays to provide both chemical and spatial information on materials, the development of advanced in situ sample environment techniques, and of high-pressure applications, as well as the use of coherent X-rays to capture the temporal correlation for kinetics and dynamics, such as fluctuation scattering. These developments have been accompanied by further improvement of high-performance computation tools for scattering modeling and data analysis.

This session aimed to bring experts in the forefront of SAS development to discuss recent advances and to foster novel ideas and solutions to the increasing challenges of complex structures in modern materials science. Researchers from Austria, France, Germany, Japan and the USA presented their advanced projects. Topics covered the latest trends in instrumentation development, from state-of-the-art laboratory SAXS equipment to synchrotron-based SAS systems, which use both hard and soft, as well as intermediate energy, X-rays. The research topics included a broad range of structural results for nanocomposite materials, organic electronic materials and biological complexes.

The session was well attended and the talks were followed by lively discussions, indicating a significant interest in modern SAS techniques.

3.3.1 Evening session on diversity and inclusion

Evening session on diversity and inclusion speakers (l-r): Catherine Drennan, Krystle McLaughlin, Stephanie Wortel.

C. Drennan (USA), in her talk 'Does diversity training work?', described stereotype threat training that was developed in her lab and is now being used to train teaching assistants at MIT. Stereotype threat is the perceived risk of confirming a negative stereotype. S. Wortel (USA) described an after-school STEM Mentoring Program she has directed at NYAS for the past five years that connected elementary and middle school students with professional scientists and how professional scientists can reach young community members by leveraging existing community structures.

4.1.1: Structural glycobiology

A model of β-hexosaminidase A and the G_M2 activator protein with bound substrate G_M2.

A new form of β-hexosaminidase A, an enzyme mutated in some forms of lysosomal storage disease, has been patented by B. Mark (Canada). HexA normally forms a heterodimer of α and β subunits. Brian has engineered a homodimer, HexM, that may rescue the phenotype when either HexA or B is knocked out. P. Emsley (UK) addressed the characterization of N-glycans on protein structures. Paul has developed a builder/refinement routine within the Coot software for fitting N-glycan structures to electron-density maps in realistic conformations. P. Zaloba (Canada) is studying a glycosidase family from Salmonella. H. Blanchard (Australia) described the design of the first high-affinity selective gal-3 inhibitors, potential anti-leukemic agents, based on her crystal structures of galectins. M. Saper (USA) used a combination of crystallographic, binding and computational methods to understand how LpoA can span a periplasmic space of variable width in H. influenzae bacteria. M. Chaudet (Canada) has been testing the hypothesis that enzymes from the gut microbe play a role in digesting starch products that are resistant to the action of the human starch digestion system. K. Wangkanont (USA) presented the first structures of X-type lectins including human intelectin-1, and is attempting to identify the physiological substrate of the human lectin.

4.1.5: (Bio)Chemistry in the X-ray beam

(Bio)Chemistry in the X-ray beam session speakers (l-r): Sean McSweeney, Yasufumi Umena, Robert Thorne, Nigel Moriarty (back), Carrie Wilmot, Garth Simpson, Elspeth Garman. (Photo courtesy of Elspeth Garman.)

The session addressed kinetic processes that may be occurring intentionally or unintentionally in the X-ray beam. C. Wilmot (USA) used specific examples to highlight the importance of understanding oxidation state during a reaction. Y. Umena (Japan) discussed the determination of the valence states of the Mn atoms in photosystem-II. He demonstrated that high-resolution structures and anomalous dispersion techniques can help elucidate the water-splitting reaction of this system. G. Simpson (USA) discussed imaging of the electrical field developed through photo-electron escape and showed that it is possible to visualize the local changes to crystalline structure. N. Moriarty (USA) discussed the methods employed to provide appropriate chemical restraints in Phenix that allow for correct modeling of the species present in a crystal structure.

4.2.1: General interest III

I. Guzei (USA) entertained and inspired with his description of the Crystal-Growing Competition that he organized for high-school students in Wisconsin. A. Sarjeant (USA) used the CSD to track the top 61 journals reporting crystal structures between 1997 and 2012 and found that there was no correlation between the R factor of reported crystal structures and the impact factor of the journal. She found some other interesting trends in the popularity of certain structures/materials over time, revealing that culinary and crystallography fads are not so different. P. Forster (USA) described how his crystallographic studies are guiding synthetic efforts to produce new novel T_c compounds. L. Falvello (Spain) described analyses of samples that can only be formed and studied in situ by carefully controlling experimental conditions. T. Ramadhar (USA) discussed the crystalline sponge method, in which highly porous framework materials are used to incorporate and thereby 'crystallize' compounds that otherwise cannot be crystallized. Timothy emphasized the importance of having a well characterized framework material with the right pore sizes for the target molecule. J. Rose (USA) reported on the increasing success of the native SAD method due to advances in hardware and software that enable better data collection. B. Chakoumakos (USA) described the fascinating microstructure of sturgeon ear bones and how careful powder XRD analyses are providing a new level of understanding about the habitat and growth of these fish. A. Mesbah (France) discussed synchrotron powder diffraction experiments that led to a new monoclinic structure for hydrated rhabdophane in which the water molecules could be located.

4.2.2: Cool structures

Cool structures session speakers (l-r): Allen Oliver, Soorya Kabbekodu, Karina Heffernan, Yulia Sevryugina, Craig Bridges (at rear), Elinor Spencer, Patrick Carroll (at rear), Christopher Durr.

The Cool structures session commenced with an engaging talk on high-pressure crystallography by E. Spencer (USA). She described the challenges of high-pressure experiments and fundamentals of this field. She concluded with a discussion of how structural changes in lanthanide complexes over a range of pressures alter their luminescent properties. Etter Student Lecturer, K. Heffernan (USA), described how variation of pressure can alter topological characterization of rare earth phosphates. Y. Sevryugina (USA) presented a series of borate structures and described how borate topology is developed. S. Kabbekodu (USA) described the internal structure of the Powder Diffraction File and how inorganic materials are classified within the database. C. Bridges (USA) presented the mechanism of charge transport in Li-ion batteries and discussed modified battery materials designed to carry a higher charge and ultimately reduce reliance on fossil fuels. P. Carroll (USA) gave a talk on some 'un-cool structures'. He described in-depth analysis of four challenging studies undertaken during the past year.

4.2.3: Structured nucleic acids

The session featured talks on reverse transcriptase bound to a DNA template (S. Martinez, USA), a transcriptional regulator bound to a cognate DNA promoter (S. Wang, USA) and a catalytic RNA with an unusual 2',5'-phosphodiester linkage (N. Toor, USA). H. Zheng (USA) presented a new online tool called Mg-RNA Server (www.csgid.org/metalnas) to assist in the identification/validation of bound magnesium ions in crystal structures, which can be particularly difficult to assign properly. B. Mooers (USA) discussed challenges that can arise during structure determination of long duplex nucleic acids that harbor intramolecular pseudo-translational symmetry. M. Wahl (Germany) presented work on the structure and function of protein-RNA sub-complexes belonging to the spliceosome, including the structure of an ATP-dependent RNA helicase, which is located near to the spliceosome's catalytic core.

4.2.4: Imaging with X-rays and electrons

Winner of the Etter Student Lecturer Award, Mariana Verezhak, showed a three-dimensional reconstruction of human dentine samples visualized with a voxel size of 28 nm, the highest attainable resolution reported so far.

The session included a report on a new discovery, in addition to reports on imaging techniques using photons and particles, and the complementarity of synchrotrons and electron microscopes. A wide range of applications in medical, biological, chemical, physical, materials and engineering sciences were discussed. D. Chapman (Canada) discussed diffraction-enhanced imaging and explained that, using multiple X-ray energies, it is possible to differentiate soft from hard tissues, improving and expanding the study of living subjects. V. Stanic (Brazil) and K. Evans-Lutherodt (USA) discovered an intermediate structure of hair between the cuticle and cortex. The structure is composed of β-keratin, which has toughness and elasticity and is usually associated with reptiles and birds. Further study may help explain why humans in different parts of the world have different hair types. B. Raghothamachar (USA) correlated electronic/optoelectronic device performance and defect distribution in nanomaterials and protein crystals. G. Calero (USA) is using transmission electron microscopy (TEM), bright-field microscopy and ultraviolet fluorescence microscopy to characterize the growth and quality of submicron-sized macromolecular crystals. He can distinguish nanocrystals from granular precipitates, vizulize crystal lattices and use electron diffraction patterns to identify crystal forms with higher order X-ray diffraction. A. Fluerasu (USA) described the use of X-ray photon correlation spectroscopy to analyze the speckle patterns of colloidal particles. A change of the speckle pattern reveals the dynamic behavior of the sample near the colloidal glass transition. M. Verezhak (France) showed the first three-dimensional reconstruction of human dentine samples visualized with coherent X-ray diffraction imaging. She used bone and dentine samples as models for heterogeneous composite materials. The three-dimensional dentine nanoporosity is believed to have a biological role in cell communication and mechano-sensing. C. Jacobsen (USA) presented the current status of soft X-ray cryomicroscopy to image cells and tissues using ionizing radiation with maximum preservation of structure and chemistry. Jacobsen argued that electrons excel for high-resolution imaging of samples thinner than a micrometre, while X-rays offer a path to image thicker samples such as whole eukaryotic cells and thin tissue samples. He also highlighted the role of cryo sample-preparation methods, along with the combination of fluorescence studies with ptychography to obtain thousand-fold increases in sensitivity for elemental and spectroscopic imaging compared to electron microscopes.

4.2.5: Play it cool? Ambient and cryogenic approaches

This session focused on the effects of X-ray data collection at ambient and cryogenic temperatures upon macromolecular crystals and molecules. R. Thorne (USA) presented an overview of crystal cooling and a discussion of the effects of cooling rates on ice formation and crystal damage. T. Kumasaka (Japan) showed a novel technique of encasing crystals in a hydrogel for data collection that allows for robust ambient-temperature data collection without an additional cryoprotection step. D. Juers (USA) uses a flow of humid air over the crystal-viewing microscope that limits deleterious effects from dehydration during crystal handling, cryosoaking and cryomounting, and a new approach for cryoprotection using vapor diffusion to deliver volatile alcohols to loop-mounted crystals. A. Gonzalez (USA) compared radiation damage at ambient and low temperature (100 K) in crystals of thaumatin, lysozyme and cyclophilin A. At cryogenic temperature, greater doses yielded greater conformational variability. This was not the case at room temperature. Increased conformational heterogeneity in room-temperature crystal structures is not a result of radiation damage. D. Axford (UK) discussed data collection on beamline I24 at Diamond at both cryogenic and ambient temperature. Axford showed remarkable successes using in situ diffraction on virus crystals. D. Keedy (USA) described multi-temperature experiments on the diabetes therapeutic target PTP1B. The relative population of two conformations of an important loop was found to depend on temperature, and the impact of this conformational change on a distant ligand-binding site was explored.

The full report on the meeting can be found on the ACA website at www.amercrystalassn.org.