2007 ACA meeting

Salt Lake City, UT USA, July 21-26, 2007
www.amercrystalassn.org

Highlights of the ACA meeting included presentation of the Kenneth N. Trueblood Award to Angelo Gavezzotti (U. of Milan, Italy), the Isidor Fankuchen Award to Frank Herbstein (Technion-Israel Inst. of Technology, Israel) and the Margaret C. Etter Early Career Award to Cora Lind (U. of Toledo, USA). Lisa Randall (Harvard U., USA) was presented with the Elizabeth A. Wood Award at the banquet. There were 297 talks and 250 posters.

There was a delightful mix of science, history, celebration, reminiscences and nostalgia. Although there is no formal connection between the Trueblood and Fankuchen Awards, the many common scientific interests and colleagues shared by the awardees this year, led to combining what is normally two separate half-day functions into a daylong ‘festival.’ Carol Brock (U. of Kentucky, USA) and Joel Bernstein(Ben-Gurion U. of the Negev, Israel) jointly organized the award ceremonies and symposia. Gavezzotti recalled his early days as a Ph.D student at the U. of Milan under Massimo Simonetta (who himself had been a postdoc with Linus Pauling at Caltech), and his use of the Trueblood/Long program to solve the one (!) crystal structure that comprised his Ph.D. thesis. Herbstein presented a lecture summarizing many of the structural and spectroscopic data on the quintessential π electron acceptor tetracyanoquinodi-methane.

The Etter Early Career Award Symposium began with the award presentation by ACA President Alan Pinkerton to Cora Lind. Cora’s award lecture described her studies using powder diffraction to understand negative thermal expansion materials. Her presentation also demonstrated her flair for mentoring cited by the Etter Award selection committee.

The topic of the 2007 Transactions symposium was “Diffuse scattering for the masses: the characterization of local structural correlations in molecular, macromolecular and inorganic crystals,” which reflected the now common observation of diffuse features in area-detector images from virtually all classes of materials and the increasing awareness that local structural features strongly influence many of the useful properties of real crystals. The papers presented at the symposium will be published online at the ACA website, thanks to the efforts of our Transactions editor, Jim Britten.

A session on “Experimental Phasing with Longer Wave-length X-rays” demonstrated that a technique advocated by only a few ‘callers in the dark’ a few years ago is now nearly in the mainstream of macromolecular crystallography. At longer wavelengths the anomalous scattering of sulfur, phosphorous and other light atoms is significantly enhanced, opening up possibilities for phase determination based on just the sulfur atoms in the native proteins. However, since the sought for signals are very small, extremely accurate data collection is an absolute requirement.

A session on Computational Methods highlighted the cross-fertilization of crystallographic analysis by structural descriptions from other fields, including SAXS modeling and electron microscopy.

In a plenary lecture, Nobel Laureate Roger Kornberg described the crystal structure of RNA Polymerase II (RNA Pol II), the enzyme that copies DNA to mRNA, which is the essential intermediate in the biosynthesis of proteins. He described two decades of effort in his lab that required creativity at every step: including sample preparation and purification, crystallization and phasing. Eventually, the 10 subunit, 500 kDa enzyme structure was revealed at near atomic resolution. Kornberg’s talk emphasized recent new results where combination of the available x-ray crystal structures and electron microscopic reconstructions allowed construction of a composite model for the intact 1.5 MDa initiating Pol II holoenzyme comprised of 17 protein subunits. Thanks are due to Sue Byram and Bruker AXS whose generous support made this lecture possible.

In a session on “Large & Difficult Structures”, Venki Ramakrishnan (MRC, UK) described his remarkable successes with the determination of ribosome structures including the 2.8 Å resolution structure of the 70S ribosome complex. This is the highest resolution 70S structure currently available and reveals a remarkable level of detail - even including solvent coordination geometry for Mg2+ ions.

Speakers in a session on “Crystallography in Industry” focused on the many ways crystallography is used in diverse commercial pursuits and on the development of crystallographic tools to support these pursuits. The presentations featured characterization of industrial enzymes with potential for detergent use; development of agricultural agents to improve crop yield and resistance to blight; and three facets of drug discovery: fragment-based screening, small molecule polymorph characterization, and structure-based drug design.

A session on “Non-Ambient Crystallography” focused on phase transitions by variable temperature diffraction in alloys, ceramics, and organic/inorganic compounds with a wide range of potential applications, such as thermal barrier coatings, microwave dielectrics, and composite materials with zero thermal expansion.

The session on “Crystallographic Mineralogy”, chaired by Bryan Chakoumakos (Oak Ridge National Lab, USA) and Lee Groat (U. of British Columbia, Canada), hosted a broad range of studies concerned with deep earth and the surface of Mars; manmade problems in acid mine drainage, and the benefits of synthetic materials with useful properties. An underlying theme was that even for seemingly simple chemical compounds, the crystallography can be complex and difficult at the conditions of interest.

An emerging theme in the session on “Neutron Macromolecular Crystallography”, and one that generated a great deal of excitement and discussion, was the use of both X-ray and neutron diffraction data during “XN” refinement. This approach, originally developed by Wlodawer and Hendrickson many years ago, has the advantage of increasing the data-to-parameter ratio and hence the accuracy of the structures.

A full day session highlighted the advances in the field of structure determination from powder diffraction data and its application in various materials related research. “The crystal structure of kryptonite/jadarite”

was presented by Pamela Whitfield (NRC, Canada). This new mineral, LiNaSiB3O7(OH), which has the unique chemistry of “Kryptonite” as described in the film “Superman Returns” was identified in a mine in Serbia. Unlike the fictitious green compound that can drain Superman’s powers the real mineral is white and harmless. Pavol Juhas (Michigan State U., USA) described a very different technique to get structural information for non-crystallized molecules and nano-materials based on an atomic Pair Distribution Function (PDF) technique. He described the European-Soccer-League-inspired

Liga algorithm that was successfully used to solve the molecular structure of C60 from distances obtained from neutron PDF data. This suggests tantalizing options for studying structural properties of a vast number of systems where periodic order is not present and conventional crystallographic methods cannot be applied.

A session on “Surface and Interface Characterizations” provided a comprehensive overview of the use of scattering techniques to characterize surface chemistry, materials, and physics of nano-objects on substrates in various environments, including reactive gas, vacuum, and aqueous solutions. Developments and applications of reflectivity and grazing incident small/wide angle X-ray scattering techniques were discussed.

A symposium, emphasizing the importance of small molecule crystallography to science, was dedicated to the memory of F.A. Cotton. The depth and breadth of the research presented to a large audience provided a fitting memorial to Cotton, whose contributions to chemistry would in large part not have been possible without crystallography.

“Advances in Data Collection” focused on new techniques in sample preparation, data collection, and data processing. Talks in a session on “Detectors” ranged from detectors already in widespread use to new detector hardware designs and their potential applications for correcting and improving crystallographic data. A session on “Time and Field Dependent Responses in Scattering co-organized by the Small Angle Scattering and Materials SIGs, covered a broad range of experimental research, in which response to external fields as well as evolution over time is essential. A session on “Energy Storage and Conversion” offered a broad view of the synthesis and characterization of hydrogen storage materials.

The 2008 ACA meeting will convene in Knoxville, TN from May 31-June 5.

Condensed from ACA Reflections,
No. 3, Fall, 2007

 

 

 

 

A very well attended session on “Teaching Gadgets and Educational Tools” organized by Peter Müller (MIT) focused on physical gadgets used to teach crystallographic topics as well as on computer based teaching approaches. Peter began with “Are Teaching Gadgets Obsolete in Times of Computer Animations?” Not surprisingly, the answer to this question turned out to be no. He dedicated his talk to Wally Cordes, the “Godfather of crystallographic teaching gadgets,” and showed a large variety of teaching tools, both store bought and home made.
Wally Cordes who could not attend the session, sent the following e-mail to the organizer: Anyone who gets to teach a structure-determination class should feel a need to make at least one model for each class period. The material is such that it is not at all hard to think of what might be modeled, so that there is little excuse not to do it. There is educational value even if the model is really grubby. I almost think that the cruder the model the better it gets the point across! I have had better luck in a general chemistry class holding up a 6-foot piece of venetian blind cord to talk about DNA than showing a very intricate video of the molecule.