Oldenbourg - 22nd Annual Conference of the German Crystallographic Society. March 2014, Berlin, Germany

J. Graf 1, M. Ruf2, B. Noll2, S. Freisz3, A. Gerisch3, H. Ott3, B. Dittrich4, A. Kleine1, C. Michaelsen1

Incoatec GmbH, Geesthacht, Germany

Bruker AXS Inc., Madison, United States

Bruker AXS GmbH, Karlsruhe, Germany

Georg-August-Universitt Gttingen, Gttingen, Germany

The determination of the absolute configuration for light-atom structures has become central to research in pharmaceuticals and natural products synthesis . In the absence of elements heavier than silicon, it is often problematic to make a significant assignment of absolute configuration. Traditionally, heavy-atom derivatives were prepared which have a stronger anomalous signal compared to the native compound. However, this is not always feasible.

The assignment of the absolute structure configuration of light atom compounds has become somewhat easier with the advent of high-brightness microfocus sources in combination with multilayer mirrors. The increased flux density of these sources allows for the collection of high quality data, even on small samples, and improves the anomalous signal by improvements in counting statistics .

With the recent introduction of a liquid-metal-jet X-ray source, which uses a high-speed jet of a molten Gallium alloy as target, unprecedented beam intensities can be achieved . The shorter wavelength of the Ga K radiation compared to Cu K radiation leads to a slightly weaker anomalous signal for typical light atom structures. However, due to the shorter wavelength, the highest resolution achievable with the metal-jet X-ray source is typically at about 0.70 , compared to about 0.80 for Cu K. Hence, about 50% more unique reflections can be recorded. These additional reflections significantly improve the quality of the Flack parameter.

In this contribution, we will be demonstrating the improvement in data quality from the metal-jet X-ray source.

T. Gruene 1, H. W. Hahn1, A. V. Luebben1, F. Meilleur2, G. M. Sheldrick1

Anorganische Chemie/Georg- August- Univers itaet, Strukturchemie, Goettingen, Germany

Oak Ridge National Laboratory, Oak Ridge, United States

The refinement program SHELXL included improvements to make the program more convenient to use with macromolecular structures, e.g. the availability of Engh & Huber restraints . They include improvements to make sophisticated refinement of macromolecular structures against neutron data available even to less experienced crystallographers and promote the sophistication of SHELXL to the world of macromolecular neutron crystallography. The NEUT keyword automatically replaces X-ray scattering factors with neutron scattering lengths without further ado of the user and also adapts the hydrogen bond lengths for the AFIX keyword to correctly place hydrogen atoms in riding position. However as one of the main results, our work also shows that using (correct) restraints for hydrogen positions significantly improves the quality of the structure compared to riding position, a result which may be unexpected to many (X-ray) crystallographers. To our knowledge this work presents the first publication for Engh & Huber-like restraints for the hydrogen atoms for all 20 standard amino acids. Fig. 1 shows the hydrogen bonding network from a beta sheet from PDB ID 2ZOI and highlights incomplete hydrogen exchange during the deuteration procedure.

Sheldrick, G.M. (2008) Acta Cryst. A65, 222-122

Schneider, T. R. and Sheldrick, G. M. (1997) Methods Enzymol. 277, 319-343

Engh, R. A. and Huber, R. (1991) Acta Cryst. A47, 392-400

Berman, H. M. et al. (2000) Nucleic Acids Res. 28, 235242

Gruene, T. et al (2014) J. Appl. Cryst. 47

Figure 1

K. Merz 1, A. Kupka1, H. Gies1

Ruhr Universitt Bochum, Bochum, Germany

The famous Miller experiment to model the primordial soup demonstrated that amino acids can form spontaneously as the essential building blocks of life in solutions. It is, however, still an open question how self-recognition processes influence the transformation of these spontaneously formed amino acids in solvents into higher ordered structures in the solid state, thereby creating chiral materials and catalytically competent structures. The understanding of the first steps of molecular self-assembly processes in such environments will thus give important clues towards the understanding of biological evolution.

Most of intermolecular interactions are not very strong and their formation is related to and affected by small changes in the molecular structure and the crystallisation conditions. Continuing our investigations on aggregation of substituted aromatic molecules in the solid state, we studied the influence and boundaries of weak directing substituents like deuterium on the aggregation of small molecules .

Within our project, the molecular aggregation of amino acids in solution with the formation of molecular aggregates and pre-nucleation clusters in deuterated and non-deuterated systems, and in particular the role of the solvent in these processes, will be studied in both experiment and theory.