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For those solids that can be prepared only as microcrystalline powders, and are not suitable for investigation by single crystal diffraction methods, it is necessary to carry out structure determination using powder diffraction data. Here we highlight recent developments in the opportunities for solving molecular crystal structures from powder diffraction data, focusing on a direct-space strategy in which a hypersurface based on the powder profile R-factor R wp is searched using a Genetic Algorithm. Recent fundamental developments are described, and the application of the method is illustrated by the structure determination of two oligopeptide materials. [ABSTRACT FROM AUTHOR]

Many solids can be prepared only as microcrystalline powders and are not suitable for structural characterization by single crystal diffraction techniques. In such cases, it is necessary to carry out structure determination using powder diffraction data. There has been considerable recent interest in this field, and considerable progress has been achieved both in the development of new techniques and in the application of these techniques to tackle a wide range of structural problems. This article highlights recent developments of techniques in this field, and their application in the field of molecular solid state chemistry. [Copyright &y& Elsevier]

Abstract: We report the crystal structure of the 5-residue peptide acetyl-YEQGL-amide, determined directly from powder X-ray diffraction data recorded on a conventional laboratory X-ray powder diffractometer. The YEQGL motif has a known biological role, as a trafficking motif in the C-terminus of mammalian P2X4 receptors. Comparison of the crystal structure of acetyl-YEQGL-amide determined here and that of a complex formed with the μ2 subunit of the clathrin adaptor protein complex AP2 reported previously, reveals differences in conformational properties, although there are nevertheless similarities concerning aspects of the hydrogen-bonding arrangement and the hydrophobic environment of the leucine sidechain. Our results demonstrate the potential for exploiting modern powder X-ray diffraction methodology to achieve complete structure determination of materials of biological interest that do not crystallize as single crystals of suitable size and quality for single-crystal X-ray diffraction. [Copyright &y& Elsevier]

Abstract: We report the formation and structural properties of co-crystals containing gemfibrozil and hydroxy derivatives of t-butylamine H2NC(CH3)3− n (CH2OH) n , with n=0, 1, 2 and 3. In each case, a 1:1 co-crystal is formed, with transfer of a proton from the carboxylic acid group of gemfibrozil to the amino group of the t-butylamine derivative. All of the co-crystal materials prepared are polycrystalline powders, and do not contain single crystals of suitable size and/or quality for single crystal X-ray diffraction studies. Structure determination of these materials has been carried out directly from powder X-ray diffraction data, using the direct-space Genetic Algorithm technique for structure solution followed by Rietveld refinement. The structural chemistry of this series of co-crystal materials reveals well-defined structural trends within the first three members of the family (n=0, 1, 2), but significantly contrasting structural properties for the member with n=3. [Copyright &y& Elsevier]

Abstract: Structural properties of 2,4,6-trimethoxybenzaldehyde, 2,4,6-trimethoxybenzyl alcohol and 2,4,6-trimethoxyacetophenone have been determined directly from powder X-ray diffraction data, using the direct-space Genetic Algorithm (GA) technique for structure solution followed by Rietveld refinement. Structural similarities and contrasts within this family of materials are elucidated. The work illustrates the value of utilizing information from other sources, including spectroscopic data and computational techniques, as a means of augmenting the structural knowledge established from the powder X-ray diffraction data. [Copyright &y& Elsevier]