Eugene Y. Cheung

Developments in genetic algorithm techniques for structure solution from powder diffraction data

Abstract This paper presents an overview of developments that have taken place in recent years in the genetic algorithm technique for structure solution from powder diffraction data. After a brief resumé, of the essential features of the genetic algorithm technique for structure solution, the paper highlights recent developments in fundamental aspects of the technique, including the development of parallel computing concepts, the analysis of the evolutionary history in genetic algorithm structure solution calculations and the combination of energy information together with the powder diffraction data in structure solution. Several examples are also given to illustrate the application of the genetic algorithm technique to solve crystal structures of different types of organic molecular materials, including oligopeptides and multi-component co-crystals.

C-H...O hydrogen bond mediated chain reversal in a peptide containing a γ-amino acid residue, determined directly from powder X-ray diffraction data

The finding that peptides containing -amino acid residues give rise to folding patterns hitherto unobserved in -amino acid peptides[1] has stimulated considerable interest in the conformational properties of peptides built from , and residues,[2] as the introduction of additional methylene (CH2) units into peptide chains provides further degrees of conformational freedom.

Recent advances in opportunities for solving molecular crystal structures directly from powder diffraction data: new insights in crystal engineering contexts

Crystalline solids that can be prepared only as microcrystalline powders are not suitable for structural investigation using single crystal diffraction techniques, and it is necessary instead to carry out structure determination using powder diffraction data. In this paper we highlight recent advances in the opportunities for solving molecular crystal structures directly from powder diffraction data, focusing on a direct-space strategy in which a hypersurface based on the powder profile R-factor Rwp is searched using a Genetic Algorithm. Some recent fundamental developments are described, and the application of the method is illustrated by the structure determination of a range of materials, giving particular focus to the opportunities to exploit these techniques within the context of structural rationalization towards crystal engineering strategies.

Recent advances in the opportunities for solving molecular crystal structures directly from powder diffraction data

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.

Structural properties of methoxy derivatives of benzyl bromide, determined from powder X-ray diffraction data

Structure determination of 3,5-dimethoxybenzyl bromide and 3,4,5-trimethoxybenzyl bromide has been carried out from laboratory powder X-ray diffraction data using the direct-space Genetic Algorithm technique for structure solution followed by Rietveld refinement. These two compounds are of interest for their potential use as building blocks for the synthesis of dendritic materials. Although the two molecules differ only in the presence/absence of the methoxy group at the 4-position of the aromatic ring, the structural properties of the two materials are significantly different

Fundamental Developments in Direct-Space Techniques for Structure Solution from Powder Diffraction Data

Solids that can be prepared only as microcrystalline powders are not suitable for structural investigation using single crystal diffraction techniques, and it is necessary instead to carry out structure determination using powder diffraction data. In this paper, we focus on a direct-space strategy for solving crystal structures directly from powder diffraction data in which a hypersurface based on the powder profile R-factor Rwp is searched using a Genetic Algorithm, and we highlight some recent fundamental developments relating to this methodology.