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Eugene Y Cheung

Publications and source records attributed to Eugene Y Cheung.

9 recordsLinked to original sources
PubMed2006

Structure-reactivity correlations for solid-state enantioselective photochemical reactions established directly from powder X-ray diffraction.

A prerequisite for the development of structure-reactivity correlations for photoreactive crystalline materials is to have detailed knowledge of the structural properties of the reactant crystalline phase. In some cases, however, the materials of interest can be prepared only as microcrystalline powders and are not amenable to structural characterization by single-crystal X-ray diffraction. This paper demonstrates the utility of modern powder X-ray diffraction techniques for obtaining structural understanding in such cases, leading to the development of structure-reactivity correlations. In particular, a series of three photoreactive organic salts are considered, which undergo the same photochemical asymmetric reaction but with high enantiomeric excess in two cases and low enantiomeric excess in the other case. The structural properties of the three salts determined from powder X-ray diffraction data are shown to provide a direct rationalization of these observations.

Journal Article↗
PubMed2006

Understanding the structural properties of a dendrimeric material directly from powder X-ray diffraction data.

Complete structure determination of an early-generation dendrimeric material 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. This work represents the first application of modern direct-space techniques for structure determination from powder X-ray diffraction data in the case of a dendrimeric material and paves the way for the future application of this approach to enable complete structure determination of other dendrimeric materials that cannot be prepared as single crystal samples suitable for single crystal X-ray diffraction studies.

Letter↗
PubMed2004

How to determine structures when single crystals cannot be grown: opportunities for structure determination of molecular materials using powder diffraction data.

Many crystalline solids cannot be prepared as single crystals of sufficient size and/or quality for structure determination to be carried out using single crystal X-ray diffraction techniques. In such cases, when only polycrystalline powders of a material are available, it is necessary instead to tackle structure determination using powder X-ray diffraction. This article highlights recent developments in the opportunities for determining crystal structures directly from powder diffraction data, focusing on the case of molecular solids and giving particular attention to the most challenging stage of the structure determination process, namely the structure solution stage. In particular, the direct-space strategy for structure solution is highlighted, as this approach has opened up new opportunities for the structure determination of molecular solids. The article gives an overview of the current state-of-the-art in structure determination of molecular solids from powder diffraction data. Relevant fundamental aspects of the techniques in this field are described, and examples are given to highlight the application of these techniques to determine crystal structures of molecular materials.

Journal Article↗
PubMed2004

Rationalizing the structural properties of bupivacaine base--a local anesthetic--directly from powder X-ray diffraction data.

Bupivacaine belongs to a family of 1-alkyl-2',6'-pipecoloxylidides, which has shown promise as reversible action potential blockers that can introduce prolonged local anesthetic effects. The crystal structure of the free-base form of bupivacaine has been determined directly from powder X-ray diffraction data using the Genetic Algorithm technique for structure solution, followed by Rietveld refinement. This work further emphasizes the scope and utility of ab initio structure solution directly from powder X-ray diffraction data for tackling structural problems within the biomedical field, leading to opportunities for the investigation of structure-property relationships.

Anesthetics, Local↗
PubMed2003

Direct structure determination of a multicomponent molecular crystal prepared by a solid-state grinding procedure.

A three-component molecular cocrystal material has been prepared by a solvent-free route involving mechanical grinding of the pure phases of the individual components. This material is not accessible from conventional solution-state crystallization procedures. Due to the fact that the grinding procedure intrinsically leads to a microcrystalline powder sample, the use of powder X-ray diffraction data is essential for structure determination. This work emphasizes the scope and utility of ab initio structure solution directly from powder X-ray diffraction data for carrying out structural characterization of new materials prepared via the solid-state grinding route, leading to the opportunity to establish structure-property relationships for such materials.

Journal Article↗
PubMed2003

Polymorphism of a novel sodium ion channel blocker.

2-[[4-(4-Fluorophenoxy)phenyl]-methylene]-hydrazinecarboxamide, a member of the semicarbazone family which has shown potential therapeutic use as anticonvulsants, has been found to exist in two polymorphic forms denoted A and B. In addition to reporting aspects of the physical characterization of both forms, the crystal structure of polymorph A has been determined directly from powder X-ray diffraction data using the Genetic Algorithm technique for structure solution, followed by Rietveld refinement. This structure is compared with that of polymorph B, which was determined previously from single crystal X-ray diffraction data. Knowledge of the crystal structures of the two polymorphs provides the opportunity for establishing structure-property relationships. This work further emphasizes the scope and utility of ab initio structure solution from powder X-ray diffraction data in the pharmaceuticals field.

Calorimetry, Differential Scanning↗