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Imaging the Absolute Configuration of a Chiral Epoxide in the Gas Phase

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Science  29 Nov 2013:
Vol. 342, Issue 6162, pp. 1084-1086
DOI: 10.1126/science.1246549

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Foil-Forged Images

X-ray diffraction is widely used to determine molecular geometries and can often distinguish mirror image isomers (enantiomers), which generally requires well-ordered crystals. Herwig et al. (p. 1084) report an imaging technique to characterize enantiomers in the gas phase. A succession of ionization events were induced by passage through a carbon foil that culminated in a Coulomb explosion of mutually repelling nuclei. The trajectories of these nuclei precisely reflected the original molecular structure.

Abstract

In chemistry and biology, chirality, or handedness, refers to molecules that exist in two spatial configurations that are incongruent mirror images of one another. Almost all biologically active molecules are chiral, and the correct determination of their absolute configuration is essential for the understanding and the development of processes involving chiral molecules. Anomalous x-ray diffraction and vibrational optical activity measurements are broadly used to determine absolute configurations of solid or liquid samples. Determining absolute configurations of chiral molecules in the gas phase is still a formidable challenge. Here we demonstrate the determination of the absolute configuration of isotopically labeled (R,R)-2,3-dideuterooxirane by foil-induced Coulomb explosion imaging of individual molecules. Our technique provides unambiguous and direct access to the absolute configuration of small gas-phase species, including ions and molecular fragments.

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