Chemistry

Zeolites Left and Right

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Science  06 Mar 2009:
Vol. 323, Issue 5919, pp. 1266
DOI: 10.1126/science.323.5919.1266c

Formally, a chiral substance is one that changes its appearance upon rotation about any axis, followed by reflection in a perpendicular plane. This property can arise from arrangements as simple as four elementally distinct atoms bonding to a central carbon, or as complex as hundreds of atoms mutually adopting slight positional shifts in an extended crystal lattice. From a practical standpoint, however, most chirally selective processes in chemical syntheses and separations rely on the influence of purified small molecules, whether free in solution or tethered to an achiral solid support. Dryzun et al. have now analyzed the parameters of previously characterized solid zeolite structures and uncovered 20 bulk crystal lattices that manifest extended chirality. Moreover, calorimetry revealed that several such zeolites distinguish between the enantiomers (mirror-image isomers) of the amino acid histidine. Given the widespread role of zeolites in catalysis, the authors envision potential for enantioselective extensions of their current applications. — JSY

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