A Jolt from Ethanol

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Science  24 Oct 2008:
Vol. 322, Issue 5901, pp. 506-507
DOI: 10.1126/science.322.5901.506c

One advantage enzymes tend to have over synthetic catalysts is their capacity as very large molecules to create an environment that fully surrounds a substrate and thereby mediates efficient reactivity through delocalized polarity effects. A simplified means of probing these reaction medium influences is to vary the solvent in which small-molecule catalysts operate. Liu et al. have explored the medium effects in a phosphate diester hydrolysis reaction catalyzed by a di-zinc complex that models enzymes that cleave nucleic acids at backbone sites. They find that although the catalyst is not highly active in aqueous solution, a shift into ethanol solvent results in marked acceleration. Moreover, the catalyst is remarkably selective for hydrolysis over ethanolysis, yielding a nearly 1:1 mixture of the competing products at an ethanol:water ratio exceeding 600:1. Based on comparison with the rate of the uncatalyzed background hydrolysis in ethanol, the authors posit a 1017-fold accelerating effect of the catalyst in this conducive medium. — JSY

J. Am. Chem. Soc. 130, 13870 (2008).

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