Chemistry

Cavity Complexities

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Science  02 Nov 2012:
Vol. 338, Issue 6107, pp. 583
DOI: 10.1126/science.338.6107.583-b
CREDIT: F. UHLIG ET AL., J. PHYS. CHEM. LETT. 3, 3071 (5 OCTOBER 2012) © 2012 AMERICAN CHEMICAL SOCIETY

High-energy irradiation of water can transiently liberate reactive electrons, which are implicated in pathways that chemically damage biomolecules. Such hydrated electrons have been spectroscopically detected, and decades of associated modeling suggested that the charge resides in a cavity, with surrounding water molecules displaced. Recently, however, a theoretical study challenged this model and instead supported a region of increased water density in the vicinity of the charge. Yet, more studies, performed in response, claimed reaffirmation of the traditional structure. In each of these cases, the simulations involved parameterized pseudopotentials. Seeking to resolve the impasse, Uhlig et al. carried out a series of ab initio calculations that treated the electron as well as a subset of surrounding water molecules quantum-mechanically; a molecular mechanics approach was applied to model long-range effects. The result did suggest that ∼40% of the spin density resides in a cavity, but also partitioned the remaining fraction among neighboring water molecules and a diffuse tail between them. Thus, the cavity description alone appears to oversimplify a complex geometry.

J. Phys. Chem. Lett. 3, 3071 (2012).

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