Downsizing the Hydrated Electron's Lair

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Science  02 Jul 2010:
Vol. 329, Issue 5987, pp. 42-43
DOI: 10.1126/science.1191707

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The hydrated electron is a key reactive intermediate in many chemical reactions, including those responsible for the biological effects of radiation. When water molecules (or molecules dissolved in it) encounter radiation, they ionize and emit electrons that can react with biomolecules, often in deleterious ways. Despite being so reactive, these electrons can have appreciable lifetimes because they are stabilized by surrounding water molecules. The hydrated electron, eaq, has been understood for more than 50 years in terms of a cavity model in which the electron is excluded from regions where the water molecules have appreciable electron density, and the void or cavity it occupies is stabilized by the interaction of the charge with the dielectric medium outside the void (13). On page 65 of this issue, Larsen et al. (4) challenge both of these traditional views with a new model in which the eaq not only penetrates the charge distribution of the water molecules but also is associated with a region of enhanced water density rather than a cavity. The electron wave function is distributed like tentacles that wrap around and between the water molecules.