Insights into the Solvation and Mobility of the Hydroxyl Radical in Aqueous Solution.

A detailed description of the local solvation structure and mobility of hydroxyl radicals (OH*) in aqueous solution near ambient conditions is provided by Car–Parrinello molecular dynamics simulations. Here, we demonstrate that for HCTH/120 and BLYP functionals, smaller systems (i.e., 31·H2O–OH*) are contaminated by system size effects, being biased for the presence of a three-electron two-centered hemibond structure between the oxygen atoms of a water molecule and the radical. Radial and spatial distribution functions of relatively large 63·H2O–OH* systems reveal the existence of a 4-fold coordinated “inactive” OH* structure with three H-bond donating neighbors and a strongly coordinated H-bond accepting neighbor. The local hydration structure around the radical exhibits more H-bond ordering than has been predicted by recent simulations employing classical force fields. Local structural fluctuations can end with spontaneous H-transfer reactions from the nearest H-bond donor water molecule, facilitated by...