Evidence of Variable H-Bond Network for Nitroxide Radicals in Protic Solvents

This letter presents the results of a thorough computational investigation of two prototypical nitroxide spin probes in two different protic solvents, namely water and methanol, based on the combined use of Car-Parrinello mol. dynamic simulations and static cluster/continuum quantum chem. computations. Remarkable changes in solvation networks were found on going from aq. to methanolic solns. Moreover, despite their structural similarity, the two nitroxide probes display quite different behaviors in water. This provides a rationalization of indirect exptl. available indications. Eventually, the combination of static and dynamical ab initio methods exploited in the present study allows to dissect many subtle features of the nitroxide-solvent interaction, and also allows for an anal. of solvent effects on magnetic parameters (hyperfine coupling consts. and g-tensor shift).