Abstract
Reactions of peroxynitrite with guanine were investigated using density functional theory (B3LYP) employing 6β31G** and AUGβccβpVDZ basis sets. Single point energy calculations were performed at the MP2/AUGβccβpVDZ level. Genuineness of the calculated transition states (TS) was tested by visually examining the vibrational modes corresponding to the imaginary vibrational frequencies and applying the criterion that the TS properly connected the reactant and product complexes (PC). Genuineness of all the calculated TS was further ensured by intrinsic reaction coordinate (IRC) calculations. Effects of aqueous media were investigated by solvating all the species involved in the reactions using the polarizable continuum model (PCM). The calculations reveal that the most stable nitroβproduct complex involving the anion of 8βnitroguanine and a water molecule i.e. 8NO~2~G^β^ + H~2~O can be formed according to one reaction mechanism while there are two possible reaction mechanisms for the formation of the oxoβproduct complex involving 8βoxoguanine and anion of the NO~2~ group i.e. 8OG + NO~2~^β^. The calculated relative stabilities of the PC, barrier energies of the reactions and the corresponding enthalpy changes suggest that formation of the complex 8OG + NO~2~^β^ would be somewhat preferred over that of the complex 8NO~2~G^β^ + H~2~O. The possible biological implications of this result are discussed. Β© 2007 Wiley Periodicals, Inc. J Comput Chem 2007