DFT Study of NBO, NICS and 14N NQR Parameters of Guanine Tautomers in the Gas Phase

Abstract

Abstract The NBO (natural bond orbital analysis), NICS (nucleus independent chemical shift) and 14N NQR (nuclear quadrupole resonance) parameters of the most stable tautomers of guanine in the gas phase were predicted using density functional theory (DFT) method. The NBO analysis indicated the π clouds in the both considered heterocyclic ring contained six electrons, and these tautomers have the aromatic character. The NICS study utilizing the gauge-invariant atomic orbital (GIAO) method showed that there are diatropic currents in the heterocyclic rings of the tautomers, so we determined the order of overall aromaticity of these tautomers. The results of NQR parameter calculations showed that the p character value of lone pair electrons of nitrogens, the related occupancies and degree of participation of lone pair electrons of nitrogens in the diatropic currents of ring or intramolecular interactions are effective on nuclear quadrupole coupling constant.