The Theoretic Study Of The Structure And Aromaticity Of Purines

The B3LYP method of DFT theory was used to predict the geometries and property of the purines (Allopurinol, Hypoxanthine and their monoanion and monocation and 2, 6- dithiopurine) and the structure and aromaticity of Nitrogen-Containing Thiocarbon.The aromaticity of a series gaseous purines, including Allopurinol, Hypoxanthine and their monoanion and monocation was evaluated by the calculation of the aromaticity criterions including bond-length equalization, magnetic criteria, magnetic susceptibility isotropic and nucleus independent chemical shifts (NICS), all of the calculation were performed by DFT methods at the B3LYP/6-311++G** level with Gaussian 03 program package. The calculation results indicated that the aromaticity order of the purines is: the monoanions > the molecules > the monocations.The interaction of the DTP with series first and second periods metal cations (Li+, Na+, K+, Be2+, Mg2+, and Ca2+) were studied by DFT methods at the B3LYP/6-311++G** level. Our data support the experimental findings that the studied metal cations will form bicoordination complexes with DTP. The energetically favored interaction sites for monovalent metal cations were found to be the N3 and S2 positions of the DTP, while divalent metal cations will interact through the N7 and S6 sites of DTP in the gas phase. Generally, the nature of interaction of monovalent metal cations with DTP in the water solution was found to be similar to that in the gas phase. However, divalent cation containing complexes were found to be stabilized significantly in the water solution.Density functional theory was used to investigate the structure, stability and aromaticity of a series of nitrogen-containing Thiocarbons, the most stable geometries of which were obtained at the B3LYP/aug-cc-pVDZ level. On this basis, the aromaticity of these compounds was evaluated by several aromaticity criterions. The calculation results indicated that the Thiocarbons of three membered rings and a few five membered rings showed aromaticity, while that of four and most five membered rings basically showed no aromaticity.