Automatização do processo de obtenção das conformações mais estáveis para pentoses por métodos ab initio

Abstract

Carbohydrates are molecules with very high configurational and conformational versatility. The proper energetic ordering of these conformations in only possible if theoretical studies are performed. Basically two theoretical approaches are used to sample on the potential energy surface of carbohydrates: classical and quantum mechanical. In this work, the conformational sampling was performed for D-ribose molecule. All the most likely orientations for the hidroxyl groups were investigated, for both andanomers, in both chair conformations 1C4 and 4C1Thewhole set of 324 conformational possibilities was studied. Among them, only 78 conformations were found as thermodynamically stable. Two different descriptions were used: B3LYP/6-31+G(d,p) and MP2/6-31+G(d,p). The results obtained from both descriptions were similar. An algorithm was written to generate the geometrical coordinates of all starting geometries for the conformational possibilities investigated. The number of stable conformations found was larger than that one found when classical techniques are employed to sample on the same potential energy surface.