DFT and MP2 conformational study of 3,6-anhydro-α-D-galactose in gas phase and in aqueous solvent

Density functional and MP2 calculations have been carried out on 3,6-anhydro-alpha-o-galactose, one of the monosaccharides constituting carrageenans. In order to determine the impact of the orientations of the hydroxyl groups on the energy landscape, we generated three isoenergetic maps using B3LYP/6-31G(d) first in the gas phase and then in aqueous medium using two models to simulate the solvent effect; the Onsager and the polarized continuum models. In order to test the effect of the influence of the diffuse function, we decided to produce two others isoenergetic maps using B3LYP/6-31+G(d) level, first in the gas phase and the second in the implicit solvent using the PCM model. The obtained lower energy conformers were then fully optimized using B3LYP, B3PW91 and MP2 with different basis sets. The results are then compared with those reported in previous works using molecular mechanics or dynamics calculations. (C) 2018 Elsevier B.V. All rights reserved.