Anharmonic Vibrational Self-Consistent Field Calculations as an Approach to Improving Force Fields for Monosaccharides

Abstract

An Amber-type of force field, based on experimental vibrational frequencies which is suitable for monosaccharides, is presented. In the present force field, the atomic partial charges and some torsional parameters are derived from a fit of calculated vibrational energy levels to known experimental spectra for α-d-glucose. The vibrational spectra were calculated using the vibrational self-consistent field (VSCF) method, which includes contributions from both anharmonic and mode-coupled terms. We find that with a reparametrization of the force field the agreement between the experimental and calculated vibrational spectra is ±3.3 cm-l for α-glucose and ±5.1 cm-l for β-glucose. Using the VSCF method, we are also able to lend support to the idea that the COH bending motion is strongly coupled to the methylene and methine modes, as well as the other internal modes. We then test our spectroscopically derived force field by calculating the anomeric effect for α → β glucose. Molecular dynamics simulations are per...