A theoretical study on stability of hexopyranose anomer in vacuo and in solution

Abstract

Monosaccharide such as glucose exists as a pyranose form. Hexopyranose has C1 asymmetric carbon atom and has a stereoisomer which is called an anomer (α or β). In aqueous solution at room temperature, glucopyranose exists as a mixture of about 64% β-anomer and 36% α-anomer. However, mannopyranose exists as a mixture of about 68% α-anomer and 32% β-anomer. In this study, we reveal structures and stabilities of glucopyranose and mannopyranose in vacuo and in aqueous solution. In vacuo, geometry optimization calculations were carried out to obtain the structures of α- and β-anomers of glucopyranose and mannopyranose. It was shown that glucopyranose is more stable than mannopyranose and that α-anomer is more stable than β-anomer. In aqueous solution, QM/MM-MD simulations were performed to clarify solvation stabilization energy. For glucopyranose, solvation stabilization energy of β-anomer is more than that of α-anomer and β-anomer is more stable than α-anomer. As to mannopyranose, due to the large difference in the intrinsic energy between α-anomer and β-anomer, α-anomer is more stable than β-anomer in aqueous solution.