Conformational analyses of Xanthan gum polymer: experimental, molecular dynamics and quantum mechanical studies

The effect of temperature on the conformational behaviour of xanthan gum polymer in an aqueous solution (XG _(aq)) was investigated. Viscosity values of XG _(aq) were measured in the temperature range of 20–60°C. Traditionally, density and concentration have similar nature. However, conformational changes of polymers in aqueous solutions may lead to alteration of density values while such structural changes do not alter concentrations. The plots of density values versus concentrations reveal abnormal behaviours of XG _(aq) at 35–60°C, which may be attributed to the conformational changes. The interactions of XG _(aq) with human serum albumin (HSA) protein were explored via fluorescence studies. The rate of change of the Stern–Volmer constant as well as bonding parameters demonstrates a turning point at 37°C. Molecular dynamics (MD) simulations of XG _(aq) were performed after equilibrium and at the last 60 ns. Three different conformational variables, namely at the backbone of β-1,4-D-glucopyranose glucan linkage, at the side chain of mannose (β-1,4) linkage and at the side chain of glucuronic acid (β-1,2) linkage were defined. Density functional theory (DFT) studies verified the existence of intra- and intermolecular interactions. The combination of xanthan gum polymer with metformin as an anti-diabetic drug has the most stability at normal body temperature.