Molecular dynamics study of water rotational relaxation in saccharide solution for the development of bioprotective agent

Abstract

Saccharides are often used as bio-protective agent owing to their unique interactions with the solvent water to change the water dynamics which dominate biomolecule deterioration. In this work, we present some basic laws for controlling water rotational relaxation time by performing molecular dynamics (MD) simulations of saccharide solutions. It is revealed that the water rotational relaxation time in saccharide solution is exponentially proportional to its residence time. Interestingly, the larger the solute dipole moment, the smaller the prerequisite residence time to obtain a tenfold retardation of the water relaxation time (the decuple-retarding period), which means the higher the increasing rate of the relaxation time vis-à-vis the residence time. We also find that water residence time exhibits a Gaussian distribution for various sugar solutions. This random walk of water within the solution further suggests that the larger ratio of the hydration layer volume to the overall water accessible space results in a longer residence time, thus a longer relaxation time distribution. We finally conclude that the protective agent with a large specific surface area and a large dipole moment is effective to retard the water rotational relaxation.