The effect of the cryoprotectant dimethyl sulfoxide on water upon supercooling: A molecular dynamics study

We investigated a 10 wt. % aqueous solution of dimethyl sulfoxide (DMSO), a concentration widely used in cryopreservation, using molecular dynamics simulations to examine how DMSO modifies water structure and dynamics upon supercooling. The translational dynamics of water, analyzed via oxygen self-intermediate scattering functions, follow Mode-Coupling Theory in the mildly supercooled regime, similarly to pure water. A fragile-to-strong crossover in water's structural relaxation times occurs at TFSC ≈ 225 K, slightly below that of pure water (TFSC ≈ 230 K), in spite of the changes induced by DMSO. Below 230 K, water in the DMSO solution exhibits faster dynamics and shorter relaxation times than in pure water, consistent with a higher water density revealed by oxygen-oxygen radial distribution functions. At low temperatures, DMSO disrupts the hydrogen-bond network, reducing the population of tetrahedrally coordinated water molecules (i.e., those with four hydrogen bonds). These results indicate that DMSO stabilizes the high-density liquid phase of water at low temperatures, which contributes to its cryoprotective effect by inhibiting ice formation.