Influence of dimethyl sulfoxide on membrane fluidity under rapid supercooling

The effect of dimethyl sulfoxide (DMSO) on a model 1,2-dimyristoyl-sn-glycero-3-phosphocholine lipid membrane is investigated during a rapid supercooling from 350 to 250 K using a total of \(165.0198~\upmu\)s all-atom molecular dynamics simulations. Our findings reveal that the addition of DMSO above a critical concentration induces significant alterations in the gel phase of the membrane at supercooled temperatures, shifting the gel phase to a fluid phase evident from area per lipid, order parameter, and d-spacing. Notably, an anomalous contraction is observed in bilayers in the presence of DMSO with the same critical concentrations as the temperature is cooled from 300 K. As the concentration of DMSO rises at supercooled temperatures, the interface becomes increasingly populated with DMSO molecules, approaching a two-dimensional percolation threshold. This process leads to an expansion in the area occupied by each lipid molecule, creating free space around the lipid tails. Subsequently, the population of DMSO and water at the hydrophobic core becomes energetically favorable at a supercooled temperature compared to the higher temperature above the critical concentration of DMSO. The higher population of DMSO and water at the interface and at the hydrophobic core increases the disorder and fluidity of the lipids and gradually changes the gel phase toward the fluid phase. Thus, our results provide the molecular mechanism of DMSO-induced fluidity of the membrane at supercooled temperature relevant for cell banking in the future.