Dimethyl sulfoxide (DMSO) is widely used in a number of biological and biotechnological applications, mainly because of its effects on the cell plasma membrane, but the molecular origins of this action are yet to be fully clarified. In this work, we used two-and three-component synthetic membranes (liposomes) and the plasma membrane of human erythrocytes to investigate the effect of DMSO when added to the membrane-solvating environment. Fourier transform infrared spectroscopy and thermal fluctuation spectroscopy revealed significant differences in the response of the two types of liposome systems to DMSO in terms of the bilayer thermotropic behavior, available free volume of the bilayer, its excess surface area, and bending elasticity. DMSO also alters the mechanical properties of the erythrocyte membrane in a concentration-dependent manner and is capable of increasing membrane permeability to ATP at even relatively low concentrations (3% v/v and above). Taken in its entirety, these results show that DMSO is likely to have a differential effect on heterogeneous biological membranes, depending on their local composition and structure, and could affect membrane-hosted biological functions.

The free volume distribution and the picosecond dynamics inside a model lipid membrane are explored in a wide temperature range and at different solvating conditions.

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The properties of lipid membranes at low temperature are important for a number of biomedical and biotechnological applications, and the success of these applications depends on understanding the effects of temperature changes on intermolecular lipid-lipid and lipid-water interactions. Here, we use Fourier transform infrared spectroscopy to study lipid suspensions in water/dimethyl sulfoxide (DMSO) solutions in the -60 to 30 °C range. DMSO is a cryopreservative agent of cellular systems, and its action is largely related to its interaction with the lipid membrane, especially in the low-temperature regime. In the present work, we analyze the effects of solvent composition on the structural and thermotropic properties of cholesterol (chol)-loaded liposomes of palmitoyl-oleylphosphatidylcholine (POPC) because POPC/chol liposomes are suitable models of the plasmatic membrane. To this extent, we compare the properties of lipid vesicles suspended in water and water/DMSO solution at 0.10 DMSO mole fraction and we observe that the gel phase of the membrane has an increased thermal stability on DMSO addition. We estimate that the amount of unfrozen water at T = -60 °C is much reduced by the presence of DMSO, both in the gel- and the liquid-ordered phase of the membrane. Interestingly, we also evidence a reduced hydration of the lipid heads in the presence of DMSO when the vesicles are dispersed in a liquid solution, whereas the addition of DMSO does not alter the hydration state of phosphate and carbonyl groups in the frozen state of the membrane.