DSC study on the effect of dimethylsulphoxide (DMSO) and diethylsulphoxide (DESO) on phospholipid liposomes.

In this paper, the DSC thermal behaviour of DMPC and DMPE liposomes in the presence of increasing amounts of both DMSO and DESO was investigated. In the presence of low amounts of both dialkylsulfoxides (DASO), the main effect was an increase in the transition temperatures, more enhanced in the presence of DMSO, together with an increase in the ΔH values, more enhanced in the presence of DESO. With a high sulfoxide content, a noticeable increase, with marked differences between the two compounds, was observed in all thermal parameters and the whole thermogram was strongly affected by memory effects. The data suggest that the partial dehydration of the lipid surface together with the modification induced on the water structure might explain the effects of sulfoxides on biomembranes in the presence of low DASO content. On the contrary, with higher DASO concentrations, the main role is played by the direct interactions of DASO with the liposome surface, which we found to be noticeably greater for DESO than for DMSO, with the contemporary existence of metastable lipid phases. The unusually high cryoprotective effect found in the presence of high DESO content (≥40%, w/w), might be due to the strong, direct hydrophobic interactions with biomembranes besides its ability to produce, by freezing, a stable glassy ice layer near to the lipidic surface.