The effect of dimethyl sulphoxide on the structure and phase behaviour of palmitoleoylphosphatidylethanolamine

The thermotropic phase behaviour and structure of a nonbilayer-forming lipi d, 1-palmitoyl-2-oleoyl-phosphatidylethanolamine, dispersed in water and in aqueous solutions of up to 50 wt% dimethyl sulphoxide (DMSO) have been cha racterised using synchrotron X-ray diffraction methods. It was found that t he presence of DMSO in the solvent induced an increase in the temperature o f lamellar-gel to lamellar-liquid-crystal phase transition and a decrease i n the temperature of the lamellar-liquid-crystal to inverted-hexagonal phas e transition of the phospholipid. The presence of DMSO also caused a decrea se in the X-ray repeat spacings of all the phases studied. Electron density profiles of the phospholipid dispersed in water and 50 wt% DMSO in the bil ayer gel state were calculated. The presence of 50 wt% DMSO caused the appa rent disappearance of the solvent layer separating phospholipid bilayers in the gel state. The results suggest that DMSO contributes to the bilayer el ectron density profile and that the amphiphilic solvent molecules partition into the interfacial region. (C) 2000 Elsevier Science B.V. All rights res erved.