Lipid membrane structure and interactions in dimethyl sulfoxide/water mixtures

In this paper we have investigated via x-ray diffraction the influence of dimethyl sulfoxide (DMSO), known for its biological and therapeutic properties, on the structure of lipid membranes of dipalmitoylphosphatidylcholine (DPPC) in excess of the solvent (DMSO/water) at mole DMSO fractions X-DMSO is an element of (0.1) and under equilibrium conditions. At small X-DMSO less than or equal to 0.133 the repeat distance d is reduced remarkably, whereas wide-angle x-ray diffraction pattern remains almost unchanged with the increase in X-DMSO. It agrees well with previous study (Yu and Quinn, 1995). At 0.133 < X-DMSO < 0.3 the repeat period d reduces slowly; however, an orthorombic in-plane lattice of hydrocarbon chains transfers to a disordered quasihexagonal lattice. The increase in X-DMSO from 0.3 up to similar to 0.9 leaves d almost unchanged, whereas it leads to less disordered packing of hydrocarbon chains. At X-DMSO approximate to 0.9, L-beta' phase transfers into interdigitated phase. The chain-melting phase transition temperature of DPPC membranes increases by several degrees with the increase of DMSO concentration. It points to a strong concentration-dependent solvation of membrane surface by DMSO. Thus DMSO strongly interacts with the membrane surface, probably displacing water and modifying the structure of the lipid bilayer. It appears to determine some of the properties of DMSO as a biologically and therapeutically active substance.