INTERACTION BETWEEN SULFOGALACTOSYLCERAMIDE AND DIMYRISTOYLPHOSPHATIDYLCHOLINE INCREASES THE ORIENTATIONAL FLUCTUATION OF THEIR LIPID HYDROCARBON CHAINS

The objective of this study was to investigate the interaction between sulfogalactosylceramide (SGC) and dimyristoylphosphatidylcholine (DMP C) in a mixed model liposomal system (molar ratio SGC:DMPC, 2,3). Stru ctural and dynamic changes of the liposome components were monitored b y Fourier-transform infrared spectroscopy (FTIR). Thermotropic FTIR an alysis of the mixed liposomes showed a single gel/liquid crystalline p hase transition, centered at similar to 42 degrees C. Spectral changes of the amide and ester C=O bands arising from functional groups at th e interfacial region indicated a reduced hydrogen bonding of these gro ups in the mixed liposomes. Pressure-tuning FTIR of mixed liposomes sh owed that the methylene chains of SGC and DMPC were more orientational ly disordered than those of the individual lipid SGC liposomes or DMPC liposomes. These results suggest that the mixed liposomes (molar rati o SGC,DMPC, 2:3) consisted of a homogeneous mixture of SGC and DMPC mo lecules in which mutual shielding reduced hydrogen bonding in the inte rfacial region, with a concurrent increase in the orientational disord er of the hydrocarbon chains of both SGC and DMPC. (C) 1998 Elsevier S cience Ireland Ltd. All rights reserved,