Temperature dependence of the topology of supported dimirystoyl-distearoylphosphatidylcholine bilayers

Topology of fluid and gel domains in the supported bilayer two-component sy stem formed from equimolar mixtures of dimyristoylphosphatidylcholine (DMPC ) and distearoylphosphatidylcholine (DSPC) was determined by AFM, at variou s temperatures corresponding to the gel and the gel + fluid region of the p hase diagram. The data show that, in the disconnected fluid part of the DMP C/DSPC gel-liquid crystal-phase-separation region, the size of fluid domain s markedly exceeds that predicted from spectroscopic experiments or from Mo nte Carlo simulations. They provide a direct evidence for the transition fr om the disconnected fluid to the disconnected gel region of the phase diagr am, again with gel-phase domains much larger than expected. Finally, images of the gel phase at different temperatures suggest that structural rearran gements of the phospholipids can disrupt the continuity of the supported bi layer. (C) 2001 Elsevier Science B.V. All rights reserved.