Effects of anisodamine on the phase behavior of DPPG/DMPC binary mixtures

Fluorescence polarization of n-(9-anthroyloxyl)-stearic acid (n-AS), 16-(9-anthroyloxyl)-palmitic acid (16AP) and differential scanning calorimetry (DSC) experiments have been carried out to examine the influence of anisodamine on the phase behavior of dipalmitoylphosphatidylglycerol (DPPG)/dimyristoylphosphatidylcholine (DMPC) binary mixtures. The experiments of fluorescence polarization indicated that the bilamellar vesicles of non-interdigitated DPPG/DMPC systems showed clear polarization gradient in the acyl chains. In DPPG/DMPC systems with 3 mM anisodamine, when the molar ratio of DMPC was below 50%, the normal polarization gradient almost disappeared, the interdigitation of fatty acid chains occurred with the end carbon groups inserting into the opposite layer and reaching the level of 5C. When DMPC was above 60% however, the polarization gradient bf carbon chains reappeared, which suggested non-interdigitation. Results of DSC showed that in various DPPG/DMPC systems, T-m and Delta H decreased with the increase of DMPC concentration. The DPPG-DMPC phase diagram, derived from calorimetric data, exhibited the compatibility of DPPG and DMPC although DMPC tended to prevent the mixtures from forming interdigitated structure in the gel state. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.