STUDIES OF ALCOHOL-INDUCED INTERDIGITATED GEL PHASE IN PHOSPHATIDYLCHOLINE MULTILAMELLAR VESICLES BY THE EXCIMER METHOD

We have developed a new spectroscopic method (excimer method) for detecting the interdigitated gel phase (L(beta-I)) in phospholipid vesicles. This method is based on the disappearance of an excimer fluorescence peak of pyrenephosphatidylcholine (pyrene-PC) in the L(beta-I) phase. Using this method we have studied the phase transition from gel phase (L(beta')) to L(beta-I) phase of dipalmitoylphosphatidylcholine multilamellar vesicles in the presence of ethanol or ethylene glycol (EG). In both the cases of ethanol and EG, a sharp decrease in the ratio of excimer to monomer fluorescence intensity (E/M) of pyrene PC appeared at the same concentration of the transition from L(beta') to L(beta-I) as determined by the X-ray diffraction method or the scanning density method. After the transition to the L(beta-I) phase, E/M values became very low. This excimer method enables us to detect the L(beta-I) phase in unilamellar vesicles of phospholipids, which can hardly be studied by other methods such as X-ray diffraction.