Phase transitions and cholesterol effects in phospholipid liposomes. A new method employing the enhancement of the O-O vibronic transition of pyrene.
The enhancement of the weakly allowed 0-0 vibronic transition in the fluorescence spectrum of the probe pyrene, which we previously showed to result from ground-state complexation with polar groups, has been shown in the present study to offer a new method for determining phase transition temperatures of liposomes and for studying the effects of cholesterol on the structure of their semipolar glycerol backbone. For dipalmitoylphosphatidylcholine it is found that small cholesterol contents (approximately 9 mol%) induce an increase in the polarity of the microenvironment of the probe, whereas contents greater than or equal to 13 mol% induce a decrease in the polarity. The results are discussed in terms of cholesterol effects on the frequency and extent of thermally-induced structural fluctuations which, in turn, affect the penetration of the probe into the bilayer.
D055598:Chemical Phenomena; D002621:Chemistry; D002784:Cholesterol; D008081:Liposomes; D010743:Phospholipids; D011721:Pyrenes; D013050:Spectrometry, Fluorescence; D013696:Temperature; D013816:Thermodynamics
D008081:Liposomes; D010743:Phospholipids; D011721:Pyrenes; D002784:Cholesterol