title: Phase equilibria in binary mixtures of phosphatidylcholine and cholesterol.
abstract: The paramagnetic resonance spectra of two spin-labels, 2,2,6,6-tetramethylpiperadinyl-1-oxy and a head-group spin-labeled phosphatidylethanolamine (L-alpha-dipalmitoylphosphatidyl-N-ethanolamine), have been used to study solid-liquid and liquid-liquid phase separations in binary mixtures of dimyristoylphosphatidylcholine and cholesterol. A quantitative analysis of these resonance spectra supports the view that at temperatures below theta m, the chain-melting temperature of the phospholipid, and at cholesterol mole fractions Xc less than 0.2, these mixtures consist of two phases, a solid phase of essentially pure dimyristoylphosphatidylcholine and a fluid phase having a mole fraction of cholesterol equal to 0.2. The spin-label data also provide evidence for fluid-fluid immiscibility in the bilayer membrane at temperatures above the chain melting transition temperature of dimyristoylphosphatidylcholine.
mesh_terms: D002784:Cholesterol; D004134:Dimyristoylphosphatidylcholine; D004578:Electron Spin Resonance Spectroscopy; D008051:Lipid Bilayers; D008433:Mathematics; D008968:Molecular Conformation; D010713:Phosphatidylcholines; D013113:Spin Labels
chemical_list: D008051:Lipid Bilayers; D010713:Phosphatidylcholines; D013113:Spin Labels; D002784:Cholesterol; D004134:Dimyristoylphosphatidylcholine