H-2-NMR AND DSC STUDY OF SEPC-CHOLESTEROL MIXTURES

Deuterium nuclear magnetic resonance (H-2-NMR) and differential scanni ng calorimetry (DSC) have been used to investigate the phase behaviour of mixtures of earoyl(d35)-2-elaidoyl-sn-glycero-3-phosphocholine (d3 5-SEPC) with varying amounts x(C) of cholesterol at temperatures betwe en 10 and 55-degrees-C. The analysis of the specific heat traces C(x(C ), T) and the first moments of the H-2-NMR spectra M1(x(C), T) gave th e characteristics of the chain melting transition T(C) as a function o f cholesterol concentration. The location of the 'solid ordered'-'liqu id disordered' coexistence region was obtained by the use of the H-2-N MR spectral subtraction technique. The form of the resulting partial p hase diagram for the SEPC/cholesterol mixtures is similar to the one o btained for DPPC/cholesterol mixtures (M. Vist and J. Davis (1990) Bio chemistry 29, 451-464.). The hydrophobic bilayer thickness expansivity alpha(h)(x(C), T) was calculated from the first moments M1(x(C), T). Using general thermodynamic relations it was possible to explain the c lose agreement between the specific heat traces C(x(C), T) and the hyd rophobic bilayer-thickness expansivity curves alpha(h)(x(C), T).