Deuterium magnetic resonance of selectively deuterated cholesteryl esters in phosphatidylcholine vesicles

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Abstract
2H NMR experiments were performed on selectively deuterated cholesteryl palmitate (CP) and cholesteryl stearate (CS) in egg phosphatidylcholine (PC) unilamellar vesicles. Egg PC vesicles incorporated up to 5 mol % ester and had a mean diameter of 22 nm. Addition of 20 mol % cholesterol decreased the solubility of cholesteryl ester in the bilayer to .apprx. 2-3 mol %, but the vesicle size remained unchanged. The 2H NMR results reveal that the acyl chains of CP and CS are highly disordered (SCD < 0.10) both in the presence and absence of cholesterol. T1 measurements for selectively deuterated CP and CS in egg PC vesicles indicate that the high degree of disorder of the ester molecule is not associated with an increase in the rate of gauche-trans chain isomerization. Possible explanations for the low order parameters in terms of molecular motions and orientations are offered.