SELF-ASSOCIATION OF CHOLESTEROL AND ITS INTERACTION WITH TRIGLYCERIDES - AN INFRARED STUDY

The self-association of cholesterol due to hydrogen bonding has been studied by infrared measurements of its OH-stretching band. At concentrations below 0.014 M in CCl4, cholesterol exists only as a monomer. As the concentration is increased it associates to form a dimer and at a concentration of ~0.06 M a higher aggregate begins to form which becomes the predominant species at a concentration of ~0.2 M. The dimerization constant has been determined (Kd,23° = 4.5 1. mole-1) at different temperatures from which the enthalpy of dimerization has been evaluated (ΔH = -1.8 kcal mole-1). The vmax of the OH-stretching bands of the dimer and trimer have also been reported. Infrared spectra of mixed solutions of cholesterol and the triglycerides gave evidence of formation of a 1:1 hydrogen-bonded complex. The equilibrium constants and enthalpies of formation of the complexes of cholesterol with triacetin, tributy-rin, and trilaurin have been reported (K23° = 2.4-3.7 1. mole-1; ΔH = -3.5 to -5.4 kcal mole-1). The hydrogen-bonding properties of cholesterol are suggested as factors in the mechanism of plaque formation in atherosclerosis. © 1968, American Chemical Society. All rights reserved.