Mixed association of cholesterol with methyl cholate and methyl lithocholate in chloroform solutions

The concentration-dependent mixed association behavior of cholesterol with methyl cholatc (MeC) and methyl lithocholate (MeLC) in chloroform at 37°C has been studied by vapor pressure osmometry (VPO). This study is part of a larger project to investigate the effect of number and position of hydroxyl-bearing steroids. Using theories developed by Adams and by Steiner. the model and appropriate parameters for the nonideal mixed associations were elucidated. For the MeLC/choIesterol system. no mixed association was observed. For the MeC/choIeslerol system, both methods of analysis indicate that a nonideal AB complex formation occurs. The best parameters to explain the experimental data are k ab = 0.04 1/g: B AB (the nonideal term) = 1.5 ×10 −5 1 mol g −2.