THERMODYNAMICS OF ASSOCIATION OF CHOLESTEROL IN AN APROTIC-SOLVENT

The colligative properties of benzene solutions of cholesterol up to 0 .25 mol kg-1 in the temperature range 298-333 K have been determined b y vapour pressure osmometry. The relations for the concentration depen dence of the osmotic coefficient, activity coefficient and excess ther modynamic functions are given in analytical form, in which the regress ion coefficients are correlated with the virial coefficients, which, a ccording to the McMillan-Mayer theory, characterize the contributions arising from the formation of pairs, triplets etc. of solute particles in a definite medium. On the basis of Prigogine's theory for associat ed solutions it may be concluded that the solvent-solute interactions are weak. In addition, the non-ideal behaviour of the system investiga ted was discussed on the basis of an association model, including an e xtended series of multimers, the formation of which is described in te rms of two independent parameters: the dimerization constant beta2 and constant K. The values of the dimerization constant beta2 and constan t K were determined by the curve-fitting method, whereas the concentra tion of monomer was obtained via Bjerrum's integral. On the basis of v an't Hoff's relation for the temperature dependence of the equilibrium constants, the thermodynamic functions of association processes were determined and are discussed with respect to the oligomeric species fo rmed.