SELF-ASSOCIATION OF CHOLESTEROL IN SOME CHLORINATED-HYDROCARBON SOLVENTS

The self-association of cholesterol in dilute solutions in 1,2-dichlor oethane, trichloromethane and tetrachlorormethane and over the tempera ture range 298-328 K was investigated using conventional infrared spec troscopy. The information on the size of the predominant cholesterol s pecies was obtained by numerical processing of the solution spectra, r ecorded in the fundamental OH stretching range. Formation constants we re derived from monomer absorbances measured as a function of choleste rol concentration. The following prevailing species and their enthalpi es of formation were established: the monomer A(1) and monomer-solvent complex A(1)() (Delta H-1(*)=-9 +/- 3 kJ mol(-1)) in 1,2-dichloroeth ane: the monomer and open dimer ((A) over tilde(2)) (Delta (H) over ti lde(2) = -15.0 +/- 1.2 kJ mol(-1)) in trichloromethane; the monomer, o pen trimer ((A) over tilde(3)) (Delta (H) over tilde(3) = -31 +/- 3 kJ mol(-1)) and cyclic hexamer ((A) over cap(6)) (Delta (H) over cap(6) = -70 +/- 10 kJ mol(-1)) in letrachloromethane. (C) 1997 Elsevier Scie nce B.V.