Enthalpies of transfer of ubiquinone-0 from water to aqueous surfactant solutions at various temperatures

Abstract

Mixing and dilution enthalpies of aqueous solutions of 2,3-dimethoxy-5-methyl-1,4-benzoquinone (UQ0) and of N,N-dimethyl-dodecylamine-N-oxide (DDAO) were measured and used to calculate the enthalpies of transfer δH(W →W +S) of UQ0 from water to DDAO aqueous solutions at 20‡, 25‡, 30‡, and 35‡C. From the dependence of δH(W →W +S) on surfactant concentration, the distribution constant between aqueous and micellar phases and the standard transfer enthalpy of UQ0 from water to DDAO micelles were evaluated along with the standard transfer free energy and entropy. The approach used required knowledge of the CMC and micellization enthalpy at each temperature. Thus, the thermodynamics of micellization of DDAO was studied by means of dilution enthalpy measurements at the several temperatures.