Solubilization of polycyclic aromatic compounds into n-decyltrimethylammonium perfluorocarboxylate micelles

Solubilization of polycyclic aromatic compounds in aqueous di lute solution s of three cationic amphiphiles was studied. The maximum additive concentra tions (MACs) of the aromatic compounds were constant below their critical m icelle concentrations (cmcs) and monotonically increased above the cmcs. Th e first stepwise association constants ((K) over bar)(1) between a solubili zate monomer and a vacant micelle were evaluated from the MACs for the solu bilizates using the mass action model for solubilization into micelles in t he dilute solution. The standard Gibbs energy changes of solubilization (De ltaG degrees) were calculated from (K) over bar (1), and the enthalpy and e ntropy changes of solubilization were estimated from the temperature depend ence. MACs of each surfactant at the same surfactant concentration above th e cmc were different depending on the cmc, but there was little difference in the DeltaG degrees values. Some differences appeared in the enthalpy and entropy values in accordance with their micellar size or degrees of counte rion binding to micelles. DeltaG degrees for solubilization decreased linea rly with carbon number of aromatic solubilizate for each micellar solution. (C) 2000 Academic Press.