Micellar binding of α-diimine-chromium(III) complexes (Cr(NN)33+) to sodium dodecyl sulfate (SDS)

Binding interactions of alpha-diimine-chromium(III) complexes with sodium dodecyl sulfate (SDS) were studied in air-saturated solution and in N-2-purged solution using lifetime measurements. The lifetime titration curves consisted of two regions with different slopes: one of them negative and more pronounced at low concentrations of SDS until reaching a minimum and the other, at a later stage, with a less pronounced positive slope till a plateau was reached. This biphasic behavior of lifetime-SDS concentration data revealed the presence of premicellar aggregates at low SDS concentration and the formation of normal micelles at high surfactant concentration. The results were analyzed with a model that includes binding of the sensitizer to micelles and to small premicellar aggregates. Binding constants obtained by fitting of lifetime titration curves are in agreement with the electrostatic interactions between the complexes and the surfactant and with the hydrophobic interactions between the ligands of the complexes and the formed micelle, (C) 1999 Academic Press.