Spectroscopic and hydrodynamic investigations of nonionic and zwitterionic detergents

Abstract

Selected nonionic and zwitterionic detergents have been investigated by sedimentation velocity and equilibrium runs in the analytical ultracentrifuge in a systematic manner. UV-visible absorption spectroscopy and determinations of the partial specific volumes were used as complementary techniques. Pilot tests comprised the following detergents: Nonidet P40, Triton X-100 and X-114, Tween 20 and 80, C_7-, C_8-, C_9-, and C_10-glucosides, C_8-thioglucoside, and Zwittergents 3–08, 3–10, 3–12, 3–14, and 3–16.

Application of analytical ultracentrifugation to detergents requires a series of adaptations and improvements of the conventional techniques, in addition to the consideration of possible pitfalls and precautions required for certain detergents. In this context, the necessity to differentiate between the signals of monomeric and micellar detergents, on the one hand, and (macro)solutes of different size, on the other, has to be mentioned. Monitoring the sedimentation profiles of weakly absorbing detergents becomes feasible by labeling the detergent micelles using the fluorescent dye N-phenyl-1-naphthylamine. Owing to the chemical nature of the detergents under analysis and differences in size and shape of the corresponding micelles, the results reveal significant differences in the behavior of the detergents, depending on the experimental conditions. The detergents exhibit a broad mass distribution, caused by heterogeneity and impurities of commercial samples.