Probing of micellar and biological systems using 2-(p-dimethylaminostyryl)benzoxazole: An intramolecular charge transfer fluorescent probe

A new and highly sensitive molecular probe namely, 2-(p-dimethylaminostyryl)benzoxazole (DMASBO) has been employed to follow the micellar aggregation of three commonly used anionic, cationic and neutral surfactants. These are sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (CTAB) and Triton X-100 (TX-100), respectively. From the fluorescence characteristics of DMASBO in dioxane–water mixtures and different surfactant concentrations, the effective polarity of micelle–water interfaces (expressed as dielectric constant and ET (30)) and critical micelle concentrations (cmc) have been measured. In addition, the viscosity of the DMASBO’s environment has been determined from comparison of the fluorescence quantum yield in micellar solutions and methanol–glycerol mixtures. The effect of micelles on the protonation constants of both the ground and excited state has also been studied. The spectral studies in micelles as well as in human serum albumin (HSA) reveal that the intramolecular charge transfer emission of DMASBO is an efficient tool for monitoring and exploring the properties of micelles and the hydrophobic interactions in HSA. The location and orientation of DMASBO probe in micelles and HSA have been discussed.