Formation of premicellar clusters of 2-p-toluidino naphthalene-6-sulfonate with cationic detergents

Abstract

2-p-Toluidinonaphthalene-6-sulfonate (TNS), a well-known fluorescent probe, forms premicellar aggregates with detergents such as cetyltrimethylammonium bromide (CTAB) at concentrations just below their critical micelle concentration. A narrow fluorescent band, very small Stokes shift, and very high quantum yield are the characteristics of the hydrophobic environment provided by the premicellar aggregates. Studies of the temperature dependence of fluorescence indicated that these species exist in solution as a separate microheterogeneous phase. These results are corroborated by results obtained from fluorescence polarization studies. The length of the alkyl chain is very critical in this case, and no such phenomenon is observed when the chain length is less than 14 carbon atoms. We propose that these species are formed by the enwrapment of TNS by the alkyl chains of CTAB molecules.