Dye-surfactant interaction: chain folding during solubilization of styryl pyridinium dyes in sodium dodecyl sulfate aggregates

Cationic dyes are known to interact with membranes and, therefore, are used as membrane probes. The alkyl chains of the dyes play a role in modifying the environment of the chromophore and affect the nature of interaction wit h the micelle. A number of cationic dyes with varying alkyl chains (C-1 to C-18) have been synthesized and their interaction with sodium dodecyl sulfa te (SDS) is reported. From the absorption, fluorescence spectra and binding constant values it has been proposed that: (a) C1-Cs dyes solubilize in th e micelle and the chromophore occupies a methanolic/ethanolic environment, (b) C-10-C-14 dyes exist both as an extended monomer and as folded species in presence of SDS, which is reflected in two Gaussian peaks, (c) the exper imentally obtained absorption spectra for C-16 and C-18 dyes can be explain ed by three Gaussian peaks due to monomer reversible arrow dimer in the abs ence of surfactant and two such peaks due to monomer and folded monomer in the presence of surfactants. The binding constant and fluorescence intensit y values support this proposition. (C) 1999 Elsevier Science S.A. All right s reserved.