Photophysics of a cyanine dye in the protein-surfactant aggregates

Abstract

In this work we have studied the photophysical properties of a cyanine dye merocyanine 540 (MC540) in the presence as well as in the absence of bovine serum albumin (BSA) along with anionic surfactants sodium dodecyl sulfate(SDS) and sodium tetradecyl sulfate (STDS) and cationic surfactants cetrimonium bromide (CTAB) and dodecyltrimethylammonium bromide (DTAB) with the help of various spectroscopic methods. MC540 in protein-surfactant aggregates as well as surfactant aggregates interacts differently with anionic and cationic surfactants. MC540 exits in both monomer and dimer form in the buffer medium however, in protein-surfactant aggregates and surfactant aggregates monomer–dimer equilibrium is perturbed, where only the monomer form exists. By employing various spectroscopic methods it is evident that in the presence of cationic and anionic surfactants, MC540 strongly interacts with cationic micelles compared to anionic micelles. MC540 being a negatively charged molecule in the buffer medium, electrostatic repulsion is predominant with anionic surfactants whereas, electrostatic attraction is predominant with cationic surfactants in protein-surfactant aggregates as well as in micelles.