Biophysical Studies on the Interaction of Insulin with a Cationic Gemini Surfactant

Abstract

A novel quaternary ammonium-based cationic gemini surfactant (S₆) having 1,6 di-bromo hexane as a spacer, have been used and its interaction with insulin in aqueous solution (pH, 7.40) was investigated by several methods including fluorescence spectroscopy, UV-Vis spectroscopy, circular dichroism, dynamic light scattering, ζ-potential measurements, conductivity and transmission electron microscopy. Conductometry and fluorescence studies confirmed the complex formation between S₆and insulin. TEM micrographs revealed that the S₆ micelles were of spherical shape with size distribution between 101-140 nm. The critical micelle concentration and some physicochemical properties were determined by conductance measurements. Fluorescence quenching studies in the presence of acrylamide indicated that in the protein-surfactant interaction the solvent accessibility of Tyr residues is reduced. Furthermore CD experiments (far- and near-UV CD) showed that, the content of alpha-helix increases with increasing S₆ concentration and some conformational changes occur in protein structure. The results from dynamic light scattering and ζ-potential measurements showed that insulin charge neutralization and hexamer dissociation take place in the presence of surfactant. Altogether, the S6 cationic Gemini surfactant can be considered as a candidate for insulin delivery.