Effect of hydrophilic atenolol and lipophilic propranolol β-blockers on the surface and bulk aggregation of quaternary ammonium bromide surfactants: A comparative study

The variations in the surface and bulk properties of alkyltrimethylammonium bromide (ATAB) surfactants (C12 to C16) in presence of a hydrophilic beta-blocker drug atenolol (ATL) and a lipophilic beta-blocker drug propranolol (PPL), have been investigated using three independent techniques, viz; electrical conductivity, surface tension and cyclic voltammetry. Electrical conductivity measurement indicates that both ATL and PPL at low concentrations of 0.5 mM and 1.0 mM brings about almost equal changes to the critical micelliastion concentration of all ATAB surfactants. However, at higher concentrations (3 mM to 10 mM), PPL seems to be more effective, than ATL, in reducing the cmc and hence favouring micellization. Various interfacial parameters at the air-water interface have been determined through the measurements of surface tension of the surfactants in varying concentrations of ATL and PPL ranging from 0.5 mM to 10 mM. The thermodynamic parameters of micellization are evaluated from the temperature dependence of cmc. The variation of Gibbs energy with temperature is small while large changes in enthalpy and entropy of micellization are observed in the temperature range studied. The effect of TTAB on the electrolytic solutions of ATL and PPL on the voltametric response of glassy carbon electrode (GCE) was examined. TTAB enhanced the current signal of ATL while opposite effect was observed for PPL. The experimental results have been analysed in terms of the difference in the hydrophobicities of the two beta-blocker drug molecules.