An Investigation of Drug Binding Ability of a Surface Active Ionic Liquid: Micellization, Electrochemical, and Spectroscopic Studies

Keeping in view the use of surfactants in drug delivery, the interactions of surface active ionic liquids, such as 1-tetradecyl-3-methylimidazolium bromide (C(14)mimBr), with drugs, viz., dopamine hydrochloride (DH) and acetylcholine chloride (AC), have been studied, and the results are further compared with that of the structurally similar conventional cationic surfactant tetradecyltrimethylammonium bromide (TTAB). The micellization and interfacial behavior of C(14)mimBr and TTAB, in the presence of DH and AC, has been investigated from conductivity and surface tension measurements. Various micellar and adsorption characteristics for these drug-surfactant systems (DH/AC + C(14)mimBr/TTAB) have been investigated, indicating favorable interactions between them. The more detailed information regarding the nature of interactions between C(14)mimBr/TTAB and DH/AC is obtained from cyclic voltammetry (CV) and H-1 NMR measurements. CV measurements have been employed to evaluate the binding constant (K) and the Gibbs free energy change (Delta G) for these drug surfactant complexes. These measurements indicate the existence of cation-pi as well as pi-pi interactions between drugs and surfactants. A detailed analysis of chemical shifts of protons of drug molecules (DH and AC) in the presence of C(14)mimBr and TTAB has been done by H-1 NMR. The results obtained from H-1 NMR are in agreement with those of CV measurements. NMR studies along with the conductivity and surface tension measurements help in predicting the possible location of adsorption of these drug molecules in C(14)mimBr and TTAB micelles.