Interactions Between Surface Active Ionic Liquid and Procaine Hydrochloride Drug in Aqueous Solution

Abstract

Complex formation between the anesthetic drug, procaine hydrochloride and a surface active ionic liquid (SAIL), 1-tetradecyl-3-methylimidazolium chloride, [C14mim][Cl], in aqueous medium has been investigated using surface tension, fluorescence and DLS measurements at 298.15 K and conductance at 288.15, 298.15 and 308.15 K. Critical aggregation concentration (CAC), degree of ionization (α), and various thermodynamic parameters were determined using the conductivity measurements. The interfacial behavior of SAIL at different concentrations of the drug was evaluated from surface tension measurements by calculating a series of surface parameters and CAC values. Fluorescence spectroscopy was used to evaluate the binding constant (K) and the standard state Gibbs energy change (ΔG°) for the formation of drug–SAIL complexes, which confirms the existence of cation–π interactions between the drug molecules and imidazolium ring of the SAIL molecules. The CAC values were found to decrease with increase in the concentration of the drug, which is due to the balancing between hydrophobic and electrostatic interactions. Dynamic light scattering provides sufficient information about the size of the aggregates and the variation in the hydrodynamic diameters pertaining to the changes in the drug concentration. The results from above methods show that the aggregation process of SAIL is favored by increases in the concentration of the drug. It is demonstrated that with the better understanding of the interactions, [C14mim][Cl] can be judiciously utilized in making use of procaine hydrochloride.