Interactions of procaine hydrochloride with different micellar environments: A study on mimetic single and mixed micelle models

The micellar environment formed by surfactants behaves like a simple biological membrane system. Based on this property of micelles, which can be considered a pseudo-model of the biological systems, the presented study aimed to study the interactions of procaine hydrochloride (PrHy) with ionic, nonionic, and mixed micelles of nonionic and ionic surfactants. As a model for mimetic systems, nonionic Brij 35, lithium lauryl sulfate (LDS; anionic), sodium lauryl sulfate (SLS; anionic), sodium hexadecane-1-sulfonic acid (SHSA; anionic), dodecyltrimethyl ammonium bromide (DTAB; cationic), and didodecyldimethylammonium bromide (DDAB; cationic) were selected. Absorption spectrophotometry was employed to characterize the degree of association between the drug and surfactant micelles and to determine the micellar binding constants. The binding ability of PrHy is also further compared to the ionization degree and counterion binding parameter, which have been obtained from conductivity measurements. When the behavior of PrHy in micelle systems with different hydrophobicity was evaluated and the magnitude of binding constants was compared, it was determined that the most potent interaction was in the presence of Brij 35 micelles. The binding constant values of PrHy to micelles had been calculated via the Benesi-Hildebrand Equation, and the binding of PrHy accompanied the order as: Brij 35 > SHSA > SLS > LDS > DDAB > DTAB To understand the influence of mixed micelles on the binding degree of PrHy, constant concentrations of ionic micelles concerning their interaction with Brij 35 were also monitored. It was concluded that the micellar binding of PrHy on mixed micelle systems was due to hydrophobic interaction, with the contribution of electrostatic interactions. In an attempt to better understand the nature of the drug-surfactant interaction, this study employed both conductometric and spectrophotometric methods. The binding ability of PrHy for all anionic micelles examined enhanced considerably as the hydrophobic nature increased; however, the presence of PrHy lowered the CMC of anionic surfactants. The experimental results were compatible with both the conductivity and spectrophotometric techniques.