Bile salt-surface active ionic liquid mixtures: mixed micellization and solubilization of phenothiazine

Abstract

The present work deals with the mixed micellization behavior of bile salts (sodium cholate, NaC and sodium deoxycholate, NaDC) with surface active imidazolium ionic liquid, (SAIL) 1-dodecyl-3-methylimidazolium bromide (C₁₂mimBr). Surface tension and steady state fluorescence measurements were employed to gain a detailed picture of the interactions between NaC/NaDC and C₁₂mimBr molecules in the mixed monolayer and in the mixed micelles, where the interactions have been found to be highly synergistic. The bile salt–SAIL mixtures have been thoroughly characterized through the evaluation of various micellar and interfacial parameters like critical micellar concentration (cmc), micellar interaction parameter (β^m), surface excess concentration (Г_max), minimum area per molecule (A_min), surface pressure at cmc (π_cmc) and hydrodynamic radius (R_h). Dynamic light scattering (DLS) measurements revealed the formation of the biggest mixed micelles at a mole fraction of 0.4 : 0.6 of NaC/NaDC : C₁₂mimBr. Furthermore the solubilization of phenothiazine (Pz) has been studied in pure bile salts as well as in mixed micelles of bile salts + C₁₂mimBr employing UV-visible measurements. From the evaluation of various solubilization parameters viz. molar solubilization ratio (MSR, χ), micelle-water partition coefficient (K_m) and standard free energy of solubilization (ΔG^°_s), it was established that the solubilization capacity of bile salts for Pz were enhanced when mixed with C₁₂mimBr, the effect being more pronounced for NaDC than NaC.