Interactions of new 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) based surface active ionic liquids with amitriptyline hydrochloride: Micellization and interfacial studies

Abstract

A new series of cationic surface active ionic liquids (SAILs) based on DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) was synthesized through the quaternization of DBU by alkyl bromides. The SAILs viz. DBU-C12 (8-N-dodecyl-1,8-diazabicyclo[5.4.0]undec-7-en-8-ium bromide), DBU-C14 (8-N-tetradecyl-1,8-diazabicyclo[5.4.0]undec-7-en-8-ium bromide) and DBU-C16 (8-N-hexadecyl-1,8-diazabicyclo[5.4.0]undec-7-en-8-ium bromide) were obtained and their aggregation behaviour was examined by surface tension and conductivity measurements. The SAILs investigated displayed better surface activity than the imidazolium based SAILs (CnmimBr) as well as the conventional cationic surfactants, alkyltrimethylammonium bromides (CnTAB). They also showed a decrease in critical micelle concentration (cmc) values with an increase in the alkyl chain length. Further, their interactions with amphiphilic drug, amitriptyline hydrochloride (AMT) have also been studied by employing the theoretical models proposed by Rubingh, Motomura and Gibbs. The micellar interaction parameter (βm) is negative for most of the mole fractions of AMT (αAMT) in DBU-C14/DBU-C16+AMT systems, indicating attractive interactions. The interfacial parameters such as surface tension reduction efficiency (pC20), effectiveness of surface tension reduction (πcmc), maximum surface excess concentration at the air-water interface (Γmax) and minimum area per surfactant molecule (Amin) were also evaluated for the mixed systems of DBU based SAILs with AMT. The standard Gibbs free energy of micellization (ΔG°m) and the standard free energy of adsorption at the air/water interface (ΔG°ad) for these systems were found to be negative, confirming the feasibility of these drug–SAIL interactions.