Zwitterionic asparagine as a molecular modulator of cetyltrimethylammonium chloride micellization and drug–micelle interactions: a detailed study

Abstract

Micellar surfactant systems are widely explored for physicochemical and pharmaceutical applications; however, strategies to rationally modulate micellization and drug–micelle interactions using small, biocompatible additives remain limited. In this work, the influence of the zwitterionic amino acid asparagine (ASP) on the self-assembly, interfacial behavior, and drug-binding characteristics of the cationic surfactant cetyltrimethylammonium chloride (CTAC) was systematically investigated. Surface tension and conductivity measurements reveal that ASP progressively increases the critical micelle concentration of CTAC, indicating partial inhibition of micellization due to zwitterion-assisted electrostatic screening and steric effects. Interfacial characteristics show that adsorption efficiency goes up at low ASP concentrations, whereas packing compactness goes down at higher levels. This shows that interfacial rearrangement depends on concentration. Thermodynamic research verifies that micellization remains spontaneous, although somewhat less favorable in the presence of ASP, whereas adsorption at the air–water interface becomes progressively advantageous. Fluorescence, DLS, and zeta potential tests jointly demonstrate ASP-induced alterations in micellar compactness and surface charge, without significant morphological changes. Studies into drug binding using valacyclovir hydrochloride (VAC) show heightened affinity and partitioning within micelles; but there is a diminishing in micellar occupancy at higher employed ASP concentrations, suggesting spatial constraints within restructured micelles. Overall, the existing results indicate that a neutral zwitterionic amino acid can separate the thermodynamics of micellization from the capability of drug–micelle interactions. Current research supports a physical basis for the use of amino acids in altering micellar systems.