Thermodynamics and Solution Properties of CTAB in Aqueous Media, and Its Interaction With Isoniazid: An Experimental Approach With Some Molecular Simulations

ABSTRACT Molecular interactions between isoniazid (INH) and cetyltrimethylammonium bromide (CTAB) in aqueous media were investigated by the measurements of conductivity, surface tension, viscosity, and density at different temperatures and 0.005–0.0001 M CTAB in 0.001 M INH. The dissociation constant ( α ), critical micelle concentration (CMC), and mole fraction of CMC ( X CMC ), and thermodynamic parameters such as enthalpy (, entropy (), and free energy () change were determined. In the presence of the drug, the CMC value decreases, and when the temperature rises, it increases. The solubility of CTAB in both water and in the drug solution is an exothermic process, i.e., negative. The more positive values of suggest an increased hydrophobic interaction in the presence of the drug. The negative values observed for the aqueous and INH‐mediated micellization of CTAB indicate a thermodynamically spontaneous process. Also, the maximum surface excess concentration ( max ), the minimum area occupied by surfactant molecule ( A min ) at the air–water interface, p C 20 , Gibbs' energy of adsorption (Δ G ads ), molar Gibbs' energy at CMC at maximum adsorption attained (Δ G min ), and apparent molar volume ( V φ ) from density were determined. “ A ” (Falkenhagen coefficient) and “ B ” (Jones–Dole coefficient) were computed. Molecular dynamics simulations (MDS) were also included to obtain density, viscosity, and surface tension.