Interaction of cetyltrimethylammonium bromide with drug in aqueous/electrolyte solution: A combined conductometric and molecular dynamics method study

Abstract : Interaction between beta-lactum antibiotic drug ciprofloxacin hydrochloride (CFH) and cationic surfactant cetyltrimethylammonium bromide (CTAB) was performed conductometrically in aqueous as well as in the occurrence of different salts (NaCl, KCl as well as NH₄Cl) over the temperature range of 298.15–323.15 K at the regular interval of 5 K. CFH drug has been suggested for the treatment of bacterial infections such as urinary tract infections and acute sinusitis. A clear critical micelle concentration (CMC) was obtained for pure CTAB as well as (CFH + CTAB) mixed systems. The decrease in CMC values of CTAB caused by the addition of CFH reveals the existence of the interaction between the components and therefore it is the indication of micelle formation at lower concentration of CTAB and their CMC values further decrease in attendance of salts. A nonlinear behavior in the CMC versus T plot was observed in all the cases. The ∆ G⁰_m values are found to be negative in present study systems demonstrated the stability of the solution. The values of ∆ H⁰_m and ∆ S⁰_m reveal the existence of hydrophobic and electrostatic interactions between CFH and CTAB. The thermodynamic properties of transfer for the micellization were also evaluated and discussed in detail. Molecular dynamic simulation disclosed that environment of water and salts have impact on the hydrophobic interaction between CFH and CTAB. In water and salts, CTAB adopts spherical micelle in which charged hydrophilic groups are interacted with waters whereas hydrophobic tails form the core of the micelle. This hydrophobic core region is highly conserved and protected. In addition, micelle formation is more favorable in aqueous NaCl solution than other solutions.