Effect of sodium chloride on the interactions of ciprofloxacin hydrochloride with sodium dodecyl sulfate and hexadecyl trimethylammonium bromide: Conductometric and spectroscopic approach

Interactions of ciprofloxacin hydrochloride (CF) with sodium dodecyl sulfate (SDS) and hexa- decyl trimethylammonium bromide (HTAB) have been studied in aqueous as well as in aqueous NaCl medium by conductivity measurement over a temperature range. Values of critical micelle concentration (CMC), degree of ionization (alpha) and various thermodynamic parameters have been determined for both the systems. In aqueous medium the CMC values of HTAB decrease while CMC values of SDS increase in the presence of CF. In the presence of NaCl, CMC values of both the surfactants are found to decrease and Delta G(m)degrees values are negative which indicate drug mediated ionic micelle formation process is thermodynamically more spontaneous in the presence of NaCl. In addition to it absorption spectra of CF have been recorded as a function of surfactant concentration ranging from pre-micellar region to post-micellar region in aqueous medium as well as in the presence of 10 mM NaCl solution. UVvisible studies were used to calculate partitioning/binding constant (K) and free energy of partitioning/binding (Delta G(x)degrees) in the post-micellar region. The presence of NaCl increases the partitioning/binding of CF to both the surfactant micelles. This leads to enhancement of hydrophobic interactions for both the surfactants and thus CF supported ionic micelle formation is much favored in the presence of NaCl. Proton NMR studies have been performed in aqueous and NaCl solution to determine the locus of solubilization of CF within micelle. (C) 2018 Elsevier B.V. All rights reserved.