Interactions of diazepam with sodium dodecylsulfate and hexadecyl trimethyl ammonium bromide: Conductometric, UV-visible spectroscopy, fluorescence and NMR studies

The interactions between anti-anxiety drug diazepam (DZM) and ionic surfactants [sodium dodecyl sulfate (SDS) and hexadecyltrimethylammonium bromide (HTAB)] in 0.57 mol% aqueous ethanol solution have been studied by employing conductivity measurements over a range of temperature [288.15 to 318.15 K in case of SDS and 298.15 to 318.15 K in case of HTAB]. From these measurements, critical micelle concentration (CMC), degree of dissociation of counter ion (alpha), standard free energy (Delta G(m)(omicron)), standard enthalpy (Delta H-m(omicron)) and standard entropy (Delta S-m(omicron)) of micellization were calculated. UV-visible and fluorescence studies were carried out for DZM-surfactant complex in the pre-micellar and post-micellar region. From these studies various parameters like partition coefficient (K-x), binding constant (K-b), free energy of partition (Delta G(x)(omicron)), free energy of binding (Delta G(b)(omicron)) and number of drug molecules per micelle (n) were calculated. Proton (H-1) NMR studies show upfield shift which indicates shielding of protons of SDS and HTAB. From UV-visible, fluorescence and H-1 NMR studies it was concluded that drug molecules lie in the palisade layer or the interface of the SDS/HTAB micelles. (C) 2017 Elsevier B.V. All rights reserved.