An investigation of kinetic and physicochemical properties of vesicular surfactants with oximate and hydroxamate ions: Hydrolytic reactions of organophosphorus pesticides

Rate constants have been determined spectrophotometrically for the reaction of paraoxon, parathion and fenitrothion (OP pesticides) with oximate (Ox−) and hydroxamate (HA−) ions in aqueous and cationic vesicular media at 300K. All reactions followed the pseudo-first-order kinetics. The surface properties i.e. the critical vesicle concentration (cvc), maximum surface access (Γmax), surface pressure at the cvc (Πcvc) and minimum surface area per molecule (Amin) of vesicular surfactants dioctadecyldimethylammonium chloride (DODAC) and didodecyldimethylammonium bromide (DDAB) with Ox− and HA− ions have been evaluated by conductivity and surface tension measurements at 300 K. The standard Gibbs free energy of vesicle formation (ΔG0v), Standard Gibbs free energy of adsorption (ΔG0ad), and standard Gibbs free energy of vesicle formation per alkyl chain (ΔG0v, tail) of cationic vesicular surfactants with Ox− and HA− ions have also been evaluated. SEM (Scanning Electron Microscope) and TEM (Transmission Electron Microscope) were used to investigate the morphological behavior and size of vesicular surfactants. We observed a well-defined contour of vesicular surfactants that are mostly spherical and globular shape. The effects of vesicular morphology and chemical reactivity have been discussed.