Base-Catalyzed Hydrolysis of Acetylcholine Chloride in the Presence of Anionic and Nonionic Surfactants

Abstract

Abstract Base-catalyzed hydrolysis of acetylcholine chloride (Ach) in the presence of anionic and nonionic surfactants was investigated. The rate of hydrolysis was determined by measuring the rate of disappearance of Ach with a spectrophotometer. At a constant pH of 9.0, addition of heptaethylene glycol dodecyl ether (HED) at concentrations above the critical micelle concentration (cmc) results in a slight increase in the apparent rate, υ, which is expressed by two reaction rates, υf and υm, in the aqueous and micellar phases, respectively. The increase in the apparent rate is due to increase in υm. In the presence of sodium dodecyl sulfate (SDS), the apparent rate constant, kapp, is approximately constant at concentrations below the cmc, and kapp decreases above the cmc. In the presence of SDS–HED mixed micelles, kapp decreases with the mole fraction of SDS. In these cases, the decrease in the apparent rate is due to the decrease in both υf and υm. These two kapp decreases are due, respectively, to the decrease in Ach in the aqueous phase and the electrostatic repulsion between OH− and DS− at the micelle surface in conformity with the Gouy-Chapman theory.