Catalytic Effect of Micellar Systems Based on Hydroxypiperidinium Surfactants in the Hydrolysis of a p-Nitrophenyl Phosphonate¹

Abstract—The aggregation behavior, solubilization effect, and catalytic activity of hexadecylpiperidinium surfactants (including ones functionalized with hydroxyl substituents) have been investigated. The kinetics of hydrolytic cleavage of the irreversible cholinesterase inhibitor ethyl p-nitrophenyl ethylphosphonate (armine) in the micellar solutions of these surfactants has been studied using spectrophotometry. It has been shown that the micellar catalytic effect increases in the following order: methyl(hexadecyl)piperidinium bromide < methyl(hexadecyl)-3-hydroxypiperidinium bromide < hexadecyl(2-hydroxyethyl)piperidinium bromide < 2-hydroxyethyl-4-hydroxypiperidinium bromide. The acceleration observed can be as high as almost two orders of magnitude.