Improving the Lipase Activity Profile in Cationic Water-in-Oil Microemulsions of Hydroxylated Surfactants

Abstract

The activity of Chromobacterium viscosum lipase (CV-lipase) in cationic water-in-oil (w/o) microemulsions is significantly lower compared to that in bis(2-ethylhexyl)sulfosuccinate sodium salt (AOT)-based (anionic) systems.26,36,38,39 In the present study, we estimated the second-order rate constants k2 in lipase-catalyzed hydrolysis of p-nitrophenylcaproate, in newly developed cationic w/o microemulsions of synthesized surfactants (2−6, Chart 1) containing hydroxyethyl moieties at the polar headgroup. The kinetic studies at pH = 6.0 (pH refers to the pH of the aqueous buffer solutions used in preparing the w/o microemulsions) show that the catalytic efficiency of CV-lipase was systematically increased with the sequential increment of hydroxyethyl groups at the polar heads of surfactants (1−4, Chart 1), possibly due to the increase in the interfacial concentration of water [H2O]i in consequence of the added hydrogen bonding ability of hydroxyl groups. To this end, we found that in a 0.05 M 4/water/32.3:1 ...