Surfactant tail length-dependent lipase activity profile in cationic water-in-oil microemulsions

Abstract

The catalytic activity of Chromobacterium viscosum lipase (CV-lipase) was estimated across varying surfactant tail lengths (C-10–C-18) in water-in-oil (w/o) microemulsions of cationic surfactants containing four different hydroxyethyl-substituted head groups. An attempt to find a correlation, if any, between the activity of interfacially solubilized lipase and the varying surfactant tails was made for the first time in micellar enzymology. The second-order rate constant, k 2 , in lipase-catalyzed hydrolysis of p-nitrophenyl- n-hexanoate at pH 6.0 and 25 °C shows an improvement in enzyme activity (∼30–140%) across different head groups of amphiphiles with increasing tail lengths in varying solution compositions. Improvement of enzyme activity is prominent in ascending from C-10 to C-14/C-16, depending on the nature of polar head group. The hydrolytic activity of lipase in different surfactant (50 mM)/water/isooctane/ n-hexanol with varying z= [alcohol]/[surfactant] (6.4 or 4.8) was amplified by 25–250% with increment in surfactant tail length in comparison with widely used cationic w/o microemulsions having solution compositions ( z = 16 ) . As a notable outcome of this research, we found w/o microemulsions of 25 mM tetradecyltrimethylammonium bromide/water/isooctane/ n-hexanol ( z = 8 ) producing the highest ever activity of lipase in any w/o microemulsions.