| Abstract
| - The primary objective of the present study is to understand how the different nonionic surfactants modify theanisotropic interface of cationic water-in-oil (W/O) microemulsions and thus influences the catalytic efficiency ofsurface-active enzymes. Activity of Chromobacterium viscosum lipase (CV-lipase) was estimated in several mixedreverse micelles prepared from CTAB and four different nonionic surfactants, Brij-30, Brij-92, Tween-20, and Tween-80/water/isooctane/n-hexanol at different z ([cosurfactant]/[surfactants]) values, pH 6 (20 mM phosphate), 25 °Cacross a varying range of W0 ([water]/[surfactants]) using p-nitrophenyl-n-octanoate as the substrate. Lipase activityin mixed reverse micelles improved maximum up to ∼200% with increasing content of non-ionic surfactants comparedto that in CTAB probably due to the reduced positive charge density as well as plummeted n-hexanol (competitiveinhibitor of lipase) content at the interfacial region of cationic W/O microemulsions. The highest activity of lipasewas observed in CTAB (10 mM) + Brij-30 (40 mM)/isooctane/n-hexanol)/water system, k2 = 913 ± 5 cm3 g-1 s-1.Interestingly, this observed activity is even higher than that obtained in sodium bis (2-ethyl-1-hexyl) sulfosuccinate(AOT)/n-heptane reverse micelles, the most popular W/O microemulsion in micellar enzymology. To ascertain theinfluence of non-ionic surfactants in improving the activity of surface-active enzymes is not limited to lipase only,we have also investigated the catalytic activity of Horseradish peroxidase (HRP) in different mixed W/O microemulsions.Here also following the similar trend as observed for lipase, HRP activity enhanced up to 2.5 fold with increasingconcentration of nonionic surfactants. Finally, the enzyme activity was correlated with the change in the microenvironmentof mixed reverse micelles by steady-state fluorescence study using 8-anilino-1-napthalenesulphonic acid (ANS) asprobe.
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