Biamphiphilic ionic liquid based aqueous microemulsions as an efficient catalytic medium for cytochrome c

Abstract

Considering the remarkable applicability of ionic liquids (ILs) in bio-catalysis involving enzymes, herein, we report new IL based aqueous microemulsions as a catalytic reactor for cytochrome c (Cyt-c). Microemulsions (μEs), comprising water as the polar component, imidazolium (cation) and dioctylsulfosuccinate (AOT) (anion) based biamphiphilic ionic liquid (BAIL) as the surfactant and a hydrophobic ionic liquid (HIL) as the non-polar component have been prepared and characterized. The use of BAIL has promoted the formation of μEs without any co-surfactant, owing to its higher surface activity. The effect of ester- or amide-functionalization of the alkyl chain of the imidazolium cation of BAILs on the phase behavior of μEs has been investigated. The prepared μEs have been characterized via conductivity, dynamic light scattering (DLS), UV-vis absorption and steady-state fluorescence (using external polarity probes) techniques. The prepared μEs have been employed as nano-reactors for exploring the catalytic activity of Cyt-c. The formed BAIL–water nano-interfaces in reverse μEs have exerted a positive effect on the catalytic activity of Cyt-c stored in a water pool of reverse μEs. A five-fold higher rate constant in μEs as compared to buffer establishes μEs as a better catalytic medium. Furthermore, the differing nature of nano-interfaces created by BAILs and water in reverse μEs, depending on the functionalization of the alkyl chain of the cationic part of BAIL, has exerted varying influence on the catalytic activity of Cyt-c. It is expected that the present work will result in providing a versatile platform for the creation of new IL and water based μEs for bio-catalytic applications.