![]() ![]() Several enzymatic reactions with different enzymes have been conducted and studied in microemulsions. Catalytic reactions with water insoluble substrates can occur at the large internal water-oil interface ( 14). W/o microemulsions also provide an interesting alternative to normal organic solvents in enzyme catalysis with hydrophobic substrates. It has also been reported that once these nanostructures are used as the reaction media, the activity and stability of the enzymes may be significantly improved and can be controlled mainly by the concentration of water in these media ( 8- 13). In addition to these advantages, microemulsion droplets can entrap the enzyme at a molecular scale and the dynamic and flexible characters of the droplets are profitable to the enzyme reactivity. Microemulsions are formed spontaneously and therefore the effect of shear stress forces on the sensitive enzyme structure, due to the mixing of the reaction system, is reduced. They also provide an enormous water-oil interfacial area through which catalytic reactions with water-insoluble substrates can occur. W/o microemulsions can host biomolecules such as enzymes through homogenous solubilization of the biomolecule in their water core and protect them from unfavorable contact with the surrounding organic phase. The rationale of using these systems as a media for enzymatic reactions is the potential advantages and possibilities they provide. These systems are homogeneous, thermodynamically stable, isotropic and optically transparent. W/o microemulsions are self-organized aggregates of surfactant molecules (sometimes with co-surfactants) which are dispersed in a non-polar organic phase and contain nanometer-sized water cores. Water-in-oil (w/o) microemulsions are considered as an interesting alternative to conventional aqueous media for conducting enzymatic reactions ( 7). Laccases have been investigated extensively and found wide application potential in various areas, including environmental pollution control, textile industry, biosensors, food industry, pharmaceutical industry and organic synthesis ( 5, 6). These enzymes have attracted more attentions since they are generally eco-friendly, they only require oxygen as the co-substrate, they release water as the only by-product and they a wide substrate range. Laccases catalyze the reduction of molecular oxygen to water and simultaneously conduct single-electron oxidation of various inorganic and aromatic substrates, particularly phenols ( 1- 4). Laccases (benzenediol: oxygen oxidoreductase, EC 1.10.3.2) belong to a family of copper-containing oxidases which are widespread in fungi and have been isolated from higher plants, insects and some bacteria. Laccase Enzyme activity W/o microemulsions CTAB Introduction It was suggested that the conformational changes due to the electrostatic interactions between the cationic head group of CTAB and the negative enzyme might be the reason for the reduction of laccase activity, once entrapped in the microemulsion. Results revealed that the catalytic activity of laccase in CTAB-based w/o microemulsions decreased considerably, compared with its activity in the buffer solution, the extent of which depended upon the type of component and their compositions in the microemulsions. On each phase diagram, three different water-in-oil (w/o) microemulsion systems with less than 50 wt% surfactant mixture and less than 20 wt% of aqueous phase were selected for laccase loading and activity measurements. A monophasic, transparent, non-birefringent area (designated as microemulsion domain) was seen to occur in some phase diagrams along the surfactant/organic solvent axis, the extent of which was dependent mainly upon the nature of co-surfactant and R sm. Phase behavior studies were conducted by constructing partial pseudo-ternary phase diagrams for systems comprising of cetyltrimethylammonium bromide (CTAB), various organic solvents as the oil phase (i.e., hexane, cyclohexane, heptane, octane, isooctane, toluene, isopropyl myristate), two co-surfactants (i.e., 1-butanol and 1-hexanol) and citrate buffer solution, at various surfactant/co-surfactant weight ratios ( R sm). The aim of this study was to develop a microemulsion system as a medium for laccase-catalyzed reactions.
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