Biocatalysis in water-in-oil microemulsions: Chemicals and materials synthesis in a microstructured environment
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Description
The catalytic behavior of three enzymes was analyzed with relevance to applications in chemicals and novel materials synthesis. The reactions were carried out in nonaqueous media, with a special emphasis on water-in-oil microemulsions, also known as reversed micellar systems. First, esterification of long chain fatty acids and small/medium chain alcohols was chosen as a model reaction to characterize an industrially important enzyme, lipase. It was realized that the enzyme forms an intermediate complex with acyl group carrying substrates, such as fatty acids. This complex formation was found to be important in positioning lipase correctly at the micellar interface, and in sustaining the enzyme activity over extended periods of time. The dependence of lipase activity on the micellar size, surfactant concentration, and the temperature of the reaction mixture was characterized A novel technique was developed to modify enzyme activity in reversed micelles by manipulating the micellar size in situ and reversibly through clathrate hydrate formation. The technique was successfully tested on two model reaction systems. Hydrate formation has an indirect influence on the enzyme activity. First, the micellar size is modified at sub-ambient temperatures by hydrate formation which enhances the enzyme activity to its optimal level. On the other hand, hydrate forming gases, such as xenon and ethylene, were found to directly inhibit the enzyme activity at ambient temperature. The thermodynamics and a potential application of this phenomenon are discussed. The pressure effect on membrane-bound enzymes, such as lipase, was found to be related to the biophysical action of anesthetics reported in literature From materials synthesis standpoint, reversed micellar systems are very suitable as reaction media. The synthesis of different polyphenols catalyzed by horseradish peroxidase was conducted in reversed micelles for the first time. The polymers have high molecular weight with relatively narrow molecular weight distribution. High monomer conversions and polymer yields were realized. The kinetics of the reaction were examined, and the polymer was characterized using various techniques. The molecular weight was found to be controllable by manipulating the micellar size and the surfactant concentration. The results from Scanning Electron Microscopy indicate that the polymer particles formed in reversed micelles are spherical