Self-Assembly and Biocatalysis of Polymers and Polymer-Ceramic Composites
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Surfactant microstructures provide a unique environment for the enzymatic synthesis of polymers. Surfactants can create large oil–water interfaces, which can be exploited for biocatalysis where the enzyme is resident in the aqueous phase and the monomer is resident in the oil phase or at the oil–water interface. The polymerization of substituted phenols using an oxidative enzyme, horseradish peroxidase (HRP), is explored. The surfactant microstructures used in enzymatic synthesis include the system of bis(2-ethylhexyl) sodium sulfosuccinate (AOT) water-in-oil microemulsions, cetyltrimethylammonium bromide (CTAB) micelles, and a novel gel system formed by the addition of lecithin and water to AOT water-in-oil microemulsions. The monomers partition to the oil–water interface, and polymerization is extremely feasible.
The use of enzymes in synthesis represents an inherently environmentally benign approach to chemical processing. In addition to catalytic function at or near ambient conditions, the exquisite specificity of enzyme biocatalysis can be potentially exploited to develop processes with minimal side products. Advances in large-scale enzyme production and purification, and synthetic enzyme mimetic chemistry, are eventually expected to lead to enzyme-based processes that are economically viable. The use of enzymes to synthesize polymers is one such area of research undergoing rapid development. Enzymatic polymerization exhibits a wonderful aspect of biomimetics, as enzymes function in the biological world in the synthesis and degradation of polysaccharides, proteins, polyphenols, and polynucleic acids. If such enzyme action can be exploited in the in vitro synthesis of polymers with commercial significance, it may be possible to obtain polymers with unique material properties that are inherently biodegradable and in specific cases, biocompatible. Examples of enzyme biocatalysis for polymer synthesis include the use of lipases for polyester synthesis, peroxidases for polyphenol synthesis, and cellulases for polysaccharide synthesis.
In developing enzymes for synthesis, the reaction environment plays a vital role in determining the activity and catalytic efficiency of the enzyme. The ability of enzymes to function in nonaqueous environments when properly conditioned has brought about the development of an entire field of biocatalysis in organic solvents. A parallel development is the field of enzyme chemistry in surfactant systems, in particular the system of water-in-oil microemulsions, conventionally referred to as reversed micelles.