Enzyme mediated synthesis of therapeutic materials, semiconducting polymers and biomimetic catalysts

The past few decades have seen an upsurge in the use of enzymes for accomplishing certain unique transformations and polymerization reactions under environmentally friendly conditions. The work presented in this thesis involves the use of enzymes as catalysts for the synthesis of (1) therapeutic materials, (2) semi-conducting oligomers and (3) water-soluble conducting polymers and (4) novel biomimetic catalysts.;Green tea and its constituents (referred to as 'catechins') have elicited tremendous interest due to their potent anti-oxidant activity and distinct anti-cancer activity. In this research work, the green tea catechins have been enzymatically modified to yield oligomeric catechins with enhanced stability and anti-proliferative activity. The oligomers exhibited statistically significant growth inhibition of high and low metastatic human breast cancer cells with minimal effect on the growth of normal mammary cells.;Enzymes have also been used as catalysts for the synthesis of semiconducting polymers. In the field of semi-conducting polymers/oligomers, thiophene oligomers are considered to be one of the more promising organic materials for electrical and electro-optical applications. Sexithiophene is one of the most investigated members of the oligothiophene series. In the area of electrically conducting polymers, PEDOT/PSS is one of the most processable pi-conjugated polymer with good conducting & electro-optical properties. PEDOT/PSS is a complex of the polymer poly (3,4-ethylenedioxythiophene) [PEDOT] and polystyrenesulfonic acid [PSS].;In this thesis, biocatalytic routes have been developed to the syntheses of these thiophene based oligomers/polymers. Sexithiophene has been synthesized via a single-step biocatalytic route involving the enzyme catalyzed coupling of terthiophene in mixed solvent systems. The enzymatically synthesized sexithiophene exhibited similar spectroscopic characteristics when compared to the commercially available material.;PEDOT/PSSNa has been synthesized enzymatically from 3,4-ethylenedioxythiophene (EDOT) using terthiophene as a redox mediator/initiator in the presence of poly (styrenesulfonic acid)sodium salt (PSSNa). The choice of a thiophene-based material as the redox mediator ensures that any residual mediator that might be incorporated in the final polymer would still be composed of only conjugated thiophene segments. The unique combination of this redox-mediator approach with enzyme catalysis vastly expands the range of monomers (with higher oxidation potentials) that can potentially be polymerized to yield conducting polymers.;Biocatalytic routes have also been used for the synthesis of biomimetic catalysts, capable of mimicking naturally occurring enzymes. Hematin, a naturally occurring iron porphyrin, has been functionalized with monomethoxy polyethylene glycol (mPEG) through a one-step lipase catalyzed esterification reaction. The modified Hematin (PEG-Hematin) was water-soluble and catalyze the polymerization of aniline and phenol based monomers. In order to further enhance the stability of the catalyst at a low pH, Hematin was functionalized with a mPEG containing a terminal free amine group. This Hematin functionalized amide exhibited better stability especially at low pH conditions. It is envisioned that these biomimetic catalysts can be used as a viable and economical alternative to naturally occurring enzymes.