Design of transition state analogue (TSA) imprinted polymers for the catalytic hydrolysis of Amino acid esters

Abstract

Transition state analogue imprinted polymeric catalysts for the hydrolysis of p-nitrophenyl esters of Z-L-phenylalanine were prepared by bulk polymerisation method. For comparing and evaluating imprinting efficiency non-imprinted polymers were also prepared. Various spectroscopic techniques like FT-IR, 1H, 13C and 31P NMR were used for analysing the prepared monomer, transition state analogue and the polymers. Scanning electron microscopy was used for studying the surface morphology of the imprinted and non-imprinted polymers. BET surface area analysis was carried out for finding out the surface area of imprinted and non-imprinted polymers. Emphasis is given to the design of an effective catalyst by changing the nature and extent of crosslinking, porogen, copolymer composition with different functional groups for enhancing catalytic activity, and metal coordination during the prepolymerisation stage. The catalytic activities of the imprinted, non-imprinted polymers and uncatalysed reaction were carried out using the UV-vis. spectroscopic method and the kinetics of the reaction followed by pseudo-first order kinetics. The substrate selectivity and enantioselectivity of the imprinted polymers evaluated towards structurally related esters and enantiomers. Optimisations of the hydrolytic conditions were carried out by changing the pH and solvent ratio of the reaction medium. The results indicated that by imprinting a transition state analogue of the amino acid ester an effective catalyst could be synthesised and applied for the specific and selective catalysis of the corresponding amino acid ester. Keywords: molecular imprinting, transition state analogue, crosslinking agent, hydrolysis, amino acid ester, cooperative effect, stereospecificity, enantioselectivity, metal ion coordination