Mimics, enzyme molecularly imprinted polymers

In addition to studies where the nature of the recognition events per se has been the major issue, a number of application areas have been explored for imprinted matrices viz. (A) Chromatography, where the imprinted polymer is used as the stationary phase for separation and isolation (Chapter 20). This application is based on the fact that the imprinted polymer has a better retention for the template molecules than others. A related area of application is solid-phase extraction, where the imprinted polymer is used as a sponge to concentrate the molecule of interest (Chapter 23). (B) Immunoassay-type analyses in which molecularly imprinted polymers are used as antibody and receptor mimics (Chapter 25). (C) Catalysis where the molecularly imprinted polymers are used as enzyme mimics (Chapter 24). (D) Sensors and biosensor-like devices where the molecularly imprinted polymer is the recognition element (Chapters 26 and 27). 

Reported applications of MIMIC procedures are the patterning of ceramic and metal oxide materials in sol-gel processes [11]. Other authors used MIMIC to produce well-defined molecular imprinted polymer microstructures for applications in immunoassays, sensors and enzyme mimics [43]. 

Abstract Molecular imprinting has grown considerably over the last decade with more and more applications being developed. The use of this approach for the generation of enzyme-mimics is here reviewed with a particular focus on the most recent achievements using different polymer formats such as microgels and nanogels, beads, membranes and also silica nanoparticles. 

The bulk polymeric format, characterised by highly cross-linked monolithic materials, is still widely used for the preparation of enzyme mimic despite some of its evident drawbacks. This polymerisation method is well known and described in detail in the literature and has often be considered the first choice when developing molecular imprinted catalysts for new reactions. The bulk polymer section is presented in three subsections related to the main topics covered hydrolytic reactions, carbon-carbon bond forming reactions and functional groups interconversion. 

Molecular imprinting in synthetic polymers was reported for the first time in 1972 [1--4]. The initial idea was to obtain in the polymer highly specific binding clefts with a predetermined size, shape and three-dimensional arrangement of functional groups. Later on, further experiments demonstrated that such functionalised cavities could be tailored to mimic the active sites of enzymes ( enzyme analogue built polymer ). 

Molecular imprinting recent innovations in synthetic polymer receptor and enzyme mimics... 

Nolte et al 46) produced an artificial enzyme based on the T4 replisome and applied it to the epoxidation of double bonds in synthetic polymers. Smith et al 51) reported that horseradish peroxidase catalyzes the oxidative polymerization of glucuronic acid. In recent literature, many biomimetic macromolecules with enzyme-like structures or functions have been reported including those that are dendrimers 64-66), those that have specified three-dimensional structures or recognition elements created by molecular imprinting 67), and other enzyme mimics 68). 

Schematically shown in Fig. 5 is the preparation of an enzyme mimic for the hydrolysis of ester 6 by molecular imprinting. Phosphonate 5 is an analog of the transition state for the alkaline hydrolysis of Ester 4. It was used as a template for polymerization with two equivalents of the binding-site monomer iVJV -diethyl-4-vinyl-benzamidine. Amidinium groups were chosen, because they can interact electrostatically with the side carboxyl-ate group as well as with the anionic transition state of the alkaline hydrolysis, thus achieving substrate recognition and transition-state stabilization. Polymerization of the preassembled binding-site monomer with the template (Fig. 5A) followed by template removal (Fig. 5B) leaves a cavity that acts as transition-state receptor for the ester substrate (Fig. 5C). The imprinted polymer accelerates the hydrolysis of 6 more than 100-fold compared to the reaction at the same pH in buffer solution without the polymer. The reaction kinetics is of the Michaelis-Menten type. A polymer obtained with amidinium benzoate as a control, with a statistical distribution of amidinium groups, is ca. one order of magnitude less active in the hydrolysis of 6.

Following these results, Kulkarni and coworkers [17] examined the role of molecular imprinting and metal coordination in a second generation of polymeric mimics of chymotrypsin. The monomers previously utilized for cooperative rate enhancing effects were replaced by polymerizable amino acids that are present in the active site of the enzyme. A series of polymers were synthesized in which one. 

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