Catalytic MIPs

In the future, porous catalytic MIP membranes could also serve as a key element for advanced integrated bio-mimetic processes in reaction engineering [112,113]. 

As described in previous chapters, MIPs prepared by modern protocols are robust materials capable of highly specific molecular recognition. Since specific molecular recognition is the hallmark of enzyme catalysis, it is apparent that MIPs are potentially suited for catalytic applications. And indeed, investigations have shown that catalytic MIPs can be produced and successively more active and selective MIP catalysts were presented over the last years. In the following, the basic ideas and principles of catalytic MIPs are described using selected examples from the literature. For supplementary reading on this topic, review articles by Wulff (1), Whitcombe et al. [2] and Davis et al. [3] are recommended. 

Avery similar strategy has been applied to generate catalytic MIPs TSAs have been used as a template to generate specific binding sites in polymers using covalent and noncovalent imprinting techniques. As for catalytic antibodies, hydrolysis reactions of esters have been the focus of interest. One of the most successful systems described so far will be our first example [14]. 

Figure 6 Generation of a catalytic MIP using a phosphonic acid monoesters as a template which imitates the transition state of the reactions.

Figure 7 Imprinting with amidinium-phosphonate complexes to generate catalytic MIPs for the hydrolysis of carbonates and carbamates.

The construction of catalysts for bimolecular reactions represents a special challenge. Due to entropic reasons, the product- catalyst complex is likely to be more stable than the ternary substrate-catalyst-complex. Consequently, turnover is often low or not even observed. For Diels-Alder reactions, the difficulty to obtain turnover is further increased by the fact that the transition-state and the final product are similar in shape. Nevertheless, a catalytic MIP for a Diels-Alder reaction has successfully been prepared [17]. The trick employed to overcome the problem of similarity between TSA and product is the utilization of a reaction in which the product spontaneously decomposes (Fig. 9). The same reaction had been previously studied with catalytic antibodies. For the catalytic MIP, significant rate enhancements and Michaelis-Menten kinetics were observed. Addition of the template reduces the rate of the reaction to 41% of the original value whereas the control... 

An attractive alternative to improve the general activity of catalytic MIPs is the utilization of transition metal catalysts. In this case, polymeric catalyst with turnover frequencies of >100 h and turnover numbers of >100 can be prepared. For this type of MIP catalysts, the imprinting procedure should be regarded as a method to... 

---