Molecularly imprinted polymers first reported

This first part of the chapter was intended to give the reader an overview of the first examples of catalytic imprinted polymers based on the use of the TSA as template. However, a more detailed discussion about imprinted polymers with synthetic and catalytic properties can be found in the reviews by G. Wulff et al. [27,28] and by C. Alexander et al. [29] The second part of this chapter will focus on the most successful examples of molecular imprinted polymers with catalytic activity that have been reported in the last decade. 

Finally, the last few years have seen the first examples of the use of molecular-imprinted, polymer-supported catalysts for achieving product selectivity. The imprinted cavities are tailored in such a way that the course of a chemical reaction is directed towards one of the possible products. In the previous section it has already been shown that molecularly imprinted polymers used as microreactors are able to impart to a given reaction a different regio- and stereo-selectivity with respect to the same reaction in solution. Attempts towards an imprinted enantio-selective catalyst were reported by Gamez and co-workers who employed as template monomer an optically active, polymerisable ruthenium complex bearing in its coordination sphere an enantiomerically pure alkoxide [121]. After polymerisation, the alkoxide was split off and the resulting polymer-supported catalyst was used for enantio-selective hydride transfer reductions. The obtained selectivity was higher than for a polymer prepared without the optically active alkoxide but lower than for the same ruthenium complex in solution. 

Although the first report on boronic acids was published in 1862, boronate affinity materials have not been extensively investigated until recently. In recent years, various boronate-functionalized materials, " such as macroporous monoliths, " " nanoparticles, and mesoporous materials, have been developed into important tools for the facile selective extraction of cis-diol-containing compounds. With these matrices, several important materials with teamed boronate affinity and boronate avidity as well as boronate affinity-based molecularly imprinted polymers have been prepared. 

The first reported attempt of using MIPs to control the stereochemical course of a reaction dates back to 1980, when the two research groups of Neckers and Shea published, simultaneously, examples of bulk polymers able to control the formation of the product by using a chiral template. Shea et al. reported that bulk polymers imprinted with stereochemically pure ( )-/ra/w-l,2,cyclobutane-dicarboxyilic acid (6) were able to keep a molecular memory of the asymmetry of the template [8]. In fact, this was transferred to an achiral substrate, such as fumaric acid (7), inducing a diastereoselective methylation, which led to trans-1,2,cyclopropane-dicarboxyilic... 

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 ). 

The first reported preparation of capillary columns containing MIPs utilised a thermally initiated dispersion polymerisation procedure [58], The functional monomer MAA and the cross-linking monomer EDM A were used. Agglomerates of micrometre-sized globular polymer particles were claimed to be prepared in situ in the capillary. Molecular imprinting of L-phenylalanine anilide, pentamidine and benzamidine was undertaken. A pH-dependent retardation of pentamidine over benzamidine in the pentamidine capillary was observed, while the opposite. 

The first attempt to imprint a metal complex with a reaction intermediate coordinated to the metal center was reported by Mosbach and coworkers [51], A Co monomer coordinated with dibenzoylmethane, which is as an intermediate for the aldol condensation of acetophenone and benzaldehyde, was tethered to a styrene-DVB copolymer matrix. After, the template, dibenzoylmethane was removed from the polymer, the resulting molecularly imprinted cavity had a shape similar to the template due to the interaction of the template with the polymerized styrene-DVB monomers through n-n stacking and van der Waals interactions. The rate of aldol condensation of adamantyl methyl ketone and 9-acetylanthracene was lower than the rate of condensation with acetophenone, indicating some degree of increased substrate selectivity. This is the first known formation of a C-C bond using a molecularly imprinted catalytic material. 

The molecular imprinting method can be used to synthesize enantioselective solid materials for asymmetric organic synthesis. The first attempt to use a metal complex with an attached chiral ligand as a template was attempted by Lemaire [52]. The Rh complex, ((15,25)-V,V -dimethyl-l,2-diphenylethane diamine)-[Rh(CgHj2)Cl]2 coordinated with optically pure l-(5)-phenylethoxide or phenylethoxide (Rh 1-phenylethanolate) (template) was polymerized in the presence of isocyanate, and the polyurea-supported Rh complex is reacted with isopropanol to extract the template from the polymer backbone. They reported the influence of molecular imprinting on catalytic performance (conversion and enantiomeric excess) for the asymmetric transfer hydrogenation (Table 22.2). The imprinted polymer exhibited higher enantioselectivity compared to a nonimprinted... 

Thus far, in this chapter, organic polymers have been used to create molecular imprinted networks but alternative supports have also been employed. Indeed, the first reported example of molecular imprinting was achieved with silica. Dickey precipitated silica gel using a dye as a template, and the corresponding matrix exhibited an increased affinity... 

In addition, molecular imprinting technique is also used in anion recognition. Ozkutuk et al. reported the preparation and adsorption ability of the phosphate-imprinted chitosan-succinate beads [34]. Chitosan was modified with succinic anhydrides firstly. Second the mixture of chitosan-succinate and Fe (III) ions stirred continuously at room temperature. And Na3P04 was added to Fe (III)-chitosan-succinate mixture. This mixture was slowly dropped into NaOH solution to form beads. Afterwards, beads were crosslinked with epichlorohydrin and the template (phosphate ions) was removed using IM KOH solution. Selective cavity for the phosphate ion was obtained in the phosphate imprinted metal-chelate polymer. The phosphate-imprinted metal-chelate polymer was used in the adsorption-desorption process. The adsorption process was fast and equilibrium was reached around 30 min. The adsorption behaviour of this system was described approximately by the Langmuir equation. 

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