Molecular imprinting strategies

The molecular imprinting is classified into three types according to the t5 e of interactions between functional monomer and target molecules in the pre-polymerization complex and during the re-binding of the template (Komiyama et al., 2003 Sellergren and Hall, 2001). 

The template and monomers are covalently linked to form a template-monomer pre-polymerization complex in the covalent imprinting. The template is removed from the polymeric matrix by chemical cleavage after polymerization. The functionality remaining in the binding site is capable of binding the target molecule by re-establishment of the covalent bond. 

The template is covalently bound to a polymerizable group and the functionality is recovered after cleavage of the templates. The re-binding takes place via non-covalent interactions such as hydrogen bond or ionic interactions. 

The approach relies on the formation of a pre-polymerization complex between monomers carrying suitable functional groups and the template. A cross-linker is then added and the polymerization initiated. Then, the highly cross-linked polymer forms around the template-monomer complexes. The template is then removed from the polymer via extraction with a solvent, which disrupts the non-covalent interactions present in the pre-polymerization complex. Subsequent template re-binding takes place through the formation of the same non-covalent interactions. 

The advantages of non-covalent imprinting over the preceding approaches include the following  

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The molecular imprinting strategy can be applied for the recognition of different kinds of templates from small organic molecules to biomacromolecules as proteins. Some examples of separations investigated with MIP monoliths in CEC and LC are shown in Table 2. The influence of the imprinted monolithic phase preparation procedure and of the separation conditions on the selectivity and chromatographic efficiency have been widely studied [154, 157, 161, 166, 167, 192]. The performance of imprinted monoliths as chromatographic stationary phase has also been compared to that of the traditional bulk polymer packed column [149, 160]. It was shown that the monolithic phases yielded faster analyses and improved chiral separations. 

Fig. 24 Molecular imprinting strategy for the detection of TNT (see text for details)...

Liu JQ, Wulff G (2004) Functional mimicry of the active site of carboxypeptidase A by a molecular imprinting strategy cooperativity of an amidinium and a copper ion in a transition-state imprinted cavity giving rise to high catalytic activity. J Am Chem Soc 126(24) 7452-7453... 

As noted earlier, biomaterials (and other bio-related materials) comprise one of most active research areas today. Major research themes in biomaterials include tissue engineering 58), molecular imprinting strategies 59), biosensors 60), stimuli responsive materials 61), biodegradable polymers 62), and smart biomaterials 63). 

Recently, an in-depth review on molecular imprinted membranes has been published by Piletsky et al. [4]. Four preparation strategies for MIP membranes can be distinguished (i) in-situ polymerization by bulk crosslinking (ii) preparation by dry phase inversion with a casting/solvent evaporation process [45-51] (iii) preparation by wet phase inversion with a casting/immersion precipitation [52-54] and (iv) surface imprinting. 

Molecularly imprinted polymers (MIPs) can be prepared according to a number of approaches that are different in the way the template is linked to the functional monomer and subsequently to the polymeric binding sites (Fig. 6-1). Thus, the template can be linked and subsequently recognized by virtually any combination of cleavable covalent bonds, metal ion co-ordination or noncovalent bonds. The first example of molecular imprinting of organic network polymers introduced by Wulff was based on a covalent attachment strategy i.e. covalent monomer-template, covalent polymer-template [12]. 

This chapter focuses on several recent topics of novel catalyst design with metal complexes on oxide surfaces for selective catalysis, such as stQbene epoxidation, asymmetric BINOL synthesis, shape-selective aUcene hydrogenation and selective benzene-to-phenol synthesis, which have been achieved by novel strategies for the creation of active structures at oxide surfaces such as surface isolation and creation of unsaturated Ru complexes, chiral self-dimerization of supported V complexes, molecular imprinting of supported Rh complexes, and in situ synthesis of Re clusters in zeolite pores (Figure 10.1). 

Sellergren B, Andersson L. Molecular recognition in macroporous pol3miers prepared by a substrate-analog imprinting strategy. J Org Chem 1990 55 3381-3383. 

Shea and colleagues [109-111] added an exciting contribution to this field They created molecular imprints for the peptide melittin, the main component of bee venom, in polymer nanoparticles, resulting in artificial antibody mimics that can be used for the in vivo capture and neutralization of melittin. Melittin is a peptide comprising 26 amino acids which is toxic because of its cytolytic activity. Shea and colleagues strategy was to synthesize cross-linked, acrylamide-based MIP nanoparticles by a process based on precipitation polymerization using a small amount of surfactant. To maximize the specificity and the affinity for melittin, a number of hydrophilic monomers were screened for complementarity with the template. The imprinted nanoparticles were able to bind selectively the peptide with an apparent dissociation constant of Ax>app > 1 nM [109]. 

Strategies for the Preparation of Molecularly Imprinted Monolithic Phases... 58... 

As it was shown in the previous sections, there is at present a wide variety of available methods for the preparation of molecularly imprinted micro-and nanoparticles. Little has been done however to compare directly two or more of these various synthetic strategies in order to better ascertain their advantages and limitations, and in particular their capability to yield efficient MIPs. 

Nicholls IA et al (2009) Theoretical and computational strategies for rational molecularly imprinted polymer design. Biosens Bioelectron 25(3) 543-552... 

Although the emphasis in this review has been on the manipulation of synthetic polymers it would not be appropriate to omit entirely the complementary work on biopolymers. Two important strategies are evolving here, both of which involve molecular imprinting. The first concerns specifically chemically modified proteins, and the second the generation of catalytic antibodies with functions similar to enzymes, but potentially with much greater scope in terms of the reactions catalysed. 

The ability of molecular imprinting technology to offer a generic synthetic strategy to prepare robust molecular recognition materials has been exploited to... 

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