Covalent imprinting/noncovalent binding

There are two general classes of imprinted polymers covalent and noncovalent MlPs. These two categories refer to the types of interactions between the functional monomer and the template in the prepolymerization complex. There are also hybrid MlPs that utilize a combination of covalent and noncovalent interactions in the preparation and rebinding events (Klein et al. 1999). Covalent MlPs utilize reversible covalent interactions to bind the template to the functional monomers. In contrast, noncovalent MlPs rely on weaker noncovalent functional monomer-template interactions. Each type has specific advantages and disadvantages with respect to sensing applications that will be addressed in subsequent sections. 

Boronic acid binding sites can also be used in combination with other covalent or noncovalent interactions. Glyceric acid and derivatives were thus bound as boronic esters aided by electrostatic, hydrophobic, charge-transfer interactions, or hydrogen bonding [39]. A boronic ester bond and a Schiflf base have been used for the imprinting of D-glyceraldehyde [4] and of l-DOPA in 8 [48]. 

A scaffolding monomer having multi-interaction sites for the target molecule is a general approach that can utilize the principles of both covalent and noncovalent imprinting. Many cases have been described using scaffold multi-mers, which interact with the template via multiple binding interactions and subsequently cross-linked... 

Examples of this technique are described for artificial receptors for the alkaloid yohimbine binding peptides obtained from a phage display library [57], for the steroid libraries related to lla-hydroxyprogesterone [58], corticosterone [58] (reported in Fig. 12), and cortisol [59]. A molecularly imprinted polymer working as a synthetic receptor for a series of chiral benzodiazepines [47], artificial receptors for the tricyclic antidepressant drug nortriptyline—obtained by covalent and noncovalent molecular imprinting and studied by capillary liquid chromatography with a simulated combinatorial library [60,61]—were also examined. 

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]. 

The third item to consider in the development of an affinity technique is the way in which the ligand is attached to the solid support, or the immobilization method. There are many ways immobilization can be accomplished. These approaches include simple adsorption to a solid support, bioselective adsorption to a secondary ligand (e.g., the noncovalent binding of antibodies to immobilized protein A), entrapment, imprinting, and covalent attachment. 

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]. 

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