Sacrificial spacer

Molecularly imprinting sol-gel using a sacrificial spacer was successful in creating a material that could bind DDT82 with a moderate degree of... 

Fig. 7.1. The sacrificial spacer methodology. Imprinting of cholesterol via the 4-vinylphe-nyl carbonate ester (1). AIBN = 2,2 -azobisisobutyronitrile. Adapted from [9].

Fig. 7.3. Synthesis of polymeric receptors for TCDD by a modified sacrificial spacer approach using the urea monomer (7). DVB = divinylbenzene. Adapted from [23],...

Scheme 2 The preparation of polymers by the sacrificial spacer approach imprinted against (a) cholesterol and (b) pyridine.

The cavity left behind after cleaving off the covalently bound template moiety is often too small to accommodate the target molecule during non-covalent rebinding. This problem was addressed by Whitcombe in 1994 when the sacrificial spacer approach was introduced [72]. In this approach, the template and the monomer is joined by a spacer, which is cleaved off when the template is cleaved from the polymer (Figure 2.3). The sacrificial spacer approach has been applied to the imprinting of cholesterol [73], DDT [74] and heterocyclic aromatic compounds [75]. 

Figure 2.3 Semi-covalent molecular imprinting of cholesterol using the sacrificial spacer approach. Polymerization (1) cleavage and extraction (2) rebinding (association) (3) and dissociation (4).

Zimmerman et al. were the first to have synthesised a dendrimer imprinted with a porphyrin derivative using the sacrificial spacer methodology a single cavity within a single polymer confinement structure [30]. 

Whitcombe, M.J. Vulfson, E.N. Covalent imprinting using sacrificial spacers. In Molecularly Imprinted Polymers—Man-Made Mimics of Antibodies and their Application in Analytical Chemistry, Sellergren, B., Ed. Elsevier Amsterdam, 2001, 203-212 pp. 

Figure 7 Sacrificial spacer method, as exemplified by the imprinting of cholesterol (a) cholesteryl (4-vinyl)phenyl carbonate 8 is used as the template monomer to form a covalently imprinted polymer (b) in the polymerization step, the carbonyl group of the carbonate ester holds the functional monomer and template oxygen atoms apart by two bond distances (c) hydrolysis results in loss of the template and loss of the spacer as CO2 (d) rebinding can now occur with the cholesterol ligand occupying essentially the same space as the template cholesteryl group (adapted from Ref. 10).

Figure 8 (a) Binding of cholesterol to cholesterol-imprinted and control polymers, from a 2 mM solution of cholesterol in hexane, as a function of polymer concentration, (b) Binding of cholesterol and various cholesterol analogues (2 mM) to the cholesterol-imprinted polymer, prepared by the sacrificial spacer method. Reprinted with permission from Journal of the American Chemical Society. Copyright 1995 American Chemical Society (Ref. 10). 

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