Molecular imprinting in organic polymers

It was in 1972 that the groups of Klotz and Wulff independently presented the first examples of molecular imprinting in synthetic organic polymers. Briefly, the 

The past few years have witnessed an almost exponential increase in interest in molecular imprinting, as illustrated by the number of publications appearing in the area. From 1931 to the time of writing, around 500 original papers have been published by close to 700 co-authors from more than 100 groups [86]. MIPs anno 1998 are indeed stable, batch reproducibility is excellent and a wide range of compound classes can be successfully imprinted. 

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Fig. 1.8. The covalent approach to molecular imprinting in organic polymers, as introduced by the group of Wulff, exemplified by the o-glyceraldehyde MIP reported in 1972 [1],...

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]. 

The role of template-template self-association in molecular imprinting was the subject of extensive debate during the early work with silica-based systems [1]. Its involvement in organic polymer imprinting has, however, attracted much less... 

Marx, S., Liron, Z. Molecular imprinting in thin films of organic-inorganic hybrid sol-gel and acrylic polymers Chem. Mater., 2001, 13, 3624-3630... 

It is known that molecularly imprinted [3-CD polymer may be used as optical receptor for detection of organic compounds. The molecularly imprinted [3-CD polymer was prepared from [3-CD, using TDI as a crosslinking agent in this procedure A-phenyl-l-naphthylamine (35) served as a template. The molecularly inprinted polymer was fluorometrically characterized using a fibre optic cable attached to a flow-cell. The above sensor was investigated for analytical determination of 35 [82]. 

Molecular imprinting is not limited to organic polymer matrices, but can also be applied to silica-based materials and even proteins. Proteins freeze-dried in the presence of a transition state analogue as template have been used successfully as catalysts, e.g., for the dehydrofluorination of a fluorobutanone. For instance, lyophilized 3-lactoglobulin imprinted in this manner with N-isopropyl-N-ni-trobenzyl-amine could accelerate the dehydrofluorination by a factor of 3.27 compared to the non-imprinted protein see Table 5 [62]. In a similar procedure, BSA was imprinted with N-methyl-N-(4-nitrobenzyl)-S-aminovaleric acid and showed an enhancement of the catalytic effect by a factor of 3.3 compared to the control protein for the same reaction see Table 5 [113]. 

Kim H, Guiochon G. Thermodynamic studies of the solvent effects in chromatography on molecularly imprinted polymers. 3. Nature of the organic mobile phase. Anal Chem 2005a 77 2496-2504. 

Molecular imprinting is a special polymerization technique making use of molecular recognition [18] consisting in the formation ofa cross-linked polymer around an organic molecule which serves as a template. An imprinted active site capable of binding is created after removal of the template. This process can be applied to create effective chromatographic stationary phases for enantiomers separation. An example of such a sensor is presented in Section 6.3.2.3. 

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. 

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