Organic polymers molecular imprinting

Wulff, G. Templated synthesis of polymers— molecularly imprinted materials for recognition and catalysis. In Templated Organic Synthesis, Diederich, F., Stang, P.J., Eds. Wiley-VCH Weinheim, 1999, 39-73 pp. 

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]. 

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. 

Martin-Esteban A (2001) Molecularly imprinted polymers new molecular recognition materials for selective solid-phase extraction of organic compounds. Fresenius J Anal Chem 370(7) 795-802... 

There are several future trends for the development of passive sampling techniques. The first is the development of devices that can be used to monitor emerging environmental pollutants. Recently, attention has shifted from hydrophobic persistent organic pollutants to compounds with a medium-to-high polarity, for example, polar pesticides, pharmaceuticals, and personal care products.82 147148 Novel materials will need to be tested as selective receiving phases (e.g., ionic liquids, molecularly imprinted polymers, and immunoadsorbents), together with membrane materials that permit the selective diffusion of these chemicals. The sample extraction and preconcentration methods used for these devices will need to be compatible with LC-MS analytical techniques. 

Whilst the development of new adsorbents on monolithic [62] or fibrous supports [63] to cut pressure drops, of high-capacity metal organic frameworks (MOFs) [64], or of highly selective molecularly imprinted polymers (MIPs) [65], is certainly beneficial for the realization of novel adsorptive reactive concepts, the serendipity of catalytic chemistry and the accompanying adsorption process remains the crucial factor for the success or otherwise of an adsorptive reactor. Thus, although a healthy degree of skepticism is appropriate when assessing the suitability of an adsorptive... 

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