Selectivity, MIPs

Various novel imprinting techniques have also been presented recently. For instance, latex particles surfaces were imprinted with a cholesterol derivative in a core-shell emulsion polymerization. This was performed in a two-step procedure starting with polymerizing DVB over a polystyrene core followed by a second polymerization with a vinyl surfactant and a surfactant/cholesterol-hybrid molecule as monomer and template, respectively. The submicrometer particles did bind cholesterol in a mixture of 2-propanol (60%) and water [134]. Also new is a technique for the orientated immobilization of templates on silica surfaces [ 135]. Molecular imprinting was performed in this case by generating a polymer covering the silica as well as templates. This step was followed by the dissolution of the silica support with hydrofluoric acid. Theophylline selective MIP were obtained. 

Kubo et al. [122] have covered the sensing area of a gold electrode lattice with a polyimide layer which supports an atrazine selective MIP prepared with MAA and EDMA and functional monomer and cross linker, respectively. The detection limit was 50 nM (11 ppb) with a working range up to 15 pM atrazine. Other herbicides... 

A histamine selective MIP chemosensor, based on impedimetric transduction, has been devised [136]. Its preparation involved immobilization of the histamine imprinted MIP particles in apoly[2-methoxy-5-(3,7-dimethyloctyloxy)-l-4-pheny-lene vinylene] (OCiCi0-PPV) film deposited on aluminium electrodes. Preparation of these particles comprised thermally induced co-polymerization of MAA (functional monomer), EGDMA (cross-linker) and AIBN (initiator) in the presence of histamine. This film efficiently rebound histamine in the presence of histidine and... 

One should note that, according to the authors of this paper (submitted in April 2007), only three other papers had dealt before with using selective MIP HPLC columns for determinations from real samples. 

A relatively low pH (pH 4.5) was necessary to obtain a selective MIP-catalyzed hydrolysis of ester 77 (Scheme 13.19) this was most likely due to the involvement of the carboxylic acid moieties in substrate binding. In addition, at this pH, the... 

Bulk imprinted polymers [38] Various combinations of porogens, functional monomers (MAA and DEAEMA) and functional monomer/template ratios were compared and the most selective MIP was that obtained using a mixture of DEAEMA, CAP (functional monomer template ratio 2 1) and EDM A in THF. The mixture was polymerised, washed and particles sized to 25-63 m in diameter were packed into HPLC columns. 

The stereoselective release behaviors of low-swelling molecularly imprinted polymer bead matrices in pressed-coat tablets were studied using either R- or S-propranolol selective MIPs. The in vitro release profiles of the low-swelling matrices showed a difference in the release of enantiomers, in that the nontemplate isomer was released faster than the template isomer. However, in the last phase of dissolution this difference was reduced and later reversed [64]. Stereoselectivity of release profiles for propranolol enantiomers were identified in MIP synthetic membranes from tablet formulations with significant differences between enantiomers [65]. Release of the enantiomer used as the print was always faster than the... 

Highly selective MIP-coated quartz crystal microbalance (QCM) sensors have been prepared for nandrolone [16], a performance-enhancing substance that has been banned in international sports. The authors hope to address the need for a sensor to rapidly detect this substance of abuse. MIP was prepared with a 4-vinylphenol carbonate ester of the template, but also in the presence of methacrylic acid to target the ketone functionality. The sensor was able to detect nandrolone down to 0.2 ppm and was highly selective over closely related structures such as testosterone and epitestosterone. 

VII. CASE STUDY 2 THE DESIGN, SYNTHESIS, AND EVALUATION OF EPHEDRINE SELECTIVE MIPS... 

Langmuir-Freundlich (LF) isotherm (Eq. (14)) to characterize MIPs [26]. For example, the LF isotherm is superior to the Freundlich isotherm in fitting the experimental binding isotherm of a trimethoprim-selective MIP synthesized and characterized by Sellergren and coworkers (Fig. 13) [27]. 

As described in previous chapters, MIPs prepared by modern protocols are robust materials capable of highly specific molecular recognition. Since specific molecular recognition is the hallmark of enzyme catalysis, it is apparent that MIPs are potentially suited for catalytic applications. And indeed, investigations have shown that catalytic MIPs can be produced and successively more active and selective MIP catalysts were presented over the last years. In the following, the basic ideas and principles of catalytic MIPs are described using selected examples from the literature. For supplementary reading on this topic, review articles by Wulff (1), Whitcombe et al. [2] and Davis et al. [3] are recommended. 

If the selectivity of the MIP catalyst is the main objective, the partial poisoning of active centers might be a way to improve the performance of the system. The imprinting procedure generates a statistical distribution of selective and less selective reactions centers. Studies indicate that the least selective sites are the most reactive [27]. The reaction of an MIP catalyst with sub-stoichiometric amounts of a catalyst poison under kinetic control should, therefore, result in a less active but more selective MIP catalyst. As a poisoning reaction, the covalent modification of functional groups or the irreversible complexation of a metal center could be employed (Fig. 20). 

Dopamine might be a pharmaceutical for which the highest number of MIP based sensors have been constructed. Voltammetry [361,413] and its derivative techniques like differential pulse voltammetry [347,395,418], differential pulse anodic and cathodic stripping voltammetries [353,387,415] ion selective electrodes [372], as swell as piezoelectric microgravimetry [401] and thermogravimetry [427] are among the mechanisms used for the detection in dopamine selective MIP based sensors. 

An ion selective MIP sensor for dopamine was introduced by M. Pesavento et al. [372]. This all-solid-state ion selective electrode was prepared through screen printing a graphite electrode which was modified with a multiwalled carbon nanotubes, with a dopamine selective MIP membrane based on methacrylic acid monomers and ethyl-eneglycole dimethacrylate cross-linker [372]. 

Guo et al. reported a potentiometric tetracycline selective MIP electrode using tetracycline as template, methacrylic acid as the functional monomer, and ethylene glycol dimethacrylate as crosslinker during the polymerization of the MIP in a methanol-water... 

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