Analytica Chimica Acta (v.435, #1)
CALENDAR OF FORTHCOMING MEETING (N1-N3).
Preface by Chris J. Allender; Hakan S. Andersson; Keith R. Brain; Olof Ramstrom (1-2).
Toward the next generation of molecular imprinting with emphasis on the formation, by direct molding, of compounds with biological activity (biomimetics) by Klaus Mosbach (3-8).
I would like to share with the participants the background and insights that made us work in what is now called molecular imprinting. In retrospect, for us it came as an intellectual by-product from early studies on immobilized/entrapped enzymes and cells and that of affinity chromatography. As for the former aspect, once it was shown that enzymes could be entrapped in a gel matrix and remain active, the idea came up of whether it would be possible to subsequently remove the bio-catalyst, leaving a cavity (shape) behind, specific for rebinding the very same protein. As to the other aspect, that of bio-affinity chromatography, this gave us the insight that most biological interactions such as those between inhibitor and enzyme or antigen and antibody are non-covalent by nature. This is why in our studies trying to mimic these systems, we chose print (template) molecules and polymerizable monomers that will lead to non-covalent interactions. Combining these two principles (shape and functional complementarity) various specific imprints were prepared over the years, the properties of some of which (especially ‘plastibodies’) will be discussed. Subsequently I intend to discuss research done in our laboratory over the last number of years with the goal of synthesizing directly on a bio-molecule such as an enzyme or cell, structures complementary for instance to the active site, e.g. by a polymerization process; a kind of direct molding. Examples of such studies with the aim of creating inhibitors, agonists or artificial competing affinity ligands will be given. Studies in these directions might contribute to what could be called the next generation of molecular imprints.
Keywords: Molecular imprinting; Biomimetics; Direct molding;
Can we rationally design molecularly imprinted polymers? by Ian A Nicholls; Karina Adbo; Håkan S Andersson; Per Ola Andersson; Jonas Ankarloo; Jimmy Hedin-Dahlström; Päivi Jokela; Jesper G Karlsson; Linus Olofsson; Jenny Rosengren; Siamak Shoravi; Johan Svenson; Susanne Wikman (9-18).
The nearly exponential growth in the molecular imprinting literature has to a large extent been fuelled by an increasing awareness of the potential of molecular imprinting based technologies. Despite the acceptance of the technique by cognate disciplines and the demonstration of its usefulness in a number of enabling technologies, relatively little is known about the molecular level events underlying the imprinting process and subsequent recognition events. What rules govern imprint formation? Can we use such rules to rationally design molecularly imprinted polymers?
Keywords: Molecularly imprinted polymers; Template; Monomer;
On the thermal and chemical stability of molecularly imprinted polymers by Johan Svenson; Ian A Nicholls (19-24).
The thermal and chemical stability of a theophylline imprinted methacrylic acid–ethylene glycol dimethacrylate co-polymer has been investigated. Radioligand binding studies have been used to study the changes in theophylline recognition characteristics of this and a non-imprinted, reference polymer arising from exposure to elevated temperatures and a range of chemical environments. Polymers were shown to withstand exposure to temperatures of up to 150°C (for 24 h) without loss of affinity for the template. Temperatures above this point induced a rapid loss in binding capacity and a concomitant mass loss. FT-IR indicated that this arises from decarboxylation of the polymer. The polymers exhibited remarkable resistance to extremes of pH, organic base and to autoclave treatment. This study provides an indication as to the limits of polymer stability, which is of significance for the practical use of this type of polymer, e.g. in sensor-based applications.
Keywords: Polymer stability; Polymers; Molecular imprinting;
Molecular imprinting of cyclodextrin in water for the recognition of nanometer-scaled guests by Hiroyuki Asanuma; Tomohiro Akiyama; Kentaro Kajiya; Takayuki Hishiya; Makoto Komiyama (25-33).
Acryloyl-cyclodextrins were synthesized as functional vinyl monomers, and various antibiotics and oligopeptides were molecularly-imprinted to them in water. The imprinting promoted the binding activity toward the template compared with non-imprinted polymer. The imprinting effect was eminent when the template involved more than two hydrophobic residues on a rigid molecular-frame. From Langmuir analysis, the promotion of binding by the imprinting was attributed to the increase in the binding constant, not increase in the number of binding sites. The present imprinting also provided eminent guest selectivity including enantioselectivity.
Keywords: Molecular imprinting; Cyclodextrin; Guests; Antibiotics; Oligopeptides; Enantioselectivity;
Application of the Freundlich adsorption isotherm in the characterization of molecularly imprinted polymers by Robert J Umpleby; Sarah C Baxter; Miguel Bode; John K Berch; Ripal N Shah; Ken D Shimizu (35-42).
The binding isotherm for a polymer molecularly imprinted with ethyl adenine-9-acetate was observed to obey the common Freundlich isotherm. To test the generality of the Freundlich isotherm with respect to molecularly imprinted polymers (MIPs), a survey of systems from the literature was conducted, revealing that the Freundlich isotherm gives a good mathematical approximation of the binding characteristics for non-covalently imprinted polymers. The utility of the Freundlich isotherm in the calculation of binding parameters, as well as its limitations and implication of an exponential distribution of binding sites in imprinted polymers have been discussed.
Keywords: Freundlich adsorption isotherm; Molecularly imprinted polymers; Binding parameters;
Rapid electrochromatographic enantiomer separations on short molecularly imprinted polymer monoliths by Leif Schweitz; Lars I Andersson; Staffan Nilsson (43-47).
Very rapid capillary electrochromatography (CEC) mode enantiomer separations of propranolol using short super-porous monolithic molecularly imprinted polymers (MIPs) were studied. MIP stationary phases were synthesised by an in situ photo-initiated polymerisation reaction. The effect of electrolyte composition on the enantiomer separation and the stability of the MIP-column performance was investigated. The optimised MIP–CEC separation system was able to resolve the enantiomers of propranolol in less than 1 min.
Keywords: Capillary electrochromatography; Molecularly imprinted polymer; Enantiomer;
Molecular imprinting of a small substituted phenol of biological importance by Miruna Petcu; Janine Cooney; Christian Cook; Denis Lauren; Peter Schaare; Pat Holland (49-55).
A polymer capable of recognising small phenolic molecules is described. Analysis based on batch binding experiments followed by HPLC was used to determine propofol concentration in different test solutions. Polymer particle size and contact time between propofol test solutions and polymers were modified to yield a fast and reliable system for propofol detection. The polymer thus synthesised had little cross-reactivity when tested against other structurally related phenols.
Keywords: Popofol; Molecular imprinting; Anaesthetic;
Probing the molecular basis for ligand-selective recognition in molecularly imprinted polymers selective for the local anaesthetic bupivacaine by Jesper G Karlsson; Lars I Andersson; Ian A Nicholls (57-64).
Molecularly imprinted polymers (MIPs) are an interesting novel class of sorbent for analytical separation science, with one particular area of potential being in the development of highly selective solid-phase extraction systems. In order to optimise polymer–ligand selectivity and to examine the underlying physical mechanisms, polymers with selectivity for the local anaesthetic bupivacaine have been synthesised and their ligand-recognition characteristics examined. The influence of rebinding media parameters (pH, ionic strength, polarity) have been studied and optimised with respect to selective MIP-ligand binding, and the working range of the polymers with respect to these parameters has been mapped. These results highlight the robustness of MIPs and the breadth of potential assay conditions that may be employed. Finally, competitive binding studies using the closely related structures mepivacaine, ethycaine, ropivacaine and pentycaine in solvent mixtures of different polarity revealed that the entropy-driven hydrophobic effect is significant in polar solvents, whereas enthalpy-driven electrostatic interactions dominate in non-polar media.
Keywords: Ligand; Sorbent; Molecularly imprinted polymer; Radioligand binding arnal; Solid phase extraction;
Investigation into the scope and limitations of molecular imprinting with DNA molecules by David A Spivak; Kenneth J Shea (65-74).
A brief account of the historical development of molecular imprinting introduces the connection between materials properties and recognition in molecularly imprinted polymers (MIPs). Polymers imprinted with DNA derivatives were investigated to understand the underlying principles governing the design, synthesis and application of imprinted polymer materials. A survey of 9-ethyladenine (9EA) imprinted polymers revealed an optimum mol% of cross-linking monomer to be in the range 70–80%, due to a balance of pre-polymer complexation and restriction of random polymer chain motion. MIPs to 9-ethyladenine using different porogens determined that binding site fidelity is best preserved when rebinding solvent matches the porogen. Colder temperatures and initiator concentration of 1 mol% or higher also improve the performance of 9EA imprinted polymers. All nucleosides were imprinted, revealing that only those with the 2-aminopyridine substructure show binding affinity and selectivity. Last, polymer complements to an adenine dimer and tetramer showed selectivity for the dimer, however, the tetramer exhibited little affinity for any imprinted or control polymers. If the lack of binding exhibited by the tetramer is due to size effects, this would set the upper limit of molecular size for molecular imprinting at approximately 20–30 Å.
Keywords: Molecular imprinting; Adenine; Morphology; DNA; Oligomers;
Ionic imprinted resins based on EDTA and DTPA derivatives for lanthanides(III) separation by Olivier Vigneau; Catherine Pinel; Marc Lemaire (75-82).
Ionic imprinting resins bearing polycarboxylic acids groups were studied in lanthanides(III) separation. Two monomers, diethylenetriamine pentaacetic acid (DTPA) and ethylenediaminetetraacetic acid (EDTA) derivatives, were synthesised and then polymerised in alcoholic medium using a free radical source. Solid–liquid competitive extraction was carried out using an aqueous solution containing gadolinium(III) and lanthanum(III) cations. Crosslinking ratios, conditioning of resins and type of chelating monomers were studied. Best results were obtained when polymers based on DTPA derivative were converted to H+ form.
Keywords: Lanthanide; DTPA derivatives; EDTA derivatives; Ionic recognition;
Molecular imprinting for the selective adsorption of organosulphur compounds present in fuels by Beatriz Castro; Michael J Whitcombe; Evgeny N Vulfson; Rafael Vazquez-Duhalt; Eduardo Bárzana (83-90).
A novel approach to the potential desulphurisation of fuels such as diesel is proposed. It relies on the creation of recognition sites complementary to sulphur-containing compounds in highly cross-linked polymeric matrices using the molecular imprinting technique. Dibenzothiophene sulphone (DBTS) was used as template for the preparation of molecularly imprinted polymers (MIPs). Four different polymers were synthesised using 5-octyloxy-1,3-bis(4-ethenylphenyl)-benzenedicarboxamide or methacrylic acid and divinylbenzenes or ethylene glycol dimethacrylate as functional monomers and cross-linkers, respectively. Three polymers showed better binding of DBTS than non-imprinted controls, and were also superior in adsorption of organosulphur compounds such as dibenzothiophene (DBT) and benzothiophene (BT) present in a model mixture. A maximum adsorption of 66 mg DBT per gram of polymer was observed at a polymer load of 10 g l−1 and an initial DBT concentration of 3.69 g l−1. The polymers also showed selectivity for fluorene.
Keywords: Desulphurisation; Dibenzothiophene; Organosulphur compounds; Molecular imprinting; Molecularly imprinted polymers; Solid-phase extraction;
Development of a semiautomated procedure for the synthesis and evaluation of molecularly imprinted polymers applied to the search for functional monomers for phenytoin and nifedipine by F Lanza; A.J Hall; B Sellergren; A Bereczki; G Horvai; S Bayoudh; P.A.G Cormack; D.C Sherrington (91-106).
A previously described scaled-down version of the established monolith procedure, where molecularly imprinted polymers (MIPs) are prepared on the bottom surface of chromatographic vials [Anal. Chem. 71 (1999) 2092] has been here further optimised with respect to its full automation. The protocol results in savings of time and reagents compared to the monolith procedure, allowing ca. 60 polymers (∼50 mg each) to be synthesised in parallel. Both blank and imprinted polymers are then evaluated in situ by equilibrium batch rebinding tests. Each step in the synthesis and evaluation was considered with the aim of achieving an automated method with wide applicability with regards to template targets and monomer compositions. A system based on thermal initiation was considered easier to implement and applicable to a larger number of templates than one based on photo-initiation. For the purpose of choosing a suitable initiator, azo-initiators with different dissociation energies were compared. 2,2′-Azobis(2,4-dimethylvaleronitrile) (V-65) was selected as the initiator of choice based on the observed rebinding selectivity and the low temperature of use (45°C). The time of degassing and polymerisation were also considered. With respect to the reproducibility of the automated procedure, confidence values of the mean rebinding percentage of 12 and 8 were found, respectively, for the blank and imprinted polymers when five parallel batches of ametryn blanks and imprints were submitted to rebinding tests. The small-scale protocol was then applied to the search for functional monomers for two further templates of interest: phenytoin and nifedipine. The results of the rebinding experiments on the small scale were found to be in agreement with the equilibrium rebinding evaluation of the regular scale batches. However, the equilibrium rebinding results cannot be used as a general predictor for the chromatographic selectivity of the MIPs.
Keywords: Molecularly imprinted polymers; MiniMIPs; Phenytoin; Nifedipine; Search for functional monomers;
Separation of individual antiviral nucleotide prodrugs from synthetic mixtures using cross-reactivity of a molecularly imprinted stationary phase by C.J Allender; K.R Brain; C Ballatore; D Cahard; A Siddiqui; C McGuigan (107-113).
2′,3′-Dideoxynucleosides (ddNs) are among the most potent of nucleoside analogues active against human immunodeficiency virus (HIV) in cell culture. d4T (2′,3′-dideoxy-2′,3′-didehydrothymidine) is clinically effective acting through competitive inhibition of viral reverse transcriptase and/or incorporation and subsequent chain termination of the growing viral chain. Activation occurs via intracellular conversion to the 5′-triphosphate, the kinase-mediated formation of the monophosphate being the rate-limiting step and, therefore, strategies to deliver the monophosphate have been sought. This study uses a molecularly imprinted HPLC stationary phase to separate single diastereomers for a number of nucleoside monophosphates prodrugs from synthetic mixtures. The biological activity of some individual diastereomers are unknown and a need to efficiently separate them from synthetic mixtures, has been identified. Due to cross-reactive affinity for the imprinted polymer one imprinted stationary phase was used to isolate a single diastereomer from a range of prodrug synthetic mixtures.
Keywords: 2′,3′-Dideoxynucleotide; Nucleoside reverse transcriptase inhibitor; HIV; Nucleotide prodrug; Molecularly imprinted polymer;
Enantioselective solid-phase extraction using Tröger’s base molecularly imprinted polymers by Karina Adbo; Ian A Nicholls (115-120).
Molecularly imprinted polymers (MIPs) selective for Tröger’s base were designed and synthesised, and HPLC-chromatographic evaluation of polymer recognition characteristics was undertaken. Baseline separation of racemic Tröger’s base was readily achieved, and enantioseparation factors (α) of up to 4.8±0.2 were obtained. The high enantioselectivity demonstrated by these materials prompted their use to examine the kinetics and thermodynamics of individual enantiomers in a solid-phase extraction (SPE) process. Enantiomer-dependent differences in the rates and extent of adsorption were observed. Furthermore, the enantiomeric enrichment of racemates was demonstrated in batch studies.
Keywords: Tröger’s base; Polymers; Solid-phase extraction;
Determination of degradation products of nerve agents in human serum by solid phase extraction using molecularly imprinted polymer by Meng Zi-Hui; Liu Qin (121-127).
Molecularly imprinted polymers (MIPs) for pinacolyl methylphosphonate, ethyl methylphosphonate and methane phosphonic acid were prepared. By taking the advantage of their cross selectivity, the MIPs could recognize not only the print molecule, but also the degradation products of the other nerve agents. The absorbed degradation products could be quantitatively extracted using distilled water. The pinacolyl methylphosphonate-imprinted polymer was used as a solid phase extraction sorbent for all possible degradation products of nerve agents from human serum. Following the solid phase extraction procedure, accurate analysis for the degradation products was carried out using capillary electrophoresis directly. A detection limit of 0.1 μg/ml and an R.S.D. of <9.12% were obtained. A good linearity (r>0.99, n=4) in the concentration range of 0.1–10 μg/ml was also obtained.
Keywords: Molecular imprinting; Chemical warfare; Nerve agents; Solid phase extraction; Capillary electrophoresis;
Selectivity of response in fluorescent polymers imprinted with N1 -benzylidene pyridine-2-carboxamidrazones by Daniel L Rathbone; Yi Ge (129-136).
Fluorescent polymers imprinted with various N1 -benzylidene pyridine-2-carboxamidrazones were evaluated for their recognition of the original template and cross-reactivity to similar molecules. Dramatic quenching of fluorescence approaching background levels was observed for most cases where the “empty” MIP was re-exposed to its template. Molecules too large to enter the imprinted cavities gave no reduction of fluorescence. Other compounds were found to quench the fluorescence and are assumed to have entered the imprinted cavities. There is also evidence for partial responses which may give some measure of partial binding. The fluorescence response profiles of substrates containing polycyclic aromatics were found to be quite different from those containing flexible substituents. In order to make this approach more suitable for high-throughput screening a method has been validated wherein the extent of substrate-induced fluorescence quenching may be obtained without having to know how much polymer is present.
Keywords: Imprinted polymers; Fluorescent monomer; Recognition; Molecular modelling; High-throughput screening;
Simple NMR experiments as a means to predict the performance of an anti-17α-ethynylestradiol molecularly imprinted polymer by Irene Idziak; Amina Benrebouh; François Deschamps (137-140).
The affinity and specificity of 17α-ethynylestradiol (EE) molecularly imprinted polymers (MIPs), prepared with methacrylic acid or vinylpyridine (VP) in toluene or methylene chloride, were evaluated by radioassay. Proton NMR model studies into complex formation between the template and functional monomer analogues, acetic acid and deuterated pyridine were performed in the same solvents that were used as porogens for the MIP. A correlation was found to exist between the binding strength and specificity of a particular polymer and the extent of complex formation shown by the corresponding NMR spectrum.
Keywords: Molecular imprinting; 17α-Ethynylestradiol; Hydrogen bonding; NMR;
Molecular imprinting of caffeine and its recognition assay by quartz-crystal microbalance by Takaomi Kobayashi; Yasuhiro Murawaki; Puchalapalli Sreenivasulu Reddy; Masanori Abe; Nobuyuki Fujii (141-149).
Phase inversion precipitation method was applied to prepare molecularly imprinted polyacrilonitrile (PAN) copolymers. Three types of PAN copolymers with pyridine and styrene moieties were used for caffeine (CAF) imprinting. For encoding shape of the template molecules into the polymer, polymer solution involving the template molecule was coagulated in water non-solvent. After the template extraction from the resultant polymer, binding amounts of CAF and CAF analogous molecules to the CAF-imprinted polymer were evaluated by using 6 MHz quartz-crystal microbalance (QCM). As QCM attached with CAF-imprinted polymer was immersed into CAF solution, the QCM frequency decreased and then saturated at constant value. We demonstrated recognition properties of the CAF-imprinted polymers by observation of the frequency change for various imprinted and unimprinted polymers. It was observed that PAN copolymer having 4-vinylpyridine (4-Py) moieties showed a large difference of the frequency decrease between the imprinted and unimprinted polymers. Evidence was presented that the CAF-imprinted polymer having 4-Py moieties highly recognize CAF molecules. Also, the selectivity of the CAF-imprinted polymers was investigated using CAF analogous molecules.
Keywords: Molecularly imprinting; Phase inversion method; Quartz-crystal microbalance; Molecular recognition;
A new concept for the construction of an artificial dehydrogenase for fructosylamine compounds and its application for an amperometric fructosylamine sensor by Koji Sode; Yuka Takahashi; Shigenori Ohta; Wakako Tsugawa; Tomohiko Yamazaki (151-156).
For the construction of an artificial dehydrogenase and an artificial dehydrogenase based sensor, the potential application of polyvinylimidazole (PVI) was investigated as the catalyst for the fructosylvaline (Fru-val) oxidation, a model compound for the glycated hemoglobin. The presence of PVI catalyzed the oxidation of Fru-val in the presence of an electron acceptor. A colorimetric determination of Fru-val was possible with the detection range from 50 μM to 10 mM utilizing PVI as the catalyst. An amperometric sensor for Fru-val was constructed using carbon paste electrode immobilized PVI. Using the sensor system, Fru-val could be measured from 20 μM to 0.7 mM. These results indicated the further possible application of PVI as the catalyst for fructosylamine compounds as well as various glycated proteins including glycated hemoglobin.
Keywords: Glycated hemoglobin; Fructosylamine; Fructosylamine oxidase; Polyvinylimidazole; Artificial dehydrogenase; Amperometric sensor;
Impedometric herbicide chemosensors based on molecularly imprinted polymers by Tanya Panasyuk-Delaney; Vladimir M Mirsky; Mathias Ulbricht; Otto S Wolfbeis (157-162).
The technique of grafting polymerization has been used for preparation of thin films of molecularly imprinting polymers on the surface of polypropylene membranes and on hydrophobized gold electrodes. The herbicide desmetryn was used as a template. The solid supports used were hydrophobic, while the polymer was hydrophilic. The adsorbed layer of benzophenone, irradiated by UV-light, initiated a radical polymerization near the surface. Polymer films were characterized by weighing, contact angle measurements and impedance spectroscopy. The electrodes coated with the molecularly imprinted polymers displayed fairly specific binding of desmetryn, as detected by the decrease in the capacitance of the electrode. Only small capacitive effects were observed on addition of terbumeton or atrazine, while metribuzine displayed capacitance decrease similar to desmetryn.
Keywords: Molecular imprinting; Capacitive sensor; Chemical sensor; Grafting polymerization; Photopolymerization;
Fabrication of molecularly imprinted polymer microstructures by Mingdi Yan; Alika Kapua (163-167).
We report the combination of soft lithography and molecular imprinting for the fabrication of molecularly imprinted polymer (MIP) microstructures on silicon wafers. Proof-of-concept experiments were carried out using 2,4-dichlorophenoxyacetic (2,4-D) acid as the template molecule. The MIP microstructures were fabricated by employing micromolding in capillaries (MIMIC) and a soft poly(dimethylsiloxane) (PDMS) stamp containing 20 μm feature size relief structures. MIP micromonoliths with a cross-sectional dimension of 20 μm×20 μm were isolated and used directly after extraction of the template. The binding characteristics of these imprinted polymer micromonoliths were studied using radioligand binding analysis.
Keywords: Molecular imprinting; Micromolding in capillaries; Micromonoliths; 2,4-Dichlorophenoxyacetic acid;
Matrix-induced modification of imprinting effect for Cu2+ adsorption in hybrid silica matrices by Rajendra D Makote; Sheng Dai (169-175).
Matrix-induced modification of the imprinting effect for Cu2+ adsorption in sol–gel sorbents has been investigated. This investigation shows that the hydrophobicity of the sol–gel matrices enhances the imprinting effect and selectivity of the sorbents toward target ions. Modification of the matrix hydrophobicity can be easily achieved by copolymerizing tetramethylorthosilicate and methyltrimethoxysilane or phenyltrimethoxysilane.
Keywords: Sol–gel sorbents; Polymer; Matrix-induced modification;
Surface-imprinted silica particles: the effects of added organosilanes on catalytic activity by Michael A Markowitz; Paul R Kust; John Klaehn; Gang Deng; Bruce P Gaber (177-185).
Silicate surfaces were molecularly imprinted with a surfactant derivative of an α-chymotrypsin transition state analog (TSA) during particle formation in a water-in-oil microemulsion. The organosilanes N-(3-aminoethylaminomethyl)-phenyltrimethoxysilane (PEDA), carboxyethylsilanetriol (CTES), and N-(3-triethoxysilylpropyl)-4,5-dihydroimidazole (IPTES) were added along with tetraethoxysilane (TEOS) to imprint the chemical functionality of the imprint molecule. Surfaces imprinted with N-α-decyl-d-phenylalanine-2-aminopyridine enantioselectively catalyzed the hydrolysis of benzoyl-l-arginine-p-nitroanilide (l-BAPNA). No hydrolysis of d-BAPNA was observed. The catalytic activity of surface-imprinted particles formed with TEOS and PEDA was significantly greater than that of surface-imprinted particles formed with TEOS and IPTES. Particles formed with added 10 mol% (total silica) of PEDA hydrolyzed dl-BAPNA at a rate equivalent to that of surface-imprinted particles formed with the mixture of 5 wt% (total silica) of PEDA, CTES, and IPTES suggesting a cooperative effect with the organosilane mixture that promoted catalytic activity.
Keywords: Surface-imprinted silica particles; Organosilanes; Enantioselectivity; Catalysis; Ceramic;
Molecular imprinting on microgel spheres by Lei Ye; Peter A.G Cormack; Klaus Mosbach (187-196).
Molecularly imprinted polymers have been prepared in various configurations including, for example, polymer beads, monoliths and membranes for different applications. The most common form of imprinted polymer is, however, still the irregularly shaped particle obtained by grinding the traditional, macroporous polymer monolith. We herein present a novel and efficient approach leading to imprinted microspheres, i.e. microgels bearing binding sites specific to target molecules. Imprinted microgels are proposed to be the basic components in previously reported, molecularly imprinted, cross-linked polymers, although the polymers themselves may exist in different forms depending on the preparation method utilised. Chemical modification of the molecularly imprinted microspheres introduces additional functionalities that may be used to couple sensing elements in various assay formats, or for the immobilisation of the imprinted microspheres on various transducers towards the development of biomimetic sensors.
Keywords: Molecular imprinting; Microgel; Microspheres; Precipitation polymerisation; 17β-estradiol; Theophylline;
Chemical reaction engineering using molecularly imprinted polymeric catalysts by Oliver Brüggemann (197-207).
Enzymes play an important role as highly specific catalysts in biotechnology [J. Biotechnol. 66 (1998) 3; Hydrolases in Organic Synthesis, Wiley, New York, 1999] as well as in chemical reaction engineering [J. Biotechnol. 59 (1997) 11; Trends Biotechnol. 13 (7) (1995) 253]. However, the drawbacks of these biomaterials are poor durability and relatively high costs of production. Thus, the technique of molecular imprinting [Bio/Technology 14 (1996) 163; Angew. Chem. Int. Ed. Engl. 34 (1995) 1812; Anal. Commun. 36 (9) (1999) 327; J. Chromatogr. 781 (1997) 43] can be applied for generating much more stable polymeric mimics of biological enzymes. For this purpose, a stable transition state analogue (TSA) of a selected reaction must be chosen as template [Macromol. Rapid Commun. 19 (1998) 671; Curr. Opin. Chem. Biol. 3 (1999) 759]. The imprint of the TSA acts like a catalytically active centre. This binding site shows its catalytic effect by reducing the activation energy of the specific reaction.In the work presented here, molecularly imprinted catalytically active polymers have been generated and investigated in chemical reaction engineering processes, using batch reactors and continuously driven reactors equipped with these polymers. Parameters such as temperature, concentration of substrate or volume flow have been varied, reaction rates measured and kinetic data recorded. Based on this information, the rate constants of the reaction have been calculated, as well as the relative catalytic effects. It is demonstrated that imprinted polymer catalysts show obvious catalytic properties and can be used as an alternative for traditional catalyst materials.
Keywords: Molecular imprinting; Transition state analogue; Catalyst; Chemical reaction engineering;
Towards the use of molecularly imprinted polymers containing imidazoles and bivalent metal complexes for the detection and degradation of organophosphotriester pesticides by Tomohiko Yamazaki; Ecevit Yilmaz; Klaus Mosbach; Koji Sode (209-214).
For the preparation of an enzyme mimic for phosphotriester hydrolysis, we have introduced catalytic groups in a polymer, mimicking the structure of the catalytic center of the enzyme phosphotriesterase. The polymers containing Co2+–imidazole complexes show a hydrolyric activity which was 20 times higher than polymers containing only imidazole or a solution containing only cobalt ions. Additionally, a molecularly imprinted polymer that was synthesized using a paraoxon analogue as template showed higher paraoxon hydrolysis activity than a control polymer prepared in the same way but without the template molecule.
Keywords: Molecularly imprinted polymers; Imidazoles; Organophosphotriester pesticides;