Journal of Chromatography B (v.804, #1)
Molecularly imprinted polymers in separation science by Lars I. Andersson; Ian A. Nicholls (1).
Molecularly imprinted polymer formats for capillary electrochromatography by Jakob Nilsson; Peter Spégel; Staffan Nilsson (3-12).
The research aimed towards the adaptation of molecularly imprinted polymers (MIPs) to the capillary format and the use of these highly selective matrices for capillary electrochromatography (CEC) is reviewed in this article. The MIP is prepared by incorporation of a template molecule into a polymerization protocol. After polymerization and extraction of the template from the resulting polymer a highly selective material with recognition cavities complementary to the template in size, shape and chemical functionality is obtained. MIPs have been used as recognition elements in several different analytical techniques. In combination with CEC a novel separation system with a unique selectivity towards a predetermined target (the template) is achieved. The merge of molecular imprinting technology (MIT) and CEC have introduced several interesting polymer formats, due to the adaptation of the MIP to the miniaturized capillary format. The polymer formats can be classified according to their preparation protocols and appearance into three conceptually different categories, i.e. the monolith, the coating and the nanoparticles. The preparation protocols, characteristics and applications of these formats will be discussed.
Keywords: Reviews; Molecularly imprinted polymers;
Short columns with molecularly imprinted monolithic stationary phases for rapid separation of diastereomers and enantiomers by Xiaodong Huang; Feng Qin; Xiaoming Chen; Yueqi Liu; Hanfa Zou (13-18).
Three molecularly imprinted monolithic columns with different length but almost identical column volume had been prepared. It was observed that the separation factors of diastereomers and enantiomers were almost unaffected by column length. However, the short column with dimension of 38 mm×8 mm i.d. showed much lower resistance to flow rate so that it could be operated at much higher flow rates. By combining stepwise gradient elution with elevated flow rate, the diastereomers of cinchonine and cinchonidine and the enantiomers of Cbz-DL-Trp and Fmoc-DL-Trp were successfully separated within 3 min on the short column with dimension of 38 mm×8 mm i.d.. Based on the above results, a cinchonine imprinted monolithic disk with dimension of 10 mm×16 mm i.d. was further developed. The SEM image and the pore size distribution profile showed that large flow-through pores are present on the prepared monolith, which allowed mobile phase to flow through the disk with very low resistance. Chromatographic performances on the monolithic disk were almost unchanged compared with the long columns. A rapid separation of cinchonine and cinchonidine was achieved in 2.5 min at the flow rate of 9.0 ml/min. Furthermore, it was observed that there was almost no effect of the flow rate on the dynamic binding capacity at high flow rates. In addition, the effect of the loading concentration of analytes on the dynamic binding capacity, namely adsorption isotherm, was also investigated. A non-linear adsorption isotherm of cinchonine was observed on the molecularly imprinted monolith with cinchonine as template, which might be a main reason to result in the peak tailing of template molecule.
Keywords: Enantiomer separation; Stationary phases, LC; Molecularly imprinted monoliths; Cinchonine; Cinchonidine;
Retentivity and enantioselectivity of uniformly sized molecularly imprinted polymers for d-chlorpheniramine and -brompheniramine in hydro-organic mobile phases by Jun Haginaka; Chino Kagawa (19-24).
Uniformly sized molecularly imprinted polymers (MIPs) for d-chlorpheniramine (CP) and -brompheniramine (BP) have been prepared by a multi-step swelling and polymerization method using methacrylic acid (MAA) or 2-(trifluoromethyl)acrylic acid (TFMAA) and ethylene glycol dimethacrylate (EDMA) as a functional monomer and cross-linker, respectively. The retentive and enantioselective properties of CP, BP and their structurally related compounds on the MIPs were evaluated using hydro-organic mobile phases. CP and BP enantiomers were retained the most as a monovalent cation on MAA-co-EDMA polymers and a divalent cation on TFMAA-co-EDMA polymers. Ion exchange and hydrophobic interactions could mainly work for the retention and enantioseparation of CP and BP on both MAA-co-EDMA and TFMAA-co-EDMA polymers in hydro-organic mobile phases. Though the respective MIPs gave the highest enantioselectivity for the template molecule, cross-reactivity for CP and BP was observed with them.
Keywords: Enantiomer separation; Molecularly imprinted polymers; Chlorpheniramine; Brompheniramine;
Separation and determination of astaxanthin from microalgal and yeast samples by molecularly imprinted microspheres by Jia-Ping Lai; Yue Jiang; Xi-Wen He; Jun-Chao Huang; Feng Chen (25-30).
In this work, molecularly imprinted microspheres (MIMs) were synthesized by aqueous microsuspension polymerization using astaxanthin (3,3′-dihydroxy-β,β′-carotene-4,4′-dione) as imprinting molecule. The MIMs obtained were subsequently packed into the stainless steel column and the chromatographic characterization of the column was investigated. The effects of pH and composition of the mobile phase on the retention factor (k′) were investigated in detail. The mixture of methanol and dichloromethane (DCM) (8:2, v/v) was used as mobile phase A while the mixture of methanol and water (5:5, v/v) as mobile phase B. The separation of astaxanthin and zeaxanthin (3,3′-dihydroxyl-β-carotene) was obtained when the concentration of mobile phase B was higher than 30% (v/v) due to their strong lipophilicity. The method developed was successfully applied to separate astaxanthin in the saponified samples of the microalga Haematococcus pluvialis and the yeast Phaffia rhodozyma. The recovery of adding 40 mg astaxanthin to 1.0 g microalgal sample was 95.5% with an R.S.D. (n=5) of 5.3%. The results of determination of astaxanthin in the microalga and the yeast were 3.7% (R.S.D.=1.5%, n=9) and 0.041% (R.S.D.=7.3%, n=9), respectively.
Keywords: Molecularly imprinted microspheres; Astaxanthin;
Multivariate analysis of the selectivity for a pentachlorophenol-imprinted polymer by C. Baggiani; L. Anfossi; C. Giovannoli; C. Tozzi (31-41).
A pentachlorophenol (PCP)-imprinted polymer (MIP) was obtained by thermal polymerization of a mixture of template, 4-vinylpyridine and ethylene glycol dimethacrylate with molar ratio 1+3+27, using as porogenic solvent methanol–water (3+1 (v/v)). The polymer was packed in an HPLC column and selectivity towards 52 PCP-related phenols (22-chloro-, 21-alkyl-, 4-aryl-, 3-methoxy- and 6-polyphenols) was measured using acetonitrile–acetic acid (99+1 (v/v)) as mobile phase. The same was made for a reference polymer obtained without pentachlorophenol (NIP). The molecular recognition properties of the imprinted polymer were expressed in terms of selectivity index (SI), calculated for each phenol as k NIP/k MIP. Sixteen molecular descriptors were calculated for each molecule: qO, the partial charge of the phenolic oxygen atom; qH, the partial charge of the phenolic hydrogen atom; Δq, the absolute value of the difference qO − qH; HOMO, the highest occupied molecular orbital; LUMO, the lowest unoccupied molecular orbital; Δorb, absolute value of the difference HOMO − LUMO; μ 2, the square of total dipole moment; MW, the molecular weight; SAS, the solvent-accessible molecular surface area; hSAS, the hydrophobic solvent-accessible molecular surface area; Svdw, the van der Waals molecular surface area; hSvdw, the hydrophobic part of Svdw; MOv, the molecular ovality; RG, the radius of gyration; log P, the logarithm of n-octanol–water partition coefficient; pK, the phenolic dissociation constant. Correlations between selectivity index and these descriptors were searched utilizing multivariate principal component analysis (PCA). The multivariate model obtained by regression on the principal components correlate collectively several of the calculated descriptors with the polymer selectivity. The magnitude of the model’s parameters shows that selectivity is strongly influenced by molecular descriptors having structural character, such as MW, hSvdw and log P, while the effect of molecular descriptors having electronic character, such as qO and pK, is much less marked.
Keywords: Multivariate analysis; Selectivity; Pentachlorophenol; Molecularly imprinted polymers;
Synthesis and evaluation of molecularly imprinted polymers for enalapril and lisinopril, two synthetic peptide anti-hypertensive drugs by Georgios Theodoridis; Georgia Konsta; Christina Bagia (43-51).
Molecularly imprinted polymers (MIPs) for the recognition of enalapril and lisinopril were prepared using 4-vinylpyridine as the functional monomer. Following thermal polymerisation the resulting materials were crushed, ground and sieved. First generation MIPs were produced in protic polar porogenic solvents (mixture of methanol (MeOH) and acetonitrile (ACN)). These MIPs were used and validated as sorbents for solid phase extraction and binding assays. Second generation MIPs were produced with polar aprotic porogenic solvent (DMSO). These polymers were packed in HPLC columns in order to investigate their molecular recognition properties in a dynamic mode. The study of the mobile phase composition included two major parameters: organic modifier content and pH value. Retention factors illustrate selective binding of the template from the imprinted polymers, compared to structurally related compounds.
Keywords: Molecularly imprinted polymers; Enalapril; Lisinopril;
Influence of polymerization temperature on the molecular recognition of imprinted polymers by Yan Lu; Chenxi Li; Xudong Wang; Pingchuan Sun; Xianghua Xing (53-59).
This paper aimed at investigating the influence of polymerization temperature on the molecular recognition of molecularly imprinted polymers (MIPs) based on multiple non-covalent interactions. 3-l-Phenylalanylaminopyridine (3-l-PheNHPy) imprinted polymers were prepared using azobisnitriles as either thermal initiators or photoinitiators at various temperatures of 10, 40 and 60 °C, respectively. These polymers were subsequently evaluated in the high-performance liquid chromatographic (HPLC) mode for enantioselectivity. An unexpected result shows that polymer prepared at 40 °C has the highest enantioselectivity, but not the polymer prepared at lower temperature of 10 °C. Further, the effect of elution temperature and sample load on the selectivity of polymers was investigated in detail. In order to get a better understanding of the “exception”, the influence of polymerization temperature on the polymerization extent and polymer morphology was studied by FT-IR spectrum test, cross-polarization magic angle spinning (CP-MAS) 13 C NMR spectra experiment and pore analysis. Based on these results we attribute this “exception” to that there is a tradeoff between the extent of polymerization and stabilization of the template–functional monomer complexes. And an optimal polymerization temperature can be found for each combination of template and monomer.
Keywords: Polymerization temperature; Molecular recognition; Molecular imprinting polymers;
Separation and screening of compounds of biological origin using molecularly imprinted polymers by Xiaojie Xu; Lili Zhu; Lirong Chen (61-69).
Molecularly imprinted polymers (MIPs) represent a new class of materials possessing high selectivity and affinity for the target molecule. Since their discovery in 1972, molecularly imprinted polymers have attracted considerable interest from bio- and chemical laboratories to pharmaceutical institutes. They have been utilized as sensors, catalysts, sorbents for solid-phase extraction, stationary phase for liquid chromatography, mimics of enzymes, receptors and antibodies. Among which, the application of molecularly imprinted polymers for molecular recognition-based separation and screening of compounds has undergone rapid extension and received much attention in recent years. This article mainly focuses on the separation and screening of certain pharmacophoric compounds of interests from biological origin using molecular imprinting technology. Examples of extraction and recognition of active components as anti-tumors or anti-Hepatitis C virus inhibitors from Chinese traditional herbs using molecularly imprinting technology are particularized in this article. Comparison between the screening effect based on MIPs and that based on antibodies is also represented. Consequently the merits and demerits of these two technologies are highlighted.
Keywords: Reviews; Screening; Molecularly imprinted polymers;
Molecularly imprinted polymers for the determination of a pharmaceutical development compound in plasma using 96-well MISPE technology by C Chassaing; J Stokes; R.F Venn; F Lanza; B Sellergren; A Holmberg; C Berggren (71-81).
The use of molecularly imprinted polymers (MIPs) as sorbents for the solid phase extraction (SPE) of a pharmaceutical compound in development, prior to quantitative analysis was investigated. Three MIPs were synthesised using a structural analogue as the template molecule. Each polymer was prepared with different monomers and porogens. The MIPs were then tested for their performance both in organic and aqueous environments, the final aim being to load plasma directly onto the polymers. At an early development stage, there is a limited amount of compound available. Due to this limitation, reducing the amount of template required for imprinting was investigated. A MIP capable of extracting the analyte directly from plasma was produced. The specificity of the polymer allowed the method to be validated at a lower sensitivity than a more conventional SPE assay. For the first time, MIPs were packed into 96-well blocks enabling high throughput analysis. The analytical method was fully validated for imprecision and inaccuracy down to 4 ng/ml in plasma.
Keywords: Molecularly imprinted polymers;
Characterisation and quality assessment of binding sites on a propazine-imprinted polymer prepared by precipitation polymerisation by C. Cacho; E. Turiel; A. Martin-Esteban; C. Pérez-Conde; C. Cámara (83).
In this paper, the Langmuir–Freundlich isotherm (LF) is used to characterise a propazine-imprinted polymer obtained by precipitation polymerisation (MIP-P). Different rebinding studies were carried out allowing to explain the different interactions taking place between the molecularly imprinted polymer and six triazinic herbicides (desisopropylatrazine, desethylatrazine, simazine, atrazine, propazine and prometryn). The LF fitting parameters obtained (total number of binding sites, heterogeneity index and mean binding affinity) were compared to those obtained in a previous work for a propazine-imprinted polymer prepared by bulk polymerisation (MIP-B). From that study, it was concluded that precipitation polymerisation yielded polymers with a more homogeneous binding site distribution and higher affinity constants.
Keywords: Precipitation polymerisation; Quality assessment; Molecular imprinting; Propazine;
Evaluation of MISPE for the multi-residue extraction of β-agonists from calves urine by Christine Widstrand; Fredrik Larsson; Maurizio Fiori; Cinzia Civitareale; Sabrina Mirante; Gianfranco Brambilla (85-91).
Methods based on molecular recognition mechanisms for the clean-up of veterinary drugs and their residues, such as immuno-, receptor- and acceptor-affinity and molecularly imprinted polymers (MIPs), have been described as selective tools to improve the selectivity and the reliability of analytical results. In this work, we tested the extraction recovery performances of a MISPE column, designed for multi-residual clean-up of β-agonists. For this purpose, 18 different samples of calf urine were spiked at 0.25, 0.50 and 1.00 ppb with pooled standard solutions of clenbuterol (Clen), tulobuterol (Tolu), isoxsuprine (Isox), brombuterol (Brom), mapenterol (Mape) and ractopamine (Racto) and analysed on two independent analytical sessions, on a LC–MS/MS ion trap detector. Averaged recoveries, constant for each molecule considered, were 64.6% for Racto, 63.0% for Salm, 59.9% for Form, 54.7% for Brom, 52.0% for Clen, 41.8% for Mape, 38.6% for Tolu and 34.5% for Isox, respectively. Reproducibility studies gave a CV<11% at the 0.25 ppb level. The decision limit for the identification of the target drugs ranged from 0.01 ppb for mapenterol to 0.19 ppb for salmeterol, when considering one precursor, and two product ions as identification points. Such findings indicate that the choice of the appropriate molecule as template in the MIP preparation is the critical factor to guarantee a reliable analytical multi-residue approach for β-agonists, despite the structural differences among molecules exploiting almost the same pharmacological effect.
Keywords: Molecular imprinting; β-Agonists;
Retention mechanism of analytes in the solid-phase extraction process using molecularly imprinted polymers by F Chapuis; V Pichon; F Lanza; B Sellergren; M.-C Hennion (93-101).
Two molecularly imprinted polymers (MIPs), prepared in dichloromethane with terbutylazine and ametryn as template molecules, were evaluated for the selective extraction of triazines from complex matrices. Various parameters affecting extraction recoveries on MIPs were studied in order to obtain an optimized extraction procedure allowing to reduce non-specific interactions. In order to test the selectivity of the MIPs, the same procedure was applied to the extraction of compounds possessing the same polarity and size as the triazines. By means of molecular modeling, the effects of the electric charge distribution and of the size of the molecules on the retention mechanism were studied. The value of capacity for terbutylazine MIP was also measured. At last, the high selectivity resulting from the use of MIPs was clearly demonstrated by their applications to the clean-up of grape juice and soil extracts spiked with triazines. In addition, the soil extract was cleaned-up by immunoextraction allowing the comparison of both approaches in terms of selectivity.
Keywords: Retention mechanism; Molecularly imprinted polymers; Triazines;
Molecularly imprinted polymer-assisted sample clean-up of ochratoxin A from red wine: merits and limitations by Norbert M. Maier; Gerhard Buttinger; Silvia Welhartizki; Elena Gavioli; Wolfgang Lindner (103-111).
A new analytical method for the determination of the carcinogenic mycotoxin ochratoxin A (OTA) in red wines has been developed involving a two-dimensional solid-phase extraction (SPE) clean-up protocol on C18-silica and a target-selective molecularly imprinted polymer (MIP). Prior removal of the interfering acidic matrix compounds by C18 solid-phase extraction was crucial for a successful clean-up as direct sample loading onto the MIP led to poor recoveries. The combined solid-phase extraction protocol afforded extracts suitable for sensitive ochratoxin A quantification by HPLC-fluorescence detection. Preliminary validation of the method performance with spiked (0.033–1.0 ng OTA/ml) and commercial red wines provided recoveries >90% and R.S.D.r<10%, with limit of detection (LOD) and limit of quantification (LOQ) of 0.01 and 0.033 ng/ml. However, a similarly favorable performance characteristics was observed in control experiments in which the MIP was replaced by the corresponding non-imprinted polymer (NIP). These findings provide evidence that under the employed experimental conditions specific analyte binding to imprinted binding sites plays a minor role in selective OTA retention. In the framework of this study, other problems inherent to MIP-based solid-phase extraction have been addressed. These include the reproducible preparation of MIP materials with consistent molecular recognition characteristics, the potential for repeated use of MIP, unfavorable polymer swelling in application-relevant solvents, potential sample contamination by template bleeding, and slow analyte binding kinetics.
Keywords: Mycotoxin analysis; Ochratoxin A; Molecularly imprinted polymers;
Membrane separations using molecularly imprinted polymers by Mathias Ulbricht (113-125).
This review presents an overview on the promising field of molecularly imprinted membranes (MIM). The focus is onto the separation of molecules in liquid mixtures via membrane transport selectivity. First, the status of synthetic membranes and membrane separation technology is briefly summarized, emphasizing the need for novel membranes with higher selectivities. Innovative principles for the preparation of membranes with improved or novel functionality include self-assembly or supramolecular aggregation as well as the use of templates. Based on a detailed analysis of the literature, the main established preparation methods for MIM are outlined: simultaneous membrane formation and imprinting, or preparation of imprinted composite membranes. Then, the separation capability of MIM is discussed for two different types, as a function of their barrier structure. Microporous MIM can continuously separate mixtures based on facilitated diffusion of the template, or they can change their permeability in the presence of the template (“gate effect”). Macroporous MIM can be developed towards molecule-specific membrane adsorbers. Emerging further combinations of molecularly imprinted polymers (MIPs), especially MIP nanoparticles or microgels, with membranes and membrane processes are briefly outlined as well. Finally, the application potential for advanced MIM separation technologies is summarized.
Keywords: Reviews; Membrane separations; Molecularly imprinted polymers;
Molecularly imprinted copolymer membranes functionalized by phase inversion imprinting for uracil recognition and permselective binding by Hong Ying Wang; Shao Ling Xia; Hong Sun; Yu Kun Liu; Shao Kui Cao; Takaomi Kobayashi (127-134).
Uracil (URA) was selected as a template for preparing molecularly imprinted membranes of poly(acrylonitrile-co-methylacrylic acid) [P(AN-co-MAA)] using the phase inversion technique. This study used Fourier transform infra-red (FT-IR) and 1 H nuclear magnetic resonance (NMR) spectroscopic studies to characterize the polymer-template interaction and scanning electron microscopy (SEM) and atomic force microscopy (AFM) for morphology of the URA imprinted membrane. Resultant membranes had typical ultrafiltration structure with porous morphology and showed a permeation flux of 3.5×10−5 m3/(m2 s) for 32 μM URA aqueous solution. Permselective binding to the target molecule was observed in permeation experiments with 7.9 μmol/g binding capacity of URA. Binding selectivity was discussed for URA and its analogs, dimethyluracil (DMURA) and caffeine (CAF), with 0.6 and 0.8 μmol/g binding capacity, respectively.
Keywords: Molecular imprinting; Membranes; Phase inversion; Permselective binding; Uracil;
Screening combinatorial libraries of molecularly imprinted polymer films casted on membranes in single-use membrane modules by Faissal-Ali El-Toufaili; Aleksandra Visnjevski; Oliver Brüggemann (135-139).
A new and fast technique for screening combinatorial libraries of molecularly imprinted polymers is presented. The procedure is based on commercially available membrane modules which are rinsed with pre-polymerization imprinting mixtures. After the in situ polymerization and generation of MIP films on the PTFE membranes within the modules, the membranes are evaluated in terms of affinity towards the target molecule (template) R-(−)-phenylbutyric acid. Therefore, after template extraction from the freshly produced membranes a solution of this target molecule is flushed through the module. By analyzing the remaining analyte concentration in the permeate, the amount of analyte adsorbed on the membrane can be calculated and related to specific interactions with the molecular imprints. By this means, optimized recipes in terms of cross-linker to template ratios could be obtained in combination with the optimal porogen, when screening p-divinylbenzene or ethylene glycol dimethacrylate as cross-linker and porogens like acetonitrile, dimethylsulfoxide and methanol.
Keywords: Combinatorial libraries; Single-use membrane modules; Molecularly imprinted polymers;
Characterization of the heterogeneous binding site affinity distributions in molecularly imprinted polymers by Robert J. Umpleby; Sarah C. Baxter; Andrew M. Rampey; Gregory T. Rushton; Yizhao Chen; Ken D. Shimizu (141-149).
Molecularly imprinted polymers (MIPs) are polymers that can be tailored with affinity and selectivity for a molecule of interest. Offsetting the low cost and ease of preparation of MIPs is the presence of binding sites that vary widely in affinity and selectivity. Presented is a review of methods that take into account binding site heterogeneity when calculating the binding properties of MIPs. These include the bi-Langmuir, Freundlich, and Langmuir–Freundlich binding models. These methods yield a measure of heterogeneity in the form of binding site affinity distributions and the heterogeneity index. Recent developments have made these methods surprisingly easy to use while also yielding more accurate measures of the binding properties of MIPs. These have allowed for easier comparison and optimization of MIPs. Heterogeneous binding models have also led to a better understanding of the imprinting process and of the advantages and limitations of MIPs in chromatographic and sensor applications.
Keywords: Reviews; Binding site heterogeneity; Affinity distribution; Molecularly imprinted polymers;
Molecularly imprinted polymers in pseudoimmunoassay by Richard J Ansell (151-165).
Immunoassays are a class of analytical techniques based on the selective affinity of a biological antibody for its antigen. Competitive binding assays, of which the radioimmunoassay (RIA) was the first example, are based on the competition between analyte and a labelled probe for a limited number of binding sites. Molecularly imprinted polymers (MIPs) have been shown to be suitable replacements for biological antibodies in such techniques. Molecularly imprinted sorbent assays (MIAs) similar to RIA have been developed for a range of analytes of clinical and environmental interest. Limits of detection and selectivities of such assays are often similar to those using biological antibodies. Some assays have been used for measurements directly in biological fluids. The field is reviewed and it is shown that some perceived disadvantages of MIPs do not hinder their application in competitive binding assays: many MIAs have been demonstrated in aqueous solvents, and it has been shown that the quantity of template required to prepare imprinted polymers can be drastically reduced, and that binding site heterogeneity is not a problem as long as the sites which bind the probe most strongly are selective. Finally, recent developments including assays in microtitre plates, the use of enzyme-labelled probes, flow-injection assays and a scintillation proximity MIA are discussed.
Keywords: Reviews; Molecularly imprinted polymers;
Binding assays with molecularly imprinted polymers—why do they work? by Tı́mea Pap; George Horvai (167-172).
The design of homologous displacement ligand binding assays based on molecularly imprinted polymers (MIP) is discussed in terms of the MIP adsorption isotherm. It is shown that only MIPs having a binding isotherm with varying slope are suitable for the assay, but there is no need to interpret the isotherm in terms of site affinity and population. One can calculate the calibration plot of the binding assay from the isotherm and vice versa.
Keywords: Binding assays; Molecularly imprinted polymers;
Molecularly imprinted polymers: synthesis and characterisation by Peter A.G Cormack; Amaia Zurutuza Elorza (173-182).
This short review aims to present, in clear English, a summary of the principal synthetic considerations pertaining to good practice in the polymerisation aspects of molecular imprinting, and is primarily aimed at researchers familiar with molecular imprinting methods but with little or no prior experience in polymer synthesis. It is our hope that this will facilitate researchers to plan their own syntheses of molecular imprints in a more logical and structured fashion, and to begin to appreciate the limitations of the present synthetic approaches in this molecularly complex area, as well as the scope for rationally designing improved imprinted materials in the future.
Keywords: Reviews; Synthesis; Characterisation; Molecularly imprinted polymers;
Designing selective sites in templated polymers utilizing coordinative bonds by Susanne Striegler (183-195).
This review gives a survey over recent achievements on the design of selective sites in templated polymers. Particularly, coordinative bonds as driving force for the interaction between a substrate and a templated polymer are discussed. Recent achievements on the selective recognition of larger molecules, such as dipeptides and disaccharides, are highlighted that promise a fast development on biomolecule templated material towards enzyme-like catalysis in the up-coming years. Additionally, the achievements on the incorporation of catalytic centers based on transition metal complexes are summarized.
Keywords: Reviews; Selective sites; Coordinative bonds; Templated polymers;
Covalent molecular imprinting of bisphenol A using its diesters followed by the reductive cleavage with LiAlH4 by Takashi Ikegami; Woo-Sang Lee; Hiroyuki Nariai; Toshifumi Takeuchi (197-201).
Bisphenol A (BPA) recognition materials were synthesized by a covalent imprinting technique using BPA–dimethacrylate or BPA–diacrylate as the template monomer. Binding sites in the polymers consisted of two hydroxyl groups that are generated by reducing the ester bonds of the template monomer with lithium aluminum hydride. The polymers strongly adsorbed BPA and structurally related compounds, however, other endocrine disruptors were hardly adsorbed. The BPA–dimethacrylate-based polymer interacted with the samples more strongly than the BPA–diacrylate-based polymer.
Keywords: Molecular imprinting; Reductive cleavage; Bisphenol A;
Performance analysis of molecularly imprinted polymers for carboxylate and aminophosphate templates using commercially available basic functional monomers by Ryan L. Simon; David A. Spivak (203-209).
A survey of commercially available amine-based monomers for binding and selectivity of carboxylate and phosphonic acid templates has revealed that the best selectivity is found for the pyridine-based monomers, while the highest affinity was found for 2-(dimethylamino)ethyl methacrylate (2-DEMA, 1). In fact, a more general finding is that selectivity is higher for aromatic amine-based monomers even though affinity remains higher for aliphatic amine-based monomers. An attempt to combine the optimal properties of these two classes of amine monomers, i.e. 2-vinylpyridine (2-VPY, 2), and 2-DEMA by using both simultaneously in a single imprinted polymer resulted in an MIP whose properties were dominated by the aliphatic amine-based monomer 2-DEMA. A controversy between the two commercially available vinylpyridine monomers, 2-VPY and 4-vinylpyridine (4-VPY, 3), was investigated, revealing that neither monomer is generally better for molecular imprinting; rather, the choice of 2-VPY or 4-VPY is template specific (although the preponderance of data tends to frequently favor 4-VPY). Phosphonic acid templates proved to be less successful as templates for molecular imprinting versus carboxylate functionalized templates, although binding was obtained and shown to be controllable via an ion-exchange process.
Keywords: Carboxylate; Aminophosphate; Molecularly imprinted polymers;
Enhanced capacities and selectivities for cholesterol in aqueous media by molecular imprinting: role of novel cross-linkers by M.A Gore; R.N Karmalkar; M.G Kulkarni (211-221).
Molecularly imprinted polymers are being increasingly investigated as selective sorbents. For the recovery of cholesterol from aqueous media, the utility of the molecularly imprinted polymers has been limited by modest capacities and selectivities, especially when compared with alternative adsorbents reported for the binding of bile acids [Macromolecules 34 (2001) 1548]. This paper describes the use of cholesterol conjugated monomers and cross-linkers, which bind to the template cholesterol molecule by hydrophobic interactions. This leads to enhanced capacities and selectivities during the recovery of cholesterol from aqueous media. The templating effect is clearly seen in the enhanced capacity and selectivity in the retention of cholesterol vis-a-vis stigmasterol and testosterone.
Keywords: Molecular imprinting; Cross-linkers; Cholesterol;
Synthetic cinchonidine receptors obtained by cross-linking linear poly(methacrylic acid) derivatives as an alternative molecular imprinting technique by Jun Matsui; Norihito Minamimura; Kenji Nishimoto; Katsuyuki Tamaki; Naoki Sugimoto (223-229).
A molecular imprinting approach to construct synthetic receptors was examined, wherein a linear pre-polymer bearing functional groups for intermolecular interaction with a given molecule is cross-linked in the presence of the molecule as a template, and subsequent removal of the template from the resultant network-polymer is expected to leave a complementary binding site. Poly(methacrylic acid) (PMAA) derivatized with a vinylbenzyl group as a cross-linkable side chain was utilized as the pre-polymer for the molecular imprinting of a model template, (−)-cinchonidine. Selectivity of the imprinted polymer was evaluated by comparing the retentions of the original template, (−)-cinchonidine and its antipode (+)-cinchonine in chromatographic tests, exhibiting a selectivity factor up to 2.4. By assessment of the imprinted polymers in a batch mode, a dissociation constant at 20 °C for (−)-cinchonidine was estimated to be K d=2.35×10−6 M (the number of binding sites: 4.54×10−6 mol/g-dry polymer). The displayed affinity and selectivity appeared comparable to those of an imprinted polymer prepared by a conventional monomer-based protocol, thus showing that the pre-polymer, which can be densely cross-linked, is an alternative imprinter for developing template-selective materials. (−)-Cinchonidine-imprinted polymers were prepared and assessed using the pre-polymers bearing different densities of the vinylbenzyl group and different amounts of the cross-linking agent to examine the appropriate density of the cross-linking side chain that was crucial for developing the high affinity and selectivity of the imprinted polymers.
Keywords: Molecular imprinting; Cinchonidine; Poly(methacrylic acid);
Molecularly imprinted polymers for drug delivery by Carmen Alvarez-Lorenzo; Angel Concheiro (231-245).
Molecular imprinting technology has an enormous potential for creating satisfactory drug dosage forms. Although its application in this field is just at an incipient stage, the use of MIPs in the design of new drug delivery systems (DDS) and devices useful in closely related fields, such as diagnostic sensors, is receiving increasing attention. Examples of MIP-based DDS can be found for the three main approaches developed to control the moment at which delivery should begin and/or the drug release rate, i.e. rate-programmed, activation-modulated, or feedback-regulated drug delivery. The utility of these systems for administering drugs by different routes (e.g. oral, ocular or transdermal) or trapping undesired substances under in vivo conditions is discussed. This review seeks to highlight the more remarkable advantages of the imprinting technique in the development of new efficient DDS as well as pointing out some possibilities to adapt the synthesis procedures to create systems compatible with both the relative instable drug molecules, especially of peptide nature, and the sensitive physiological tissues with which MIP-based DDS would enter into contact when administered. The prospects for future development are also analysed.
Keywords: Drug delivery; Molecularly imprinted polymers;
Assessment of molecularly imprinted sol–gel materials for selective room temperature phosphorescence recognition of nafcillin by A Fernández-González; R Badı́a Laı́ño; M.E Diaz-Garcı́a; L Guardia; A Viale (247-254).
Sol–gel imprinted materials were prepared against nafcillin, a semisynthetic β-lactamic antibiotic employed in the treatment of serious infections caused by penicillinase-producing staphylococci. Two approaches were addressed for preparation of the imprinted materials and the controls: as conventional monoliths, which were ground and sieved to a desired particle size for rebinding analysis, and as films on supporting glass slides. The specific binding sites that are created during the imprinting process are analyzed via selective room temperature phosphorescence (RTP) (sol–gel films) measurements as well as via competitive room temperature phosphorescence ligand assay. Results demonstrated the importance of the physical configuration of the imprinted material for minimizing non-specific binding. The close similarities between the structures of different β-lactamic antibiotics made it possible to interpret the roles of the template structure on specific molecular recognition. In this article, we introduce the use of room temperature phosphorescence as selective transduction method for the template. The imprinted sol–gel films displayed enhanced specific binding characteristics respect to the monolithic sol–gel and can be envisaged for the use as recognition matrices for the screening and rapid selection of antibiotics from a combinatorial library or for the rapid control of nafcillin in biological samples (e.g. milk, serum, urine).
Keywords: Molecularly imprinted sol–gel materials; Phosphorescence recognition; Nafcillin;