Correlated theoretical, spectroscopic and X-ray crystallographic studies of a non-covalent molecularly imprinted polymerisation system

The correlation of the recognition properties of a molecularly imprinted polymer (MIP) with the recognition events in pre-polymerisation mixtures is of central importance to our understanding of the molecular imprinting technique. Using the NSAID naproxen as a model template, we have applied parallel theoretical (molecular dynamics) and practical ((1)H-NMR, X-ray crystallography, HPLC, radioligand binding) methods to examine the nature of template-functional monomer complexation. An effective imprint is achieved, despite the presence of only one site on the template which provides for the formation of effective electrostatic interactions with the functional monomer used, 4-vinylpyridine. This is attributed to the creation of a well-defined receptor site for the acidic terminus of the molecule and complementary van der Waals interactions, as described in preliminary simulations of the pre-polymerisation system, and as confirmed for the resultant MIP by HPLC data. Qualitative agreement is also observed between simulation and proton NMR data examining monomer self-association in the presence and absence of the template. On the basis of the data obtained, the role of a cross-linker appears to be more significant for this system than previously anticipated.     

环丙沙星分子印迹聚合物的合成及识别性能研究

采用分子印迹技术合成了以环丙沙星为印迹分子,以甲基丙烯酸和4-乙烯基吡啶同时为功能单体的分子印迹聚合物。运用平衡结合实验研究了印迹聚合物的吸附特性和选择识别能力。Scatchard分析表明,在所研究的浓度范围内,分子印迹聚合物中形成了两类不同的结合位点。底物选择实验表明,这种聚合物对环丙沙星呈现高的选择结合能力。     

Synthesis, characterization, and ab initio theoretical study of a molecularly imprinted polymer selective for biosensor materials

Despite the complex phenomena involved in encoding template molecule information within stable synthetic polymers to yield selective and efficient molecular recognition processes, molecularly imprinted polymers (MIP) are increasingly finding broad areas of application. Molecular interactions, both during the polymerization of the functional monomers in the presence of the template and during the processes of specific recognition after template removal, are key determinants of an effective MIP. Covalent and noncovalent template imprinting have been employed to achieve specific recognition sites. In the present study, a molecularly imprinted biocompatible polymer, having a high capacity and affinity for the dye template, nickel(II) phthalocyanine tetrasulfonic acid, has been prepared. UV-visible spectroscopy, FTIR spectroscopy, and ICP analysis were used to investigate the aspects of the synthesis, binding capacity, and adsorption kinetics of the system. Poly(allylamine) cross-linked with epichlorohydrin has been used to represent an amino-functional receptor. Binding isotherms and capacities were correlated with the degree of template removal. Kinetic studies of binding allowed diffusion mechanisms to be evaluated for the fine particulate MIP. Ab initio molecular orbital calculations were performed using Hartree-Fock, MP2, and density functional theory methods to determine the most likely mechanisms of molecular imprinting. Suitable theoretical models have been constructed to mimic the interactions between the template molecule and the polymer. Simulation of the vibrational spectra was also undertaken to make meaningful assignments to experimentally determined spectral bands resulting from these template MIP receptor interactions.     

Direct determination of ciprofloxacin by mass spectrometry after a two-step solid-phase extraction using a molecularly imprinted polymer

A molecularly imprinted polymer (MIP) has been prepared for the first time with ciprofloxacin (CIPRO) as the template molecule, via a noncovalent synthetic procedure. Prior to its use as a sorbent in SPE, the MIP was evaluated chromatographically to confirm that it was indeed molecularly imprinted. The MIP was then used to extract CIPRO selectively from urine samples by means of a two-step SPE procedure in which a commercial Oasis cartridge and a molecularly imprinted SPE cartridge were combined in series. This approach allowed the matrix compounds present in the samples to be removed effectively. The urine extracts obtained after this two-step SPE procedure was applied were relatively clean compared to the original samples, and this made it possible to inject directly the extracts into a mass spectrometer and thus quantify CIPRO in urine samples at low levels and reduce the time of analysis.     

Extraction of crocin from saffron (Crocus sativus) using molecularly imprinted polymer solid‐phase extraction

A new molecularly imprinted polymer for extraction of crocin from saffron stigmas was prepared using gentiobiose (a glycoside moiety in crocin structure) as a template. Crocin binding to gentiobiose imprinted polymer (Gent‐MIP) was studied in comparison with a blank nonimprinted polymer in aqueous media. Affinity of the Gent‐MIP for the crocin was more than the nonimprinted polymer at all concentrations. In Scatchard analysis, the number of binding sites in each gram of polymer (maximum binding sites) and dissociation constant of crocin to binding sites were 18.4 μmol/g polymer and 11.2 μM, respectively. The Gent‐MIP was then used as the sorbent in an SPE method for isolation and purification of crocin from methanolic extract of saffron stigmas. The recovery of crocin, safranal and picrocrocin was determined in washing and elution steps. The Gent‐MIP had significantly higher affinity for crocin than other compounds and enabled selective extraction of crocin with a high recovery (84%) from a complex mixture. The results demonstrated the possibility of using a part of a big molecule in preparing a molecularly imprinted polymer with a good selectivity for the main structure.     

Recognition of Staphylococcus enterotoxin via molecularly imprinted beads

The synthesis of molecularly imprinted beads for the recognition of the protein Staphylococcus enterotoxin B (SEB) is described. Two kinds of organic silane (3-aminopropyltrimethoxysilane (APTMS) and octyltrimethoxysilane (OTMS)) were polymerized on the surface of polystyrene microspheres after the SEB template was covalently immobilized by forming imine bonds. The resulting imprinted beads were selective for SEB. The Langmuir adsorption models were applied to describe the equilibrium isotherms. The results showed that an equal class of adsorption was formed in the molecularly imprinted polymer (MIP) with the maximum adsorption capacity of 3.86 mg SEB/g imprinted beads. The MIP has much higher adsorption capacity for SEB than the nonimprinted polymer, and the MIP beads have a higher selectivity for the template molecule.     

Selective extraction of organophosphorus nerve agent degradation products by molecularly imprinted solid-phase extraction

The analysis of alkyl alkylphosphonic acids, the degradation products of V and G nerve agents as VX, Sarin or Soman, is an important task for the verification of compliance to the Chemical Weapons Convention. The detection of these contaminants at low concentration levels is often difficult in complex matrices due to the amount of interfering substances. Molecularly imprinted solid-phase extraction technique should allow a selective extraction of these compounds from complex samples, and thus make their detection easier. Two molecularly imprinted polymers (MIPs) prepared with methacrylic acid (MAA) as monomer and pinacolyl methylphosphonic acid (PMPA) as template molecule were synthesised and tested. The first polymer, MIP A, was prepared with ethylene glycol dimethacrylate (EGDMA) in dichloromethane. The second polymer, MIP B, was synthesised using trimethylolpropane trimethacrylate (TRIM) in acetonitrile. To evaluate the selectivity provided by these MIPs, the retention of the ethyl methylphosphonic acid (EMPA) target molecule was studied in parallel on a non-imprinted polymer (NIP). While MIP A does not show any difference compared to NIP A, a good selectivity was obtained for MIP B. After the optimisation of the extraction process, 60% of EMPA can be removed from the NIP B without affecting the retention on the MIP B. A recovery of extraction of 93% was then obtained on the MIP B. Its capacity was then measured and corresponds to 97 microg of EMPA per gram of MIP. Finally, the selectivity of MIP B was clearly demonstrated by applying it to the clean-up of a soil extract spiked with EMPA.     

Analytical followup of the gamma initiated synthesis of a molecularly imprinted polymer

A molecularly imprinted polymer (MIP) for the template phenytoin has been prepared by gamma initiated copolymerization of methacrylamide and ethylene glycol dimethacrylate. The progress of polymerization was studied by measuring the monomer conversions and the template binding properties of the resulting polymers, respectively. The consumption rate of the two monomers showed different course. There was no difference observed in the polymerization rates of the MIP and the control polymer (NIP). The template binding properties of the MIP and the NIP changed considerably with the progress of the polymerization process and became similar to those of the thermally initiated polymers after full conversion.     

Selective solid-phase extraction of amoxicillin and cephalexin from urine samples using a molecularly imprinted polymer

In this paper we describe, for the first time, a molecularly imprinted polymer (MIP) for the antibiotic amoxicillin (AMX), synthesised by a noncovalent molecular imprinting approach and used to extract AMX selectively from urine samples. The MIP was applied as a molecularly selective sorbent in molecularly imprinted SPE (MISPE) in an off-line mode, where it showed useful cross-selectivity for a structurally related antibiotic, cephalexin (CPX). By using a MISPE protocol, the MIP was able to selectively extract both AMX and CFX from 5 mL of water spiked with 10 mg/L with recoveries of 75 and 78% for AMX and CFX, respectively. When applied to real samples (urine) at clinically relevant concentrations, recoveries from 2 mL of human urine spiked with 20 mg/L decreased slightly to 65 and 63% for AMX and CFX, respectively. To demonstrate further the selectivity of the MIP obtained, a comparison with commercially available SPE cartridges was performed. Improvements in the retention of both AMX and CFX on the MIP were obtained relative to the commercially available cartridges, and the MISPE extracts were considerably cleaner, due to molecularly selective analyte binding by the MIP.     

An optical reflected device using a molecularly imprinted polymer film sensor

A novel and highly selective optical sensor with molecularly imprinted polymer (MIP) film was fabricated and investigated. The optical sensor head employing a medium finesse molecularly imprinted polymer film has been fabricated and characterised. A blank polymer and formaldehyde imprinted polymer were using methacrylic acid as the functional monomer and the ethylene glycol dimethacrylate as a crosslinker. The transduction mechanism is discussed based on the changes of optical intensity of molecularly imprinted polymer film acting as an optical reflected sensor. Template molecules, which diffused into MIP, could cause film density, and refractive index change, and then induce measurable optical reflective intensity shifts. Based on the reflective intensity shifts, an optical reflection detection of formaldehyde was achieved by illuminating MIP with a laser beam. For the same MIP, the reflective intensity shift was proportional to the amount of template molecule. This optical sensor, based on an artificial recognition system, demonstrates long-time stability and resistance to harsh chemical environments. As the research moves forward gradually, we establish the possibilities of quantitative analysis primly, setting the groundwork to the synthesis of the molecular imprinted optical fiber sensor. The techniques show good reproducibility and sensitivity and will be of significant interest to the MIPcommunity.     

A molecularly imprinted polymer as the sorptive phase immobilized in a rotating disk extraction device for the determination of diclofenac and mefenamic acid in wastewater

The microextraction of diclofenac and mefenamic acid from water samples was performed by using rotating disk sorptive extraction (RDSE) with molecularly imprinted polymer (MIP) as the sorptive phase. The MIP was synthesized from the monomer 1-vinylimidazol (VI) together with the cross-linker divinylbenzene (DVB) using diphenylamine as the template molecule. Scanning electron microscopy (SEM) analyses of the MIP revealed clusters of spherical particles having a narrow size distribution, with diameters of approximately 1 μm.     

Recognition characteristics of dibenzofuran by molecularly imprinted polymers made of common polymers

Dibenzofuran (DBF) recognition was studied by a molecularly imprinted polymer (MIP) made of commercially available polymers: polyvinyl chloride (PVC), polysulfone, polystyrene, and polyacrylonitrile. Preparation of MIPs was carried out by phase inversion of the polymer. Respective polymer solutions were coagulated with DBF template in water (non-solvent). In addition, reference polymers without the template were prepared in same manner as unimprinted polymers. After the DBF template was extracted from the solidified polymers by washing with methanol (MeOH), recognition experiments of DBF by the imprinted polymers were carried out for DBF in MeOH solutions. Equilibrium constants for DBF were calculated from saturation binding kinetics. Equilibrium experiment results reveal that recognition was effective for DBF binding to the DBF-imprinted polymer, especially for the imprinted PVC.     

Investigation of enantiomer recognition of molecularly imprinted polymeric monoliths in pressurized capillary electrochromatography screening the amino acids and their derivatives

Molecularly imprinted monolithic columns were prepared for chiral separation of tyrosine and its amino acid derivatives by in situ therm-initiated copolymerization of methacrylic acid, 4-vinylpyridine and ethylene glycol dimethacrylate. The enantiomers were rapidly separated on monolithic columns in less than 10 min by pressurized capillary electrochromatography (pCEC). The influences of several parameters such as the content of cross-linking monomer on the composition of the pre-polymerization mixture were systematically investigated. The influence of the pCEC conditions including the composition of the mobile phase was also optimized to obtain the good enantioseparation. It was found that in addition to molecularly imprinted recognition, chromatographic retention and electrophoretic migration play important roles in the retention and chiral recognition of molecularly imprinted polymer (MIP) columns. The cross-selectivity for similar amino acids and its derivatives were systematical investigated for understanding the recognition mechanism on the MIP monolithic columns. The results indicated that molecularly imprinted polymer recognizes the template molecule by its molecular shape defined binding cavity.     

Synthesis and application of molecularly imprinted polymer on selective solid-phase extraction for the determination of monosulfuron residue in soil

A novel sample clean-up procedure using molecularly imprinted polymer as the solid-phase extraction material for the determination of monosulfuron residue in soil samples has been developed. The molecularly imprinted polymer (MIP) was synthesized by non-covalent method with monosulfuron as the template. The selectivity and affinity of the MIP was evaluated by equilibrium adsorption and HPLC experiments, which demonstrated that the MIP has specific affinity for the template. The template-MIP interaction was studied by investigating the influence of different mobile phases on the retention of the template, which provided basic knowledge for the selection of the washing and elution solutions in the molecularly imprinted solid-phase extraction (MISPE) process. The study indicated that polar organic solvents with hydrogen bonding abilities have stronger eluting strength for the monosulfuron. After the MISPE procedure, a clean baseline was obtained in the HPLC quantification analysis. The recoveries of the method using the combination of MISPE and HPLC were above 93% and the R.S.D. was less than 3.2% in the soil sample determinations. Low detection limit (0.08 microg g(-1), when defined as 3 times of the noise) was also obtained in the method evaluation study.     

First example of a molecularly imprinted polymer incorporating a difunctionalized alloxazine flavin isomer

High-quality alloxazine (a flavin isomer) imprinted polymers have been made for the first time. A molecularly imprinted polymer (MIP) for the N1,N3-di-functionalized alloxazine template 2 was made. The MIP prepared for 2 exhibited excellent, highly selective molecular recognition for template 2, as determined by HPLC analysis using columns prepared with the MIP. This has also demonstrated that the core flavin structure can survive the imprinting process.     

Preparation and evaluation of a macroporous molecularly imprinted hybrid silica monolithic column for recognition of proteins by high performance liquid chromatography

A novel type of macroporous molecularly imprinted hybrid silica monolithic column was first developed for recognition of proteins. The macroporous silica-based monolithic skeleton was synthesized in a 4.6 mm i.d. stainless steel column by a mild sol–gel process with methyltrimethoxysilane (MTMS) as a sole precursor, and then vinyl groups were introduced onto the surface of the silica skeleton by chemical modification of γ-methacryloxypropyltrimethoxysilane (γ-MAPS). Subsequently, the molecularly imprinted polymer (MIP) coating was copolymerized and anchored onto the surface of the silica monolith. Bovine serum albumin (BSA) and lysozyme (Lyz), which differ greatly in molecular size, isoelectric point, and charge, were representatively selected for imprinted templates to evaluate recognition property of the hybrid silica-based MIP monolith. Some important factors, such as template–monomer molar ratio, total monomer concentration and crosslinking density, were systematically investigated. Under the optimum conditions, the obtained hybrid silica-based MIP monolith showed higher binding affinity for template than its corresponding non-imprinted (NIP) monolith. The imprinted factor (IF) for BSA and Lyz reached 9.07 and 6.52, respectively. Moreover, the hybrid silica-based MIP monolith displayed favorable binding characteristics for template over competitive protein. Compared with the imprinted silica beads for stationary phase and in situ organic polymer-based hydrogel MIP monolith, the hybrid silica MIP monolith exhibited higher recognition, stability and lifetime.     

Identification of 3-chloro-1,2-propandiol using molecularly imprinted composite solid-phase extraction materials

A novel molecularly imprinted material based on silica microparticles was synthesized by surface polymerization with 3-chloro-1,2-propandiol (3-MCPD) as a template molecule. The molecularly imprinted polymer (MIP) was characterized by infrared spectroscopy and scanning electron microscopy. The adsorption of 3-MCPD by MIP was measured by gas chromatography with electron capture detection (GC-ECD) and an equilibrium binding experiment. Scatchard analysis revealed that the maximum apparent binding capacities of the MIP and non-imprinted polymer (NIP) were 67.64 and 23.31 μmol/g, respectively. The new adsorbent was successfully used in solid-phase extraction (SPE) to selectively enrich and determine 3-MCPD in soy sauce samples. The MIP-SPE column achieves recoveries higher than 92.7 % with a relative standard deviation of less than 1.83 %. The MIP-SPE-GC protocol improved the selectivity and eliminated the effects of template leakage on quantitative analysis and could be used for the determination of 3-MCPD in other complex food samples. Graphical Abstract

The MIP-SPE column developed by us achieves recoveries higher than 92.7 % with a relative standard deviation of less than 1.83 % for determining the 3-MCPD in the soy sauce matrix (mixed with 3-MCPD, 2-MPCD and 1,3-DCP).      

A selective molecularly imprinted polymer-solid phase extraction for the determination of fenitrothion in tomatoes

A new and selective sorbent for molecularly imprinted solid-phase extraction (MISPE) was developed and applied for the determination of residues of fenitrothion (FNT) in tomatoes, using HPLC coupled to photodiode array detection (HPLC-DAD). Using FNT as the template molecule, methacrylic acid as the functional monomer, ethylene glycol dimethacrylate as the cross-linker, toluene as the porogenic solvent, and bulk polymerization as the synthetic method, a molecularly imprinted polymer (MIP) was synthesized. In order to choose the medium which promotes the best molecular recognition of FNT by the MIP, the adsorption of FNT by the MIP was studied in different media containing acetonitrile and toluene. Besides FNT, three structurally related compounds were used to evaluate the selectivity of the FNT-molecularly imprinted polymer. The MIP exhibited the highest selective rebinding to FNT. The method developed was validated, using fortified blank tomato samples. The extraction efficiency was 96%. The limits of detection and quantitation were 0.050 and 0.130 μg g⁻¹, respectively. The intra-day precision was 5.9% and the inter-day precision 8.1%. The accuracy was higher than 89% for a concentration level around the maximum residue limit of 0.5 μg g⁻¹.     

Selective extraction of clonazepam from human plasma and urine samples by molecularly imprinted polymeric beads

A molecularly imprinted polymer (MIP) based on free‐radical polymerization was prepared with 1‐(N,N‐biscarboxymethyl)amino‐3‐allylglycerol and N,N‐dimethylacrylamide as functional monomers, N,N‐methylene diacrylamide as the cross‐linker, copper ion‐clonazepam as the template and 2,2‐azobis(2‐methylbutyronitrile) as the initiator. The imprinted polymer was characterized by Fourier transform infrared spectroscopy, elemental analysis, thermogravimetric analysis, and SEM. The MIP of agglomerated microparticles with multipores was used for SPE. The imprinted polymer sorbent was selective for clonazepam. The optimum pH and sorption capacity were 5 and 0.18 mg/g at 20°C, respectively. The profile of the drug uptake by the sorbent reflects good accessibility of the active sites in the imprinted polymer sorbent. The MIP‐SPE was the most feasible technique for the extraction of clonazepam with a high recovery from human plasma and urine samples.     

Preparation of “dummy” l‐phenylalanine molecularly imprinted microspheres by using ionic liquid as a template and functional monomer

In this study, dummy imprinting technology was employed for the preparation of l‐ phenylalanine‐imprinted microspheres. Ionic liquids were utilized as both a “dummy” template and functional monomer, and 4‐vinylpyridine and ethylene glycol dimethacrylate were used as the assistant monomer and cross‐linker, respectively, for preparing a surface‐imprinted polymer on poly(divinylbenzene) microspheres. By the results obtained by theoretical investigation, the interaction between the template and monomer complex was improved as compared with that between the template and the traditional l‐ phenylalanine‐imprinted polymer. The batch experiments indicated that the imprinting factor reached 2.5. Scatchard analysis demonstrated that the obtained “dummy” molecularly imprinted microspheres exhibited an affinity of 77.4 M·10^?4, significantly higher that of a traditional polymer directly prepared by l‐ phenylalanine, which is in agreement with theoretical results. Competitive adsorption experiments also showed that the molecularly imprinted polymer with the dummy template effectively isolated l‐ phenylalanine from l‐ histidine and l‐ tryptophan with separation factors of 5.68 and 2.68, respectively. All these results demonstrated that the polymerizable ionic liquid as the dummy template could enhance the affinity and selectivity of molecularly imprinted polymer, thereby promoting the development of imprinting technology for biomolecules.