Chromatographic evaluation of polymers imprinted with analogs of chloramphenicol and application to selective solid-phase extraction

To obtain a highly selective material for the antibiotic chloramphenicol, which has several harmful side effects in humans, different molecularly imprinted polymers (MIPs) were prepared. In order to avoid a major traditional drawback associated with MIPs of residual template bleeding, molecules that are structurally related to chloramphenicol were used as templates for polymer synthesis. Chromatographic evaluation indicated that the employed template imparted a significant influence on the recognition properties of the corresponding polymer. A strong retention of chloramphenicol under nonpolar elution conditions (k = 68.03, IF = 17.72) and under aqueous elution conditions (k = 92.44, IF = 1.35) was achieved. After chromatographic evaluation, the MIP was utilized as the recognition sorbent in a solid-phase extraction to determine chloramphenicol using either an organic or aqueous washing solvent. Recoveries of nearly 100% from the chloramphenicol standard solution and nearly 90% from honey samples spiked with chloramphenicol were attained. Furthermore, the applicability of the MIP for sample cleanup was demonstrated.     

Chromatographic Separation of the Enantiomers of a Series of C2-Asymmetric Bi-Naphthyl Compounds by Molecularly Imprinted Polymers

The aim of this study was to observe the chiral separation of a series of C₂-asymmetric bi-naphthyl compounds on molecularly imprinted polymers (MIPs) using 1,1′-bi-2-naphthol (BINOL) as template. MIP prepared using 4-vinylpyridine as the functional monomer showed better chiral recognition for the template than the MIPs prepared using acrylamide, 2-(diethylamino)ethylmethacrylate and 2-vinylpyridine, respectively. ¹H-NMR was used for comparison of the interactions between template and functional monomers. For chromatographic analysis the effects of mobile phase and temperature on the chiral separation were investigated. When 4-vinylpyridine was employed as the functional monomer, chiral separation of 1,1′-bi-2-naphthol and its analogues were studied. The MIP also demonstrated an ability to discriminate between enantiomers of structurally related compounds that had not been imprinted. The thermodynamic parameters of interactions between substrates and MIP in acetonitrile based mobile phase were investigated by the Van’t Hoff equation. In this study, the specific hydrogen-bonding interactions seemed to be the key factor to achieve chiral separation.     

Preparation of bovine hemoglobin-imprinted polymer beads via the photografting surface-modified method

Molecularly imprinted polymers (MIPs), based on photografting surface-modified polystyrene beads as matrices, were prepared with acrylamide as the functional monomer, bovine hemoglobin as the template molecule and N, N′-methylene bisacrylamide as the crosslinker in a phosphate buffer. The results of IR, scanning electron microscope (SEM) and elemental analyses demonstrated the formation of a grafting polymer layer on the polystyrene-bead surface. Subsequent removal of the template left behind cavities on the surface of the polymer matrix with a shape and an arrangement of functional groups having complementary binding sites with the original template molecule. The adsorption studies showed that the imprinted polymers have a good adsorption capacity and specific recognition for bovine hemoglobin as the template molecule. Our results demonstrated that the polymer prepared via the photografting surface-modified method exhibited better selectivity for the template. Attempts to employ the new method in molecular imprinting techniques may introduce new applications for MIPs and facilitate probable protein separation and purification. __________ Translated from Chemical Journal of Chinese Universities, 2008, 29(1): 64–70     

Evaluation of the Polymerization and Recognition Mechanism for Phenol Imprinting SPE

In order to develop more efficient preparation technologies for imprinted polymers (MIPs), the nature of pre-polymerization and molecular recognition in MIP was investigated by molecular dynamics modeling (MD), ¹H NMR, FTIR and some indirect techniques. Phenol was used as the template for the study of mechanism through the analysis of hydrogen bonding, hydrophobic and π–π bonding interaction. The 4-vinylpyridine-based MIP had the highest selectivity to its phenol template. Hydrogen bonding was proved to be present by characterizing the pre-polymerization complex and evaluating the recognition process and the effects of rebinding solvents were also studied. It was found that a good rebinding solvent should have less affinity with both template and polymer, but good solubility. MD modeling and some indirect techniques demonstrated that 4-vinylpyridine-based MIP recognized phenol mainly through hydrophobic interactions when the rebinding medium was water, while hydrogen bonding was present in the recognition process when the rebinding solvent was n-hexane.     

Supramolecular recognition of estrogens via molecularly imprinted polymers

The isolation and preconcentration of estrogens from new types of biological samples (acellular and protein-free simulated body fluid) by molecularly imprinted solid-phase extraction has been described. In this technique, supramolecular receptors, namely molecularly imprinted polymers (MIPs) are used as a sorbent material. The recognition sites of MIPs were prepared by non-covalent multiple interactions and formed with the target 17β-estradiol as a template molecule. High-performance liquid chromatography with spectroscopic UV, selective, and a sensitive electrochemical CoulArray detector was used for the determination of 17β-estradiol, estrone, and estriol in simulated body fluid which mimicked human plasma.     

Empirical estimation of the energetic contribution of individual interface residues in structures of protein–protein complexes

We report a simple algorithm to scan interfaces in protein–protein complexes for identifying binding ‘hot spots’. The change in side-chain solvent accessible area (ΔASA) of interface residues has been related to change in binding energy due to mutating interface residues to Ala (ΔΔG _X → ALA) based on two criteria—hydrogen bonding across the interface and location in the interface core—both of which are major determinants in specific, high-affinity binding. These relationships are used to predict the energetic contribution of individual interface residues. The predictions are tested against 462 experimental X → ALA mutations from 28 interfaces with an average unsigned error of 1.04 kcal/mol. More than 80% of interface hot spots (with experimental ΔΔG ≥ 2 kcal/mol) could be identified as being energetically important. From the experimental values, Asp, Lys, Tyr and Trp are found to contribute most of the binding energy, burying >45 Å² on average. The method described here would be useful to understand and interfere with protein interactions by assessing the energetic importance of individual interface residues. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Molecularly Imprinted Polymers: Compromise between Flexibility and Rigidity for Improving Capture of Template Analogues

New synthetic strategies for molecularly imprinted polymers (MIPs) were developed to mimic the flexibility and mobility exhibited by receptor/enzyme binding pockets. The MIPs were prepared by bulk polymerization with quercetin as template molecule, acrylamide as functional monomer, ethylene glycol dimethacrylate as cross‐linker, and THF as porogen. The innovative grafting of specific oligoethylene glycol units onto the imprinted cavities allowed MIPs to be obtained that exhibit extended selectivity towards template analogues. This synthetic strategy gives promising perspectives for the design of molecular recognition of molecules based on a congruent pharmacophore, which should be of interest for drug development.     

Synthesis and characterization of sol–gel-derived molecular imprinted polymeric materials for cholesterol recognition

The sol–gel-derived host matrices are well known for biosensor applications where various types of organic and biological molecules can be immobilized and can act as recognition elements. The molecular imprinting technology is an attractive alternative method where expensive and labile biorecognition elements can be replaced by molecular imprinted polymers (MIPs), which are capable of recognizing a target molecule of an interest. In the present study, hybrid sol–gel MIPs were synthesized in the form of crushed powder (CP) by both non-hydrolytic and hydrolytic method for cholesterol recognition. These MIPs were characterized by scanning electron microscopy (SEM), fourier transform-infrared (FT-IR), liquid chromatography-mass spectrometry (LC–MS) and nitrogen adsorption–desorption isotherm measurements. The template molecule was extracted by means of soxhlet extraction and calcination method. The cholesterol adsorption experiments were performed by using non-imprinted (NI) and extracted crushed powder (ExCP) and the percentage of adsorption was determined by measuring the residual quantity in the analyte solution using Liebermann-Burchard (L-B) reagent. The adsorption studies with non-imprinted crushed powder (NICP) showed interference with L-B reagent as well as non-specific binding between analyte molecules and silica matrix. The percentage of adsorption or rebinding was found to be higher for phenyl triethoxysilane (PhTEOS)-derived ExCP (composition 3) which was synthesized by the aqueous sol–gel processing method at low pH as compared to PhTEOS-derived (composition 1) and 3-aminopropyltriethoxysilane (APTES)-derived ExCP (composition 2) prepared by non-hydrolytic method. The reusability of used ExCP after re-extraction was also investigated. The various factors affecting rebinding of template molecules were discussed along with interference study. The study provided information on molecular imprinting of cholesterol in sol–gel matrix and highlighted the importance of characterization of MIPs before applying it for sensing applications.     

Probing cavity versus surface preference of fluorescent template molecules in molecularly imprinted polystyrene microspheres

Functional polystyrene (PS) crosslinked microbeads were developed by dispersion polymerization as fluorescent molecularly imprinted polymers (MIPs) having cavities with specific recognition sites. The functional azobenzene molecule modified with pyridine was self‐assembled with Pyrenebutyric acid (template molecules), and introduced during the second stage of dispersion polymerization of polystyrene. The template molecule was removed from MIP by Soxhlet using acetonitrile as solvent. Non imprinted polymer (NIP) having no template was also synthesized for comparative study. Fluorescence spectroscopy could be used as a tool to derive insight into the location of the template molecules on the MIP or NIP. The template molecules were adsorbed on the surface of the NIPs during binding studies, which was evidenced from the pyrene excimeric emission observed at 440 nm. The template binding efficiency of the NIPs were much lower compared to MIPs. Pyrene emission from MIP upon rebinding showed typical monomeric emission in the 375–395 nm range, confirming its location in isolated cavities. In rebinding studies of the template molecules, the MIPs selectively took up the template for which the cavity was designed, which demonstrated their selectivity towards template molecules. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 1558–1565     

Application of Molecularly Imprinted Polymers in the Analysis of Waters and Wastewaters

The increase of the global population and shortage of renewable water resources urges the development of possible remedies to improve the quality and reusability of waste and contaminated water supplies. Different water pollutants, such as heavy metals, dyes, pesticides, endocrine disrupting compounds (EDCs), and pharmaceuticals, are produced through continuous technical and industrial developments that are emerging with the increasing population. Molecularly imprinted polymers (MIPs) represent a class of synthetic receptors that can be produced from different types of polymerization reactions between a target template and functional monomer(s), having functional groups specifically interacting with the template; such interactions can be tailored according to the purpose of designing the polymer and based on the nature of the target compounds. The removal of the template using suitable knocking out agents renders a recognition cavity that can specifically rebind to the target template which is the main mechanism of the applicability of MIPs in electrochemical sensors and as solid phase extraction sorbents. MIPs have unique properties in terms of stability, selectivity, and resistance to acids and bases besides being of low cost and simple to prepare; thus, they are excellent materials to be used for water analysis. The current review represents the different applications of MIPs in the past five years for the detection of different classes of water and wastewater contaminants and possible approaches for future applications.     

Influence of intramolecular hydrogen bond of templates on molecular recognition of molecularly imprinted polymers

Three molecularly imprinted polymers (MIPs) were prepared corresponding to three structurally related template compounds 4-hydroxybenzoic acid (4-HBA), gentisic acid (GA) and salicylic acid (SA) that differ in intramolecular hydrogen bonding ability using acrylamide (AA) as a functional monomer. HPLC method was used to evaluate the binding performances of the MIPs to the templates and several analogues. The results showed that the difference in their molecular recognition ability was pronounced. The highest molecular recognition ability was observed for 4-HBA-imprinted polymer. It was proved that the hydrogen bond interaction between the functional monomer and the template (4-HBA) played a major role in the recognition process and Scatchard analysis showed that two classes of binding sites were formed in 4-HBA-imprinted polymer. Their dissociation constants were estimated to be 1.76×10⁻⁴ and 1.40×10⁻³ mol l⁻¹, respectively. But for GA- or SA-imprinted polymer the molecular recognition ability was not improved compared to the blank polymer (BP). By comparison of the structures of the three templates, it was concluded that the molecular recognition ability will decrease when the template itself is able to form intramolecular hydrogen bond in the molecular imprinting process. This study will be helpful for us to understand the molecular recognition mechanism of MIPs and of instructive significance for the prediction of the selectivity of MIPs.     

Application of multivariate analysis to the screening of molecularly imprinted polymers for bisphenol A

A key issue in the synthesis of molecularly imprinted polymers (MIPs) is the identification and optimisation of the main factors that affect the material structure and its molecular recognition properties. This paper describes the application of an experimental design and multivariate analysis method for the synthesis of bisphenol A (BPA)-selective MIPs. Six factors with a large impact on the MIP synthesis and its analytical performance have been optimised: the amount of template, the type and the percentage of functional and cross-linking monomers, the polymerisation method (i.e. thermal or UV initiation) and the porogenic solvent. The polymers have been prepared in small-scale (mini-MIPs) and, after careful removal of the template, their BPA rebinding capacity has been evaluated and related to the MIP composition. Among the two functional monomers tested, namely 4-vinylpyridine (4-vpy) and methacrylic acid (MAA), the former rendered the best selectivity for BPA analysis. The partial least squares (PLS) models revealed that the photoinitiated polymers with a 1:1 ratio of 4-vinylpyridine to cross-linker (EDMA or TRIM) yield the highest specific binding. Such procedure is time and cost effective and can be used as a general tool in the preparation of MIPs for different analytes.     

Synthesis and chromatographic evaluation of molecularly imprinted polymers prepared by the substructure approach for the class-selective recognition of glucuronides

Two series of molecularly imprinted polymers (MIPs) for the class-selective recognition of glucuronides have been prepared by using lipophilic substructures of the target analyte as template molecule and potent host monomers against oxyanions, that are expected to establish a strong stoichiometric interaction with the single carboxylic group of the template. The polymers were tested as stationary phases in liquid chromatography for specific recognition. A preliminary investigation of the imprinting properties of eleven MIPs was carried out, by comparing the retention time of the template and of structurally related compounds on the MIP column with that on the corresponding non-imprinted polymer (NIP). The two polymers showing the best performance were selected to further test cotinine, mycophenolic acid, testosterone and their respective glucuronides as model compounds. The high specificity obtained against glucuronides and the different chemical structure of the parent drug make the two MIPs class-selective imprinted receptors, also suitable for SPE application.     

Dopamine sensor based on molecularly imprinted electrosynthesized polymers

Molecularly imprinted polymers (MIPs) have been applied as molecular recognition elements to chemical sensors. In this paper, we combined the use of MIPs and electropolymerization to produce a sensor which was capable of detecting dopamine (DA). The MIP electrode was obtained by electrocopolymerization of o-phenylenediamine and resorcinol in the presence of the template molecular DA. The MIP electrode exhibited a much higher current response compared with the non-imprinted electrode. The response of the imprinted sensor to DA was linearly proportional to its concentration over the range 5.0 × 10⁻⁷-4.0 × 10⁻⁵ M. The detection limit of DA is 0.13 μM (S/N = 3). Moreover, the proposed method could discriminate between DA and its analogs, such as ascorbic acid and uric acid. This method was successfully applied to the determination of DA in dopamine hydrochloride injection and healthy human blood serum. These results revealed that such a sensor fulfilled the selectivity, sensitivity, sped, and simplicity requirements for DA detection and provided possibilities of clinical application in physiological fields.     

Development of a broad selective molecularly imprinted polymers-based solid phase extraction of contraceptive drug levonorgestrel from water samples

A broad selective molecularly imprinted polymers-based solid phase extraction (MISPE) for levonorgestrel (LNG) from water samples was developed. Using LNG as a template molecule, acrylamide (AA) as functional monomer, ethylene glycol dimethacrylate (EGDMA) as linking agent and bulk polymerisation as a synthetic method, the molecularly imprinted polymers (MIPs) were synthesised and characterised. The MIPs displayed a high specific rebinding for LNG with the imprinting factor of 3.71. The Scatchard analysis showed that there was at least one class of binding site for LNG formed in the MIPs with the dissociation constant of 8.046?µg?mL^?1. The results of selectivity testing indicated that the MIPs also exhibited high cross-reactivity with structurally related compounds (estrone, methylprednisolone and ethinyl estradiol), but no recognition with non-structurally related compound (indomethacin), suggesting that the MIPs could be used as a broad recognition absorbent. MISPE column was prepared by packing MIPs particles into a common SPE cartridge. The MISPE extraction conditions including loading, washing and eluting solutions were carefully optimised. Water samples spiked with LNG were extracted by MISPE column and detected by high-performance liquid chromatography. The recoveries were found to be 79.97?～?132.79% with relative standard deviations (RSD) of 1.92?～?10.43%, indicating the feasibility of the prepared MIPs for LNG extraction.     

μ3-ethylidyne-triphenylphosphine-octacarbonyltricobalt: a re-determination from diffractometer data

The structure of the title compound was originally reported from film data (Brice et al., Inorg Chem 9:362, 1970) and comprises a triangle of cobalt atoms capped by an ethylidyne substituent to form an approximately tetrahedral cluster unit. The triphenylphosphine ligand lies in an equatorial position with respect to the plane of the cobalt triangle. Two carbonyl groups, one axial the other equatorial, complete the coordination sphere of the cobalt atom bound to phosphorus. The other two cobalt atoms each carry two equatorial and one axial carbonyl ligand. The Co–Co bond cis to the phosphine substituent is significantly longer than the other two Co–Co distances. The crystal structure is stabilised by C—H···π interactions and C—H···O hydrogen bonds. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Optical recognition of salivary proteins by use of molecularly imprinted poly(ethylene-co-vinyl alcohol)/quantum dot composite nanoparticles

Molecularly imprinted polymers (MIPs) have long been studied for applications in biomolecule recognition and binding; compared with natural antibodies, they may offer advantages in cost and stability. We report on the development of MIPs that “self-report” concentrations of bound analytes via fluorescence changes in embedded quantum dots (QDots). Composite QDot/MIPs were prepared using phase inversion of poly(ethylene-co-vinyl alcohol) (EVAL) solutions with various ethylene mole ratios in the presence of salivary target molecules (e.g. amylase, lipase, and lysozyme). These major protein components of saliva have been implicated as possible biomarkers for pancreatic cancer. The optimum (highest imprinting effectiveness) ethylene mole ratios of the commercially available EVALs were found to be 32, 38, and 44 mol% for the imprinting of amylase, lipase, and lysozyme, respectively. QD fluorescence quenching was observed on binding of analytes to composite MIPs in a concentration-dependent manner, and was used to construct calibration curves. Finally, the composite MIP particles were used for the quantitative detection of amylase, lipase, and lysozyme in real samples (saliva) and compared with a commercial Architect ci 8200 chemical analysis system.     

Synthesis and characterization of molecularly imprinted polymers for recognition of ciprofloxacin

A molecularly imprinted polymer (MIP), with special molecule recognition properties of ciprofloxacin (CIP), was prepared by thermal polymerization in which ciprofloxacin acted as template molecule, α-methacrylic acid (MAA) acted as functional monomer and trimethylolpropane trimethylacrylate (TRIM) acted as crosslinker. The optimized ratio was determined to be n(CIP): n (MMA):n(TRIM)51:6:16 by investigation of the effects of different concentrations of functional monomer and the crosslinker on the MIP’s recognition properties. Equilibrium binding experiment was used to investigate the adsorption dynamics, the binding ability to template molecule and the substrate selectivity. Scatchard analysis was used to study the MIP’s binding characteristic to template molecule. The results indicated that MIP has higher adsorption ability and selectivity. The equilibrium distribution coefficient K _D was 41.64 and the separation factor α was 1.62. Scatchard analysis showed that two different kinds of binding sites were produced in the polymer matrix and their dissociation constants were calculated to be K _d1 = 5.249 × 10⁻⁵ mol·L⁻¹, K _d2 = 2.237 × 10⁻³ mol·L⁻¹. __________ Translated from Chemistry, 2008, 71(2): 132–137     

Highly selective separations by capillary electrochromatography: molecular imprint polymer sorbents

Molecular imprint polymers (MIPs) are synthesized in the presence of a template, or 'imprint' molecule which results in the formation of specific recognition cavities complementary to the template in shape and chemical functionality. The resultant MIP then acts as a selective binding medium for the template molecule. The utility of MIPs lies in the selectivity of the rebinding process, which is based on molecular recognition. In many cases, the selectivity achieved with MIPs toward a particular molecule is comparable to that observed with antibodies. This has led to the application of MIPs to several areas of analytical chemistry including immunoassays, sensors and separations media. One of the most successful application areas of MIPs has been as chromatographic sorbents, where they have been utilized predominately in chiral separations. The use of MIP sorbents in CEC is attractive in that it combines the selectivity of a molecular recognition process with the enhanced flow dynamics of CEC, which can result in higher efficiency and shorter analysis times. This paper will review the use of molecular imprinted stationary phases in CEC. Following a brief introduction to molecular imprinting, various methodologies for preparation of MIP-CEC capillaries in addition to applications of the technique will be discussed.     

Synthesis and characterization of molecularly imprinted polymer for controlled release of tramadol

In this paper, we describe how to prepare a highly selective imprinted polymer by a bulk polymerization technique. We used tramadol as the template, (MAA) as functional monomers, and (EGDMA) as the cross-linker in chloroform as solvent. Results from Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric Analysis (TGA), Scanning Electron microscopy (SEM) show that this imprinted sorbent exhibits good recognition and high affinity for tramadol. Selectivity of molecularly imprinted polympers (MIP) was evaluated by comparing several substances with similar molecular structures to that of tramadol. Controlled release of tramadol from MIPs was investigated through in vitro dissolution tests and by measuring the absorbance at λ _max of 272 nm by (HPLC-UV). The dissolution media employed were hydrochloric acid pH 3.0 and phosphate buffers, pH 5.0 and 7.4, maintained at 37 and 25 ± 0.5°C. The results show the ability of MIP polymers to control tramadol release. In all cases, the release of MIPs was deferred for a longer time as compared to NMIP. At a pH of 7.4 and 25°C slower release of tramadol imprinted polymer occurred.