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.     

Molecular imprinting of natural flavonoid antioxidants: application in solid-phase extraction for the sample pretreatment of natural products prior to HPLC analysis

As shown in the past years, SPE based on molecularly imprinted polymers (MIPs) may provide significant enhancement of selectivity in sample preparation and analyte preconcentration. The objective of this work was the fabrication of MIPs for the specific adsorption of rutin and quercetin. The two flavonoids were used as the template molecules for the preparation of MIP phases in a self-assembly (noncovalent) approach. The produced MIPs were validated with regard to the imprinting efficiency as media for LC and SPE. The retention behavior of several flavonoid compounds was studied using as stationary phases imprinted, control nonimprinted polymers, and commercial silica-based materials. MIPs were applied as materials for the selective SPE and preconcentration of the flavonoids from white and red wine, orange juice, and tea. The collected fractions were analyzed by high-pressure LC. MIP-SPE facilitated specific analyte isolation and effective sample clean-up. The results show that molecularly imprinted SPE can be a useful tool for the simple, selective, and cost-effective pretreatment of samples containing natural antioxidants.     

Synthetic creatinine receptor: imprinting of a Lewis acidic zinc(II)cyclen binding site to shape its molecular recognition selectivity

Molecularly imprinted polymers (MIPs) from polymerizable Lewis acidic zinc(II)cyclen complexes and ethylene glycol dimethyl acrylate have been prepared. For the imprinting process the template molecule creatinine is reversibly coordinated to the zinc atom. The high strength of this interaction allows analyte binding to the MIP from aqueous solution with high affinity. Its pH dependence is used for controlled guest release with nearly quantitative analyte recovery rate. The binding capacity and selectivity profile of the MIP remains constant through several pH controlled binding and release cycles. MIPs missing a suitable metal binding site showed no significant affinity for thymine or creatinine. Flavin adsorbs nonspecifically to all polymers. The imprinting process reverses the binding selectivity of zinc(II)cyclen for creatinine and thymine from 1:34 in homogeneous solution to 3.5:1 in the MIP. Scatchard plot analysis of creatinine binding isotherms reveals uniform binding of the imprint, with fits indicating a one-site model; however, similar analysis for thymine indicate high and low affinity sites. This corresponds to unrestricted coordination sites freely accessible for thymine, e.g., at the polymer surface, and misshaped imprinted sites, which still can accommodate thymine. More than 50% of all binding sites exclusively bind creatinine and are not accessible to thymine. The binding properties of a copolymer of polymerizable zinc(II)cyclen and ethylene glycol dimethyl acrylate missing the creatinine template, which match the binding selectivity of the complex in solution, confirm that the origin of altered selectivities is the imprinting process. With binding ability at physiological pH, the MIPs are applicable for tasks in medicinal diagnostics or biotechnology. Imprinted zinc(II)cyclen complexes provide, like a metalloenzyme binding motif, high binding affinity by reversible coordination while the surrounding macromolecule determines binding selectivity.     

表面分子印迹材料和技术在分离分析中的应用进展

复杂体系的高选择性分析对分离新材料和新方法提出了迫切需求。分子印迹聚合物（MIPs）以其特异性高、化学稳定性好、制备简单且成本低等优点,在高选择性分离分析中展现出巨大的应用前景。但以本体聚合为代表的传统合成方法获得的MIPs存在识别位点位于聚合物内部难以识别、模板分子洗脱不彻底、传质速率慢、结合容量低等问题。表面印迹技术制备的核-壳型表面分子印迹材料是解决上述难题的有效途径。通过核体和壳层结构的设计和构建,表面分子印迹材料还可具备多功能、多响应的特性,适于现代分离分析对快速、高效、高选择性的要求。该文主要综述了近几年表面分子印迹技术在样品前处理、化学/生物传感分析及靶向药物递送领域的应用进展。     

核-壳型厚朴酚印迹聚合物的制备及性能研究

以表面修饰功能基团的SiO2微球为基体,以厚朴酚为模板分子,丙烯酰胺为功能单体,丙烯酸乙二醇二甲酯为交联剂,在SiO2微球表面制备对厚朴酚具有较好选择识别能力的核-壳型印迹聚合物.采用红外光谱及扫描电镜等技术表征聚合物的结构及形态.结果表明,该印迹聚合物表面成功制备了壳层厚度约为200nm的均匀印迹层.通过静态吸附、Scatchard分析法以及竞争吸附实验研究了该聚合物的吸附性能和选择性,结果表明,它对厚朴酚形成均一结合位点,离解常数为0.19mg/mL.     

Recent advances in molecular imprinting technology: current status, challenges and highlighted applications

Molecular imprinting technology (MIT) concerns formation of selective sites in a polymer matrix with the memory of a template. Recently, molecularly imprinted polymers (MIPs) have aroused extensive attention and been widely applied in many fields, such as solid-phase extraction, chemical sensors and artificial antibodies owing to their desired selectivity, physical robustness, thermal stability, as well as low cost and easy preparation. With the rapid development of MIT as a research hotspot, it faces a number of challenges, involving biological macromolecule imprinting, heterogeneous binding sites, template leakage, incompatibility with aqueous media, low binding capacity and slow mass transfer, which restricts its applications in various aspects. This critical review briefly reviews the current status of MIT, particular emphasis on significant progresses of novel imprinting methods, some challenges and effective strategies for MIT, and highlighted applications of MIPs. Finally, some significant attempts in further developing MIT are also proposed (236 references).     

Low cross-linked molecularly imprinted monolithic column prepared in molecular crowding conditions

Molecular crowding is a new approach to promoting molecular imprinting more efficiently. In this work, this concept was applied to the preparation of low cross-linked imprinted polymers in the presence of an immobilised template for stabilizing binding sites and improving molecular recognition. An imprinted monolithic column was synthesized using a mixture of 2,4-diamino-6-methyl-1,3,5-triazine (template), 2,4-diamino-6-(methacryloyloxy) ethyl-1,3,5-triazine (polymerisable template), methacrylic acid, ethylene glycol dimethacrylate, and polystyrene (molecular crowding agent). Some polymerization factors, such as template-monomer molar ratio, the composition of the porogen and crosslinking density, on the imprinting effect of resulting MIP monolith were systematically investigated. The results indicated that the imprinted monolithic columns prepared in the presence of molecular crowding agent retained affinity and specificity for template even when prepared with a level of cross-linker as low as 9%. Moreover, a stoichiometric displacement model for retention was successfully applied to evaluate the interaction between the solute and the stationary phase. Compared with the low cross-linked MIP prepared by conventional polymerization, the molecular crowding-based low cross-linked monolithic MIPs showed higher selectivity. The results suggested that molecular crowding is a powerful strategy to increase the effect of molecular imprinting at a low level of crosslinker.     

Molecularly imprinted beads by surface imprinting

Molecular imprinting is a state-of-the-art technique for imparting molecular recognition properties to a synthetic polymeric matrix. Conventionally, the technique is easily carried out using bulk imprinting, where molecularly imprinted polymers (MIPs) are prepared in large chunks and post-treatment processes like grinding and sieving are then required. However, this strategy tends to produce sharp-edged, irregular MIP bits with a limited scope of direct application. In addition, due to the creation of binding sites within the polymeric bulk, the issue of the hindrance of adsorbate diffusion (especially in the case of macromolecules) during template rebinding makes the MIPs prepared through this approach unsuitable for practical applications. Thus over the years, many efforts to address the limitations of conventional molecular imprinting techniques have resulted in new imprinting methodologies. Systems like suspension and precipitation polymerization, where MIPs with tunable morphologies can be prepared, have been developed. Additionally, strategies like surface imprinting have also been employed. Ultimately, both of these approaches have been combined to prepare regularly shaped surface-imprinted MIP beads. Such an approach incorporates the advantages of both methodologies at the same time. Given their desirable physical morphologies and favorable adsorption kinetics, MIPs prepared in this manner show significant promise for industrial applications. Therefore, they will be the main focus of this review.     

槲皮素金属配位分子印迹聚合物的识别性能

以槲皮素与Zn(Ⅱ)的配合物为模板,在甲醇溶液中制备金属配位分子印迹聚合物.通过紫外光谱研究了槲皮素与Zn(Ⅱ)的配位方式及配位比,验证了槲皮素、Zn(Ⅱ)和4-乙烯基吡啶之间的三元配位作用.利用红外光谱对产物的结构进行了表征.用平衡结合实验考察了功能单体及交联剂用量对聚合物吸附性能的影响,优化了聚合物的反应配比.同时对系列印迹聚合物的识别体系进行了考察.结果表明,槲皮素-Zn(Ⅱ)模板印迹聚合物对槲皮素-Zn(Ⅱ)的配合物表现出明显的吸附选择性和特异性,对槲皮素结构类似物芦丁和柚皮素的吸附选择性较差,分离因子分别为3.21和1.91.     

Via protoporphyrin to the synthesis of levofloxacin‐imprinted polymer

A new molecularly imprinted polymer (MIP) for levofloxacin was prepared by the combined use of methacrylic acid and protoporphyrin as functional monomers. The adsorption properties of resultant imprinted polymers were evaluated by equilibrium rebinding experiments. The highest binding capacity of levofloxacin achieved from the optimized imprinted polymer in acetonitrile was 246.26 µmol/g with an imprinting factor of 2.05. A ?uorescence quenching effect was observed when a protoporphyrin‐based imprinted polymer was incubated in the solutions of levofloxacin. The results indicated that the protoporphyrin‐based MIPs were able to create higher binding cavities for template compared with MIPs using only methacrylic acid as a functional monomer. It should be expected that the cooperative use of the protoporphyrin with supplemental different functional monomers may be an alternative to obtain MIP with the improvement of the selectivity. Copyright © 2010 John Wiley & Sons, Ltd.     

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 of molecularly imprinted polymers via ring-opening metathesis polymerization for solid-phase extraction of bisphenol A

The use of molecularly imprinted polymers (MIPs) prepared by ring-opening metathesis polymerization (ROMP) for bisphenol A (BPA) was reported in this article. The resulting MIPs have high imprinting and adsorption capacities, and can be used for separation and determination of BPA in environmental water samples. The successful application of ROMP in the molecular imprinting field is described here. For the first time, two cross-linkers (dicyclopentadiene and 2,5-norbornadiene) and two Grubbs catalysts (first and second generation) were investigated to compare their effects on the binding performance of MIPs. The ROMP technique is able to create the imprinted polymers within 1 h under mild conditions. Furthermore, it can provide MIPs with obvious imprinting effects towards the template, very fast template rebinding kinetics, high binding capacity and appreciable selectivity over structurally related compounds. The adsorption process for MIPs in this study can be completed within 45 min, which is much faster than that of bulk MIPs synthesized by traditional free-radical polymerization. The resulting imprinting polymer was evaluated for its use as a sorbent support in an off-line solid-phase extraction approach to recover BPA from diluted aqueous samples. The optimized extraction protocol resulted in a reliable MISPE method suitable for selective extraction and preconcentration of BPA from tap water, human urine and liquid milk samples. This article demonstrates the practical feasibility of the MIPs prepared via ROMP as solid-phase extraction materials.     

模板结构与分子印迹效果间关系的研究

以一些分子量和体积都较小的简单化合物作为模板分子,合成分子印迹聚合物 。通过总结43种化合物的分子印迹聚合物的色谱数据,来研究模板分子的分子量、 作用位点数目、分子刚性等因素与印迹效果的关系。根据免疫学中免疫原性的定义 ,我们提出“印迹原性”的概念,即,化合物能够产生印迹效应的性质称为印迹原 性;具有印迹原必的化合物称为印迹原;并讨论了具有较强选择性的印迹原的化学 基础。所得到的结论将有助于对分子印迹聚合物的识别机理的进一步理解,并且对 于根据模板分子性质预测MIP分子识别能力将具有一定的指导意义。     

表面分子印迹聚合物纳米线用于蛋白质的特异性识别

手性配体交换色谱是拆分手性化合物,特别是氨基酸和羟基酸对映体的一种有效方法,通常以光活性氨基酸或其衍生物为手性选择子,可通过键合及涂渍制备手性固定相,也可作为流动相添加剂来实现手性配体交换色谱分离分析,配体交换键合固定相需要完成载体和手性选择子之间的偶联,键合量因受到载体和制备条件的影响而较难控制,且柱效较低。     

胆酸印迹聚合物的制备及在含水介质中的结合性能

为了在含水介质中进行有效印迹,本研究中以双甲基丙烯酰-β-环糊精（BMA-β-CD）和2-(二乙基胺基)乙基甲基丙烯酸酯(DEAEM)为功能单体制备了胆酸印迹聚合物MIP1,并用平衡结合实验研究了MIP1在含水介质中对模板分子的识别能力。结果表明,MIP1比单独以BMA-β-CD或DEAEM为功能单体制备的印迹聚合物MIP2和MIP3,显示出对模板分子更好的选择性结合能力。MIP1的特异性吸附量ΔCP为38.81μmol/g,印迹因子IF为2.46。研究表明,在含水介质中,利用模板分子与功能单体之间的疏水作用和离子作用是提高印迹聚合物分子识别能力的关键。研究还表明,在识别过程中,疏水作用在驱动分子进入印迹孔穴时起重要作用。     

基于银增强金标记物的阳极溶出伏安免疫分析用于补体第三成分的测定

分子印迹是制备对特定分子具有专一性结合能力的聚合物的技术,所制备的聚合物被称为分子印迹聚合物（Molecularly imprinted polymers,MIPs）,此类聚合物在分离提纯、模拟酶和传感器等方面均显示出广阔的应用前景,迄今,小分子化合物的印迹技术已经十分成熟。     

Synthesis and Molecular Recognition of Molecularly Imprinted Polymer with Ibuprofen as Template

Ibuprofen and ketoprofen are chemically similar non‐steroidal anti‐inflammatory drugs widely used in the treatment of arthritis. Using a molecular imprinting technique, a simple and rapid method was developed for the simultaneous separation and determination of ibuprofen and ketoprofen. Molecular imprinting introduces artificial binding sites into a synthetic polymer matrix, allowing it to exhibit selective rebinding of template molecules. Imprinted polymers can be regarded as an HPLC stationary phase, important for pharmaceutical analysis. Most molecularly imprinted polymers (MIPs) are synthesized by free radical polymerization of functional monomers, resulting in an excess of crosslinking monomers. In this study, MIPs have been prepared with a ibuprofen template, which can form intramolecular hydrogen bonds. Methacrylic acid (MAA) and ethyleneglycol dimethacrylate (EGDMA) were used as the functional monomer and cross‐linker, respectively. Bulk polymerization was carried out at 4 °C under UV radiation. The resulting MIP was ground into 25?44 μm particles, which were slurry‐packed into analytical columns. Template molecules were removed by methanol‐acetic acid (9:1, v/v). We evaluated the template binding performance of the MIP using HPLC, with ultraviolet (UV) detection at 234 nm. Chromatographic resolution of ibuprofen and ketoprofen on the MIPs were appraised using buffer/acetonitrile (45/55, v/v) as the mobile phase. Results show that the MIPs prepared using ibuprofen as the template had a significant molecular imprinting effect. The method was successfully applied to the separation and analysis of ibuprofen and ketoprofen in pharmaceuticals.     

Synthesis and Evaluation of Molecularly Imprinted Polymers as Sorbents for Selective Extraction of Coumarins

Coumarin, 7-hydroxycoumarin and dicoumarol molecularly imprinted polymers (MIP) were synthesized by bulk polymerization. Methacrylic acid and 4-vinylpyridine were tested as functional monomers and methanol, ethanol, acetonitrile, toluene and chloroform were tested as porogens. The binding capabilities of the imprinted polymers were assessed by equilibrium binding analysis. Highest binding capacity was obtained for MIP prepared for the template 7-hydroxycoumarin synthesized in methacrylic acid as functional monomer, chloroform as porogen and methanol/water as analyte solvent. Scanning electron microscopy analysis documented its appropriate morphology. ATR-FTIR spectra confirmed successful polymerization of MIP. Coumarin structural analogues were employed to evaluate the polymer selectivity and it was found that polymer prepared for 7-hydroxycoumarin was selective for its template molecule. Kinetic studies showed relatively fast adsorption of analytes to MIPs (1 h). Rebinding properties of MIPs were evaluated by adsorption isotherms. The calculated data fitted well with experimental data showing that Freundlich isotherm is suitable for modelling the adsorption of tested coumarins on prepared MIPs. Applicability of polymer prepared for 7-hydroxycoumarin was tested for the selective extraction of coumarins from the sample of chicory.     

Surface imprinted polymers for oil denitrification with the combination of computational simulation and multi‐template molecular imprinting

Multi‐template molecular imprinting technique was employed for the theoretical study about industrial oil denitrification. Prior to the preparation of multi‐template molecularly imprinted polymers (MT‐MIPs), density functional theory was used for simulating the imprinted pre‐assembly systems composed of template (aniline, indole, or 3‐methylinndole) and monomer [methacrylic acid, acrylamide (AM), and 4‐vinylpyridine]. MT‐MIPs were synthesized as surface MIPs simply and successively by seeded emulsion polymerization or two‐stage precipitation polymerization. The experimental results were consistent with the simulative results, which demonstrated that AM was more suitable monomer together. In addition, seeded emulsion polymerization synthesized MT‐MIPs with better performance compared with two‐stage precipitation polymerization. The adsorption kinetics and adsorption isotherm of MT‐MIP prepared with AM using seeded emulsion polymerization were fitted with different models. The fitting results indicated that pseudo‐second‐order kinetics model and Freundlich isotherm model were suitable for describing the adsorption process of AM seeded emulsion polymerization. This study will provide a certain guidance and theoretical basis for introducing the combination of multi‐template molecular imprinting technique and computational simulation into the field of industrial denitrification. Copyright © 2015 John Wiley & Sons, Ltd.     

The development of a semiautomated procedure for the synthesis and screening of a large group of molecularly imprinted polymers

A method for synthesis and evaluation of molecularly imprinted polymers (MIPs) on a semiautomated miniature scale is reported. This technique combines molecular imprinting with the combinatorial chemistry approach, allowing rapid screening and optimizations of libraries of MIPs. The polymers were prepared and evaluated in situ by rebinding utilizing powder dispensing and liquid handling systems. MIPs were prepared by a combinatorial approach using methacrylic acid (MAA), 4-vinylpyridine (4-VP), acrylamide, and styrene as functional monomers, and acetonitrile and toluene as porogenic solvents. A drug substance having aromatic, hydroxyl, -O-CONH2 functional groups was selected as the template molecule for this study. The MIP library results demonstrated that the polymer prepared with MAA as functional monomer shows the strongest binding affinity, and therefore, is preferred for the preparation of this particular template molecule. Due to the low consumption of reagents, and more importantly, the demonstrated ability of this method to effectively identify optimal imprinting conditions, this small-scale combinatorial protocol is well suited for fast and efficient screening and optimizations of MIPs.