Thin layer molecularly imprinted microfiltration membranes by photofunctionalization using a coated alpha-cleavage photoinitiator.

A novel approach towards thin-layer molecularly imprinted polymer (MIP) composite membranes was developed based on using benzoin ethyl ether (BEE), a very efficient alpha-scission photoinitiator. The triazine herbicide desmetryn was used as the template, and a mixture of the functional monomer 2-acrylamido-2-methyl-1-propane sulfonic acid (AMPS) and the cross-linker N,N'-methylene-bis-acrylamide (MBAA) in methanol was copolymerised via photoinitiation followed by deposition on the surface of either hydrophobic or hydrophilically precoated polyvinylidene fluoride (PVDF) microfiltration membranes. Blanks were prepared under identical conditions, but without the template. Especially, the degree of functionalization (DF) of the PVDF membranes with poly(AMPS-co-MBAA), the membrane permeabilities and non-specific vs. MIP-specific template binding from aqueous solutions during fast filtration were studied in detail to evaluate the effects of the preparation conditions, in particular the coating of the membrane surface with the photoinitiator prior to UV irradiation and the influence of the precoated hydrophilic layer on PVDF. Significant template specificities of the MIP membranes compared with the blanks were only achieved for the preparations including coating the two types of PVDF membranes with BEE. In contrast, a homogeneous photoinitiation of the copolymerisation in the membrane pore volume yielded functional layers with similar DF but with only non-specific desmetryn binding. All data clearly indicate the significant contribution of MIP stabilization by the support material in layers of optimum thickness to the MIP specificity. Main advantages of the novel approach are the potential to synthesize MIP composite membranes by controlled deposition onto any kind of polymer support, and the very fast MIP preparations due to a very efficient photoinitiator and small MIP layer thickness. Due to the mechanical and chemical stability in combination with high permeabilities, thin-layer MIP composite membranes have a large application potential, e.g., in solid phase extraction.     

Molecularly imprinted polymer membranes for substance-selective solid-phase extraction from water by surface photo-grafting polymerization

Hydrophilized polyvinylidene fluoride microfiltration membranes were surface-modified in the presence of a template (terbumeton) in methanol with a graft copolymer of a functional monomer (2-acrylamido-2-methyl-1-propane sulfonic acid, AMPS, methacrylic acid, MAA, or acrylic acid, AA) and a cross-linker (N,N'-methylene-bis-acrylamide) using UV irradiation and benzophenone as photoinitiator. As result, membranes covered with a thin layer of imprinted polymer selective to terbumeton were obtained. Blank membranes were prepared with the same monomer composition, but in the absence of the template. The membranes' capacity to adsorb terbumetone from aqueous solution was evaluated yielding information regarding the effect of polymer synthesis (type and concentration of functional monomer, concentration of cross-linker) on the resulting membranes' recognition properties. UV spectroscopic studies of the interactions with terbumetone revealed that AMPS forms a stronger complex than MAA and AA. In agreement with that finding, imprinting with AMPS gave higher affinities than with MAA and AA. The terbumeton-imprinted membranes showed significantly higher sorption capability to this herbicide than to similar compounds (atrazine, desmetryn, metribuzine). With the novel surface modification technology, the low non-specific binding properties of the hydrophilized microfiltration membrane could successfully be combined with the receptor properties of molecular imprints, yielding substance-specific molecularly imprinted polymer composite membranes. The high affinity of these synthetic affinity membranes to triazine herbicides together with their straightforward and inexpensive preparation provides a good basis for the development of applications of imprinted polymers in separation processes such as solid-phase extraction.     

Porous molecularly imprinted polymer membranes and polymeric particles

Porous free-standing molecularly imprinted polymer membranes were synthesised by the method of in situ polymerisation using the principle of synthesis of interpenetrating polymer networks and tested in solid-phase extraction of triazine herbicides from aqueous solutions. Atrazine-specific MIP membranes were obtained by the UV-initiated co-polymerisation of methacrylic acid, tri(ethylene glycol) dimethacrylate, and oligourethane acrylate in the presence of a template (atrazine). Addition of oligourethane acrylate provided formation of the highly cross-linked MIP in a form of a free-standing 60 μm thick flexible membrane. High water fluxes through the MIP membranes were achieved due to addition of linear polymers (polyethylene glycol M_w 20,000 and polyurethane M_w 40,000) to the initial mixture of monomers before the polymerization. As a result, typical semi-interpenetrating polymer networks (semi-IPNs) have been formed, where the cross-linked polymer was represented by the atrazine-specific molecularly imprinted polymer, while the linear one was represented by polyethylene glycol/polyurethane. Extraction of the linear polymers from the fully formed semi-IPNs resulted in formation of large pores in the membrane structure. At the same time, extraction of the template molecules lead to formation of the sites in the polymeric network, which in shape and arrangement of functional groups are complementary to atrazine. Reference polymeric membranes were prepared from the same mixture of monomers but in the absence of the template. Recognition properties of the MIP membranes were estimated in solid-phase extraction by their ability to selective re-adsorbtion of atrazine from 10⁻⁸ to 10⁻⁴ M aqueous solutions. The imprinting effect was demonstrated for both types of the MIP membranes and the influence of the type of the linear compound on their recognition properties was estimated. The recognition properties of the MIP membranes were compared to those of the MIP particles of the same composition. Morphology of the MIP membranes was investigated using the SEM microscopy. High fluxes of the developed membranes together with high affinity and adsorption capability make them an attractive alternative to MIP particles in separation processes.     

钴离子配位分子印迹聚合物膜渗透特性的研究

采用分子印迹技术紫外光引发原位聚合的方法制备了带支撑膜的钴离子配位分子印迹聚合物膜. 用扫描电镜测定了膜的表面形貌. 通过膜渗透实验表明, 在一定浓度钴离子存在下, 印迹膜对模板分子表现出良好的渗透选择性. 分别考察了阳离子和阴离子对印迹膜渗透模板分子的影响. 本工作有助于分子印迹技术应用于传感器技术和连续分离技术的研究.     

Silica particles coated with azobenzene-containing photoresponsive molecule-imprinted skin layer

We developed a novel type of azobenzene-containing photoresponsive molecule-imprinted silica microspheres. Ibuprofen and activated silica particles were used as template molecules and substrates, respectively. Pre-synthesized azobenzene-based monomers were chemically bonded on the surface of silica particles. Template–monomer complexes were formed relying on hydrogen bonding. Then skin layer was formed by graft polymerization of azobenzene-based monomers. After that, ibuprofen molecules were removed from their embedded spaces. The vacant spaces on the surface of particles were easily accessible for the template molecules. Furthermore, photoinduced trans–cis isomerization of azobenzene chromophores within imprinted vacant spaces was able to regulate their substrate affinity. The results demonstrated that the imprinted silica microspheres possessed obvious molecular imprinting effects towards the template ibuprofen, rather fast template rebinding kinetics, and appreciate selectivity over structurally related compounds.     

Novel composite membranes embedded with molecularly imprinted porous polymeric nanospheres for targeted phenol

In the present research, novel hybrid molecularly imprinted polymer (HMIP) membranes were synthesized for selective adsorption and separation of phenol toxic molecules from aqueous solutions. Molecularly imprinted polymer (MIP) nanospheres for targeted phenol were successfully prepared using precipitation polymerization of methacrylic acid, trimethylolpropane trimethacrylate, and ethylene glycol dimethacrylate, followed by integrating into polysulfone matrix to create the HMIP membranes via a phase inversion method. The fabricated materials were characterized from the viewpoints of spectroscopic analysis, structural and surface morphological properties, porosimetry, and batch rebinding assays. The imprinted polymeric nanospheres with mean diameter value ranging from 210 to 250 nm and average pore diameter of 8 nm were obtained according to the morphological and Brunauer–Emmett–Teller analysis, respectively. Scanning electron microscopy pictures demonstrated that the MIP spheres were uniformly distributed on the surface and in the bulk polymer phase of the hybrid membrane. The surface roughness, porosity, and permeate flux of membrane were significantly augmented by addition of the imprinted polymer particles in the dope solution. HMIP‐2 membrane containing 10 wt% of MIP showed the highest binding capacity and an excellent molecular recognition for phenol with respect to the correlative blank membrane. The selective recognition of phenol on the HMIP‐2 membrane was 3.5 times larger than the analogous compound (i.e. catechol). Moreover, the maximum separation factor of phenol was obtained as 2.19 relative to catechol through selective permeation studies, which was also observed for HMIP‐2 membrane. Copyright © 2015 John Wiley & Sons, Ltd.     

白藜芦醇分子印迹复合膜的制备及其选择性能

以反式白藜芦醇为模板分子,聚偏氟乙烯微孔滤膜为支撑膜,丙烯酰胺为功能单体,乙二醇二甲基丙烯酸脂(EDMA)为交联剂,采用热引发原位聚合方法制备了白藜芦醇分子印迹聚合物膜。研究了分子印迹膜对白藜芦醇及其结构类似物(2-萘酚、白藜芦醇甙和双酚A)的结合和透过性,并用扫描电镜对膜形貌进行了表征。结果表明,印迹复合膜对模板分子白藜芦醇具有良好的吸附选择性,印迹膜对白藜芦醇的吸附量远远大于其它结构类似物,其饱和吸附量达1.72μmol/g,为非印迹膜的3倍;尺寸效应和印迹效应是影响物质在印迹膜上的透过量的两个重要因素,尺寸比模板分子小的2-萘酚最先透过,而相对于尺寸接近或大于模板分子的双酚A或白藜芦醇甙,模板分子优先透过。而且,模板分子在印迹膜上的透过量大于非印迹膜。     

邻香草醛分子印迹聚合物膜的制备及其透过选择性质的研究

采用紫外光引发原位聚合的方法制备了具有支撑膜的邻香草醛分子印迹聚合物膜. 紫外光度法测定了模板分子和功能单体之间的结合常数和化学计量比(n＝2). 用傅立叶红外光谱和扫描电镜分别测定了膜的结构和表面形貌; 膜渗透实验结果表明在干扰物存在时印迹膜对模板分子表现出良好的选择透过性能. 研究了分子印迹聚合物膜透过的机理、并为分子印迹技术应用于传感器领域增加了理论和实验方法.     

Grafting of MIPs from PVDF Membranes via Reversible Addition-fragmentation Chain Transfer Polymerization for Selective Removal of p-Hydroxybenzoic Acid

Effective molecularly imprinted membranes(MIMs) were developed as an efficient adsorbent for the selective removal of p-hydroxybenzoic acid(p-HB) from acetylsalicylic acid(ASA, aspirin). The MIMs were grafted successfully from poly(vinylidene fluoride) microfiltration membranes via reversible addition-fragmentation chain transfer(RAFT) polymerization. The graft copolymerization of acrylic acid(AA) in the presence of template p-hydroxybenzoic acid led to molecularly imprinted polymer(MIP) film coated membranes. The obtained MIMs were characterized by scanning electron microscopy(SEM), Fourier transform infrared spectrophotometer(FTIR) and Raman spectra, and batch mode adsorption studies were carried out to investigate the specific adsorption equilibrium, kinetics and selective recognition properties of different MIMs. The kinetic properties of the MIMs could be well described by the pseudo-second-order rate equation. Selective permeation experiments were performed to evaluate the permeation selectivity of the p-HB imprinted membranes. The observed performances of the MIMs are applicable to the further purification of aspirin.     

烟酸分子印迹复合膜的制备及其分离性能研究

以聚偏氟乙烯微孔滤膜为支撑膜,烟酸为模板分子,用紫外光引发表面修饰聚合制备了微孔滤膜支撑-烟酸分子印迹复合膜.电镜扫描对该印迹复合膜进行了表面形态表征.Scatchard分析表明,在所研究的浓度范围内分子印迹复合膜中存在等价的结合位点,结合位点的平衡离解常数Kd为5.55×10-2mmol·L-1.底物的结合和渗透选择性实验表明,分子印迹复合膜对烟酸有较好的结合性能,结合量是6.10μmol·g-1.与其结构类似的化合物烟酰胺相比,分子印迹复合膜对模板分子展示了更好的选择性及高度的识别能力.     

手性布洛芬对映体的选择性光电化学氧化

将光电化学方法与原位分子印迹技术相结合,通过使用手性布洛芬的对映体S-布洛芬(S-ibuprofen)和R-布洛芬(R-ibuprofen)为模板分子,在原位生长的单晶二氧化钛(TiO_2)纳米棒表面构筑S-ibuprofen和R-ibuprofen分子印迹位点,制备出能够对S-ibuprofen和R-ibuprofen选择性识别和催化氧化的印迹电极。通过扫描电子显微镜(SEM)、透射电子显微镜(TEM)、X射线衍射(XRD)和拉曼光谱(Raman)对电极的形貌、结构和组成进行表征,通过电化学阻抗对电极表面的电子传递阻力进行研究,以制备得到的印迹电极为工作电极通过光电化学方法对其印迹位点的光电识别选择性和光电降解选择性进行测试。制备得到的TiO_2为单晶纳米棒阵列,印迹位点成功构筑在TiO_2纳米棒表面且具有很好的择形吸附能力。本工作首次实现了手性医药布洛芬对映体在人工光电催化剂表面的选择性识别和选择性氧化降解。     

Electrochemical sensing with electrodes modified with molecularly imprinted polymer films

This article summarises our work on the development of voltammetric sensors based on molecularly imprinted polymers. Several recognition elements and integration strategies were used:1.membranes electropolymerised at the electrode surface; 2.casting of polymeric membranes by drop-coating a solution of pre-formed polymer (polyphosphazene) and template in a low-boiling-point solvent on to the electrode surface; 3.preparation of composite membranes containing conductive material (graphite or carbon black), acrylic-type molecularly imprinted polymers (small particle size), and PVC as binder; and 4.in-situ polymerisation of a thin layer of acrylic imprinted polymer deposited on the electrode surface by spin coating.All the options evaluated offer the possibility of controlling electrode characteristics such as hydrophobic/hydrophilic character, permeability, or film thickness, which are essential for obtaining good sensor performance.     

Synthesis of monodispersed molecularly imprinted polymer particles for high-performance liquid chromatographic separation of cholesterol using templating polymerization in porous silica gel bound with cholesterol molecules on its surface

Monodispersed molecularly imprinted polymer particles selective for cholesterol were prepared by the copolymerization of styrene and divinylbenzene in the presence of template silica gel particles (particle size: 5 μm; pore size: 10 nm) functionalized with cholesterol on the surface, followed by dissolution of the cholesterol-bonded silica gel with a NaOH aqueous solution. Transmission and scanning electron micrographs of the molecularly imprinted polymer (MIP) particles revealed good monodispersity and porous structure. The MIP particles were packed into a high performance liquid chromatographic column, and its recognition ability of cholesterol was evaluated using cholesterol, cholesterol esters and fatty acid methyl esters by comparison with the non-imprinted polymer (NIP) particles prepared from styrene and divinylbenzene without cholesterol. The MIP particles showed a high affinity for cholesterol and cholesterol esters (K(MIP)'/K(NIP)' > 5.7).     

Colorimetric test-systems for creatinine detection based on composite molecularly imprinted polymer membranes

An easy-to-use colorimetric test-system for the efficient detection of creatinine in aqueous samples was developed. The test-system is based on composite molecularly imprinted polymer (MIP) membranes with artificial receptor sites capable of creatinine recognition. A thin MIP layer was created on the surface of microfiltration polyvinylidene fluoride (PVDF) membranes using method of photo-initiated grafting polymerization. The MIP layer was obtained by co-polymerization of a functional monomer (e.g. 2-acrylamido-2-methyl-1-propanesulfonic acid, itaconic acid or methacrylic acid) with N, N′-methylenebisacrylamide as a cross-linker. The choice of the functional monomer was based on the results of computational modeling. The creatinine-selective composite MIP membranes were used for measuring creatinine in aqueous samples. Creatinine molecules were selectively adsorbed by the MIP membranes and quantified using color reaction with picrates. The intensity of MIP membranes staining was proportional to creatinine concentration in an analyzed sample. The colorimetric test-system based on the composite MIP membranes was characterized with 0.25 mM detection limit and 0.25–2.5 mM linear dynamic range. Storage stability of the MIP membranes was estimated as at least 1 year at room temperature. As compared to the traditional methods of creatinine detection the developed test-system is characterized by simplicity of operation, small size and low cost.     

孔雀石绿分子印迹膜的制备和渗透性

以0.45 μm混合纤维素酯微孔膜为支载膜,丙烯酰胺为功能单体,N, N'-亚甲基双丙烯酰胺为交联剂,通过原位聚合法制备得到孔雀石绿分子印迹膜,并研究了其对模板分子和类似物的渗透性能。以分子印迹膜作为渗透膜,单一渗透实验中,13 h后MG的渗透量达到0.118×10^-3 g/cm²,而相同时间内甲基紫、甲酚红和溴百里酚蓝的渗透量分别为0.064×10^-3、0.057×10^-3和0.044×10^-3 g/cm²,且在竞争渗透中孔雀石绿的渗透速率没有发生明显变化,而甲基紫的渗透速率却显著下降。实验表明,分子印迹膜对模板分子孔雀石绿表现出良好的渗透选择性,且在与类似物甲基紫的竞争渗透中具有优先渗透能力。     

Capacitive Chemical Sensor for Thiopental Assay Based on Electropolymerized Molecularly Imprinted Polymer

A novel capacitive sensor based on electropolymerized molecularly imprinted polymer (MIP) for thiopental detection is described. The molecularly imprinted film as a recognition element was prepared by electropolymerization of phenol on a gold electrode in the presence of thiopental (template). Cyclic voltammetry and capacitive measurements were used for characterization and evaluation of the polymeric film. The template molecules were removed from the modified electrode surface by washing with an ethanol:water solution. The sensor’s linear response range was between 3 and 20 µM, with a detection limit of 0.6 µM. The proposed sensor exhibited good selectivity, reproducibility. Satisfactory results were obtained in the direct detection of real samples.     

Fabrication and evaluation of molecularly imprinted regenerated cellulose composite membranes via atom transfer radical polymerization

A simple and effective method for surface molecularly imprinted composite membranes （MICMs） for artemisinin （Ars） based on regenerated cellulose membranes was first prepared through surface- initiated atom transfer radical polymerization （ATRP）, and the as-prepared MICMs were then evaluated as adsorbents for selective recognition and separation of Ars molecules. Batch rebinding studies were conducted to determine the specific adsorption equilibrium, kinetics and selective permeation performance. The adsorption capacity of MICMs toward Ars by the Langmuir isotherm model was 2.008 mgg-1, which was nearly 5.0 times higher than non-molecularly imprinted composite membranes （NICMs）. The kinetic property of MICMs was well-fitted by the pseudo-second-order rate equation. The selective permeation experiments were successfully investigated to prove the excellent selective permeation performance for Ars than the competitive analog （artemether）.     

A novel voltammetric sensor for ascorbic acid based on molecularly imprinted poly(o-phenylenediamine-co-o-aminophenol)

A molecularly imprinted copolymer, poly(o-phenylenediamine-co-o-aminophenol) (PoPDoAP), was prepared as a new ascorbic acid (AA) sensor. The copolymer was synthesized by incorporation of AA as template molecules during the electrochemical copolymerization of o-phenylenediamine and o-aminophenol, and complementary sites were formed after the copolymer was electrochemically reduced in ammonium aqueous solution. The molecularly imprinted copolymer sensor exhibited a high sensitivity and selectivity toward AA. Differential pulse voltammograms (DPVs) showed a linear concentration range of AA from 0.1 to 10 mM, and the detection limit was calculated to be 36.4 μM. Compared to conventional polyaniline-based AA sensors, the analytical performance of the imprinted copolymer sensor was improved due to the broadened usable pH range of PoPDoAP (from pH 1.0 to pH 8.0). The sensor also exhibited a good reproducibility and stability. And it has been successfully applied in the determination of AA in real samples, including vitamin C tablet and orange juices, with satisfactory results.     

Enantioselective sensor based on microgravimetric quartz crystal microbalance with molecularly imprinted polymer film

We report a novel quartz crystal microbalance sensor that provides enantioselectivity to dansylphenylalanine enantiomers by using a molecularly imprinted polymer film as a recognition element. The polymeric recognition thin film, imprinted with chiral dansyl-L-phenylalanine, was immobilised on a gold electrode modified with a photoactive precursor monolayer via a self-assembly process using photopolymerization. The fabricated sensor was able to discriminate between L- and D-dansylphenylalanine enantiomers in solution owing to the enantioselectivity of the imprinted sites. The enantiomeric composition of L- and D-enantiomeric mixtures could be quantitatively determined by the fabricated sensor. The detection limit is 5 micrograms mL-1 with a response range of 5-500 micrograms mL-1 at pH 10.0. The influence of the template concentration on the sensitivity and selectivity of the synthesised polymer membranes was investigated and optimised. The surface characteristics of the polymer coating were studied by varying the pH value of the buffer solution, and a convenient regeneration process was proposed to increase the reproducibility and reusability of the sensor by flushing with pH 2.0 buffer. The selectivity and recognition mechanism of the imprinted polymer film were studied with compounds that are structurally related to the template. The method presented in this work provides a novel means of preparing highly selective and sensitive chemical sensors via self-assembly and molecularly imprinting techniques.     

Water-compatible ‘aspartame’-imprinted polymer grafted on silica surface for selective recognition in aqueous solution

Molecularly imprinted polymers selective for aspartame have been prepared using N-[2-ammonium-ethyl-piperazinium) maleimidopropane sulfonate copolymer bearing zwitterionic centres along the backbone via a surface-confined grafting procedure. Aspartame, a dipeptide, is commonly used as an artificial sweetener. Polymerisation on the surface was propagated by means of Michael addition reaction on amino-grafted silica surface. Electrostatic interactions along with complementary H-bonding and other hydrophobic interactions inducing additional synergetic effect between the template (aspartame) and the imprinted surface led to the formation of imprinted sites. The MIP was able to selectively and specifically take up aspartame from aqueous solution and certain pharmaceutical samples quantitatively. Hence, a facile, specific and selective technique using surface-grafted specific molecular contours developed for specific and selective uptake of aspartame in the presence of various interferrants, in different kinds of matrices is presented.