Preparation and Recognition Properties of Vanillin‐Imprinted Polymers

Some new molecularly imprinted polymers (MIPs) were prepared by different protocols involving vanillin as the imprinted molecule, methacrylic acid (= 2‐methylprop‐2‐enoic acid; MAA) as the functional monomer, and ethylene glycol dimethacrylate (EGDMA = 2‐methylprop‐2‐enoic acid ethane‐1,2‐diyl ester) as the cross‐linking agent. The adsorption property of the imprinted polymers was studied by UV spectrophotometry and HPLC. The results indicated that the porogen solvent had a certain influence on the adsorption performance of the polymer. The vanillin‐imprinted polymer MIP₁ prepared with MeOH as porogen, exhibited advantageous characteristics, i.e., a high binding activity, a good selectivity, and a rapid adsorption equilibrium. The binding parameters studied by Scatchard analysis established that there are two types of binding sites in MIP₁. Finally, by packing an SPE column (SPE = solid‐phase extraction) with the polymer MIP₁, the vanillin was separated and enriched successfully by this sorbent from the samples of Vanilla fragrans and beer.     

Preparation and evaluation of a novel molecularly imprinted SPE monolithic capillary column for the determination of auramine O in shrimp

A novel method combining molecular imprinting and SPE was developed in a capillary column for the determination of auramine O in shrimp. The capillary monolithic column was prepared by UV‐initiated in situ polymerization, using auramine O as template and methacrylic acid and ethylene dimethacrylate as functional monomer and cross‐linker, respectively. The properties of the prepared capillary monolithic column were investigated under the optimized conditions coupled with HPLC, and then the morphologies of the inner polymers were characterized by SEM. The calibration curve was expressed as A = 103C + 19.8 (r = 0.9992) with a linear range of 0.25–25.0 μg/mL, and the recoveries of auramine O at different concentrations in shrimp ranged from 90.5 to 92.4% with RSDs ranging from 2.1 to 4.4%. The capacities of the molecularly imprinted polymer and nonimprinted polymer columns were 0.722 and 0.147 μg/mg, respectively, and the LOD (S/N = 3) of auramine O in shrimp was 17.85 μg/kg. Under the selected conditions, the enrichment factors obtained were higher than 70‐fold. The results indicate that the prepared molecularly imprinted capillary monolithic column was reliable and applicable to the analysis of auramine O in shrimp.     

电色谱模式下四肽印迹整体柱分子识别机理的研究

本文采用原位聚合法制备了以四肽YPLG为模板的毛细管分子印迹整体柱,在毛细管电色谱模式下以模板分子和它的结构类似物YPGL为样品,对分子印迹聚合物的识别机理进行了研究。这两种四肽由于化学结构相似且等电点非常相近,普通的电色谱和毛细管电泳方法分离非常困难。但我们的实验表明,印迹整体柱对模板分子具有特异性识别能力,因此YPLG与YPGL之间的分离因子为1.73,分离度达3.72。实验中系统地研究了流动相中有机溶剂的含量、缓冲溶液的pH值、缓冲溶液的盐浓度以及柱温对四肽识别的影响。实验中我们观察到模板在印迹柱上具有非线性的Van’t Hoff行为,揭示可能存在多重保留机理。本研究结果表明,在毛细管电色谱模式下,分子印迹整体柱的分子识别主要决定于样品与印迹聚合物之间的氢键作用以及印迹孔穴的三维结构。     

Selective and sensitive determination of protoberberines by capillary electrophoresis coupled with molecularly imprinted microextraction

In this work, we developed a novel molecularly imprinted solid‐phase microextraction with capillary electrophoresis method for the selective extraction and determination of protoberberines in complicated samples. The imprinted monolith was prepared in a micropipette tip‐based device by using acrylamide as the functional monomer, ethyleneglyoldimethacrylate as the cross‐linker and dimethylsulfoxide as the porogen, and exhibited an imprinting factor of 2.41 to berberine, 2.36 to palmatine and 2.38 to jatrorrhizine. Good capillary electrophoresis separation was achieved by using 20 mM phosphate buffer at pH 7 as running buffer with the addition of organic modifier of 10% methanol. Parameters such as sample pH value, sample flow rate and sample volume were investigated for imprinted monolith‐based solid‐phase microextraction. An imprinted solid‐phase microextraction with capillary electrophoresis method was developed, the method showed a wide linear range (0.3–50 μg/mL), good linearity (R² ≥ 0.9947) and good reproducibility (relative standard deviations ≤ 0.73%), the limit of detection was as low as 0.1 μg/mL, which was lower than some reported methods based on capillary electrophoresis for protoberberines. The method has been applied for determination of three common protoberberines in Cortex Phellodendri Chinensis, by using a molecularly imprinted monolith as the selective sorbent, most of the matrices in the Cortex Phellodendri Chinensis sample were removed and three protoberberines were selectively enriched and well determined.     

Preparation and characterization of a molecularly imprinted monolithic column for pressure‐assisted CEC separation of nitroimidazole drugs

A polymethacrylate‐based molecularly imprinted monolithic column bearing mixed functional monomers, using non‐covalent imprinting approach, was designed for the rapid separation of nitroimidazole compounds. The new monolithic column has been prepared via simple in situ polymerization of 2‐hydroxyethyl methacrylate, dimethylaminoethyl methacrylate and ethylene dimethacrylate, using (S)‐ornidazole ((S)‐ONZ) as template in a binary porogenic mixture consisting of toluene and dodecanol. The composition of the polymerization mixture was systematically altered and optimized by altering the amount of monomers as well as the composition of the porogenic solvent. The column performance was evaluated in pressure‐assisted CEC mode. Separation conditions such as pH, voltage, amount of organic modifier and salt concentration were studied. The optimized monolithic column resulted in excellent separation of a group of structurally related nitroimidazole drugs within 10 min in isocratic elution condition. Column efficiencies of 99 000, 80 000, 103 000, 60 000 and 99 000 plates/m were obtained for metronidazole, secnidazole, ronidazole, tinidazole and dimetridazole, respectively. Parallel experiments were carried out using molecularly imprinted and non‐imprinted capillary columns. The separation might be the result of combined effects including hydrophobic, hydrogen bonding and the imprinting cavities on the (S)‐ONZ‐imprinted monolithic column.     

Preparation of a monolithic column with a mixed‐mode stationary phase of reversed‐phase/hydrophilic interaction for capillary liquid chromatography

A monolithic capillary column with a mixed‐mode stationary phase of reversed‐phase/hydrophilic interaction chromatography was prepared for capillary liquid chromatography. The monolith was created by an in‐situ copolymerization of a homemade monomer N,N‐dimethyl‐N‐acryloxyundecyl‐N‐(3‐sulfopropyl) ammonium betaine and a crosslinker pentaerythritol triacrylate in a binary porogen agent consisting of methanol and isopropanol. The functional monomer was designed to have a highly polar zwitterionic sulfobetaine terminal group and a hydrophobic long alkyl chain moiety. The composition of the polymerization solution was systematically optimized to permit the best column performance. The columns were evaluated by using acidic, basic, polar neutral analytes, as well as a set of alkylbenzenes and Triton X100. Very good separations were obtained on the column with the mixed‐mode stationary phase. It was demonstrated that the mixed‐mode stationary phase displayed typic dual retention mechanisms of reversed‐phase/hydrophilic interaction liquid chromatography depending on the content of acetonitrile in the mobile phase. The method for column preparation is reproducible.     

Preparation of molecularly imprinted polymeric fibers using a single bifunctional monomer for the solid‐phase microextraction of parabens from environmental solid samples

In this study, molecularly imprinted polymer fibers for solid‐phase microextraction have been prepared with a single bifunctional monomer, N,O‐bismethacryloyl ethanolamine using the so‐called “one monomer molecularly imprinted polymers” method, replacing the conventional combination of functional monomer and cross‐linker to form high fidelity binding sites. For comparison, imprinted fibers were prepared following the conventional approach based on ethylene glycol dimethacrylate as cross‐linker and methacrylic acid as monomer. The recognition performance of the new fibers was evaluated in the solid‐phase microextraction of parabens, and from this study it was concluded that they provided superior performance over conventionally formulated fibers. Ultimately, real‐world environmental testing on spiked solid samples was successful by the molecularly imprinted solid‐phase microextraction of samples, and the relative recoveries obtained at enrichment levels of 10 ng/g of parabens were within 78–109% for soil and 83–109% for sediments with a relative standard deviation <15% (n = 3).     

Preparation and Characteristics of Esculin‐Imprinted Polymers

Four molecularly imprinted polymers (MIPs) were prepared in MeOH with esculin (=6,7‐dihydroxycoumarin 6‐(β‐D ‐glucopyranoside)=6‐(β‐D ‐glucopyranosyloxy)‐7‐hydroxy‐2H‐1‐benzopyran‐2‐one) as the imprinted molecule, methacrylic acid (=2‐methylprop‐2‐enoic acid; MAA), acrylamide (=prop‐2‐enamide; AM), 4‐vinylpyridine (=4‐ethenylpyridine; 4‐VP), or 2‐vinylpyridine (=2‐ethenylpyridine; 2‐VP) as the functional monomer, respectively, as well as ethylene glycol dimethacrylate (=2‐methylprop‐2‐enoic acid ethane‐1,2‐diyl ester; EGDMA) as the cross‐linking agent. The interaction between the template and the functional monomers was investigated by fluorescence and UV spectrophotometry, respectively, which revealed the presence of esculin/monomer complexes in the stoichiometric ratio 1 : 2 in the pre‐polymerization mixture. The resultant polymers were studied in equilibrium binding experiments to evaluate the recognition ability and the binding capacity towards esculin. The results showed that MIP₁, prepared with MAA as the functional monomer, exhibited advantageous characteristics of high binding capacity, optimal imprinting effect, and good selectivity towards esculin. The Scatchard analysis indicated that there are two types of binding sites in MIP₁, and its binding parameters including the apparent maximum numbers of binding sites and the dissociation constants were calculated. Finally, by packing an SPE column (SPE=solid‐phase extraction) with MIP₁, the esculin was separated and enriched successfully by this sorbent from samples of Cortex fraxini, and the average recovery was up to 74.7%.     

Preparation and Characterization of Trans‐Resveratrol Imprinted Polymers

Abstract

In order to selectively extract trans‐resveratrol from Chinese herbs, molecularly imprinted polymers (MIPs) were prepared with trans‐resveratrol as the template molecule. The influences of porogenic solvents and functional monomers on the recognition properties of the polymer were studied. The MIP, which was prepared in acetone using 4‐vinylpyridine as functional monomer, displayed good affinity and recognition property for the template molecule. This indicates that the 4‐vinylpyridine can form hydrogen‐bonding or ionic interaction with trans‐resveratrol. Experimental result also indicated that the MIP column can separate trans‐resveratrol from matrix components in the Polygonum cuspidatum extract.     

分子印迹整体柱在高效液相色谱和电色谱手性分离中的应用

在常规不锈钢色谱管中以甲基丙烯酸为功能单体,采用原位聚合法制备了(5S,11S)-特罗格尔碱(S-TB)的印迹整体柱。考察了流动相中添加不同量的醋酸和水对分离的影响,结合台阶梯度洗脱模式在S-TB整体柱上实现了对TB消旋体的快速分离。另外,以碱性单体2-二甲基乙基胺甲基丙烯酸酯(DAMA)为功能单体,在毛细管中采用原位聚合法制备了毛细管分子印迹整体柱,用于在毛细管电色谱（CEC）中对消旋体1,1′-联-2-萘酚(BNL)进行手性分离。结果表明,以AMA为功能单体可以制备其他酸性模板的分子印迹聚合物,从而扩大了分子印迹聚合物MIP）在CEC分离中的应用范围。     

Synthesis of multidentate functional monomer for ion imprinting

In this work, N,N,N‐tri(2‐carboxyethyl)‐3‐(2‐aminoethylamino)propyl‐trimethoxysilane was prepared as a multidentate functional monomer. The 3D model of the monomer coordinating with Cu²⁺ indicated that the monomer is able to provide five ligating atoms like ethylenediaminetetraacetic acid‐Cu²⁺ to complex with Cu²⁺. When Cu²⁺ was used as a template ion, the synthesis conditions of Cu²⁺‐imprinted polymers were optimized upon orthogonal design. It is interesting to find that Cu²⁺‐imprinted polymer offers a selectivity coefficient of 192.2 when the molar ratio of Cu²⁺ to monomer was exactly 1:1. That means there is no excess ligating atom in the ion‐imprinted polymer and therefore, the nonspecific adsorption could be avoided. Benefiting from the excellent selectivity of Cu²⁺‐imprinted polymer, even if the concentration of Zn²⁺ was 25 times that of Cu²⁺, Cu²⁺‐imprinted polymer still affords a high selectivity coefficient. Finally, the optimal synthesis conditions for Cu²⁺‐imprinted polymer, except the pH, were adopted to prepare Ni²⁺‐imprinted polymer, and Ni²⁺‐imprinted polymer also offered satisfying selectivity to Ni²⁺. That implies this multidentate monomer is adaptable in ion imprinting and, the optimal synthesis conditions of Cu²⁺‐imprinted polymer except pH are likely suitable for the imprinting of other ions besides Cu²⁺.     

Hydrophobic ionic liquid modified thermoresponsive molecularly imprinted monolith for the selective recognition and separation of tanshinones

A hydrophobic ionic liquid modified thermoresponsive molecularly imprinted monolith was synthesized using N‐isopropylacrylamide as a thermoresponsive monomer and a long‐chain hydrophobic ionic liquid as an auxiliary modification monomer. The ionic‐liquid‐modified thermoresponsive molecularly imprinted polymer was characterized by scanning electron microscopy and Fourier transform infrared spectroscopy. When the column temperature was 50°C, the synthesized monolithic column was successfully applied to the selective separation of homologue tanshinones within 7 min and eluted only by water (mobile phase) (theoretical plates more than 1.00 × 10⁵ per meter). The negative Gibbs free energy (≤–2.37) values showed that the transfer of the tanshinones from the mobile phase to the stationary phase on this monolithic column was a thermodynamically spontaneous process. Good linearity of the five tanshinones by thermoresponsive monolith was obtained in the range of 0.100–25.0 μg/mL. The limit of detection (S/N = 3) and limit of quantitation (S/N = 10) were less than 0.0390 and 0.0630 μg/mL, respectively, with a relative standard deviation of <4.8%. In this proposed thermoresponsive chromatography method, the separation of homologue analytes can be achieved by changing the column temperature, and the use of water as the mobile phase would decrease the economic cost and organic pollution.     

Counterflow isotachophoresis in a monolithic column

This study describes stationary counterflow isotachophoresis (ITP) in a poly(acrylamide‐co‐N,N′‐methylenebisacrylamide) monolithic column as a means for improving ITP processing capacity and reducing dispersion. The flow profile in the monolith was predicted using COMSOL's Brinkman Equation application mode, which revealed that the flow profile was mainly determined by monolith permeability. As monolith permeability decreases, the flow profile changes from a parabolic shape to a plug shape. An experimental monolithic column was prepared in a fused‐silica capillary using an ultraviolet‐initiated polymerization method. A monolithic column made from 8% (wt.) monomer was chosen for the stationary counterflow ITP experiments. Counterflow ITP in the monolithic column showed undistorted analyte zones with significantly reduced dispersion compared to the severe dispersion observed in an open capillary. Particularly, for r‐phycoerythrin focused by counterflow ITP, its zone width in the monolithic column was only one‐third that observed in an open capillary. These experiments demonstrate that stationary counterflow ITP in monoliths can be a robust and practical electrofocusing method.     

分子印迹聚合物的制备及其对香草醛的吸附行为

以香草醛为模板分子、甲基丙烯酸为功能单体、乙二醇二甲基丙烯酸酯为交联剂,制备了香草醛分子印迹聚合物(MIP);研究了以不同致孔剂合成的MIP在水溶液中对香草醛的吸附行为.结果表明,以乙腈为致孔剂合成的MIP对香草醛具有较高的识别特性,能较简便地用于香草醛的分离和富集.     

Photografted methacrylate‐based monolithic columns coated with cellulose tris(3,5‐dimethylphenylcarbamate) for chiral separation in CEC

A chiral capillary monolithic column for enantiomer separation in capillary electrochromatography was prepared by coating cellulose tris(3,5‐dimethylphenylcarbamate) on porous glycidyl methacrylate‐co‐ethylene dimethacrylate monolith in capillary format grafted with chains of [2(methacryloyloxy)ethyl] trimethylammonium chloride. The surface modification of the monolith by the photografting of [2(methacryloyloxy)ethyl] trimethylammonium chloride monomer as well as the coating conditions of cellulose tris(3,5‐dimethylphenylcarbamate) onto the grafted monolithic scaffold were optimized to obtain a stable and reproducible chiral stationary phase for capillary electrochromatography. The effect of organic modifier (acetonitrile) in aqueous mobile phase for the enantiomer separation by capillary electrochromatography was also investigated. Several pairs of enantiomers including acidic, neutral, and basic analytes were tested and most of them were partially or completely resolved under aqueous mobile phases. The prepared monolithic chiral stationary phases exhibited a good stability, repeatability, and column‐to‐column reproducibility, with relative standard deviations below 11% in the studied electrochromatographic parameters.     

Synthesis of a nano‐sized chiral imprinted polymer and its use as an (S)‐atenolol carrier in the bulk liquid membrane

In this work, nanosized chiral imprinted polymers containing (S)‐atenolol ((S)‐ATN) selective sites were synthesized by using suspension polymerization in silicon oil. (S)‐ATN, methacrylic acid, and ethylene glycol dimethacrylate were used as enantiomerically pure template, functional monomer, and cross‐linker, respectively. The prepared chiral imprinted polymers were used as the carrier elements in a bulk liquid membrane (BLM). (S)‐ATN transport capability of the chiral imprinted polymers was compared with that of the nonimprinted polymer. It was shown that chiral imprinted polymers could transport (S)‐ATN through the BLM more effectively than (R)‐ATN, whereas no difference in the facilitated transport was observed between (R)‐ATN and (S)‐ATN when using nonimprinted polymer particles as the carrier element in the BLM. A kinetic model was proposed for the transportation of (S)‐ATN through the chiral imprinted polymers based BLM. It was found that the extraction of ATN from the source to the membrane controls the chiral separation process. It was also found that the pH of source and receiving phases as well as the racemic ATN concentration in source phase had very crucial effect on the chiral separation efficiency.     

Selective enrichment and separation of phosphotyrosine peptides by thermosensitive molecularly imprinted polymers

Novel thermosensitive molecularly imprinted polymers were successfully prepared using the epitope imprinting approach in the presence of the mimic template phenylphosphonic acid, the functional monomer vinylphosphonic acid‐Ti⁴⁺, the temperature‐sensitive monomer N‐isopropylacrylamide and the crosslinker N,N′‐methylenebisacrylamide. The ratio of the template/thermosensitive monomers/crosslinker was optimized, and when the ratio was 2:2:1, the prepared thermosensitive molecularly imprinted polymers had the highest imprinting factor. The synthetic thermosensitive molecularly imprinted polymers were characterized by Fourier transform infrared spectroscopy to reveal the combination and elution processes of the template. Then, the adsorption capacity and thermosensitivity was measured. When the temperature was 28°C, the imprinting factor was the highest. The selectivity and adsorption capacity of the thermosensitive molecularly imprinted polymers for phosphotyrosine peptides from a mixture of three tailor‐made peptides were measured by high‐performance liquid chromatography. The results showed that the thermosensitive molecularly imprinted polymers have good selectivity for phosphotyrosine peptides. Finally, the imprinted hydrogels were applied to specifically adsorb phosphotyrosine peptides from a sample mixture containing phosphotyrosine and a tryptic digest of β‐casein, which demonstrated high selectivity. After four rebinding cycles, 78.9% adsorption efficiency was still retained.     

Photoirradiation surface molecularly imprinted polymers for the separation of 6‐O‐α‐d‐maltosyl‐β‐cyclodextrin

Photoirradiation surface molecularly imprinted polymers for the separation of 6‐O‐α‐d ‐maltosyl‐β‐cyclodextrin were synthesized using functionalized silica as a matrix, 4‐(phenyldiazenyl)phenol as a light‐sensitive monomer, and 6‐O‐α‐d ‐maltosyl‐β‐cyclodextrin as a template. Fourier transform infrared spectroscopy results indicated that 4‐(phenyldiazenyl)phenol was grafted onto the surface of functionalized silica. The obtained imprinted polymers exhibited specific recognition toward 6‐O‐α‐d ‐maltosyl‐β‐cyclodextrin. Equilibrium binding experiments showed that the photoirradiation surface molecularly imprinted polymers obtained the maximum adsorption amount of 6‐O‐α‐d ‐maltosyl‐β‐cyclodextrin at 20.5 mg/g. In binding kinetic experiments, the adsorption reached saturation within 2 h with binding capacity of 72.8%. The experimental results showed that the adsorption capacity and selectivity of imprinted polymers were effective for the separation of 6‐O‐α‐d ‐maltosyl‐β‐cyclodextrin, indicating that imprinted polymers could be used to isolate 6‐O‐α‐d ‐maltosyl‐β‐cyclodextrin from a conversion mixture containing β‐cyclodextrin and maltose. The results showed that the imprinted polymers prepared by this method were very promising for the selective separation of 6‐O‐α‐d ‐maltosyl‐β‐cyclodextrin.     

Preparation of Imprinted PVB/β‐CD Nanofiber by Electrospinning Technique and Its Selective Binding Abilities for Naringin

A novel molecularly imprinted composite nanofiber was prepared by a simple electrospinning technique, in which polyvinylbutyral (PVB) was chosen as matrix, β‐cyclodextrin (β‐CD) was used as a functional monomer and naringin (NG) as template molecules. After cross‐linked by hexamethylene diisocyanate (HMDI), the composite nanofiber exhibited a high specific binding capacity. The morphological structure of the nanofibers was studied by means of infrared spectrum (IR), X‐ray diffraction (XRD), and scanning electron microscopy (SEM). The β‐CD molecules were mostly homogeneously distributed within the PVB nanofiber without forming phase separated crystalline aggregates. Compared with traditional imprinted β‐CD polymer, the binding experiments demonstrated that the molecularly imprinted composite nanofiber shows the specific binding sites and the selective binding ability for NG. The molecularly imprinted nanofiber could be used at least six times without any loss in binding capacity.     

Rapid Separation of Proteins by Capillary HPLC on a Short Polymethacrylate-based Strong Cation-exchange Monolithic Column

A polymethacrylate‐based strong cation‐exchange capillary monolithic column was prepared by in‐situ copolymerization for the fast separation of proteins. Glycidyl methacrylate (GMA) was used as monomer, ethylenedimethacrylate (EDMA) as cross link agent and the mixture of 1‐propanol, 1,4‐butanediol and water as porogen solvent. The monolith was sulfonated using 1 mol/L Na₂SO₃ based on a ring opening of epoxides. The influences of the contents of the porogen solvent and GMA and the various concentration ratios of 1‐propanol to 1,4‐butanediol in the polymerization mixture on the morphology, porosity, globule size, stability and column efficiency were investigated. The morphology and pore size distribution of the monolith were characterized by SEM and mercury intrusion porosimetry, respectively. Using only 1.5 cm length of this monolithic capillary column, four kinds of proteins, trypsin, cytochrome C, lysozyme (egg white) and egg albumin, were successfully separated from each other in 5 min at a high flow rate of 110 mm/s.