Preparation and evaluation of temperature and magnetic dual‐responsive molecularly imprinted polymers for the specific enrichment of formononetin

Thermo‐responsive magnetic molecularly imprinted polymers were prepared by simple surface molecular imprinting polymerization for the selective adsorption and enrichment of formononetin from Trifolium pretense by temperature regulation. Using formononetin as a template, N‐isopropylacrylamide as the thermo‐responsive functional monomer, and methacrylic acid as an assisting functional monomer, the polymers were synthesized on the surface of the magnetic substrate. The results show that imprinted polymers attained controlled adsorption of formononetin in response to the temperature change, with large adsorption capacity (16.43 mg/g), fast kinetics (60 min) and good selectivity at 35°C compared with that at 25 and 45°C. The selectivity experiment indicated that the materials had excellent recognition ability for formononetin and the selectivity factors were between 1.32 and 2.98 towards genistein and daidzein. The excellent linearity was attained in the range of 5–100 μg/mL, with low detection limits and low quantitation limits of 0.017 and 0.063 μg/mL, respectively. Furthermore, the thermo‐responsive magnetic molecularly imprinted polymers were successfully utilized for enriching and purifying formononetin from Trifolium pretense. The analytical results indicate that the imprinted polymers are promising materials for selective identification and enrichment of formononetin in complicated herbal medicines by simple temperature‐responsive regulation.     

Molecularly imprinted polymers with synthetic dummy templates for the preparation of capsaicin and dihydrocapsaicin from chili peppers

In this work, dummy molecularly imprinted polymers with high selectivity and affinity to capsaicin and dihydrocapsaicin are designed using N‐vanillylnonanamide as a dummy template. The performance of dummy molecularly imprinted polymers and nonimprinted polymers was evaluated using adsorption isotherms, adsorption kinetics, and selective recognition capacity. Dummy molecularly imprinted polymers were found to exhibit good site accessibility, taking just 20 min to achieve adsorption equilibrium; they were also highly selective toward capsaicin and dihydrocapsaicin. We successfully used dummy molecularly imprinted polymers as a specific sorbent for selectively enriching capsaicin and dihydrocapsaicin from chili pepper samples. In a scaled‐up experiment, the selective recovery of capsaicinoids was calculated to be 77.8% using solid‐phase extraction. To the best of our knowledge, this is the first example of the use of N‐vanillylnonanamide as a dummy template in molecularly imprinted polymers to simultaneously enrich capsaicin and dihydrocapsaicin.     

Preparation of melamine molecularly imprinted polymer by computer‐aided design

Melamine was chosen as template, methacrylic acid was chosen as functional monomer, and divinylbenzene, ethylene glycol dimethacrylate, trimethylolpropane trimethylacrylate were chosen as cross‐linking agents, respectively. The WB97XD/6‐31G(d, p) method was used to calculate the geometry optimization of the different imprinting ratios, the action sites, the bonding situation, and the optimization of the cross‐linking agents. The nature of the imprinting effect was also studied by the atoms in molecules theory. The theoretical results showed that melamine interacts with methacrylic acid by hydrogen bonding, and the melamine molecularly imprinted polymers with a molar ratio of 1:6 have the most hydrogen bonds and the most stable structure. Divinylbenzene is the best cross‐linking agent for the melamine molecularly imprinted polymers. The melamine molecularly imprinted polymers were synthesized by precipitation polymerization. The results showed that the maximum adsorption capacity for molecularly imprinted polymers towards melamine is 19.84 mg/g, and the adsorption quantity of the polymers to melamine is obviously higher than that of cyromazine, cyanuric acid, and trithiocyanuric in milk. This study could provide theoretical and experimental references for the screening of the imprinting ratio and the cross‐linking agent for the given template and monomer system.     

Preparation of magnetic molecularly imprinted polymers by atom transfer radical polymerization for the rapid extraction of avermectin from fish samples

A novel and highly efficient approach to obtain magnetic molecularly imprinted polymers is described to detect avermectin in fish samples. The magnetic molecularly imprinted polymers were synthesized by surface imprinting polymerization using magnetic multiwalled carbon nanotubes as the support materials, atom transfer radical polymerization as the polymerization method, avermectin as template, acrylamide as functional monomer, and ethylene glycol dimethacrylate as crosslinker. The characteristics of the magnetic molecularly imprinted polymers were assessed by using transmission electron microscopy, Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy, vibrating sample magnetometry, X‐ray diffraction, and thermogravimetric analysis. The binding characteristics of magnetic molecularly imprinted polymers were researched through isothermal adsorption experiment, kinetics adsorption experiment, and the selectivity experiment. Coupled with ultra high performance liquid chromatography and tandem mass spectrometry, the extraction conditions of the magnetic molecularly imprinted polymers as adsorbents for avermectin were investigated in detail. The recovery of avermectin was 84.2–97.0%, and the limit of detection was 0.075 μg/kg. Relative standard deviations of intra‐ and inter‐day precisions were in the range of 1.7–2.9% and 3.4–5.6%, respectively. The results demonstrated that the extraction method not only has high selectivity and accuracy, but also is convenient for the determination of avermectin in fish samples.     

酚酞分子印迹聚合物的制备及特异吸附性能

以泻药酚酞为模板分子,4-乙烯基吡啶为功能单体制备了模板分子和功能单体不同比例的一系列酚酞分子印迹聚合物。利用扫描电镜对聚合物进行了表面形态分析,采用静态平衡实验法研究了聚合物对模板分子及其类似物的吸附行为和选择性识别能力。实验结果表明,所制备的分子印迹聚合物,吸附 3 h 后基本接近最大吸附量,其中模板分子、4-乙烯基吡啶和交联剂的摩尔比为 1∶6∶20的MIP2的印迹因子为 2.30,效果最佳。Scatchard 分析表明, 在所研究的浓度范围内,吸附过程存在两类结合位点,一类高亲和力结合位点的离解常数为Kd1= 0.63 mmol/L,最大表观结合量 Qmax1 = 25.4 umol/g,另一类低亲和力结合位点的离解常数为 Kd2 =3.5 mmol/L,最大表观结合量 Qmax2 = 61.9 umol/g,通过与酚酞类似物质在酚酞分子印迹聚合物上的吸附行为比较,表明对酚酞具有很好的选择性吸附。     

Molecularly imprinted polymer functionalized magnetic Fe3O4 for the highly selective extraction of triclosan

We present a facile strategy to prepare the molecularly imprinted polymers layer on the surface of Fe₃O₄ nanoparticles with core‐shell structure via sol–gel condensation for recognition and enrichment of triclosan. The Fe₃O₄ nanoparticles were first synthesized by a solvothermal method. Then, template triclosan was self‐assembled with the functional monomer 3‐aminopropyltriethoxysilane on the silica‐coated Fe₃O₄ nanoparticles in the presence of ethanol and water. Finally, the molecularly imprinted polymers were formed on the surface of silica‐coated Fe₃O₄ nanoparticles to obtain the product. The morphology, magnetic susceptibility, adsorption, and recognition property of magnetic molecularly imprinted polymers were characterized using transmission electron microscopy, Fourier transform infrared spectroscopy, X‐ray diffractometry, vibrating sample magnetometry, and re‐binding experiments. The magnetic molecularly imprinted polymers showed binding sites with good accessibility, fast adsorption rate, and high adsorption capacity (218.34 μg/g) to triclosan. The selectivity of magnetic molecularly imprinted polymers was evaluated by the rebinding capability of triclosan and two other structural analogues (phenol and p‐chlorophenol) in a mixed solution and good selectivity with an imprinting factor of 2.46 was obtained. The application of triclosan removal in environmental samples was demonstrated.     

Development of a molecularly imprinted solid‐phase extraction sorbent for the selective extraction of telmisartan from human urine

A novel molecularly imprinted solid‐phase extraction with spectrofluorimetry method has been developed for the selective extraction of telmisartan from human urine. Molecularly imprinted polymers were prepared by a noncovalent imprinting approach through UV‐radical polymerization using telmisartan as a template molecule, 2‐dimethylamino ethyl methacrylate as a functional monomer, ethylene glycol dimethacrylate as a cross‐linker, N,N‐azobisisobutyronitrile as an initiator, chloroform as a porogen. Molecularly imprinted polymers and nonimprinted control polymer sorbents were dry‐packed into solid‐phase extraction cartridges, and eluates from cartridges were analyzed using a spectrofluorimeter. Limit of detection and limit of quantitation values were 11.0 and 36.0 ng/mL, respectively. A very high imprinting factor (16.1) was achieved and recovery values for the telmisartan spiked in human urine were in the range of 76.1–79.1%. In addition, relatively low within‐day (0.14–1.6%) and between‐day (0.11–1.31%) precision values were obtained. Valsartan was used to evaluate the selectivity of sorbent as well. As a result, a sensitive, selective, and simple molecularly imprinted solid‐phase extraction with spectrofluorimetry method has been developed and successfully applied to the direct determination telmisartan in human urine.     

Preconcentration of indapamide from human urine using molecularly imprinted solid‐phase extraction

A simple, sensitive, and selective molecularly imprinted solid‐phase extraction and spectrophotometric method has been developed for the clean‐up and preconcentration of indapamide from human urine. Molecularly imprinted polymers were prepared by a non‐covalent imprinting approach using indapamide as a template molecule, 2‐(trifluoromethyl) acrylic acid as a functional monomer, ethylene glycol dimethacrylate as a crosslinker, N,N‐azobisisobutyronitrile as a thermal initiator and acetonitrile as a porogenic solvent. A non‐imprinted polymer was also prepared in the same way, but in the absence of template. Molecularly imprinted polymer and non‐imprinted polymer sorbents were dry‐packed into solid‐phase extraction cartridges. Eluates from cartridges were analyzed using a spectrophotometer for the determination of indapamide by referring to the calibration curve in the range 0.14–1.50 μg/mL. Preconcentration factor, limit of detection, and limit of quantification were 16.30, 0.025 μg/mL, and 0.075 μg/mL, respectively. A relatively high imprinting factor (9.3) was also achieved and recovery values for the indapamide spiked into human urine were in the range of 80.1–81.2%. In addition, relatively low within‐day (0.17–0.42%) and between‐day (1.1–1.4%) precision values were obtained as well. The proposed molecularly imprinted solid‐phase extraction and spectrophotometric method was successfully applied to selective extraction, preconcentration, and determination of indapamide from human urine samples.     

Ordered macroporous quercetin molecularly imprinted polymers: Preparation,characterization, and separation performance

Ordered macroporous molecularly imprinted polymers were prepared by a combination of the colloidal crystal templating method and the molecular imprinting technique by using SiO₂ colloidal crystal as the macroporogen, quercetin as the imprinting template, acrylamide as the functional monomer, ethylene glycol dimethacrylate as the cross‐linker and tetrahydrofuran as the solvent. Scanning electron microscopy and Brunauer–Emmett–Teller measurements show that the ordered macroporous molecularly imprinted polymers have a more regular macroporous structure, a narrower pore distribution and a greater porosity compared with the traditional bulk molecularly imprinted polymers. The kinetic and isothermal adsorption behaviors of the polymers were investigated. The results indicate that the ordered macroporous molecularly imprinted polymers have a faster intraparticle mass transfer process and a higher adsorption capacity than the traditional bulk molecularly imprinted polymers. The ordered macroporous molecularly imprinted polymers were further employed as a sorbent for a solid‐phase extraction. The results show that the ordered macroporous molecularly imprinted polymers can effectively separate quercetin from the Gingko hydrolysate.     

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     

Theoretical and experimental studies on the performances of barbital‐imprinted systems

By using density functional theory, we studied the interaction process between barbital and 2‐vinyl‐4,6‐diamino‐1,3,5‐triazine in acetonitrile at 333 K. Barbital and 2‐vinyl‐4,6‐diamino‐1,3,5‐triazine were used as the template and functional monomer, respectively. The molecularly imprinted polymer microspheres containing barbital and 2‐vinyl‐4,6‐diamino‐1,3,5‐triazine were synthesized through precipitation polymerization. After removing the template molecule barbital, the average diameter of the obtained molecularly imprinted polymers was 1.45 μm. By optimizing the molar ratio of barbital and the 2‐vinyl‐4,6‐diamino‐1,3,5‐triazine, the resulting molecularly imprinted polymers showed the highest adsorption for the barbital. The analysis of the Scatchard plot revealed that the dissociation constant (K_d) and apparent maximum adsorption quantity (Q_max) of the molecularly imprinted polymers were 30.69 mg/L and 8.68 mg/g, respectively. The study of selective adsorption showed that molecularly imprinted polymers exhibited higher selectivity for barbtital than that for 1,3‐dimethyl barbituric acid and pentobarbital. Herein, the studies can provide theoretical and experimental references for the barbital‐imprinted system.     

Highly selective and efficient imprinted polymers based on carboxyl‐functionalized magnetic nanoparticles for the extraction of gallic acid from pomegranate rind

With the combined surface imprinting technique and immobilized template strategy, molecularly imprinted magnetic nanoparticles were successfully prepared and coupled with high‐performance liquid chromatography to selectively separate and determine gallic acid from the pomegranate rind. On the surface of carboxyl‐functionalized magnetic nanospheres, thin imprinting shells were formed using dopamine as monomer and crosslinker. The characteristics, polymerization conditions, and adsorption performances of the resultant nanomaterials were investigated in detail. In addition of good crystallinity, satisfactory magnetism, and uniform morphology of the obtained polymers, they had rapid binding kinetics, high adsorption capacity, and favorable reusability. In the mixed solution of four hydroxybenzoic acids, the prepared nanomaterials have an excellent selectivity to gallic acid with an imprinting factor of as high as 17.5. Therefore, the polymers have great potentials in specific extraction and enrichment of gallic acid from the complex natural resources.     

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

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

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 molecularly imprinted polymers for strychnine by precipitation polymerization and multistep swelling and polymerization and their application for the selective extraction of strychnine from nux‐vomica extract powder

Monodisperse molecularly imprinted polymers for strychnine were prepared by precipitation polymerization and multistep swelling and polymerization, respectively. In precipitation polymerization, methacrylic acid and divinylbenzene were used as a functional monomer and crosslinker, respectively, while in multistep swelling and polymerization, methacrylic acid and ethylene glycol dimethacrylate were used as a functional monomer and crosslinker, respectively. The retention and molecular recognition properties of the molecularly imprinted polymers prepared by both methods for strychnine were evaluated using a mixture of sodium phosphate buffer and acetonitrile as a mobile phase by liquid chromatography. In addition to shape recognition, ionic and hydrophobic interactions could affect the retention of strychnine in low acetonitrile content. Furthermore, molecularly imprinted polymers prepared by both methods could selectively recognize strychnine among solutes tested. The retention factors and imprinting factors of strychnine on the molecularly imprinted polymer prepared by precipitation polymerization were 220 and 58, respectively, using 20 mM sodium phosphate buffer (pH 6.0)/acetonitrile (50:50, v/v) as a mobile phase, and those on the molecularly imprinted polymer prepared by multistep swelling and polymerization were 73 and 4.5. These results indicate that precipitation polymerization is suitable for the preparation of a molecularly imprinted polymer for strychnine. Furthermore, the molecularly imprinted polymer could be successfully applied for selective extraction of strychnine in nux‐vomica extract powder.     

Synthesis of molecularly imprinted polymers by atom transfer radical polymerization for the solid‐phase extraction of phthalate esters in edible oil

Novel molecularly imprinted polymers of phthalate esters were prepared by atom transfer radical polymerization using methyl methacrylate as functional monomer, cyclohexanone as solvent, cuprous chloride as catalyst, 1‐chlorine‐1‐ethyl benzene as initiator and 2,2‐bipyridyl as cross‐linker in the mixture of methanol and water (1:1, v/v). The effect of reaction conditions such as monomer ratio and template on the adsorption properties was investigated. The optimum condition was obtained by an orthogonal experiment. The obtained polymers were characterized using scanning electron microscopy. The binding property was studied with both static and dynamic methods. Results showed that the polymers exhibited excellent recognition capacity and outstanding selectivity for ten phthalate esters. Factors affecting the extraction efficiency of the molecularly imprinted solid‐phase extraction were systematically investigated. An analytical method based on the molecularly imprinted coupled with gas chromatography and flame ionization detection was successfully developed for the simultaneous determination of ten phthalate esters from edible oil. The method detection limits were 0.10–0.25 μg/mL, and the recoveries of spiked samples were 82.5–101.4% with relative standard deviations of 1.24–5.37% (n = 6).     

Preparation and application of magnetic molecularly imprinted polymers for the isolation of chelerythrine from Macleaya cordata

A novel type of magnetic molecularly imprinted polymer was prepared for the selective enrichment and isolation of chelerythrine from Macleaya cordata (Willd) R. Br. The magnetic molecularly imprinted polymers were prepared using functional Fe₃O₄@SiO₂ as a magnetic support, chelerythrine as template, methacrylic acid as functional monomer, and ethylene glycol dimethacrylate as cross‐linker. Density functional theory at the B3LYP/6‐31G (d, p) level with Gaussian 09 software was applied to calculate the interaction energies of chelerythrine, methacrylic acid and the complexes formed from chelerythrine and methacrylic acid in different ratios. The structural features and morphology of the synthesized polymers were characterized by using Fourier transform infrared spectroscopy, X‐ray diffraction, transmission electron microscopy, and vibration sample magnetometry. Adsorption experiments revealed that the magnetic molecularly imprinted polymers possessed rapid kinetics, high selectivity, and a higher binding capacity (7.96 mg/g) to chelerythrine than magnetic molecularly non‐imprinted polymers (2.36 mg/g). The adsorption process was in good agreement with the Langmuir adsorption isotherm and pseudo‐second‐order kinetics models. Furthermore, the magnetic molecularly imprinted polymers were successfully employed as adsorbents for the extraction and enrichment of chelerythrine from Macleaya cordata (Willd) R. Br. The results indicated that the magnetic molecularly imprinted polymers were suitable for the selective adsorption of chelerythrine from complex samples such as natural medical plants.     

Preparation of quercetin imprinted core-shell organosilicate microspheres using surface imprinting technique

In this work,the quercetin imprinted core-shell microspheres were prepared using silica surface imprinting technique.A simple sol-gel procedure was used for the synthesis of the imprinted materials with 3-aminopropyltriethoxysilane as functional monomer and tetraethyl orthosilicate as crosslinker.The SEM images indicated that the MIPs shell was successfully grafted onto the silica surface.The characteristics of the molecularly imprinted polymers such as capacity,selectivity and absorption dynamic were investigated by rebinding experiments.The results showed that the prepared MIPs had good imprinting effect and adsorption amount of quercetin.     

Optimization of Functional Monomer Content in Protein‐Imprinted Polymers

Abstract

We have prepared synthetic materials having binding specificity toward lysozyme using molecular imprinting. The lysozyme‐imprinted polymers were prepared on silica beads using acrylic acid, acrylamide, and N,N′‐methylenebisacrylamide. The molar ratio of acrylic acid to the template affected the selectivity and the maximum binding specificity was yielded with the molar ratio of 5 to 1 (acrylic acid/template). No binding specificity toward lysozyme was observed when there was no acrylic acid, and the binding specificity decreased when the amount of acrylic acid was high. The functional monomer‐template ratio indicated in this study could be useful for improving the binding specificity in molecular imprinting of proteins.     

Cost‐effective imprinting combining macromolecular crowding and a dummy template for the fast purification of punicalagin from pomegranate husk extract

The combination of molecular crowding and virtual imprinting was employed to develop a cost‐effective method to prepare molecularly imprinted polymers. By using linear polymer polystyrene as a macromolecular crowding agent, an imprinted polymer recognizable to punicalagin had been successfully synthesized with punicalin as the dummy template. The resulting punicalin‐imprinted polymer presented a remarkable selectivity to punicalagin with an imprinting factor of 3.17 even at extremely low consumption of the template (template/monomer ratio of 1:782). In contrast, the imprinted polymer synthesized without crowding agent, did not show any imprinting effect at so low template amount. The imprinted polymers made by combination of molecular crowding and virtual imprinting can be utilized for the fast separation of punicalagin from pomegranate husk extract after optimizing the protocol of solid‐phase extraction with the recovery of 85.3 ± 1.2%.