Adsorption isotherms of caffeine on molecular imprinted polymer

A molecular imprinted polymer (MIP) using caffeine as the template and methacrylic acid (MAA) as the functional monomer was prepared. Acetonitrile was used as the porogen with ethylene glycol dimethacrylate (EGDMA) as the crosslinker and 2,2′-azobis(isobutyronitrile) (AIBN) as the initiator. By a linear and nonlinear regression analysis, the experimental parameters in the equilibrium isotherms were estimated. Then, the linear and quadratic equations for concentration and sorbents to adsorption amounts were expressed, and the adsorption equilibrium data were also correlated into the Freundlich isotherm model. Comparisons of caffeine adsorption isotherm on C₁₈ particles as well as the molecular imprinted polymer were made. The results showed that the caffeine-imprinted polymer showed extraordinarily higher adsorption ability than C₁₈ particles.     

Caffeine Molecular Imprinted Microgel Spheres by Precipitation Polymerization

Imprinted uniform microgel spheres were prepared by precipitation polymerization. Acetonitrile was used as the dilute solvent with MAA as the monomer, EDMA as the crosslinker and caffeine as the print molecule. Comparison of caffeine adsorption on molecular imprinted and blank microgel spheres was made. Langmuir model was used to fit the adsorption data. It was found that the caffeine imprinted microgel spheres show specific binding sites to the target molecules. A binding study of caffeine on imprinted microgel spheres was made by Scatchard analysis; the dissociation constants (K_D) and the maximum binding capacity were K_D= 1.84×10⁻⁴mol/L,Q _max = 16.98 μmol/g for high affinity binding site and K_D=1.33×l0⁻³ mol/L, Q_max=46.84 μmol/g for lower affinity binding site, respectively This microgel spheres can be useful affinity adsorbents in further applications.     

Effect of ethanol content on supercritical carbon dioxide extraction of caffeine from tea stalk and fiber wastes

This study presents the effect of ethanol content on supercritical carbon dioxide extraction of caffeine from tea plant wastes. Tea stalk and fiber wastes of Turkish tea plants that have no economical value were evaluated as raw material throughout the caffeine extraction experiments. These wastes were supplied from tea factory marked “Çaykur” in the east blacksea region. They were separately ground, sieved and dried at 105 °C temperature in an oven. Parameters affecting caffeine leaching from tea wastes were determined to be, ethanol flow rate, extraction time, extraction temperature, carbon dioxide flow rate, process pressure and particle size. The maximum yield of caffeine from tea stalk wastes and fiber wastes were 14.95 mg/g tea stalk and 18.92 mg/g tea fiber, respectively. When the supercritical extraction conditions used of ethanol as cosolvent have been compared with the conditions of used only carbon dioxide, approximately the same yield has been reached at 2 h extraction period instead of 7 h. Beside of saving of the time and the amount of carbon dioxide, the supercritical extraction yield with cosolvent increase had been recorded as 62.5% and 63.1%, respectively, in comparison with the chloroform extraction as conventional method of tea stalk and fiber wastes.     

Adsorption isotherm of ibuprofen on molecular imprinted polymer

A molecular imprinted polymer (MIP) using (+)-(S)-2-(4-isobutylphenyl) propionic acid ((+)-(S)-ibuprofen) as the template and 4-vinylpyridine (4-VPY) as the functional monomer was prepared. Chloroform and acetonitrile were used as the porogen with ethylene glycol dimethacrylate (EGDMA) as the crosslinker and 2,2′-azobis(isobutyronitrile) (AIBN) as the initiator. Comparison of ibuprofen adsorption isotherm on molecular imprinted and blank polymers was made by the static method. The adsorption equilibrium data were correlated into the Freundlich, Langmuir, Sips (Langmuir-Freundlich) and Radke-Prausnitz isotherm models, respectively. By a nonlinear regression analysis, the experimental parameters in the equilibrium isotherms were estimated and compared. The calculated data is well fitted with the experimented data. Through the analysis, the ibuprofen imprinted polymer showed higher adsorption ability than blank polymer.     

Extraction of caffeine from tea stalk and fiber wastes using supercritical carbon dioxide

The purpose of this study was to investigate obtaining of caffeine from tea plant wastes by supercritical carbon dioxide extraction. Experiments were carried out with tea stalk and fiber wastes of Turkish tea plants that has no economical value. Stalk and fiber wastes were supplied from tea factories. These wastes were ground, sieved and dried at 105 °C temperature in an oven. Parameters affecting caffeine leaching from tea wastes were determined to be, extraction time, extraction temperature, carbon dioxide flow rate, process pressure and particle size. The maximum yield of caffeine from tea stalk wastes and fiber wastes were 14.9 mg/g tea stalk and 19.2 mg/g tea fiber, respectively. The yield increase had been recorded as 61.9% and 65.5%, respectively, in comparison with the chloroform extraction of tea stalk and fiber wastes.     

Preparation of molecularly imprinted polymers for recognition and extraction of benzoylureas from apple samples

ABSTRACT

In this work, diflubenzuron (DBZ) molecularly imprinted polymers (MIPs) were synthesized by precipitation polymerization. The polymers were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), dynamic light scattering (DLS). The influences of synthetic conditions including template molecules, functional monomers and crosslinker on the surface morphology, particle size and size distribution of polymers were investigated. Scatchard analysis indicated the presence of specified recognition sites in MIPs. The Sips model was fitted better to the equilibrium data of MIPs over whole concentrations. The pseudo-second-order kinetic model was well fitted to the experimental data of adsorption kinetic experiment, suggesting the chemisorption mechanism between MIPs and DBZ. Four structurally similar compounds were used for the selectivity test of MIPs. It was observed that MIPs can selectively rebind the template molecules (DBZ) under the interference of four other structurally similar compounds. The application of MIPs in solid-phase extraction (SPE) offers a method for extraction and determination of benzoylureas (BUs) pesticides in apple samples prior to high-performance liquid chromatography (HPLC) analysis.     

Resin selection for the separation of caffeine from green tea catechins

This work focuses on the rapid selection of a resin from a defined set of macroporous polymeric resins for the decaffeination of catechins from green tea. High-throughput experimentation and design of experiments are used in order to retrieve as much information as possible from a small set of experiments on the interaction of components with the resins. A multicomponent Langmuir isotherm model is used to describe the adsorption and parameters are regressed with high accuracy. These parameters are subsequently used for the definition of criteria to calculate a weighted resin score. The optimal resin is Diaion 20HP with a score of 90.50%, mainly due to its good selectivity for caffeine over catechin (3).     

分子印迹固相萃取法提取花生壳中木犀草素

采用分子印迹技术,以木犀草素为模板分子、丙烯酰胺为功能单体、EGDMA为交联剂,合成了木犀草素印迹聚合物。将该印迹聚合物用于固相萃取,分离提取花生壳中的木犀草素。结果表明,该印迹聚合物对木犀草素具有较高的吸附性能和选择性,用印迹柱萃取得到的木犀草素纯度高出硅胶柱分离近20个百分点,达到96.2%。且MIPs-SPE柱与普通的硅胶柱相比,经过洗脱再生后可以反复使用多次。     

Solid Phase Enhanced Direct Spectrofluorometric Determination of Polychlorinated Biphenyls (PCBs) in Natural Waters

A method of detection of PCBs in water, based on extraction/concentration with chips cut from an SPE disk-shaped C18 inverse phase coupled with a fluorescence detection and quantification directly on the phase has been evaluated. Experiments were performed with PCBs congeners IUPAC N° 3, 35, 67 and 169. Within the experimental conditions used : Hitachi F-4500 fluorometer, band-paths: 2.5 nm and extraction time: 60 min. the limits of detection were estimated to be respectively : 0.07, 0.4, 0.3 and 0.2 ppb. These values are within the range of PCB concentrations found in highly polluted waters and thus confer some interest to the method. However its sensitivity is not sufficient for application to moderately polluted natural water and the method needs some further improvements. Moreover, fluorescence quenching by humic substances was shown to substantially affect PCB's fluorescence intensity and must be taken into consideration for quantitative analysis.     

正交法对咖啡因提取与纯化工艺的优化研究

利用正交实验法优化提取茶叶中咖啡因，178℃升华进行产品纯化，产品经薄层色谱及紫外分光光度法进行鉴定和含量测量，获得白色长针状晶体，纯度98.7%，产率1.94%。该工艺节约成本，减少工时，操作简便，产品产率高，纯度好。     

水在超临界CO2脱除绿茶中咖啡因的作用研究

采用不同的茶叶预处理方式,并在不同的萃取条件下,用超临界CO2对茶叶进行脱除咖啡因试验,以考察茶叶含水量与咖啡因萃取率的关系。指出了水对咖啡因萃取的3方面影响,即脱附茶叶基质上的咖啡因、使茶叶膨胀而改善咖啡因的传质状况及抑制咖啡因从水相进入超临界流体相。同时说明了此3者对萃取过程的影响机理。     

Solid Phase Extraction for Determination of Polycyclic Aromatic Hydrocarbons from Atmospheric Wet and Dry Deposition Samples

Solid phase extraction with C-18 sorbent tubes was employed for extraction and preconcentration of trace level (ng/l) of polycyclic aromatic hydrocarbons (PAHs) from water samples obtained by collecting wet and dry atmospheric deposition. Recoveries of spiked PAHs from 0.2 to 10.0 l water samples ranged from 60% to 90%. Five deuterated PAHs (naphthalene- d 8 , acenaphthene- d 10 , anthracene- d 10 , chrysene- d 12 , and perylene- d 12 ) were added to the samples as surrogates. The recoveries of surrogates were in the same range as the spiked PAHs. The recoveries of surrogates were used to estimate the recoveries of ambient PAHs with a similar ring structure. Factors that contributed to the relatively low recoveries include breakthrough of the sorbates, adsorption on the container surface, and degradation in water during storage.     

丁二烯萃取装置聚合物产生原因分析及对策

丁二烯抽提装置因其萃取溶剂二甲基甲酰胺及丁二烯本身的特性 ,在运行过程中易产生各类聚合物 ,堵塞设备、管线、阀门等 ,制约装置的运行负荷和周期。从理论上分析了装置中各类聚合物的特性及危害 ,总结聚合物产生的原因 ,结合生产实际 ,提出了相应的对策     

从茶叶废弃液中提取咖啡因的研究

咖啡因是一种重要的医药工业原料 ,具有多种药理作用 ,从茶叶废弃液中提取咖啡因既经济又实用。对提取条件和影响因素进行了大量的实验研究 ,确立了最佳工艺路线和方法 ,结论如下 :取 30 0ml茶叶水的废弃液浓缩蒸干后 ,在所得的黑色固体中加入 15 0ml三氯甲烷于 5 0℃浸泡 2h ,然后抽滤 ,经活性炭脱色 ,重结晶得高纯度的咖啡因。提取率达到 6 5 7%。     

Atomistic molecular dynamics simulations of gas diffusion and solubility in rubbery amorphous hydrocarbon polymers

Diffusion coefficients D of H₂, He, O₂, N₂, and CO₂ in different rubbery amorphous polymeric matrices were estimated by atomistic molecular dynamics simulations at 298 K using the Einstein relationship, and compared with the relevant experimental values, where available. The simulated diffusion coefficients D of all the gases in all polymers considered almost regularly decreased with increasing molecular gas volumes and increasing polymer glass transition temperature. Further, solubility coefficients and heats of solution were obtained for all gases from Grand Canonical Monte Carlo simulations, which were also used to calculate sorption isotherms. In general, there is a good agreement between experimental and simulated values of diffusion and solubility coefficients for all gases considered.     

Computationally designed monomers and polymers for molecular imprinting of theophylline and its derivatives. Part I

The main objective of this research was to develop and apply state-of-the-art computational tools to achieve an understanding of intermolecular interactions in molecular imprinting of theophylline into complex polymeric systems. Molecular dynamics (MD) simulations were carried out for different molecular systems in order to predict the interaction energies, the closest approach distances and the active site groups between the simulated molecular systems and different bio-ligands. The minimized structures of five ligands, theophylline and its derivatives (theobromine, theophylline-8-butanoic acid, caffeine and theophylline-7-acetic acid) have been obtained with the use of molecular mechanics approach. NVT MD simulations at room temperature were carried out to obtain equilibrated conformations in all cases.The first simulated molecular systems consisted of a ligand and a commonly used functional monomer, such as acrylic acid, methacrylic acid, acrylamide, acrolein, acrylonitrile, styrene, etc. (a total number of 25 monomers were simulated). For each of the simulated monomer, molecular clusters consisting of 10 monomers were built. For each pair of molecular systems, (10 monomers with a ligand and 10 monomers without a ligand) a total energy difference, (ΔE), was calculated in order to estimate the interaction energy between a ligand and the corresponding monomers. The second simulated molecular systems consisted of a ligand and a polymer. For each of the simulated polymers, a polymeric chain with degree of polymerization (DP) 10 was simulated with theophylline or its derivative and the interaction energy (ΔE) was calculated. From simulated polymer systems it was found that just poly(acrylic acid) and poly(itaconic acid) are selective only for theophylline. The functional groups of monomers interacting with ligands are -COOH or CH₂CH-. The functional groups of polymers are predominantly -COOH. In the case of poly(acrylic acid) and poly(itaconic acid) the distance of closest approach between a polymer and theophylline was between 2.0 and 4.0 Å.     

Comonomer effects on binding performances and morphology of acrylate-based imprinted polymers

The objective of this study was to investigate the effect of different functional groups of molecularly imprinted polymers (MIPs) on the binding characteristics towards a specific template molecule by examining selectivity and recognition processes. Several non-covalent theophylline imprinted polymers (TIPs) were prepared by using only methacrylic acid (MAA), or MAA and 2-hydroxyethyl methacrylate (HEMA) comonomer, or MAA and acrylamide (ACM) comonomer. In all cases, a high amount of ethylene glycol dimethacrylate (EDMA) as crosslinker existed in the medium. The highest selective theophylline binding of TIPs was found to be 61%, 41% and 40% for MAA/EDMA, MAA/HEMA/EDMA and MAA/ACM/EDMA systems, respectively. The use of a comonomer (ACM or HEMA) reduced the binding performance of the MAA/EDMA polymer matrix, probably due to the monomer-monomer association and morphological differences. Results obtained from the batch binding experiments demonstrated that all of the TIPs have sites that have selective binding ability for theophylline, but not to another structurally similar molecule, caffeine. According to the Langmuir isotherm model, a heterogeneous distribution of binding sites was observed in the polymers. The maximum association constant and binding site density were computed as 2.3 × 10² mM⁻¹ and 8.6 μmol/g, respectively, for copolymer of MAA/EDMA under the examined concentration range.     

Coordination of Cu(II) and Ni(II) in polymers imprinted so as to optimize amine chelate formation

Molecular imprinting has become an established technique. However, little was done on direct investigation of the sorbents produced. In the present work, en ESR method was used for the investigation of the complex formation processes within the sorbents imprinted with copper(II) and nickel(II). The sorbents were synthesized from a mixture of linear low molecular weight polyethyleneimine oligomers. The composition, structure and distribution of complexes in the resin phase were investigated. The effects of the synthesis conditions, loading degree and water content were examined. The presence of certain copper complexes was found to be a convenient characteristic of the imprinting efficiency. The optimum synthesis conditions for obtaining sorbents imprinted with copper(II) or nickel(II) were identified. The imprinting results in the improvement of the stability of the complexes and the selectivity and working capacity of the sorbents. The imprinted samples are also characterized by a more even distribution of chelating sites. The synthesis conditions and loading by ions allow for the regulation of the ratio between individual complexes and magnetic associates in the resin phase. This is a critical point on the future use of the metal containing imprinted sorbents as catalysts.     

Separation of phenylalanine by ultrafiltration using D-Phe imprinted polyacrylonitrile-poly(acrylic acid)-poly(acryl amide) terpolymer membrane

A D-phenylalanine (D-Phe) imprinted terpolymer P(AN-AA-AAm) membrane was prepared by the wet phase inversion method. Acrylamide (AAm) and acrylic acid (AA) were used as the functional monomer and acrylonitrile (AN) was used as a physical cross linker. The template molecules were removed from the terpolymer matrix by washing with a 5 percent acetic acid solution. The removal of template molecules from the membrane matrix increased the population of free COOH groups and reduced that of dimerized COOH groups in the membrane matrix, which is an indirect evidence of the formation of recognition sites. The adsorption selectivity of the D-Phe imprinted terpolymer membrane prepared by in-situ implanting method was 0.37 at pH 2 after 3 h batch adsorption using 100 mg Phe/l racemate solution and reached nearly 1 after 24 h. In the ultrafiltration process, the permselectivity was 0.38 at pH 2 after 2.5 min. Separation of D-Phe from the racemate solution was demonstrated by a repeated ultrafiltration batch work.     

单体自增溶原位固相接枝法合成三单体接枝物PE-g-（GMA／St／BA）的研究

采用单体自增溶原位固相接枝技术合成PE—g-（GMA＋St＋BA）的三单体固相接枝物，采用傅立叶变红外光谱分析接枝物的结构，并探讨单体配比、单体总质量、引发剂用量等反应条件对接枝率和凝胶率的影响。结果表明，当三种单体的配比GMA／St/BA（质量比）：6／6／2，BPO用量为2phr，单体的总用量在50phr左右时，接枝率较高；苯乙烯能降低凝胶含量，BPO为2phr时凝胶含量较低。