Recognition Properties for Pyrrole

Recognition Properties for PyrrolePreparation of breakwaterecular(a)ly imprinted polymer and its intelligence properties for pyrroleX.W. Wu, J. Wang, H.X. Wang1, Q.M. Zhou, L.H. Liu. wang, Y.P. Wu, H.W. Yang, G.L. Zhao, S.X. TuoAbstract The molecularly-imprinted polymer (MIP) of pyrrole was synthesized by a precipitation polymerization method using acrylamide (AM) as operating(a) monomer and ethylene glycol dimethacrylate (EGDMA) as cross-linker agent in acetonitrile. MIP of pyrrole was stipulated by FT-IR and UV. The arise word structure and specific surface area of the MIP was characterized by S ground take to the woodsning Electron Microscope (SEM) and north adsorption (BET). The adsorption carriage of the MIP was investigated in detail, which showed high selectivity for pyrrole, the results indicated that the maximum back capacities of pyrrole on the MIP and the non-imprinted polymer ( shooting) were 404 and 265 molg1, respectively. Application of MIP with a high selec tivity to pyrrole provides a impertinent method for separating and purifying the trace nitrogenous heterocyclic compounds from baccy.Keyword molecularly imprinted polymer, pyrrole, tobacco, nitrogenous heterocyclic compounds1 INTRODUCTIONThe Pyrrole and other nitrogenous heterocyclic compounds in tobacco leaves amount mainly from the reaction products formed by the reaction of sugar and amino acid1-3, which play an important role in sensory quality of tobacco and tobacco products. They are the important parameters to evaluate the sensory quality of tobacco products and have great effects on the sensory characteristics of tobacco products and on the health of smokers4. Therefore, the studies and psychoanalysis of nitrogenous heterocyclic compounds are tributary to improve the quality of perfuming and tobacco products.Molecular Imprinting, as an interdiscipline derived from polymer chemistry, material light, and biological chemistry, is the method of preparing the polymer with p articular selection to give template blood corpuscles5-8. So far, dozens of countries, (i.e., America, Japan, Germany, Australia, France and China) hundreds of academic institutions and enterprises have been working on the research and development of the molecularly imprinted polymer (MIP).Thanks to MIP is simple in preparation and can be slow preserved, with specific selectivity, high temperature, high pressure and acid corrosion, it has been widely used in the solid phase extraction9, chromatography analysis 10, membrane time interval 11, biomimetic sensor12, ect.The separation of bioactive ingredients in natural products is difficult because of their low contents, complex structures and diversity13-15. Compared with traditional methods (high performance liquid chromatography, silica gel column chromatography, etc.), molecular imprinting method has the advantages of high molecular recognition, simple operation, low solvent consumption and recyclable16. Thus, the molecularly im printing technique has attracted considerable attention for extraction of compounds from complex mixings of chemical species17-18. However, to the best of our knowledge, no molecularly imprinted polymer has been reported for the separation and determination of pyrrole in tobacco so far.In this study, pyrrole imprinted polymer was synthesized by employing acrylamide (AM) as functional monomer and ethylene glycol dimethacrylate (EGDMA) as crosslinking. After the characteristics and analysis of the MIP and NIP, the adsorption behavior including energisings and isotherms are discussed in detail. It was found that the MIP can specifically adsorb and identify pyrrole motes, which meant the MIP can be applied to separation and enrichment of trace pyrrole in tobacco. The bewilder of this paper is to provide theoretical basis and technical supports for further study of the effects of nitrogen heterocyclic compound on tobacco quality.2 observational2.1 ReagentsPyrrole, pyridine and methan ol were obtained from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Acrylamide, methacrylic acid, acetonitrile and azodiisobutyronitrile were purchased from Tianjin Kermel Chemical Reagent Company (Tianjin, China). Ethylene glycol dimethacrylate was obtained from Aladdin reagent co., LTD (Guangdong, China). All the solvents were of analytical reagent grade and used without further purification.2.2 Synthesis of MIP and NIPThe pyrrole imprinted polymer was prepared by precipitation polymerization in the following procedures. 0.1 mmol of pyrrole and 0.4 mmol of AM were dissolved in 20 ml of acetonitrile in a 40 mL glass vessel. The mixture was sonicated at room temperature for 30 minutes for pre-polymerization, and then was incubated at 4C for 12 h. Subsequently, 2 mmol of cross-linker (EGDMA) and 10 mg of initiator (AIBN) were added stepwise. The glass vessel was degassed in a sonicating bath for 10 min, and filled with nitrogen for 30 min, and then sealed for polymerizatio n at 60 C for 24 h in a thermostat water bath. After polymerization, the resultants were extracted with a mixed solvent of methanol/acetic acid (91, v/v) for 48 h in a Soxhlet extractor to remove the template from its polymeric matrix, followed by ethanol for another 48 h to remove the acetic acid. The obtained MIP was dried in an oven at 60 C overnight. As a control, the NIP was prepared and treated under identical conditions except for the omission of the template.2.3 Morphological characterizationThe FT-IR spectra were recorded to characterize the MIP and NIP on an AVATAR 360 ESP FT-IR spectrometer (Nicolet, America). SEM images were obtained with afield-emission scanning electron microscope (FE-SEM, JSM-6700F, JEOL, Japan). The nitrogen adsorption/desorption data of MIP and NIP was determined using an ASAP2020Micromeriticsapparatus (Micromeritics Instruments, USA).2.4 Binding experimentsThe binding experiments were carried out at 30 C and 150 rpm on an orbital shaker with deoxy cytidine monophosphate mg of the MIP and NIP in a 100 mL flask containing pyrrole in 20 ml of acetonitrile. Batch experiments were performed to examine the adsorption kinetics and equilibrium. In the kinetic adsorption experiments, 2.5 mmolL-1 pyrrole in acetonitrile was used. The adsorption isotherm experiments were conducted with the sign pyrrole concentration ranging from 0.2 to 5.0 mmolL-1 for 2 h. After the adsorption, the concentration of the substrates in the supernatant solutions was determined via an UV-2450 Ultraviolet Spectrophotometer (Shimadzu, Japan). The binding capacity of pyrrole and the analogs was calculated from the equation (1)Where Q stands for the binding capacity (molg1), C0 and C are the initial and the residual concentrations (mmolL-1) of pyrrole, respectively, V is the solution volume (mL), and m is the amount (mg) of the MIP or NIP used for the adsorption experiments.3 RESULTS AND DISCUSSION3.1 Interaction between pyrrole and the functional monomersIn or der to investigate the feasibility of imprinted pyrrole, two unalike functional monomers MAA and AM were investigated for the formation of complex with the template. The maximum absorption wavelength of pyrrole was calculated by the UV-2450 Ultraviolet Spectrophotometer. As shown in Fig.1, compared with MAA, AM demonstrated much stronger interaction with pyrrole for the non-existent absorbance of pyrrole. It is possible that the complex of pyrrole with AM was formed via heat content bonding between NH of pyrrole and CONH2 of AM due to the pre-polymerization.Fig.1 Interaction between pyrrole and functional monomers3.2 The sub ratio of pyrrole to the monomerIn order to elucidate the recognition mechanism on a molecular level, spectrophotometric analysis was employed in the pyrrole imprinting process. A series solution were prepared in acetonitrile, in which the molar ratio of pyrrole and AM varied at 10, 12, 14 and 16, respectively. After equilibrium for 12 h, absorption spectrums of the mixture were measured via an UV-2450 Ultraviolet Spectrophotometer. As shown in Fig.2, the absorbance decreased with the increasing concentration of AM, When the molar ratio of pyrrole and AM up to 14, the absorption peak of pyrrole disappeared, which indicated that the pyrrole had reacted with AM completely. slice molar ratio of pyrrole and AM exceeded 14, the excess of AM could self-associate, and formed non-specific binding site, which makes the adsorption mass transfer resistance increase and is not conducive to the preparation of molecularly imprinted polymer. Therefore, the optimal molar ratio of pyrrole and AM is 14.Fig.2 Absorption spectra of pyrrole with different proportion of AM in acetonitrile3.3 Characteristics of MIP and NIP3.3.1 Characterisation of MIP and NIP by FT-IR spectraPyrrole, AM, EGDMA, MIP (before and by and by eluting templates) and NIP were compared to affirm the successful preparation of MIP by FT-IR spectra. The FT-IR spectra of the MIP before and after removal of template pyrrole are presented in Fig.3a and Fig.3b, respectively. The NH stretching vibration mountain of monomer AM (Fig.3e) appeared at 3580 cm-1 in the spectra of MIP before pyrrole removal (Fig.3a), which indicated that the template pyrrole formed hydrogen bonding interaction with monomer AM, this band is shifted to a higher wavenumber (at 3585 cm-1) after removal of pyrrole in MIP (Fig.3b). A conspicuous band at 1648 cm-1 in the spectra of MIP before removal of template pyrrole is ascribed to -C=C- aromatic ring stretching vibration of pyrrole (Fig.3d). This band disappeared after removal of pyrrole in MIP (Fig.3a) and was not observed in spectra of NIP (Fig.3c) due to absence of pyrrole. The peak at 3597cm-1 inFig.3c corresponds to the NH stretching of monomer AM in the FT-IR spectra of NIP. The absorption peaks of MIP and NIP were similar, which means that both MIP after eluting templates and NIP have the same chemical components.Fig.3 IR spectra of (a ) MIP before eluting template, (b) MIP after eluting template , (c) NIP, (d) pyrrole, (e) AM3.3.2 Morphology of MIP and NIPThe morphology of MIP and NIP was shown in Fig.4. As shown in Fig.4 (a), the prepared polymer is microsphere and the particle is uniform, which indicated the spherical particle can be synthesized at the best experiment condition. The MIP microsphere has a delimit and small particle size, and the average diameter is 2m. As for NIP, the microsphere with a narrow but big particle size, and the average diameter is 3m. a good deal imino exist in the template molecule, which may suppress the polymerization, results in the bigger particle size of NIP compared with MIP. Besides, the whole reaction system polarity change magnitude with the added template molecule, the solubility of MIP decreased, so that MIP precipitated from the whole reaction system early, which can also generate the bigger particle size of NIP.Fig.4 SEM micrographs of (a) MIP, (b) NIP.3.3.3 Charact erization of specific surface areaTable 1 lists the results of nitrogen adsorption experiments for MIP and NIP particles. It can be seen that the specific surface area and the average pore diameter were different for MIP and NIP particles.Table1 Structure parameters of MIP and NIPa Measured by BrunauerEmmettTeller (BET) method.b Measured by BarrettJoynerHalenda (BJH) method.3.4 Binding performance of MIP and NIP3.4.1 Absorption isotherms and kinetic of pyrrole on the MIP and NIPThe absorption isotherm curves of pyrrole on the MIP and NIP were plotted in Fig.5. The absorption capacity was increased gradually with increasing initial concentration of pyrrole in the range of 0.2-5.0 mmolL1. In the higher concentration range, the binding capacity was close to be stable. The binding data can be analyzed by Langmuir equation (2)Where Q stands for the binding capacity (molg1), Qmax is the maximum binding capacity (molg1), Ceq is equilibrium concentration of pyrrole (mmolL1), and B is a cons tant. In order to calculate the maximum binding capacity of pyrrole on both MIP and NIP, this equation was changed into Eq. (3) (3)Eq. (3) shows a unidimensional relationship between Ceq/Q and Ceq. From the slope of the linear plot, the maximum binding capacities of pyrrole on the MIP and NIP were calculated to be 404 and 265 molg1, respectively, which means that the maximum binding capacity of pyrrole on MIP was 1.52 times of that on NIP. In addition, under the same experimental conditions, the adsorption capacity of the MIP at each concentration was higher than that of the NIP. It was indicated that MIP offered a higher affinity for the template molecule than NIP.Fig.5 Adsorption isotherms of pyrrole on MIP and NIP3.4.2 Binding kinetic curve of pyrrole pyrrole on the MIPAs shown in Fig.6, the adsorption kinetic curves of pyrrole on MIP and MIP were shown at the pyrrole concentration of 2.5 mmolL1 in acetonitrile. It can be seen that the binding capacity of MIP increased rapidly i n the period of 0-60 min, and then the increments were reduced on the stage of 60-80 min, and the consummate(a) binding was observed after 80 min.Fig.6 Adsorption kinetic curves of pyrrole on MIP and NIP3.4.3 Selective adsorptionIn the selective adsorption test, the target molecule pyrrole and the competitive one pyridine possess similar structure and co-exist in tobacco extract as nitrogenous heterocyclic compounds. As we can see in Table 2, it is obvious that the absorption capacity of pyrrole and pyridine of MIP was much higher than that of the NIP. The selectivity of MIP was 2.17 times higher than that of NIP, which suggested that the imprinting process significantly improved adsorption selectivity to the template.Table 2 Binding capacity of different substrates on MIP and NIP4 CONCLUSIONSIn this paper, the pyrrole molecularly imprinted polymer was synthesized via the facile precipitation-polymerization method. The prepared polymer is microsphere and the diameter is about 2 m. The binding property experiments indicated the imprinted polymer can adsorb the pyrrole molecule selectively. Moreover, the adsorb effect of MIP is stronger than NIP. The selective adsorption experiments demonstrated the synthesized MIP microsphere has the obvious selective adsorption effect with pyrrole molecule when compared the similar structure pyridine. 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