1 Introduction Nasal Care Saline Water,OEM Product,Saline Water Shanghai Berry Electronic Tech Co., Ltd , http://www.chequipments.com
Molecular recognition plays a very important role in living organisms. Some biological molecules such as enzymes, antigens, and hormones in the natural world have specific molecular recognition phenomena for substrates, antibodies, and receptors, and thus determine whether organisms are normal. Grow. However, these biomolecules have disadvantages such as complicated preparation, poor stability, and inconvenient storage and operation. Molecular imprinting technology is a technique for artificially synthesizing polymers with specific recognition sites since the 1970s. Molecular imprinting technology can be used to prepare molecularly imprinted polymers with good stability, simple synthesis, and molecular recognition. The preparation of molecularly imprinted polymers is also continuously updated, from bulk polymerization [1, 2] to suspension polymerization [3, 4], precipitation polymerization [5, 6] and surface polymerization [7, 8], etc. Polymers have been widely used in chromatographic separation [9, 10], solid phase extraction [11, 12], chemical sensing [13, 14], and mimic enzyme catalysis [15, 16].
At present, there are few kinds of crosslinking agents for preparing molecularly imprinted polymer precursor materials, mainly olefin compounds that can participate in free radical polymerization, such as vinyl ethylene glycol methacrylate, trimethylol propane trimethacrylate and Divinylbenzene and so on. These crosslinkers are usually used only in organic solvents, greatly limiting the development of imprinted polymers. The use of mild sol-gel technology allows the organosilane reagents to hydrolyze in the aqueous or organic phase to form high polymers. Most organosilane compounds contain functional groups that interact with the imprinting molecules and function as functionalities. The monomer was applied to the synthesis of the imprinted polymer, and thus the imprinted polymer based on the silicon material was rapidly developed.
In order to reduce the phenomenon of “implantation†of imprinted molecules and accelerate the adsorption rate of imprinted polymers on imprinted molecules, much of the current imprinting technology has focused on the use of surface imprinting techniques to prepare imprinted polymers on the surface of a certain matrix material [ 17-19]. There are many types of matrix materials that can be used, among which the silicon-based materials are widely used in the preparation and study of surface imprinted polymers due to their outstanding compatibility, mechanical properties, good stability, and easy surface modification and other outstanding advantages. in. This article intends to give an overview of the preparation and research of molecularly imprinted polymers based on silicon materials in recent years.
2 Molecular Imprinting Technology
Molecular imprinting technology means that the imprinted molecule and the functional monomer first form a complex by a reversible reaction, and then in the presence of a cross-linking agent, a highly cross-linked rigid polymer is polymerized, and after the imprinting molecule is removed, the network structure of the polymer is eliminated. The functional groups that have the binding ability are left, and they can be used as molecular receptors to selectively recognize the imprinting molecules in many imprinted molecular structure analogues.
According to the mechanism of interaction between imprinted molecules and functional monomers in the polymerization process, molecular imprinting technology can be divided into two basic types. The first is the covalent method, founded by Wulff. A covalent bond is formed between the imprinted molecule and the functional monomer molecule to form a polymerizable monomer. After the cross-linking polymerization, the covalent bond is chemically cleaved to remove the imprinted molecule. The advantage of this method is that the interaction between the imprinting molecule and the functional monomer molecule is strong, so that the polymerization reaction can be performed in a strong polar solvent, and the imprinting site is precisely determined.
However, there are few reversible chemical reactions and the elution and binding rates of imprinted molecules are slow. The second is non-covalent law, founded by Mosbach. Between the imprinted molecule and the functional monomer, hydrogen bonding, hydrophobic interaction, charge transfer and the like are combined with each other to conduct crosslinking polymerization. The polymerization reaction is simple, the elution and recognition of imprinting molecules are relatively rapid, and the recognition process is closer to the natural molecular recognition system, and is a commonly used method. In addition, the preparation and properties of imprinted polymers are also studied by combining these two methods. That is, the mode of interaction between imprinted molecules and functional monomers during the polymerization process is covalent, and the mode of action in the identification process is It is non-covalent.
3 Preparation of Molecularly Imprinted Polymers Based on Silicon Materials
In 1949, Dickey et al. used the dye methyl orange as the imprinting molecule to acidify the silicate solution to make the dye imprinted silica gel. The adsorption material that adsorbed methyl orange was twice as high as that of ethyl orange was obtained. Preparation and study of silicon-based molecularly imprinted polymers. At present, there have been many beneficial advances in this area of ​​research, from the early preparation of imprinted polymers using silane directly as a parent material, to the preparation of imprinted polymers on the surface of different morphological silicon materials.
3.1 silane as imprinted polymer matrix material
Sol-gel techniques are generally used to prepare silicon imprinted molecularly imprinted polymers under mild conditions. Dai et al.[20] used UO2(NO3)2·6H2O as the imprinting molecule and tetramethoxysilane as the parent material for preparing the polymer. The imprinted polymer silica gel was prepared under the catalysis of nitric acid, and its adsorption capacity and adsorption selection were studied. Sex study. Compared with the non-imprinted polymer with the same surface area, the imprinted polymer silica gel has certain affinity and selectivity for UO2+2. Later, they [21] conducted a detailed study of the steady-state fluorescence and fluorescence lifetime of the imprinted polymer silica gel, further demonstrating that the prepared imprinted polymer silica gel has very good selectivity and high adsorption capacity for imprinted molecules.
Collinson et al [22, 23] used dopamine as an imprinting molecule, phenyl trimethoxysilyl and methyl trimethoxy silicon as functional monomers, and tetramethoxysilane as a cross-linking agent to catalyze hydrolysis under acidic conditions. It is applied dropwise on the surface of the electrode to form an imprinted polymer film. Cyclic voltammetry was used to characterize the properties of the imprinted polymer membrane. The results show that the imprinted polymer membrane has specific adsorption capacity for dopamine and can eliminate the interference of ascorbic acid on dopamine determination. Pinel et al [24] used acid and base catalyzed hydrolysis and condensation of tetraethoxysilane to prepare imprinted silica solids, which had a stronger adsorption capacity for the imprinted molecular methanol than blank samples. When silica solids synthesized with o-cresol as an imprinting molecule, similar results were obtained for o-cresol and p-cresol adsorption.
He et al. [25] used a water-insoluble ionic liquid as a solvent and porogen to prepare imprinted polymer silica gels that selectively recognize androgens. Puleo et al [26] combined the sol-gel technique with the epitope-determining method to prepare the entire lysozyme and the 16-residue lysozyme C polypeptide imprinted polymer silica gel. The lysozyme-imprinted polymer silica adsorbed lysozyme 4 times as much as the adsorbed non-imprinted molecular ribonuclease, whereas the 16-residue lysozyme C polypeptide imprinted polymer exhibited only slight adsorption characteristics. Ki et al. [27] used estrone as an imprinted molecule and covalently bonded with functional monomer triethoxypropyl isocyanuric silane, and then added crosslinking monomer tetraethoxysilane to polymerize, covalently heating and breaking. The bond was eluted and the imprinted molecule was eluted to prepare a spherical estrone-imprinted polymer to realize the recognition of estrone.
Ling et al [28] concentrated tetraethoxysilane under hydrothermal conditions, and added aluminum chloride to enhance the rebinding ability of imprinted molecules to prepare a molecularly imprinted polymer of catechol; investigated the factors that influence the recognition ability. , such as the acidity of the analyte, the coverage of the surface of the silica gel imprinted polymer, and the acidity of the silicon-aluminum solution, etc.; and an electrochemical sensor was constructed by modifying the catechol imprinted polymer on the surface of a quartz quartz microbalance to measure the footprint in situ. molecular. Brandy et al. [29] prepared indole trinitrobenzene molecularly imprinted periodic mesoporous organosilicon, in which porphyrin was incorporated as an optical indicator of the binding imprinting molecule. The silicone material has the advantages of good stability, strong identification ability, high sensitivity to porphyrin, and high density of selective binding sites.
Zhang et al. [30] selectively prepared 2,4,6-trinitrobenzene on the porous inner wall surface of alumina membranes by sol-gelation of tris-aminopropyltriethoxysilane and tetraethoxysilane. Imprinted silicon nanotubes. The wall of the tube is ultra-thin, with a thickness of about 15 nm, good accessibility and low mass transfer resistance.
3.2 Base on silica gel
Silica has strong mechanical properties, stable properties, and easy surface modification. The preparation of the imprinted polymer on the silica surface can, on the one hand, increase the mechanical strength of the imprinted polymer, on the other hand can greatly expose the surface area of ​​the imprinting, reduce the "embedding" phenomenon, and accelerate the adsorption rate. Therefore, the preparation and research of imprinted polymers on the surface of silicon materials have been rapidly developed.
3.2.1. Based on spherical silica
The preparation of imprinted polymers based on spherical silicas can basically be divided into two types depending on the type of silica surface modification materials.
One is the covalent bonding of the vinyl groups on the spherical silica surface, which guides the polymerization of the imprinted polymer to occur selectively on the surface of the silica. Sakai et al [31] added silica particles and initiators with surface-modified double bonds in a prepolymerized solution containing lysozyme, and prepared the polymers in the aqueous phase to obtain silica-based materials. An imprinted polymer containing a lysozyme recognition site on its surface can selectively adsorb lysozyme. Zhang et al. [32] reported the preparation of 2,4,6-trinitrobenzene imprinted polymer on the surface of vinyl functionalized silicon nanoparticles.
The results show that not only can the surface modified vinyl functional monomers on silicon surface not only selectively occur on the silicon surface through the copolymerization of the terminal vinyl group with the functional monomer, but also cause the charge of the imprinted molecule and the functional monomer to form a charge in the polymer layer. The complex is transferred so that a high density of effective binding sites is formed on the surface of the polymer, thereby making the prepared imprinted polymer have a fast adsorption kinetics and a high adsorption capacity. Our group [33] also prepared the hydroquinone imprinted polymer after modifying the surface of the self-made silica nanospheres. The imprinted polymer has a faster adsorption rate and is modified on the surface of the glassy carbon electrode, and the content of the imprinted molecule can be determined electrochemically.
Akiyama et al. [34] and Song et al. [35] used vinyl-modified silica microspheres as matrix materials in the presence of imprinted molecules and acryloylcyclodextrins to prepare molecularly imprinted polymers on their surface. Improves the mechanical properties of imprinted polymers and can be used as a HPLC stationary phase. The former achieved the separation of the L-Phe-L-Phe dipeptide enantiomers, which achieved the recognition of the polypeptides, and confirmed that the effect of the imprinting was not related to the initial structure of the imprinted polypeptide, but to the polypeptide in solution. Conformational in the relevant. Li et al [36] bonded cyclodextrin and acrylamide simultaneously on the surface of silica microspheres, then prepared tryptophan imprinted polymers, and studied the recognition performance of cyclodextrin and acrylamide on imprinted polymers. influences.
The other is the preparation of the imprinted polymer after grafting the initiator onto the spherical silica surface. 4,4-Azo-2(4-cyano-pentanoic acid) is a kind of initiator commonly used in the preparation of imprinted polymers. Generally, it is modified on the surface of the matrix material, and then the imprinted polymer is prepared. . Lorenzi et al [37] used this imprinted polymer as a capillary electrochromatographic stationary phase and showed good recognition performance for L-phenylalanine aniline. Sulitzky et al [38] improved the adsorption kinetics and adsorption capacity of the imprinted polymer by fine-tuning the polymer thickness and applied it to the chromatographic stationary phase. The polymer thickness, solvent, silica gel pore size, and cross-linker concentration were investigated. The influence of the composition of the mobile phase on the chromatographic properties.
Shamsipur et al. [39] also used the imprinted polymer prepared by this method as a chromatographic stationary phase, and examined the influence of the concentration of the imprinted molecule uranyl ion, the pH value, and the flow rate of the solution on the polymer surface. The uranyl ion exhibits a strong affinity under optimized conditions and can be used in preconcentration and determination of actual water samples. Sellergren et al. [40] used a reversible addition-fragmentation chain transfer radical polymerization (RAFT) method to modify the surface of mesoporous silica with 4, 4-azo-2 (4-cyano-pentanoic acid) on the surface. A molecularly imprinted polymer of L-phenylalanine aniline was grafted. The imprinted polymer can be used as a chiral stationary phase with high selectivity, and can achieve baseline separation of the imprinted molecular racemate and the structural analogue racemate in a relatively short time.
Husson et al [41] prepared by this method tryptophan molecularly imprinted polymer compared with the traditional liquid phase method of imprinted polymer prepared by the mass transfer rate, high adsorption capacity. The iniferter technique was introduced as a quasi-free radical polymerization method and was also applied to the preparation of imprinted polymers based on silicon materials. The method first modifies the initiating transfer terminator on the surface of silica and then prepares the imprinted polymer. Using this technique, Sellergren et al. [42] grafted L-phenylalanine aniline imprinted polymer and D-phenylalanine aniline imprinted polymer on the surface of silica microspheres, or grafted onto the layer of imprinted polymer. And a layer of non-imprinted polymer.
Among them, the further grafting of a 5 nm L-phenylalanine aniline imprinted polymer on the surface of the D-phenylalanine aniline imprinted polymer resulted in the grafting of only one layer of D-phenylalanine with aniline. The opposite selectivity of the polymer; grafted 23 nm imprinted polymer on the non-imprinted polymer surface showed higher selectivity. It was demonstrated that the thin L-phenylalanine aniline imprinted polymer grafted on the surface of the D-phenylalanine aniline imprinted polymer did not result in complete opposite selectivity but was the result of the interaction of the two imprinted polymers. Sellerg ren et al[43] grafted imprinted polymers on the surface of porous silicon, gel-type and macroporous resins by RAFT technology and found that the grafting amount increased with the increase of polymerization time, the amount of terminator and monomer concentration. Tests of these silicon-imprinted polymer composites as a stationary phase showed recognition performance for imprinted molecules.
Su et al [44] prepared a sulfamethoxazole imprinted polymer on the surface of silica gel for use as a HPLC stationary phase. Under optimal chromatographic conditions, imprinted polymer silica microspheres can be used to determine milk Sulfamethazine has a linear range of 0.1-50 μg/m and a detection limit of 25 ng/ml. In addition, the literature also reported the preparation of imprinted polymers in the pores of silica microspheres, and then etched the silica off with HF to obtain imprinted polymers with the same shape as silica microspheres. Things. In accordance with this method, Martin-Esteban et al [45] prepared Ligulon imprinted polymer for use as a chromatographic stationary phase for the direct detection of phenylurea herbicides in vegetable samples with a detection time of less than 10 minutes. Yilmaz et al [46] prepared isopropyl adipate molecularly imprinted polymers for chromatographic stationary phase, improved column efficiency, and reduced separation time.
3·2·2 Based on silicon fiber
Silicon fiber is also used as a new silicon material in the preparation of imprinted polymers. In order to enhance the selectivity and application capability of solid-phase microextraction, Hu et al [47] prepared a novel imprinted polymer package using a multi-step copolymerization method on tetracyline as an imprinting molecule on a 4-cm-long, 140-μm-diameter silicon fiber. Covered solid-phase microextraction fibers. The imprinted polymer can be directly coupled with high performance liquid chromatography for the trace analysis of tetracycline in complex samples, and exhibits specific recognition performance for tetracycline in the structural analogs oxytetracycline, doxycycline, and chloramphenicol. Koster et al. [48] compared the adsorption properties of clenbuterol imprinted and non-imprinted polymers prepared on the surface of silicon fibers under various conditions. As a solid-phase microextraction agent, it is suitable for the analysis and determination of biological samples and can selectively extract clenbuterol in human urine.
3·2·3 Based on silicon monolithic column
The monolithic silica column has been developed as a chromatographic stationary phase. In recent years, one layer of imprinted polymer has been grafted on the surface of the monolithic column to improve the separation ability of the column. Yan et al. [49] prepared silicon monoliths grafted with molecularly imprinted polymers on capillary electrochromatographic and capillary HPLC columns and evaluated them with capillary electrochromatography and capillary liquid chromatography. The prepared imprinted polymer monolithic column can separate the imprinting molecule from the isomer in a very short time, has high column efficiency, good sensitivity and long service life. Ou et al. [50] used S-Terogel's base and L-tetrahydropalmatine as imprinting molecules to immobilize a layer of molecularly imprinted membrane on a capillary silica monolithic column and applied it to capillary electrochromatography and capillary electrophoresis. Resolution of chiral compounds in the phase chromatogram. Under optimal conditions, the racemate of the imprinted molecule can be resolved on a monolithic column with a length of 8.5 cm in only 4 min.
4 Application of Imprinted Polymers Based on Silicon Materials
Silicon materials not only have good mechanical properties and thermal stability, but also have a variety of morphologies. Therefore, silicon-based molecularly imprinted polymers with molecular recognition functions have a wide range of application prospects.
4.1 chromatographic separation
Molecularly imprinted polymers based on silica gel matrix are mostly microspheres with good mechanical properties, and the imprinting sites are located on or close to the surface of the imprinted polymer. Therefore, they can be used as excellent chromatographic stationary phases and have extensive applications in chromatographic separation. Prasad et al [51] packed the oxazolidone imprinted polymer prepared on the surface of spherical silica gel into a 13 cm long, 1/4 cm inner diameter column, used as stationary phase, exhibiting high selectivity and adsorption capacity. Blotting molecules are selectively enriched and separated in a dilute aqueous solution or drug. Chang et al [52] grafted estrenone-imprinted polymer with a thickness of about 100 nm onto the surface of silica gel and used it as a chromatographic stationary phase. Compared with structural analogues of estrone, the imprinted polymer has a longer retention time for imprinted molecules and exhibits high specific recognition ability. Suliz-ky et al [53] prepared an imprinted polymer of L-phenylalanine aniline on a silica gel grafted with an initiator and used it as a chromatographic stationary phase. High performance liquid chromatography was used to characterize the affinity of the imprinted polymer. The results show that the prepared imprinted polymer shows good adsorption performance and selectivity.
4.2 solid phase extraction
The specific enrichment or repulsion of the imprinted polymer by the imprinted polymer has a higher selectivity for a single compound and a class of compounds, which can solve the non-specific adsorption problems encountered in conventional solid phase extraction. Zhu et al [54] prepared a 2,4-dinitrophenol imprinted polymer on the surface of silica gel, which has high adsorption capacity, excellent selectivity and site accessibility, and was successfully used as a solid phase extractor. Selective enrichment and determination of 2,4-dinitrophenol in water samples. The experimental results showed that the recovery rate of imprinted polymer SPE column was 92% (relative standard deviation less than 2.8%).
Combining solid-phase extraction with high-performance liquid chromatography can enrich, separate, and measure analytes, increase sensitivity, and reduce detection limits. Jiang et al.[55] prepared diethyl ethylene-estradiol imprinted polymers by combining surface imprinting technique with sol-gel technique, and determined diethyl diethylstilbestrol by solid-phase extraction-high performance liquid chromatography. The imprinted polymer prepared has a fast adsorption kinetics, can reach equilibrium in 10 min, and has a large adsorption capacity of 62.58 mg/g, and can be used to detect diethylstilbestrol in fish samples. The imprinted polymer composites prepared on the surface of silica fibers were also applied to solid-phase extraction-high performance liquid chromatography coupled with a linear range of 5-200 μg/L for tetracycline and a detection limit of 1-2 μg/L. L, which can be used for the analysis of residual tetracycline in chick feeds, chicken muscles and milk samples [47]; for clenbuterol, detection limits up to 10 ng/ml [48].
4. 3 Mimic enzyme catalysis
The imprinted sites and catalytic groups inside the molecularly imprinted polymer allow the imprinted polymer to have high selectivity and catalytic activity, comparable to natural enzymes. Brüggemann et al. [56] immobilized the imprinted molecule on the surface of silica gel and prepared an imprinted polymer that can catalyze the cycloaddition reaction between hexachlorocyclopentadiene and maleic acid. This mimetic enzyme polymer exhibits specific catalytic properties relative to non-imprinted polymers. As the temperature increases, the catalytic activity of the molecularly imprinted polymer increases. By this method, the activation energy of the reaction can be reduced from 63 kJ/mol to 55 kJ/mol.
The catalytic reaction has a Michaelis constant of 5.8 mmol/L, an effective reaction rate of 0.4 μmol/(L·s), and a reaction rate constant of 1.1×10 −3 /s. Iwasawa et al.[57] used molecular imprinting technology to attach a metal complex to the surface of silica to prepare a new molecularly imprinted polymer of hydrazine-amine. The polymer has a cavity that matches the shape of the imprinted molecule. Used as a shape-selective reaction space. The imprinted ruthenium complex has a Rh-(amine)(OSi) (HOSi) unsaturated structure, and exhibits high catalytic activity for hydrogenation of α-methylstyrene.
Visnjevski et al.[58] used the Diels-Alder transition state analog chloroanhydride as the imprinting molecule to compare the silicon surface imprinted polymers prepared by the embedding method and the sacrificial skeleton method in hexachlorocyclopentadiene and cis Catalytic activity in diels-Alder reaction of adipic acid. The results showed that the catalytic activity of the imprinted polymer prepared on the surface of the sacrificial skeleton was significantly higher than that of the imprinted polymer obtained by the embedding method, and the amount of the obtained product was three times that of the imprinted polymer. Brüggemann et al. [59] immobilized the imprinted molecule on the amino-functionalized silica gel surface, and then copolymerized with the functional monomer and the cross-linker to prepare the imprinted polymer. Then, the silica gel and the imprinted molecule were dissolved and removed by HF. Because the transition state substance that is a hydrolysis reaction is used as an imprinting molecule, it has an active site for catalytically selective hydrolysis reaction on the inner surface of the imprinted polymer and exhibits a good catalytic activity.
4·4 Electrochemical sensing
Molecularly imprinted polymers are used as molecular recognition elements, which allow the prepared sensors to increase tolerance and extend life while maintaining high selectivity and sensitivity. Prasad et al. [60] used silica-bonded uric acid imprinted polymers for solid-phase extraction and imprinted polymer-modified mercury electrode drop sensors to selectively pre-enrich imprinted molecules, increasing sensitivity and eliminating the interference of structural analogues such as ascorbic acid, The detection limit is 0·0008mg/L. Akiyama et al [34] prepared a lysozyme imprinted polymer on the surface of silica gel and modified it on the surface of the electrode to construct a quartz crystal microbalance sensor with a highly sensitive response to lysozyme.
Prasad et al [61] grafted sarcosine imprinted polymer on the surface of silica gel, combined the solid-phase extraction technique with imprinted polymer sensing technology, and determined the content of sarcosine with a detection limit of 0·0015 ng/m. ,l and for determination of sarcosine in human serum, the lowest can be measured to 50ng/ml. Marx et al. [62] prepared a parathion-imbubbled membrane sensor using silica sol-gel technology, studied the effect of functional monomers and the site of non-covalent binding of parathion, and compared blots for the first time. The bonding of molecules to imprinted polymer films under gas phase and liquid phase conditions.
5 Concluding remarks
Silicon-based molecularly imprinted polymers, from the use of spherical silicon as a host material to silicon as a host material with other morphologies, have been rapidly developed from imprinting on the surface of silicon to the porous silicon. Synthetic molecularly imprinted polymers have also been developed from the initial bulk to the current microspheres, nanotubulars, etc., reducing the complicated follow-up processes such as grinding, sieving, etc., and increasing the mechanical strength of polymers. It reduces the imprinting molecule embedding phenomenon and accelerates the adsorption rate of imprinted molecules.
It is expected that in the coming period, molecularly imprinted polymers based on silicon will be further studied and developed in the following areas:
(1) Synthesis of more types of functional monomers (silane coupling agents) that can be used in the preparation of imprinted polymers based on silicon materials to meet the needs of different types of imprinted molecules and imprinted polymer preparation;
(2) In-depth study of the recognition process and recognition mechanism of the imprinted polymer, and the identification mechanism between the imprinted polymer and the imprinted molecule at the molecular level;
(3) Because the imprinted polymer based on silicon can be prepared and identified in aqueous solution, it provides an excellent environment for the imprinting of biomacromolecules, so the biomacromolecule imprinting and recognition will be further studied and applied.
(4) Continuously develop new application areas of imprinted polymers based on silicon materials and bring them to market.