Molecular recognition properties of salicylic acid-imprinted polymers

Summary Two molecularly imprinted polymers (MIP) have been prepared using the acidic drug salicylic acid, which can form intramolecular hydrogen bond, as the template and acrylamide or 4-vinylpyridine as the functional monomer. HPLC was used to evaluate the binding performance of the MIP for the template and for several analogues. The results showed that the MIP (P₂) prepared using acrylamide as the functional monomer had no molecular imprinting effect whereas that (P₁) prepared using 4-vinylpyridine as the functional monomer had a significant molecular imprinting effect. The reason the molecular imprinting effect was different for the two MIP was elucidated and the molecular recognition properties of P₁ were studied in detail. It was confirmed that electrostatic interaction played an important role in the molecular recognition of P₁. Scatchard analysis showed that two types of binding site with distinctly different affinity were formed in P₁. Their dissociation constants were estimated to be 7.6×10⁻⁵ mol L⁻¹ and 3.2×10⁻³ mol L⁻¹, respectively. Because P₁ has high affinity and selectivity for salicylic acid not only in organic systems but also in water-containing systems, it gives P₁ the potential for use in the enrichment, separation, and detection of salicylic acid in biological fluids.     

Adsorption isotherms of a molecular imprinted polymer prepared in the presence of a polymerisable template: Indirect evidence of the formation of template clusters in the binding site

The current opinion about molecular imprinted polymers (MIPs) is that their molecular recognition properties are due to the presence of nanocavities formed during a polymerization process developed in the presence of a template molecule. According to this principle, the shape of these nanocavities is complementary to that of the template and non-covalent interactions are established between the binding site and a single template molecule. Nevertheless, there are some experimental indications that the real molecular recognition mechanism involves clusters of template molecules being packed into the binding site. Recently, it has been proposed that template molecules covalently linked to the binding site can act as nucleation points, enhancing the formation of these molecular clusters.We have tested this hypothesis by studying the adsorption isotherms of polymers prepared by imprinting them with 2,4,5-trichlorophenoxyacetic acid (2,4,5-T). Three different polymers were considered: P0, prepared without the template, P1, whose template was represented by 2,4,5-T molecules, and P2, whose template was 1/3 constituted by the polymerisable 2-(2,4,5-trichlorophenoxyacetoxy)-ethylmethacrylate (2,4,5-TEMA) and 2/3 by 2,4,5-T. The polymers were prepared by thermoinduced polymerization of template mixtures, 4-vinylpyridine and ethylene dimethacrylate. The crushed polymers were packed into HPLC columns and frontal chromatographic runs were performed by eluting the columns with a mobile phase containing variable amounts of 2,4,5-T.The experimental adsorption isotherms were fitted by using several isotherm models, and the Freundlich-Langmuir model was found to give the best fitting in terms of F-test. All the models considered showed a significant difference between the affinity constant values measured for the polymer P1 and P2, with a higher value for the polymer P2 (for Freundlich-Langmuir model: polymer P1, k=(2.00±0.43)×10⁴ M⁻¹; polymer P2, k=(1.93±0.0535)×10⁵ M⁻¹; ratio P2/P1, 9.65±2.09). Such experimental results support the hypothesis that a polymer prepared with a limited amount of template covalently attached to the binding site shows an increased affinity for the template itself.     

OH-radical induced degradation of 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) and 4-chloro-2-methylphenoxyacetic acid (MCPA): A pulse radiolysis and gamma-radiolysis study

The reactions of OH, H and e_aq⁻ with 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) and 4-chloro-2-methylphenoxyacetic acid (MCPA) were studied by pulse radiolysis. The site of OH-radicals addition to the aromatic ring of 2,4,5-T was found to be—C1: ∼18%, C2/C4/C5: total ∼28% and C3/C6: total ∼41%. The overall rate constants with OH-radicals were k(OH+2,4,5-T)=6.4 (±0.5)×10⁹ mol dm⁻³ s⁻¹ and k(OH+MCPA)=8.5 (±0.8)×10⁹ mol dm⁻³ s⁻¹. The radiation induced decomposition of the pesticides, chloride- and product formation (phenolic compounds, aliphatic acids) was studied by gamma radiolysis as a function of dose. A mechanism for acetate formation is discussed. The presence of oxygen during irradiation affected the decomposition rate only indiscernibly, however, chloride elimination, ring fragmentation (formation of aliphatic acids), TOC- and toxicity reduction were strongly enhanced. For complete removal of 500 μmol dm⁻³ herbicides a dose of ∼4 kGy was required. Using air saturation during irradiation a reduction of 37-40% of the TOC was observable at 5 kGy, detoxification (luminescence inhibition <20%) was achieved with 10 kGy.     

The effectively specific recognition of bovine serum albumin imprinted silica nanoparticles by utilizing a macromolecularly functional monomer to stabilize and imprint template

Structural stability of the template is one of the most important considerations during the preparation of protein imprinting technology. To address this limitation, we propose a novel and versatile strategy of utilizing macromolecularly functional monomers to imprint biomacromolecules. Results from circular dichroism and synchronous fluorescence experiments reflect the macromolecularly functional monomers tendency to interact with the protein surface instead of permeating it and destroying the hydrogen bonds that maintain the protein’s structural stability, therefore stabilizing the template protein structure during the preparation of imprinted polymers. The imprinted polymers composed of macromolecularly functional monomers or their equivalent micromolecularly functional monomers over silica nanoparticles were characterized and carried out in batch rebinding test and competitive adsorption experiments. In batch rebinding test, the imprinted particles prepared with macromolecularly functional monomers exhibited an imprinting factor of 5.8 compared to those prepared by micromolecularly functional monomers with the imprinting factor of 3.4. The selective and competitive adsorption experiments also demonstrated the imprinted particles made by macromolecularly functional monomers possessed much better selectivity and specific recognition ability for template protein. Therefore, using macromolecularly functional monomers to imprint may overcome the mutability of biomacromolecule typically observed during the preparation of imprinted polymers, and thus promote the further development of imprinting technology.     

Preparation and recognition performance of uric acid-imprinted material prepared with novel surface imprinting technique

Acrylonitrile (AN) was first graft-polymerized on the surfaces of crosslinked polyvinyl alcohol (CPVA) microspheres by initiating of cerium salt, and then the grafted polyacrylonitrile (PAN) was transformed to polyamidoxime (PAO) via amidoximation transform reaction, resulting in the functional microspheres PAO/CPVA. By adopting the novel surface-molecular imprinting technique put forward by us, uric acid molecule-imprinted material MIP-PAO/CPVA was prepared with glutaraldehyde as crosslinking agent The binding character of MIP-PAO/CPVA towards uric acid was investigated in depth with both batch and column methods and using guanine as a contrast substance whose chemical structure is similar to uric acid to a certain extent. The experimental results show that the surface imprinted material MIP-PAO/CPVA has excellent binding affinity (a great binding capacity of 104 mg/g) and high recognition selectivity for the template molecule, uric acid. The selectivity coefficient of PAO/CPVA microspheres (non-imprinted material) for uric acid relative to guanine is only 1.273, displaying no recognition selectivity for uric acid. However, after imprinting, the selectivity coefficient of MIP-PAO/CPVA for uric acid in respect to guanine is remarkably enhanced to 14.00, displaying the excellent recognition selectivity and binding affinity towards uric acid molecules.     

胆酸印迹聚合物的制备及在含水介质中的结合性能

为了在含水介质中进行有效印迹,本研究中以双甲基丙烯酰-β-环糊精（BMA-β-CD）和2-(二乙基胺基)乙基甲基丙烯酸酯(DEAEM)为功能单体制备了胆酸印迹聚合物MIP1,并用平衡结合实验研究了MIP1在含水介质中对模板分子的识别能力。结果表明,MIP1比单独以BMA-β-CD或DEAEM为功能单体制备的印迹聚合物MIP2和MIP3,显示出对模板分子更好的选择性结合能力。MIP1的特异性吸附量ΔCP为38.81μmol/g,印迹因子IF为2.46。研究表明,在含水介质中,利用模板分子与功能单体之间的疏水作用和离子作用是提高印迹聚合物分子识别能力的关键。研究还表明,在识别过程中,疏水作用在驱动分子进入印迹孔穴时起重要作用。     

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.     

不同硅铝比的SAPO-41分子筛物化性质及催化性能研究

磷酸硅铝分子筛（SAPO）因其温和的酸性分布和合适的孔道结构，在很多烃类反应中表现出了较好的催化性能。在二甲苯的异构化反应中，也有少量关于SAPO分子筛的应用报道，但相关的报道主要集中于SAPO-5、SAPO-11和SAPO-31，对于SAPO-41的二甲苯异构化性能的报道较少。