Enhancement of the catalytic activity of an artificial phosphotriesterase using a molecular imprinting technique

Mechanical Bond Approach to Introducing Self-Adaptive Active Sites in Covalent Organic Frameworks for Zinc-Catalyzed Organophosphorus Degradation

Mechanically interlocked molecules (MIMs) with discrete molecular components linked through a mechanical bond in space can be harnessed for the operation of molecular switches and machines, which shows huge potential to imitate the dynamic response of natural enzymes. In this work, rotaxane compounds were adopted as building monomers for the synthesis of a crown-ether ring mechanically intercalated covalence organic framework (COF). This incorporation of MIMs into open architecture implemented large amplitude motions, whose wheel slid along the axle in response to external stimulation. After impregnation with Zn²⁺ ions, the relative locations of two zinc active sites (crown-ether coordinated Zn(II) and bipyridine coordinated Zn(II)) are endowed with great flexibility to fit the conformational transformation of an organophosphorus agent during the hydrolytic process. Notably, the resulting self-adaptive binuclear zinc center in a crown-ether-threaded COF network is endowed with a record catalytic ability, with a rate over 85.5 μM min^-1 for organophosphorus degradation. The strategy of synthesis for porous artificial enzymes through the introduction of mechanically bound crown ether will enable significant breakthroughs and new synthetic concepts for the development of advanced biomimetic catalysts.

Ag(I) Pyridine-Amidoxime Complex as the Catalysis Activity Domain for the Rapid Hydrolysis of Organothiophosphate-Based Nerve Agents: Mechanistic Evaluation and Application

Two novel Ag(I) complexes containing synergistic pyridine and amidoxime ligands (Ag-DPAAO and Ag-PAAO) were first designed as complex monomers. Taking advantage of the molecular imprinting technique and solvothermal method, molecular imprinted porous cross-linked polymers (MIPCPs) were developed as a robust platform for the first time to incorporate Ag-PAAO into a polymer material as a recyclable catalyst. Advantageously, the observed pseudo first-order rate constant (k_obs) of MIPCP-Ag-PAAO-20% for ethyl-parathion (EP) hydrolysis is about 1.2 × 10⁴-fold higher than that of self-hydrolysis (30 °C, pH = 9). Furthermore, the reaction mechanism of the MIPCP-containing Ag-PAAO-catalyzed organothiophosphate was analyzed in detail using density functional theory and experimental spectra, indicating that the amidoxime can display dual roles for both the key coordination with the silver ion and nucleophilic attack to weaken the P-OAr bond in the catalytic active site.

Catalytic degradation of organophosphorous nerve agent simulants by polymer beads@graphene oxide with organophosphorus hydrolase-like activity based on rational design of functional bimetallic nuclear ligand

The degradation of organophosphorous nerve agents is of primary concern due to the severe toxicity of these agents. Based on the active center of organophosphorus hydrolase (OPH), a bimetallic nuclear ligand, (5-vinyl-1,3-phenylene)bis(di(1H-imidazol-2-yl) methanol) (VPIM), was designed and synthesized, which contains four imidazole groups to mimic the four histidines at OPH active center. By grafting VPIM on graphene oxide (GO) surface via polymerization, the VPIM-polymer beads@GO was produced. The obtained OPH mimics has an impressive activity in dephosphorylation reactions (turnover frequency (TOF) towards paraoxon: 2.3 s^-1). The synergistic catalytic effect of the bimetallic Zn²⁺ nuclear center and carboxyl groups on surface of GO possibly contributes to the high hydrolysis on organophosphate substrate. Thus, a biomimetic catalyst for efficient degradation of some organophosphorous nerve agent simulants, such as paraoxon and chlorpyrifos, was prepared by constructing catalytic active sites. The proposed mechanism and general synthetic strategy open new avenues for the engineering of functional GOs for biomimetic catalysts.

Molecularly Imprinted Porous Aromatic Frameworks Serving as Porous Artificial Enzymes

Artificially designed enzymes are in demand as ideal catalysts for industrial production but their dense structure conceals most of their functional fragments, thus detracting from performance. Here, molecularly imprinted porous aromatic frameworks (MIPAFs) which are exploited to incorporate full host-guest interactions of porous materials within the artificial enzymes are presented. By decorating a porous skeleton with molecularly imprinted complexes, it is demonstrated that MIPAFs are porous artificial enzymes possessing excellent kinetics for guest molecules. In addition, due to the abundance of accessible sites, MIPAFs can perform a wide range of sequential processes such as substrate hydrolysis and product transport. Through its two functional sites in tandem, the MIPAF subsequently manifests both hydrolysis and transport behaviors. Advantageously, the obtained catalytic rate is ≈58 times higher than that of all other conventional artificial enzymes and even surpasses by 14 times the rate for natural organophosphorus hydrolase (Flavobacterium sp. strain ATCC 27551).

Assembly of the active center of organophosphorus hydrolase in metal–organic frameworks via rational combination of functional ligands

Mimicking the total coordination sphere of the active center of organophosphorus hydrolase in MOFs to destruct nerve agents without co-catalysts.

Progress of Mimetic Enzymes and Their Applications in Chemical Sensors

The need to develop innovative and reformative approaches to synthesize chemical sensors has increased in recent years because of demands for selectivity, stability, and reproducibility. Mimetic enzymes provide an efficient and convenient method for chemical sensors. This review summarizes the application of mimetic enzymes in chemical sensors. Mimetic enzymes can be classified into five categories: hydrolases, oxidoreductases, transferases, isomerases, and induced enzymes. Potential and recent applications of mimetic enzymes in chemical sensors are reviewed in detail, and the outlook of profound development has been illustrated.

Selective extraction of dimethoate from cucumber samples by use of molecularly imprinted microspheres

Molecularly imprinted polymers for dimethoate recognition were synthesized by the precipitation polymerization technique using methyl methacrylate (MMA) as the functional monomer and ethylene glycol dimethacrylate (EGDMA) as the cross-linker. The morphology, adsorption and recognition properties were investigated by scanning electron microscopy (SEM), static adsorption test, and competitive adsorption test. To obtain the best selectivity and binding performance, the synthesis and adsorption conditions of MIPs were optimized through single factor experiments. Under the optimized conditions, the resultant polymers exhibited uniform size, satisfactory binding capacity and significant selectivity. Furthermore, the imprinted polymers were successfully applied as a specific solid-phase extractants combined with high performance liquid chromatography (HPLC) for determination of dimethoate residues in the cucumber samples. The average recoveries of three spiked samples ranged from 78.5% to 87.9% with the relative standard deviations (RSDs) less than 4.4% and the limit of detection (LOD) obtained for dimethoate as low as 2.3 μg/mL.

4-nitrophenol surface molecularly imprinted polymers based on multiwalled carbon nanotubes for the elimination of paraoxon pollution

Molecularly imprinted polymers were grafted on the surface of multiwalled carbon nanotubes (MWCNT) using the hydrolysis product of paraoxon 4-nitrophenol as template, 4-vinyl pyridine (4-VPy) as the functional monomer and divinylbenzen (DVB) as the crosslinker. The binding experiments of 4-nitrophenol indicated that the MWCNT based molecularly imprinted polymers (MWCNT-MIP) have much higher adsorption ability than the MWCNT based non-imprinted polymers (MWCNT-NIP). At the same time we found that the adsorption of 4-nitrophenol can help to increase the hydrolytic rate of paraoxon, which indicates that there is an obvious catalyzing effect on the hydrolysis of paraoxon for this kind of materials. Furthermore, the 4-nitrophenol left in the paraoxon hydrolysis medium is only 0.01056 mM for MWCNT-MIP in the catalytic experiment of paraoxon we made (the initial concentration of paraoxon is 0.5 mM and MWCNT-MIP is 4 mg), which indicates that this kind of MWCNT based imprinted polymers can not only catalyze the hydrolysis of paraoxon but also eliminate the poisonous organism product 4-nitrophenol.

Polymer imprinting with iron-oxo-hydroxo clusters: [Fe6O2(OH)2(O2CC(Cl)=CH2)12(H2O)2], [Fe6O2(OH)2(O2C-Ph-(CH)=CH2)12(H2O)2] and [{Fe(O2CC(Cl)=CH2)(OMe)2}10]

We report the syntheses of imprinted polymers using iron-oxo-hydroxo clusters as templates. Three new iron clusters, [Fe(6)O(2)(OH)(2)(O(2)CC(Cl)=CH(2))(12)(H(2)O)(2)] (1), [{Fe(O(2)CC(Cl)=CH(2))(OMe)(2)}(10)] (2) and [Fe(6)O(2)(OH)(2)(O(2)C-Ph-(CH)=CH(2))(12)(H(2)O)(2)] (3) have been prepared from commercially-available carboxylic acids. Cluster-imprinted-polymers (CIPs) of 1, 2 and 3 were prepared with ethylene glycol dimethacrylate monomer, and of 1 with methyl methacrylate monomer. The imprinted sites within the CIPs were examined using EXAFS and diffuse reflectance UV/vis spectroscopy, demonstrating that the clusters 1, 2 and 3 were incorporated intact within the polymers. Extraction of the clusters from the CIPs imprinted with 1 and 3 gave new polymers that showed evidence of an imprinting effect.

Detection of organophosphorus compounds using a molecularly imprinted photonic crystal

A label free molecularly imprinted photonic crystal (MIPC) was developed to detect the degradation product of nerve agents. Mono-dispersed poly-methyl methacrylate colloidal particles with the diameter of 280 nm were used to fabricate a closely packed colloidal crystal array (CCA), and a methyl phosphonic acid (MPA) imprinted hydrogel was prepared within the CCA using 2-hydroxyethyl-methacrylate and N-isopropylacrylamide as monomers, ethyleneglycol dimethacrylate and N, N'-methylenebisacrylamide as cross-linkers, a mixture of n-octanol and acetonitrile as porogen. The diffraction intensity of the MIPC decreased significantly upon the MPA adsorption with a limit of detection (LOD) of 10(-6) molL(-1). Furthermore, the diffraction intensity decreased and blue shifted with the increase of temperature, decreased and red shifted with the increase of ionic strength. At higher pH, the diffraction intensity increased without obvious diffraction shift. The MIPC provides an indirect path to detect nerve agents (Sarin, Soman, VX and R-VX) by monitoring the MPA released from the hydrolysis of nerve agents, with LODs of 3.5 × 10(-6) molL(-1), 2.5 × 10(-5) molL(-1), 7.5 × 10(-5) molL(-1) and 7.5 × 10(-5) molL(-1) for Sarin, Soman, VX and R-VX, respectively.

Microgels and nanogels with catalytic activity

Molecular imprinting has grown considerably over the last decade with more and more applications being developed. The use of this approach for the generation of enzyme-mimics is here reviewed with a particular focus on the most recent achievements using different polymer formats such as microgels and nanogels, beads, membranes and also silica nanoparticles.

Molecular imprinting science and technology: a survey of the literature for the years up to and including 2003

Over 1450 references to original papers, reviews and monographs have herein been collected to document the development of molecular imprinting science and technology from the serendipitous discovery of Polyakov in 1931 to recent attempts to implement and understand the principles underlying the technique and its use in a range of application areas. In the presentation of the assembled references, a section presenting reviews and monographs covering the area is followed by papers dealing with fundamental aspects of molecular imprinting and the development of novel polymer formats. Thereafter, literature describing attempts to apply these polymeric materials to a range of application areas is presented.

Construction of artificial cyclic amide amidohydrolases using molecular imprinting technique

A general molecular imprinting approach is proposed to synthesize artificial enzymes to mimic the family of cyclic amide amidohydrolases which share similar active site and catalytic mechanism. The artificial enzymes were constructed by co-polymerizing 4(5)-vinylimidazole-Co2+-methacrylic acid clusters with divinylbenzene micro-spheres in the presence of corresponding substrates. The artificial enzymes mimicked creatininase and hydantoinase by showing specific affinity towards the corresponding substrates in buffer. The artificial hydantoinase also showed specific affinity towards corresponding substrate in organic solvent, and catalyzed the hydrolysis of hydantoin.

The molecular reaction vessels for a transesterification process created by molecular imprinting technique

A polymeric catalyst was synthesized by co-polymerizing 4(5)-vinylimidazole and itaconic acid with trimethylpropanol trimethacrylate micro spheres. The catalyst obtained catalysed the transesterification process between p-nitrophenyl acetate and hexanol with maximal initial velocity(nu(max)) of 4.73 +/- 0.47 microM min(-1) mg(-1), and turnover rate (k(cat)) of 8.67 min(-1). Using p-nitrophenyl acetate as template, molecular imprinting process enhanced the nu(max) of the polymeric catalyst 3-fold. Each imprinted site can be considered as a single molecular reaction vessel, and achieved a k(cat) of 169 min(-1) towards the conversion of p-nitrophenyl acetate in hexanol.

A molecularly imprinted catalyst designed by a computational approach in catalysing a transesterification process

A computational approach was developed to optimize the monomer formulation of molecularly imprinted catalysts. A virtual library of the intermediates of a lipase-catalysed transesterification process was constructed using Chem3D software with p-nitrophenyl acetate as substrate. The energies of the intermediates were minimized using the semi-empirical MOPAC method with the most stable intermediate expected to lead to a higher turn over rate. According to the optimization results, a MIC was prepared by co-polymerising 4(5)-vinylimidazole and itaconic acid with trimethylpropanol trimethacrylate micro spheres in the presence of p-nitrophenyl acetate. The MIC achieved of the transesterification process between p-nitrophenyl acetate and hexanol with a turn over rate of 26.2 min(-1), and showed substrate specificity towards its template with a 6.5-fold preference for p-nitrophenyl acetate over p-nitrophenyl salicylate.

Molecular imprinting: a dynamic technique for diverse applications in analytical chemistry

Continuous advances in analyzing complex matrices, improving reliability and simplicity, and performing multiple simultaneous assays with extreme sensitivity are increasing. Several techniques have been developed for the quantitative assays of analytes at low concentrations (e.g., high-pressure liquid chromatography, gas chromatography, immunoassay and the polymerase chain reaction technique). To achieve highly specific and sensitive analysis, high affinity, stable, and specific recognition agents are needed. Although biological recognition agents are very specific and sensitive they are labile and/or have a low density of binding sites. During the past decade molecular imprinting has emerged as an attractive and highly accepted tool for the development of artificial recognition agents. Molecular imprinting is achieved by the interaction, either noncovalent or covalent, between complementary groups in a template molecule and functional monomer units through polymerization or polycondensation. These molecularly imprinted polymers have been widely employed for diverse applications (e.g., in chromatographic separation, drug screening, chemosensors, catalysis, immunoassays etc.) owing to their specificity towards the target molecules and high stability against physicochemical perturbations. In this review the advantages, applications, and recent developments in molecular imprinting technology are highlighted.