The Fabrication And Application Of Novel Enzyme Mimetics

Enzymes are extremely efficient at catalyzing a variety of reactions with high substrate specificity, activities, and yields under mild reaction conditions. They have been successfully used for many different targets in various fields including biosensing, agrochemical production, pharmaceutical processes, and food industry. However, natural enzymes have intrinsic drawbacks for commercial applications, including their low operational stability (denaturation and digestion), sensitivity of catalytic activity to environmental conditions, difficulties in prepare, purify, recovery and recycling. Over the past decades, enzyme mimics, have garnered increasing interest owing to their remarkable advantages over natural enzymes, such as their low cost, ease of storage, and good tunability for catalytic activity. A great deal of excellent studies have promoted the development of artificial enzyme mimics; however, their inherent disadvantages are also obvious and include aggregation and settlement of the nanozymes in aqueous systems, which affects their catalytic activity and applications, causes difficulty in separation and impaired reusability, and leads to laborious preparation procedures. Therefore, the development of innovative enzyme mimics with an excellent stability and high catalytic activity remains of great interest. In this thesis, a series of novel peroxidase (or oxidase) mimetics fabricated and studies. The main contents are as follows:1. For the first time, a facile and rapid in situ partial oxidation synthetic strategy was used to fabricate mixed valence state Ce-MOF(Ce3+/Ce4+), and explored its intrinsic oxidase-like catalytic activities detailedly. Furthermore, on the basis of the excellent catalytic activity of the MCVM, a colorimetric approach for the high-throughput detection of biothiols in serum samples was established. 2. In this part, magnetic core-shell nanoflowers Fe3O4@MnO2 were fabricated via a solvothermal method. We demonstrated that the as-synthesized magnetic nanoflowers possess intrinsic oxidaselike activity in a wide pH range and can catalytically oxidize 4-aminoantipyrine (4-AAP) and phenol substrates to form pink color products without the requirement for additional oxidizing agents. On the basis of this phenomenon, a simple colorimetric method for the determination of phenol was developed. A wide linear detection range can be obtained from 1.0 mM to 120 mM (R2=0.9962) with a detection limit of 0.15 mM. And the method was applied to determine phenol in wastewater with good recoveries ranging from 96.0 to 101.5%. Furthermore, benefitting from chemical stability and easy recovery (by simple magnetic separation) of Fe3O4@MnO2, the oxidase mimetics have excellent reusability and reproducibility in cycle analysis.3. CuS particles (PCuS) were facilely synthesized by the wet-treatment of a Cu-based metal organic framework (HKUST-1). PCuS possesses an impressive intrinsic peroxidase-like activity. As a result of this affinity, PCuS readily binds to 3,3,5’,5-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide (H2O2) (Km values of 29 mM and 150 mM toward TMB and H2O2, respectively). Interestingly, when Hg2+ was added, HgS produced in conjunction with the specific binding sites on the surface of PCuS remarkably inhibited the peroxidase-like activity of PCuS. Based on this unique property, a sensing platform for the colorimetric detection of Hg2+was established. In addition, high surface area and strong affinity for Hg2+make PCuS an excellent adsorbent for Hg2+(2105 mg g-1). These results indicate that PCuS could be a useful material for the facile detection and the efficient removal of Hg2+ using HKUST-1 as a precursor in environmental abatement applications.4. As a novel peroxidase mimic material, MIL-101(Cr)@PB was fabricated by encapsulating Prussian blue (PB) nanoparticles into the host matrix of MIL-101(Cr) via a facile and mild in situ growth synthetic strategy. The crystallographic characteristics, morphology, and porosity of the as-synthesized MIL-101(Cr)@PB composites were carefully studied using XRD, SEM, TEM, TGA, and BET. The results show that the synthesized MIL-101(Cr)@PB possesses a reproducible and impressive intrinsic peroxidase-like activity even under extreme conditions. Exploiting this, a colorimetric platform for screening xanthine oxidase inhibitors was constructed. We hope that this work will elucidate the applications of metal-organic frameworks as carriers for enzyme mimics and enable a wider application in drug screening.5. A novel and inexpensive approach was adopted to develop magnetic porous y-Fe2O3/C@HKUST-1 composites for the remove of dyes and heavy metal ions from aqueous solution. The Y-Fe2O3/C with unique functional groups present such as-OH and-NH2 was used as the support to directly grow HKUST-1 by a stepwise liquidphase epitaxy process. The crystallographic, morphology, and magnetic properties as well as porosity of the assynthesized y-Fe2O3/C@HKUST-1 composites were carefully studied by XRD, SEM, TEM, XPS, TGA, and BET. The results indicated that the BET surface area, micropore volume, and saturation magnetization of the y-Fe2O3/C@HKUST-1 are 993.4 m2 g-1,0.69 m3 g-1, and 12.6 emu g-1, respectively. In addition, a uniform distribution of ultrafine y-Fe2O3 nanoparticles with an average diameter of 2-3 nm was observed in the y-Fe2O3/C@HKUST-1 composites. Our results showed that methylene blue (MB) and Cr(VI) (used as a model for typical dye pollutants and heavy metal ions) are effectively removed from aqueous solutions by γ-Fe2O3/C@HKUST-1. The maximum adsorption capacities were 370.2 and 101.4 mg g-1 of adsorbent for MB and Cr(Ⅵ), respectively. It is further demonstrated that y-Fe2O3/C@HKUST-1 shows excellent peroxidase-like activity for the degradation of MB in the presence of H2O2.