PBA-Derived Heteroatom-Doped Mesoporous Graphitic Spheroids as Peroxidase Nanozyme for In Vitro Tumor Cells Detection.

Inspired by the two kinds of naturally occurring peroxidases (POD) with vanadium or heme (iron)-based active catalytic centers, we have developed a dual metal-based nanozyme with dual V and Fe-based active catalytic centers. Co-doping of graphene with heteroatoms has a synergistic effect on the catalytic properties of the nanomaterial as the distances of migration of the substrates drastically reduce. However, a few studies have reported the codoping of heterometallic elements in the graphene structure due to the complexity of the synthesis procedures. Herein, we report the synthesis of in situ doped bimetallic VNFe@C mesoporous graphitic spheroids nanozyme via pyrolysis without the assistance of any template assisted method. The Prussian-blue analog-based precursor material was synthesized by a facile one-step low-temperature synthesis procedure. The bimetallic spheroids showed an excellent affinity toward H2O2, with a Km value of 0.26 mM when compared to 0.436 for the natural POD, which is much better than the natural POD, which was utilized to detect tumor cells in vitro through the intracellular H2O2 produced by these cells under high oxidative stress. The VNFe@C mesoporous spheroids generate dual reactive oxygen species, including the •OH and •O2H- radicals, in the presence of H2O2, which are responsible for the POD-like activity of these nanozymes, while the bimetallic V/Fe doping plays a synergistic role in the enhancement of the activity of codoped graphitic spheroids.

Engineering at Subatomic Scale: Achieving Selective Catalytic Pathways via Tuning of the Oxidation States in Functionalized Single-Atom Quantum Catalysts.

Regulating the catalytic pathways of single-atom sites in single atom catalysts (SACs) is an exciting debate at the moment, which has redirected the research towards understanding and modifying the single-atom catalytic sites through various strategies including altering the coordination environment of single atom for desirable outcomes as well as increasing their number. One useful aspect concerning the tunability of the catalytic pathways of SACs, which has been overlooked, is the oxidation state dynamics of the single atoms. In this study, iron single-atoms (FeSA) with variable oxidation states, dependent on the precursors, are harnessed inside a nitrogen-rich functionalized carbon quantum dots (CQDs) matrix via a facile one-step and low-temperature synthesis process. Dynamic electronic properties are imparted to the FeSAs by the simpler carbon dots matrix of CQDs in order to achieve the desired catalytic pathways of reactive oxygen species (ROS) generation in different environments, which are explored experimentally and theoretically for an in-depth understanding of the redox chemistry that drives the alternative catalytic pathways in FeSA@CQDs. These alternative and oxidation state-dependent catalytic pathways are employed for specific as well as cascade-like activities simulating natural enzymes as well as biomarkers for the detection of cancerous cells.

An MMP-degradable and conductive hydrogel to stabilize HIF-1α for recovering cardiac functions.

Rationale: Although a few injectable hydrogels have shown a reliable biosafety and a moderate promise in treating myocardial infarction (MI), the updated hydrogel systems with an on-demand biodegradation and multi-biofunctions to deliver therapeutic drug would achieve more prominent efficacy in the future applications. In this report, a conductive and injectable hydrogel crosslinked by matrix metalloproteinase-sensitive peptides (MMP-SP) was rationally constructed to stabilize hypoxia-inducible factor-1α (HIF-1α) to recover heart functions after MI. Methods: Firstly, tetraaniline (TA) was incorporated into partially oxidized alginate (ALG-CHO) to endow the hydrogels with conductivity. The 1,4-dihydrophenonthrolin-4-one-3-carboxylic acid (DPCA) nanodrug was manufactured with high drug loading capacity and decorated with polymerized dopamine (PDA) to achieve a stable release of the drug. Both ALG-CHO and DPCA@PDA can be cross-linked by thiolated hyaluronic acid (HA-SH) and thiolated MMP-SP to construct a MMP-degradable and conductive hydrogel. After administration in the infarcted heart of rats, echocardiographic assessments, histological evaluation, and RT-PCR were used to evaluate therapeutic effects of hydrogels. Results: The cell viability and the results of subcutaneous implantation verify a good cytocompatibility and biocompatibility of the resulting hydrogels. The hydrogel shows remarkable strength in decreasing the expression of inflammatory factors, maintaining a high level of HIF-1α to promote the vascularization, and promoting the expression of junctional protein connexin 43. Meanwhile, the multifunctional hydrogels greatly reduce the infarcted area (by 33.8%) and improve cardiac functions dramatically with ejection fraction (EF) and fractional shortening (FS) being increased by 31.3% and 19.0%, respectively. Conclusion: The as-prepared hydrogels in this report achieve a favorable therapeutic effect, offering a promising therapeutic strategy for treating heart injury.

A Hybrid VOx Incorporated Hexacyanoferrate Nanostructured Hydrogel as a Multienzyme Mimetic via Cascade Reactions.

Inspired by the cascade reactions occurring in micro-organelles of living systems, we have developed a hybrid hydrogel, a nanozyme that mimics three key enzymes including peroxidase, superoxide dismutase, and catalase. The organic/inorganic nanostructured hydrogel constituting VOx incorporated hexacyanoferrate Berlin green analogue complex (VOxBG) is prepared by a simple one-step hydrothermal process, and its composition, structure, and properties are thoroughly investigated. Polyvinylpyrrolidone, a low-cost and biocompatible polymer, was utilized as a scaffold to increase the surface area and dispersion of the highly active catalytic centers of the nanozyme. Compared to the widely used horseradish peroxidase in enzyme-linked immunosorbent assay, our VOxBG analogue hydrogel displays an excellent affinity toward the chromogenic substrate that is used in these peroxidase-based assays. This higher affinity makes it a competent nanozyme for detection and oxidation of biomolecules, including glucose, in a cascade-like system which can be further used for hydrogel photolithography. The VOxBG analogue hydrogel also holds a good ability for the rapid and efficient oxidative degradation of environmentally unfriendly recalcitrant substrates under light irradiation. Detailed mechanistic studies of this multifaceted material suggest that different complex catalytic processes and routes are involved in these photo-Fenton and Fenton reactions that are responsible for the generation as well as consumption of reactive oxygen species, which are effectively activated by a multienzyme mimetic of the VOxBG analogue hydrogel.

Intrinsic peroxidase-like activity and enhanced photo-Fenton reactivity of iron-substituted polyoxometallate nanostructures.

Heteropolyacids (HPAs) are a class of polyoxometallates (POMs) with oxygen-rich surfaces. Herein, we have developed an Fe-containing heteropolyacid by cation-exchange and employed KFePW12O40 nanostructures for Fenton, photo-Fenton and enzyme-mimetic reactions. The as-prepared KFePW12O40 catalyst exhibits efficient degradation of Rhodamine B (RhB) via the photo-Fenton reaction. As an enzyme-mimetic, this material can effectively oxidize TMB and dopamine. The obtained nanomaterials were characterized via SEM, TEM, XPS, BET surface area, TGA, UV-Vis spectroscopy, FT-IR, and XRD techniques. The photocatalyst has a relatively large surface area of 38 m2 g-1, and the Keggin structure of phosphotungstic ions is kept intact during the preparation. The RhB dye pollutants can be efficiently bleached and degraded up to about 80% within a one hour photo-Fenton reaction under visible light irradiation. Our results indicate that the KFePW12O40 nanomaterial can effectively mimic the enzyme cascade reaction of horseradish peroxidase (HRP). It also has a high affinity toward 3,3',5,5'-tetramethylbenzidine (TMB) for oxidation and henceforth, it has been used for the colorimetric assay of dopamine and H2O2. Overall, our study suggests that KFePW12O40 can be used for the efficient degradation of environmental pollutants. The KFePW12O40 catalyst is stable and can be easily separated from the reaction system for reuse without an obvious loss of activity.

Oxygen deficient Pr6O11 nanorod supported palladium nanoparticles: highly active nanocatalysts for styrene and 4-nitrophenol hydrogenation reactions.

The design and development of highly efficient and long lifetime Pd-based catalysts for hydrogenation reactions have attracted significant research interest over the past few decades. Rational selection of supports for Pd loadings with strong metal-support interaction (SMSI) is beneficial for boosting catalytic activity and stability. In this context, we have developed a facile approach for uniformly immobilizing ultra-small Pd nanoparticles (NPs) with a clean surface on a Pr6O11 support by a hydrogen thermal reduction method. The hydrogenations of p-nitrophenol and styrene are used as model reactions to evaluate the catalytic efficiency. The results show highly efficient styrene hydrogenation performance under 1 atm H2 at room temperature with a TOF value as high as 8957.7 h-1, and the rate constant value of p-nitrophenol reduction is 0.0191 s-1. Strong metal-support interaction and good dispersion of Pd nanoparticles, as demonstrated by XPS and HRTEM results, contribute to the excellent hydrogenation performance. Electron paramagnetic resonance (EPR) results suggest the presence of oxygen vacancies in the support, which serve as electron donors and enhance the adsorption and activation of reactants and subsequent conversion into products. Moreover, the catalyst can be recovered and reused up to 10 consecutive cycles without marked loss of activity. Overall, our results indicate that oxygen-deficient Pr6O11 nanorods (NRs) not only play a role as support but also work as the promoter to substantially boost the catalytic activities for organic transformations, therefore, providing a novel strategy to develop other high-performance nanostructured catalysts for environmental sustainability.

Highly dispersed ultra-small Pd nanoparticles on gadolinium hydroxide nanorods for efficient hydrogenation reactions.

Heterogeneous catalytic hydrogenation reactions are of great importance to the petrochemical industry and fine chemical synthesis. Herein, we present the first example of gadolinium hydroxide (Gd(OH)3) nanorods as a support for loading ultra-small Pd nanoparticles for hydrogenation reactions. Gd(OH)3 possesses a large number of hydroxyl groups on the surface, which act as an ideal support for good dispersion of Pd nanoparticles. Gd(OH)3 nanorods are prepared by hydrothermal treatment, and Pd/Gd(OH)3 catalyst with a low loading of 0.95 wt% Pd is obtained by photochemical deposition. The catalytic hydrogenation of p-nitrophenol (4-NP) to p-aminophenol (4-AP) and styrene to ethylbenzene is performed as a model reaction. The obtained Pd/Gd(OH)3 catalyst displays excellent activity as compared to other reported heterogeneous catalysts. The rate constant of 4-NP reduction is measured to be 0.047 s-1 and the Pd/Gd(OH)3 nanocatalyst shows no marked loss of activity even after 10 consecutive cycles. Additionally, the hydrogenation of styrene to ethylbenzene over Pd/Gd(OH)3 nanorods exhibits a turnover frequency (TOF) as high as 6159 h-1 with 100% selectivity. Moreover, the catalyst can be recovered by centrifugation and recycled for up to 5 consecutive cycles without obvious loss of activity. Our results indicate that Gd(OH)3 nanorods act as a promoter to enhance the catalytic activity by providing a synergistic effect from the strong metal support interaction and the large surface area for high dispersion of small sized Pd nanoparticles enriched with hydroxyl groups on the surface. The high performance of Pd/Gd(OH)3 in heterogeneous catalysis offers a new, efficient and facile strategy to explore other metal hydroxides or oxides as supports for organic transformations.