An Unusual Two‐Step Hydrolysis of Nerve Agents by a Nanozyme

Grain-Boundary-Rich Ceria Metallene Nanozyme with Abundant Metal Site Pairs Boosts Phosphatase-like Activity

Natural phosphatases featuring paired metal sites inspire various advanced nanozymes with phosphatase-like activity as alternatives in practical applications. Numerous efforts to create point defects show limited metal site pairs, further resulting in insufficient activity. However, it remains a grand challenge to accurately engineer abundant metal site pairs in nanozymes. Herein, we report a grain-boundary-rich ceria metallene nanozyme (GB-CeO2) with phosphatase-like activity. Grain boundaries acting as the line or interfacial defects can effectively increase the content of Ce4+/Ce3+ site pairs to 72.28%, achieving a 49.28-fold enhancement in activity. Furthermore, abundant grain boundaries optimize the band structure to assist the photoelectron transfer under irradiation, which further increases the content of metal site pairs to 88.96% and finally realizes a 114.39-fold enhanced activity over that of CeO2 without irradiation. Given the different inhibition effects of pesticides on catalysts with and without irradiation, GB-CeO2 was successfully applied to recognize mixed toxic pesticides.

Ce-based solid-phase catalysts for phosphate hydrolysis as new tools for next-generation nanoarchitectonics

This review comprehensively covers synthetic catalysts for the hydrolysis of biorelevant phosphates and pyrophosphates, which bridge between nanoarchitectonics and biology to construct their interdisciplinary hybrids. In the early 1980s, remarkable catalytic activity of Ce4+ ion for phosphate hydrolysis was found. More recently, this finding has been extended to Ce-based solid catalysts (CeO2 and Ce-based metal-organic frameworks (MOFs)), which are directly compatible with nanoarchitectonics. Monoesters and triesters of phosphates, as well as pyrophosphates, were effectively cleaved by these catalysts. With the use of either CeO2 nanoparticles or elegantly designed Ce-based MOF, highly stable phosphodiester linkages were also hydrolyzed. On the surfaces of all these solid catalysts, Ce4+ and Ce3+ coexist and cooperate for the catalysis. The Ce4+ activates phosphate substrates as a strong acid, whereas the Ce3+ provides metal-bound hydroxide as an eminent nucleophile. Applications of these Ce-based catalysts to practical purposes are also discussed.

Nanozyme-based pollutant sensing and environmental treatment: Trends, challenges, and perspectives

Nanozymes are defined as nanomaterials exhibiting enzyme-like properties, and they possess both catalytic functions and nanomaterial's unique physicochemical characteristics. Due to the excellent stability and improved catalytic activity in comparison to natural enzymes, nanozymes have established a wide base for applications in environmental pollutants monitoring and remediation. Nanozymes have been applied in the detection of heavy metal ions, molecules, and organic compounds, both quantitatively and qualitatively. Additionally, within the natural environment, nanozymes can be employed for the degradation of organic and persistent pollutants such as antibiotics, phenols, and textile dyes. Further, the potential sphere of applications for nanozymes traverses from indoor air purification to anti-biofouling agents, and even they show promise in combatting pathogenic bacteria. However, nanozymes may have inherent toxicity, which can restrict their widespread utility. Thus, it is important to evaluate and monitor the interaction and transformation of nanozymes towards biosphere damage when employed within the natural environment in a cradle-to-grave manner, to assure their utmost safety. In this context, various studies have concluded that the green synthesis of nanozymes can efficiently overcome the toxicity limitations in real life applications, and nanozymes can be well utilized in the sensing and degradation of several toxic pollutants including metal ions, pesticides, and chemical warfare agents. In this seminal review, we have explored the great potential of nanozymes, whilst addressing a range of concerns, which have often been overlooked and currently restrict widespread applications and commercialization of nanozymes.

Hydrolytic cleavage of nerve agent simulants by gold nanozymes

Although banned by the Chemical Weapons Convention, organophosphorus nerve agents are still available and have been used in regional wars, terroristic attacks or for other crtaiminal purposes. Their degradation is of primary importance for the severe toxicity of these compounds. Here we report that gold nanoparticles passivated with thiolated molecules bearing 1,3,7-triazacyclononane and 1,3,7,10-tetraazacyclododecane ligands efficiently hydrolyze nerve agents simulants p-nitrophenyl diphenyl phosphate and methylparaoxon as transition metal complexes at 25 °C and pH 8 with half-lives of the order of a few minutes. Mechanistically, these catalysts show an enzyme-like behavior, hence they constitute an example of nanozymes. The catalytic site appears to involve a single metal ion and its recognition of the substrates is driven mostly by hydrophobic interactions. The ease of preparation and the mild conditions at which they operate, make these nanozymes appealing catalysts for the detoxification after contamination with organophosphorus nerve agents, particularly those poorly soluble in water.

Electronic-State Manipulation of Surface Titanium Activates Dephosphorylation Over TiO2 Near Room Temperature

Dephosphorylation that removes a phosphate group from substrates is an important reaction for living organisms and environmental protection. Although CeO₂ has been shown to catalyze this reaction, cerium is low in natural abundance and has a narrow global distribution (>90 % of these reserves are located within six countries). It is thus imperative to find another element/material with high worldwide abundance that can also efficiently extract the phosphate out of agricultural waste for phosphorus recycle. Using para-nitrophenyl phosphate (p-NPP) as a model compound, we demonstrate that TiO₂ with a F-modified (001) surface can activate p-NPP dephosphorylation at temperatures as low as 40 °C. By probe-assisted nuclear magnetic resonance (NMR), it was revealed that the strong electron-withdrawing effect of fluorine makes Ti atoms (the active sites) on the (001) surface very acidic. The bidentate adsorption of p-NPP on this surface further promotes its subsequent activation with a barrier ≈20 kJ mol^-1 lower than that of the pristine (001) and (101) surfaces, allowing the activation of this reaction near room temperature (from >80 °C).

Factors Influencing the Activity of Nanozymes in the Cleavage of an RNA Model Substrate

A series of 2-nm gold nanoparticles passivated with different thiols all featuring at least one triazacyclonanone-Zn(II) complex and different flanking units (a second Zn(II) complex, a triethyleneoxymethyl derivative or a guanidinium of arginine of a peptide) were prepared and studied for their efficiency in the cleavage of the RNA-model substrate 2-hydroxypropyl-p-nitrophenyl phosphate. The source of catalysis for each of them was elucidated from the kinetic analysis (Michaelis–Menten profiles, pH dependence and kinetic isotope effect). The data indicated that two different mechanisms were operative: One involving two Zn(II) complexes and the other one involving a single Zn(II) complex and a flanking guanidinium cation. The mechanism based on a dinuclear catalytic site appeared more efficient than the one based on the cooperativity between a metal complex and a guanidinium.

Cleaving DNA-model phosphodiester with Lewis acid-base catalytic sites in bifunctional Zr-MOFs

Organophosphates exist in many biomolecules. The design of artificial nucleases for efficient P-O bond cleavage is essential for the fields of genetic engineering and molecular biology. Herein, metal-organic frameworks (MOFs) with cooperatively isolated multi-catalytic active sites were utilized as heterogeneous catalysts for the hydrolytic cleavage of bis(p-nitrophenyl) phosphate (BNPP).

Crystal-facet-dependent denitrosylation: modulation of NO release from S-nitrosothiols by Cu2O polymorphs

Nitric oxide (NO), a gaseous small molecule generated by the nitric oxide synthase (NOS) enzymes, plays key roles in signal transduction. The thiol groups present in many proteins and small molecules undergo nitrosylation to form the corresponding S-nitrosothiols. The release of NO from S-nitrosothiols is a key strategy to maintain the NO levels in biological systems. However, the controlled release of NO from the nitrosylated compounds at physiological pH remains a challenge. In this paper, we describe the synthesis and NO releasing ability of Cu2O nanomaterials and provide the first experimental evidence that the nanocrystals having different crystal facets within the same crystal system exhibit different activities toward S-nitrosothiols. We used various imaging techniques and time-dependent spectroscopic measurements to understand the nature of catalytically active species involved in the surface reactions. The denitrosylation reactions by Cu2O can be carried out multiple times without affecting the catalytic activity.

Nanomaterials Exhibiting Enzyme-Like Properties (Nanozymes): Current Advances and Future Perspectives

Biological enzymes are macromolecular catalysts that catalyze the biochemical reactions of the natural systems. Although each enzyme performs a particular function, however, holds several drawbacks, which limits its utilization in broad-spectrum applications. Natural enzymes require strict physiological conditions for performing catalytic functions. Their limited stability in harsh environmental conditions, the high cost of synthesis, isolation, and purification are some of the significant drawbacks. Therefore, as an alternative to natural enzymes, recently several strategies have been developed including the synthesis of molecules, complexes, and nanoparticles mimicking their intrinsic catalytic properties. Nanoparticles exhibiting the properties of an enzyme are termed as “nanozymes.” Nanozymes offer several advantages over natural enzymes, therefore, a rapid expansion of the development of artificial biocatalysts. These advantages include simple methods of synthesis, low cost, high stability, robust catalytic performance, and smooth surface modification of nanomaterials. In this context, nanozymes are tremendously being explored to establish a wide range of applications in biosensing, immunoassays, disease diagnosis and therapy, theranostics, cell/tissue growth, protection from oxidative stress, and removal of pollutants. Considering the importance of nanozymes, this article has been designed to comprehensively discuss the different enzyme-like properties, such as peroxidase, catalase, superoxide dismutase, and oxidase, exhibited by various nanoparticles.