Over the past few decades, researchers have established artificial enzymes as highly stable and low-cost alternatives to natural enzymes in a wide range of applications. A variety of materials including cyclodextrins, metal complexes, porphyrins, polymers, dendrimers and biomolecules have been extensively explored to mimic the structures and functions of naturally occurring enzymes. Recently, some nanomaterials have been found to exhibit unexpected enzyme-like activities, and great advances have been made in this area due to the tremendous progress in nano-research and the unique characteristics of nanomaterials. To highlight the progress in the field of nanomaterial-based artificial enzymes (nanozymes), this review discusses various nanomaterials that have been explored to mimic different kinds of enzymes. We cover their kinetics, mechanisms and applications in numerous fields, from biosensing and immunoassays, to stem cell growth and pollutant removal. We also summarize several approaches to tune the activities of nanozymes. Finally, we make comparisons between nanozymes and other catalytic materials (other artificial enzymes, natural enzymes, organic catalysts and nanomaterial-based catalysts) and address the current challenges and future directions (302 references).

Nanomaterials with enzyme-like characteristics (nanozymes): next-generation artificial enzymes

Deconstructing the Crystal Structures of Metal Organic Frameworks and Related Materials into Their Underlying Nets Michael O’Keeffe* and Omar M. Yaghi* Department of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona 85287, United States Center for Reticular Chemistry, Center for Global Mentoring, Department of Chemistry and Biochemistry, University of California Los Angeles, 607 Charles E. Young Dr. East, Los Angeles, California 90095, United States Graduate School of EEWS, Korea Advanced Institute of Science and Technology, Daejeon, Korea

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Deconstructing the crystal structures of metal-organic frameworks and related materials into their underlying nets.

: The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

Because of the high catalytic activities and substrate specificity, natural enzymes have been widely used in industrial, medical, and biological fields, etc. Although promising, they often suffer from intrinsic shortcomings such as high cost, low operational stability, and difficulties of recycling. To overcome these shortcomings, researchers have been devoted to the exploration of artificial enzyme mimics for a long time. Since the discovery of ferromagnetic nanoparticles with intrinsic horseradish peroxidase-like activity in 2007, a large amount of studies on nanozymes have been constantly emerging in the next decade. Nanozymes are one kind of nanomaterials with enzymatic catalytic properties. Compared with natural enzymes, nanozymes have the advantages such as low cost, high stability and durability, which have been widely used in industrial, medical, and biological fields. A thorough understanding of the possible catalytic mechanisms will contribute to the development of novel and high-efficient nanozymes, and the rational regulations of the activities of nanozymes are of great significance. In this review, we systematically introduce the classification, catalytic mechanism, activity regulation as well as recent research progress of nanozymes in the field of biosensing, environmental protection, and disease treatments, etc. in the past years. We also propose the current challenges of nanozymes as well as their future research focus. We anticipate this review may be of significance for the field to understand the properties of nanozymes and the development of novel nanomaterials with enzyme mimicking activities.

Nanozymes: Classification, Catalytic Mechanisms, Activity Regulation, and Applications

Reactive oxygen species (ROS) play an essential role in regulating various physiological functions of living organisms. The intrinsic biochemical properties of ROS, which underlie the mechanisms ne...

Reactive Oxygen Species (ROS)-Based Nanomedicine.

We report the direct synthesis of cerium oxide nanoparticles (CNPs) in polyethylene glycol (PEG) based solutions with efficient radical scavenging properties. Synthesis of CNPs in PEG demonstrated a concentration dependent (of PEG) redox activity characterized by UV−visible spectroscopy. PEGylated CNPs acted as efficient radical scavengers, and superoxide dismutase (SOD) activity of CNPs synthesized in various concentration of PEG did not reduce compared to bare nanoceria. In addition to superoxide, PEGylated nanoceria demonstrated quenching of peroxide radicals as well. It was observed that the reaction with hydrogen peroxide leads to the formation of a charge transfer complex governed by the concentration of PEG. The stability of the charge transfer complex provides the tunable oxidation state of CNPs. The stability of this complex influences the regenerative capacity of the active 3+ oxidation state of CNPs. The cell viability as well as SOD activity of PEGylated CNPs is compared to those of bare CNPs,...

PEGylated Nanoceria as Radical Scavenger with Tunable Redox Chemistry

Important progressive alterations in chemical bonding are often realized through correlations with shifts in the x‐ray photoelectron spectroscopy (XPS) binding energies of key elements. For example, there are useful general XPS shifting schemes for such systems as oxides, nitrides, halides, and even various functional groups in organics. Very general patterns, based upon location in the periodic table, exist for many of these materials even when the structure is not strongly considered. Unfortunately, apparently because of the lack of direct XPS detection of hydrogen, there seems to be no general statements in the literature for describing hydrogen‐containing compounds, despite the fact that synergistic shifts obviously exist in the XPS spectra of elements attached to hydrogen (e.g., for M–O–H vs M–O–M units, where M is a typical metal). While not attempting a complete review paper, in the present work we use XPS shifting patterns to evolve a series of interrelated covalency/ionicity arguments to help exp...

/pdf/the-nature-of-hydrogen-in-x-ray-photoelectron-spectroscopy-56nx7t6vnb.pdf

The nature of hydrogen in x-ray photoelectron spectroscopy: General patterns from hydroxides to hydrogen bonding

There is an upsurge of interest in the synthesis of coordination polymers in contemporary supramolecular chemistry, as coordination polymerization may lead to materials with controllable functions such as porosity, sensing, nonlinear optical (NLO) activity, and chirality. Crystal engineering based on predesigned organic linkers and metal centers (building blocks) with specific coordination geometries is an important approach in the preparation of coordination materials with desired functions. Based on the knowledge of the structures of the ligands and the coordination geometries of a variety of metal centers, diverse 2D and 3D nets—several of which are analogous to structures of inorganic materials—have been engineered in the field of metal–organic frameworks (MOFs). Thus, the syntheses of 3connected nets corresponding to the topologies of SrSi2/(10,3)-a, ThSi2/(10,3)-b, [4] (12,3), (3,4)-connected nets with the topologies of boracite, Cu15Si4, [7] (5,4), [8] and (3,6)connected nets corresponding to the topologies of rutile and pyrite have been accomplished. Insofar as the 4connected nets are concerned, the syntheses of MOFs with unusual topologies and with topologies corresponding to those of diamond, NbO, quartz, and PtS have been reported. Similarly, the (4,8)and 6-connected metal– organic frameworks with fluorite and cubic topologies, respectively, have been designed and synthesized. In view of the success of such building-block approaches to realize metal–organic frameworks with specific topologies, the multidentate ligands with novel structural features offer the possibility to construct new and unique coordination poly-

Corundum, diamond, and PtS metal-organic frameworks with a difference: self-assembly of a unique pair of 3-connecting D2d-symmetric 3,3',5,5'-tetrakis(4-pyridyl)bimesityl.

Electron paramagnetic study on radical scavenging properties of ceria nanoparticles

X-Ray photoelectron spectroscopy (known as XPS or ESCA) can
differentiate between tetrahedral and octahedral Al atoms in inorganic
solids. Although primarily used for the study of aluminosilicates,
this semi-quantitative technique is applicable to other materials,
irrespective of whether they contain aluminium in one or more
coordinations with respect to oxygen. If less sensitive to the
coordination of Al, the range of ESCA, a surface-oriented technique,
is thus not very different from that of the bulk-oriented solid-state
NMR. The procedures described here are successful with any
high-resolution ESCA system, but are greatly facilitated by flood gun
technology which removes insulator-induced charging shifts. Areas of
potential difficulty are also discussed.

Krzysztof Wozniak

Papers

PEGylated Nanoceria as Radical Scavenger with Tunable Redox Chemistry

The nature of hydrogen in x-ray photoelectron spectroscopy: General patterns from hydroxides to hydrogen bonding

Corundum, diamond, and PtS metal-organic frameworks with a difference: self-assembly of a unique pair of 3-connecting D2d-symmetric 3,3',5,5'-tetrakis(4-pyridyl)bimesityl.

Electron paramagnetic study on radical scavenging properties of ceria nanoparticles

ESCA studies of the coordination state of aluminium in oxide environments