There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

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

The halogen bond occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a halogen atom in a molecular entity and a nucleophilic region in another, or the same, molecular entity. In this fairly extensive review, after a brief history of the interaction, we will provide the reader with a snapshot of where the research on the halogen bond is now, and, perhaps, where it is going. The specific advantages brought up by a design based on the use of the halogen bond will be demonstrated in quite different fields spanning from material sciences to biomolecular recognition and drug design.

The Halogen Bond

The applications of copper (Cu) and Cu-based nanoparticles, which are based on the earth-abundant and inexpensive copper metal, have generated a great deal of interest in recent years, especially in the field of catalysis. The possible modification of the chemical and physical properties of these nanoparticles using different synthetic strategies and conditions and/or via postsynthetic chemical treatments has been largely responsible for the rapid growth of interest in these nanomaterials and their applications in catalysis. In addition, the design and development of novel support and/or multimetallic systems (e.g., alloys, etc.) has also made significant contributions to the field. In this comprehensive review, we report different synthetic approaches to Cu and Cu-based nanoparticles (metallic copper, copper oxides, and hybrid copper nanostructures) and copper nanoparticles immobilized into or supported on various support materials (SiO2, magnetic support materials, etc.), along with their applications i...

http://pubs.acs.org/doi/pdfplus/10.1021/acs.chemrev.5b00482

Cu and Cu-Based Nanoparticles: Synthesis and Applications in Catalysis.

The organoselenium and organotellurium compounds have been described as promising pharmacological agents in view of their unique biological properties. Glutathione peroxidase mimic, antioxidant activity and thioredoxin reductase inhibition are some of the properties reviewed here. On the other hand, little is known about the molecular toxicological effects of organoselenium and organotellurium compounds. Most of our knowledge arose from research on inorganic selenium and tellurium. However, the ability to oxidize sulfhydryl groups from biological molecules can be involved both in their pharmacological properties and in their toxicological effects. In fact, exposition to high doses of organoselenium or to low doses of organotellurium causes the depletion of endogenous reduced glutathione in a variety of tissues. Thus, the design of compounds that cause low depletion of glutathione and react with specific targeted proteins, controlling specific metabolic pathways, will represent an important progress in understanding the field of organochalcogen compounds. Furthermore, the development of new organochalcogens with higher thiol-peroxidase activity that can use other non-toxic thiol reducing agents, such as N-acetylcysteine instead of glutathione, will permit the investigation of the co-administration of organochalcogens and thiols as a formulation for antioxidant therapy.

Organoselenium and Organotellurium Compounds: Toxicology and Pharmacology

Erratum to: ‘Tuning selenium–iodine contacts: from secondary soft–soft interactions to covalent bonds’ [Journal of Organometallic Chemistry 623 (2001) 14–28]

Among the organoselenium compounds that mimic the action of the natural enzyme glutathione peroxidase (GPx), there are certain basic differences in the activity, substrate specificity and mechanism. These differences arise mainly from the nature of the substituents near the reaction center, and stability and reactivity of the intermediates. As an attempt to draw some general concepts for the development of new mimics, a structure - activity correlation between natural GPx and some existing mimics is described.

Structure—Activity Correlation Between Natural Glutathione Peroxidase (GPx) and Mimics: A Biomimetic Concept for the Design and Synthesis of More Efficient GPx Mimics

In this chapter, several selenium‐based compounds that functionally mimic the activity of the selenoenzyme glutathione peroxidase (GPx) are discussed. These compounds include (1) cyclic selenenyl amides with a selenium‐nitrogen bond, (2) diaryl diselenides, and (3) aliphatic as well as aromatic monoselenides. On the basis of recent experimental and theoretical investigations, the reason for the poor GPx activity of ebselen in the presence of aryl or benzylic thiol cofactors such as PhSH or BnSH is described. The discrepancies in the GPx‐like activities of other classes of compounds can be ascribed mainly to the difference in the reactivity of thiol cofactors. The catalytic activity of synthetic selenium compounds is influenced to a large extend by the nature of the thiol substrate. The existence of strong Se···O/N noncovalent interactions in the selenenyl sulfide intermediates of the catalytic cycle generally decreases the antioxidant activity as such interactions facilitate an attack of thiol at selenium rather than at sulfur. In addition to the GPx activity, it is explained that several organoselenium compounds can act as efficient scavengers of peroxynitrite, a potent biological oxidant and nitrating species.

CHAPTER 10.2:Current Research on Mimics and Models of Selenium‐Containing Antioxidants

The reaction of intramolecularly coordinating 2-(4,4-dimethyloxazolino)phenyl selenolate ligand with anhydrous BiCl3 (3:1 equivalents) produces the monomeric, air stable, homoleptic bismuth(III) selenolate complex.

The First Example of a Structurally Characterized Monomeric Bismuth Selenolate

Thyroid hormones (THs) are secreted by the thyroid gland. They control lipid, carbohydrate, and protein metabolism, heart rate, neural development, as well as cardiovascular, renal, and brain functions. The thyroid gland mainly produces l-thyroxine (T4) as a prohormone, and 5'-deiodination of T4 by iodothyronine deiodinases generates the nuclear receptor binding hormone T3. In this Review, we discuss the basic aspects of the chemistry and biology as well as recent advances in the biosynthesis of THs in the thyroid gland, plasma transport, and internalization of THs in their target organs, in addition to the deiodination and various other enzyme-mediated metabolic pathways of THs. We also discuss thyroid hormone receptors and their mechanism of action to regulate gene expression, as well as various thyroid-related disorders and the available treatments.

Govindasamy Mugesh

Papers

Erratum to: ‘Tuning selenium–iodine contacts: from secondary soft–soft interactions to covalent bonds’ [Journal of Organometallic Chemistry 623 (2001) 14–28]

Structure—Activity Correlation Between Natural Glutathione Peroxidase (GPx) and Mimics: A Biomimetic Concept for the Design and Synthesis of More Efficient GPx Mimics

CHAPTER 10.2:Current Research on Mimics and Models of Selenium‐Containing Antioxidants

The First Example of a Structurally Characterized Monomeric Bismuth Selenolate

Chemistry and Biology in the Biosynthesis and Action of Thyroid Hormones