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Oxidative Medicine and Cellular... 2020Free radicals are chemical species (atoms, molecules, or ions) containing one or more unpaired electrons in their external orbitals and generally display a remarkable... (Review)
Review
Free radicals are chemical species (atoms, molecules, or ions) containing one or more unpaired electrons in their external orbitals and generally display a remarkable reactivity. The evidence of their existence was obtained only at the beginning of the 20th century. Chemists gradually ascertained the involvement of free radicals in organic reactions and, in the middle of the 20th century, their production in biological systems. For several decades, free radicals were thought to cause exclusively damaging effects . This idea was mainly supported by the finding that oxygen free radicals readily react with all biological macromolecules inducing their oxidative modification and loss of function. Moreover, evidence was obtained that when, in the living organism, free radicals are not neutralized by systems of biochemical defences, many pathological conditions develop. However, after some time, it became clear that the living systems not only had adapted to the coexistence with free radicals but also developed methods to turn these toxic substances to their advantage by using them in critical physiological processes. Therefore, free radicals play a dual role in living systems: they are toxic by-products of aerobic metabolism, causing oxidative damage and tissue dysfunction, and serve as molecular signals activating beneficial stress responses. This discovery also changed the way we consider antioxidants. Their use is usually regarded as helpful to counteract the damaging effects of free radicals but sometimes is harmful as it can block adaptive responses induced by low levels of radicals.
Topics: Animals; Antioxidants; Free Radicals; Humans; Oxidants; Oxidative Stress; Reactive Oxygen Species; Superoxide Dismutase
PubMed: 32411336
DOI: 10.1155/2020/9829176 -
Journal of Esthetic and Restorative... Sep 2019The aim is to review the most important aspects about tooth whitening treatments, their side effects, and the new emerging approaches to overcome them. (Review)
Review
OBJECTIVE
The aim is to review the most important aspects about tooth whitening treatments, their side effects, and the new emerging approaches to overcome them.
OVERVIEW
This review is focused on origin of tooth stains, the whitening systems and their chemistry, their side effects, and the new approaches. The search of bibliography of the period 1965-2018 has been analyzed.
CONCLUSIONS
Tooth whitening has become one of the most requested dental treatments by the public. Tooth stains are classified according to their origin into two categories: intrinsic and extrinsic. The whitening systems are generally organized into two classes: in-office and at-home products. Most of the whitening systems use hydrogen peroxide as the active oxidative agent to degrade the organic compounds that cause stains. The concentration ranges depending on the treatment, and it may be applied directly or produced in a chemical reaction from carbamide peroxide that is more stable. Besides its popularity, tooth whitening still has some side effects being tooth hypersensitivity the most common. In order to decrease these side effects, new treatments are constantly in renewal processes.
CLINICAL SIGNIFICANCE
Despite all the data and new strategies known about tooth whitening, there are many aspects that are not totally fully understood and methodologies that are not completely effective. Therefore, the development of effective, efficient, and long-lasting whitening treatments is still necessary.
Topics: Drug Combinations; Hydrogen Peroxide; Peroxides; Tooth Bleaching; Tooth Bleaching Agents; Urea
PubMed: 31448534
DOI: 10.1111/jerd.12519 -
Water Research Apr 2024This publication summarizes my journey in the field of chemical oxidation processes for water treatment over the last 30+ years. Initially, the efficiency of the... (Review)
Review
This publication summarizes my journey in the field of chemical oxidation processes for water treatment over the last 30+ years. Initially, the efficiency of the application of chemical oxidants for micropollutant abatement was assessed by the abatement of the target compounds only. This is controlled by reaction kinetics and therefore, second-order rate constant for these reactions are the pre-requisite to assess the efficiency and feasibility of such processes. Due to the tremendous efforts in this area, we currently have a good experimental data base for second-order rate constants for many chemical oxidants, including radicals. Based on this, predictions can be made for compounds without experimental data with Quantitative Structure Activity Relationships with Hammet/Taft constants or energies of highest occupied molecular orbitals from quantum chemical computations. Chemical oxidation in water treatment has to be economically feasible and therefore, the extent of transformation of micropollutants is often limited and mineralization of target compounds cannot be achieved under realistic conditions. The formation of transformation products from the reactions of the target compounds with chemical oxidants is inherent to oxidation processes and the following questions have evolved over the years: Are the formed transformation products biologically less active than the target compounds? Is there a new toxicity associated with transformation products? Are transformation products more biodegradable than the corresponding target compounds? In addition to the positive effects on water quality related to abatement of micropollutants, chemical oxidants react mainly with water matrix components such as the dissolved organic matter (DOM), bromide and iodide. As a matter of fact, the fraction of oxidants consumed by the DOM is typically > 99%, which makes such processes inherently inefficient. The consequences are loss of oxidation capacity and the formation of organic and inorganic disinfection byproducts also involving bromide and iodide, which can be oxidized to reactive bromine and iodine with their ensuing reactions with DOM. Overall, it has turned out in the last three decades, that chemical oxidation processes are complex to understand and to manage. However, the tremendous research efforts have led to a good understanding of the underlying processes and allow a widespread and optimized application of such processes in water treatment practice such as drinking water, municipal and industrial wastewater and water reuse systems.
Topics: Bromides; Iodides; Water Pollutants, Chemical; Oxidation-Reduction; Oxidants; Water Purification
PubMed: 38387263
DOI: 10.1016/j.watres.2024.121148 -
Molecules (Basel, Switzerland) Jul 2019Oxidation of sulfide to sulfate is known to consist of several steps. Key intermediates in this process are the so-called small oxoacids of sulfur (SOS)-sulfenic HSOH... (Review)
Review
Oxidation of sulfide to sulfate is known to consist of several steps. Key intermediates in this process are the so-called small oxoacids of sulfur (SOS)-sulfenic HSOH (hydrogen thioperoxide, oxadisulfane, or sulfur hydride hydroxide) and sulfoxylic S(OH) acids. Sulfur monoxide can be considered as a dehydrated form of sulfoxylic acid. Although all of these species play an important role in atmospheric chemistry and in organic synthesis, and are also invoked in biochemical processes, they are quite unstable compounds so much so that their physical and chemical properties are still subject to intense studies. It is well-established that sulfoxylic acid has very strong reducing properties, while sulfenic acid is capable of both oxidizing and reducing various substrates. Here, in this review, the mechanisms of sulfide oxidation as well as data on the structure and reactivity of small sulfur-containing oxoacids, sulfur monoxide, and its precursors are discussed.
Topics: Free Radicals; Hydrogen Sulfide; Kinetics; Oxidation-Reduction; Oxides; Peroxides; Safrole; Sulfates; Sulfenic Acids; Sulfides; Sulfur Compounds
PubMed: 31366103
DOI: 10.3390/molecules24152768 -
Molecules (Basel, Switzerland) Jul 2023The chemistry of hypervalent iodine reagents has now become quite valuable due to the reactivity of these compounds under mild reaction conditions and their resemblance... (Review)
Review
The chemistry of hypervalent iodine reagents has now become quite valuable due to the reactivity of these compounds under mild reaction conditions and their resemblance in chemical properties to transition metals. The environmentally friendly nature of these reagents makes them suitable for Green Chemistry. Reagents with a dual nature, such as iodine(III) reagents, are capable electrophiles, while iodine(V) reagents are known for their strong oxidant behavior. Various iodine(V) reagents including IBX and DMP have been used as oxidants in organic synthesis either in stoichiometric or in catalytic amounts. In this review article, we describe various oxidation reactions induced by iodine(V) reagents reported in the past decade.
Topics: Iodine; Oxidants; Oxidation-Reduction; Indicators and Reagents; Catalysis
PubMed: 37446912
DOI: 10.3390/molecules28135250 -
Current Organic Synthesis 2022Organoselenium chemistry has developed as an important tool in the field of synthetic and medicinal chemistry. Various organoselenium reagents have been developed and... (Review)
Review
Organoselenium chemistry has developed as an important tool in the field of synthetic and medicinal chemistry. Various organoselenium reagents have been developed and used successfully to achieve different organic transformations such as selenocyclizations, oxyselenenylations, selenoxide eliminations, etc. Additionally, organoselenium reagents' potential is not limited to their use as stoichiometric reagents, but they have been successfully used as organocatalysts in a number of synthetic transformations. Various organic and inorganic oxidants have been identified as terminal oxidants to regenerate the active catalytic species. In this review article, the recent progress of organoselenium reagents in catalysis is being highlighted along with their asymmetric variants.
Topics: Catalysis; Indicators and Reagents; Oxidants; Oxidation-Reduction; Selenium Compounds
PubMed: 35152866
DOI: 10.2174/1570179419666220211102602 -
Accounts of Chemical Research Dec 2022The stereoselective intermolecular bond-forming reactions through the direct manipulation of ubiquitous yet inert C(sp)-H bonds represent an important and long-standing...
The stereoselective intermolecular bond-forming reactions through the direct manipulation of ubiquitous yet inert C(sp)-H bonds represent an important and long-standing goal in chemistry. In particular, developing such a stereoselective bimolecular transformation involving carbocation intermediates generated via site-selective hydride abstraction or formal hydride abstraction by organic oxidants would avoid the preinstallation of directing groups and is therefore attractive. Hydride-abstraction-initiated bimolecular transformations have received considerable attention, but existing examples lack stereoselective studies. Prevalent stereoselective studies typically suffer from the narrow substrate scope of specific and highly reactive -aryl amines and diarylmethanes together with limited synthetic utility. This Account describes our recent advances in the development and synthetic application of hydride-abstraction-initiated stereoselective intermolecular C-C and C-H bond-forming processes with significantly expanded scopes involving structurally diverse -acyl amines and ethers together with nitriles, esters, and perfluoroalkyl moieties.We first explored hydride-abstraction-initiated stereoselective intermolecular C-C bond-forming processes. Utilizing triarylmethyl cations or oxoammonium ions as hydride abstractors, we accomplished the diastereoselective oxidative C-H functionalization of structurally diverse -acyl amines and ethers with a range of organoboranes and C-H components, efficiently installing a series of alkyl, alkenyl, aryl, and alkynyl species into the α-position of heteroatoms with good levels of diastereocontrol. Subsequently, we developed an "acetal pool" strategy as the toolbox to regulate the stability of cationic intermediates and the compatibility of organic oxidants with a delicate asymmetric catalysis system. Utilizing this strategy, we achieved the catalytic enantioselective oxidative C-H alkenylation, arylation, alkynylation, and alkylation of diverse -acyl heterocycles with a range of boronates and C-H components. Simultaneously, we extended this strategy to the asymmetric oxidative C-H alkylation of ethers. Notably, the method allows solvents that are used daily, such as tetrahydrofuran, tetrahydropyran, and diethyl ether, to be facilely transformed to high-value-added optically pure bioactive molecules. We further expanded the scope of this challenging area from the C(sp)-H bond adjacent to electron-donating heteroatoms to valuable electron-withdrawing functional groups including nitriles, esters, and perfluoroalkyl moieties for the stereoselective construction of single and vicinal quaternary carbon stereocenters, respectively.We studied hydride-abstraction-initiated catalytic asymmetric intermolecular C-H bond-forming processes, known as redox deracemization. Utilizing the acetal pool strategy, we reported the first redox deracemization of cyclic benzylic ethers. Later, we disclosed an aerobic one-pot deracemization of diverse α-amino acid derivatives with excellent functional group compatibility. We further achieved the deracemization of the tertiary stereogenic center adjacent to electron-withdrawing groups including perfluoroalkyl, cyano, and ester moieties, which are otherwise difficult to construct.
Topics: Acetals; Fluorocarbons; Catalysis; Amines; Ethers; Carbon; Ethers, Cyclic; Nitriles; Oxidants
PubMed: 36384272
DOI: 10.1021/acs.accounts.2c00638 -
Environmental Science & Technology Apr 2023Methylmercury (MeHg) is a potent neurotoxin and has great adverse health impacts on humans. Organisms and sunlight-mediated demethylation are well-known detoxification...
Methylmercury (MeHg) is a potent neurotoxin and has great adverse health impacts on humans. Organisms and sunlight-mediated demethylation are well-known detoxification pathways of MeHg, yet whether abiotic environmental components contribute to MeHg degradation remains poorly known. Here, we report that MeHg can be degraded by trivalent manganese (Mn(III)), a naturally occurring and widespread oxidant. We found that 28 ± 4% MeHg could be degraded by Mn(III) located on synthesized Mn dioxide (MnO) surfaces during the reaction of 0.91 μg·L MeHg and 5 g·L mineral at an initial pH of 6.0 for 12 h in 10 mM NaNO at 25 °C. The presence of low-molecular-weight organic acids (e.g., oxalate and citrate) substantially enhances MeHg degradation by MnO via the formation of soluble Mn(III)-ligand complexes, leading to the cleavage of the carbon-Hg bond. MeHg can also be degraded by reactions with Mn(III)-pyrophosphate complexes, with apparent degradation rate constants comparable to those by biotic and photolytic degradation. Thiol ligands (cysteine and glutathione) show negligible effects on MeHg demethylation by Mn(III). This research demonstrates potential roles of Mn(III) in degrading MeHg in natural environments, which may be further explored for remediating heavily polluted soils and engineered systems containing MeHg.
Topics: Humans; Manganese; Methylmercury Compounds; Mercury; Oxidants; Cysteine
PubMed: 36995950
DOI: 10.1021/acs.est.3c00532 -
Yakugaku Zasshi : Journal of the... 2023Organic nitroxyl radicals represented by 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) are known to be compounds that catalyze alcohol oxidation reactions. These... (Review)
Review
Organic nitroxyl radicals represented by 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) are known to be compounds that catalyze alcohol oxidation reactions. These catalytic reactions can be applied to a wide range of compounds with hydroxy and amino groups. It is also possible to selectively oxidize primary alcohols by designing the skeleton around the nitroxyl radical moiety for use in organic synthesis. Reactions can also be carried out by electrochemical methods, and the electrical current measured during the reaction can be used to quantify the substrates. Therefore, the combination of reactions catalyzed by nitroxyl radicals and electrochemical techniques is expected to be applied as a new analytical method. However, since the reaction does not proceed rapidly in neutral aqueous solutions, it has mostly been applied in basic aqueous solutions or organic solvents, and there have been no reports on sensor applications under physiological conditions. Herein, we have developed a novel catalyst, nortropine N-oxyl (NNO), which is highly active even in neutral aqueous solutions, and have found that it can be used for the analysis of biological components and drugs under physiological conditions. The combination of this method with enzymatic reactions made it possible to specifically detect certain compounds. In this review, we describe a novel analytical method that combines these nitroxyl radicals with electrochemical methods.
Topics: Oxidation-Reduction; Nitrogen Oxides; Catalysis; Water; Free Radicals
PubMed: 36724933
DOI: 10.1248/yakushi.22-00143 -
Chemistry (Weinheim An Der Bergstrasse,... Aug 2023Steroids are highly prevalent structures in small-molecule therapeutics, with the level of oxidation being key to their biological activity and physicochemical... (Review)
Review
Steroids are highly prevalent structures in small-molecule therapeutics, with the level of oxidation being key to their biological activity and physicochemical properties. These C(sp )-rich tetracycles contain many stereocentres, which are important for creating specific vectors and protein binding orientations. Therefore, the ability to hydroxylate steroids with a high degree of regio-, chemo- and stereoselectivity is essential for researchers working in this field. This review will cover three main methods for the hydroxylation of steroidal C(sp )-H bonds: biocatalysis, metal-catalysed C-H hydroxylation and organic oxidants, such as dioxiranes and oxaziridines.
Topics: Hydroxylation; Oxidation-Reduction; Oxidants; Steroids; Biocatalysis
PubMed: 37235530
DOI: 10.1002/chem.202301066