-
Angewandte Chemie (International Ed. in... Feb 2011Reductive elimination from partially or completely oxidized metal centers is a vital step in a myriad of carbon-carbon and carbon-heteroatom bond-forming reactions. One... (Review)
Review
Reductive elimination from partially or completely oxidized metal centers is a vital step in a myriad of carbon-carbon and carbon-heteroatom bond-forming reactions. One strategy for promoting otherwise challenging reductive elimination reactions is to oxidize the metal center using a two-electron oxidant (that is, from M((n)) to M((n+2))). However, many of the commonly used oxidants for this type of transformation contain oxygen, nitrogen, or halogen moieties that are subsequently capable of participating in reductive elimination, thus leading to a mixture of products. In this Minireview, we examine the use of bystanding F(+) oxidants for addressing this widespread problem in organometallic chemistry and describe recent applications in Pd(II) /Pd(IV) and Au(I) /Au(III) catalysis. We then briefly discuss a rare example in which one-electron oxidants have been shown to promote selective reductive elimination in palladium(II)-catalyzed C-H functionalization, which we view as a promising future direction in the field.
Topics: Carbon; Catalysis; Fluorine; Gold; Oxidants; Oxidation-Reduction; Palladium
PubMed: 21264991
DOI: 10.1002/anie.201005142 -
Journal of the American Chemical Society Oct 2022With the large number of Pd(II)-catalyzed C-H activation reactions of native substrates developed in the past decade, the development of catalysts to enable the use of...
With the large number of Pd(II)-catalyzed C-H activation reactions of native substrates developed in the past decade, the development of catalysts to enable the use of green oxidants under safe and practical conditions has become an increasingly important challenge. Notably, the compatibility of Pd(II) catalysts with sustainable aqueous HO has been a long-standing challenge in catalysis including Wacker-type oxidations. We report herein a bifunctional bidentate carboxyl-pyridone (CarboxPyridone) ligand that enables room-temperature Pd-catalyzed C-H hydroxylation of a broad range of benzoic and phenylacetic acids with an industry-compatible oxidant, aqueous hydrogen peroxide (35% HO). The scalability of this methodology is demonstrated by a 1000 mmol scale reaction of ibuprofen (206 g) using only a 1 mol % Pd catalyst loading. The utility of this protocol is further illustrated through derivatization of the products and synthesis of polyfluorinated natural product coumestan and pterocarpene from phenol intermediates prepared using this methodology.
Topics: Biological Products; Catalysis; Hydrogen Peroxide; Hydroxylation; Ibuprofen; Ligands; Oxidants; Palladium; Phenols; Phenylacetates; Pyridones; Temperature; Water
PubMed: 36137252
DOI: 10.1021/jacs.2c08332 -
Environmental Health Perspectives Dec 1994The ability of a cell, tissue, or organism to better resist stress damage by prior exposure to a lesser amount of stress is known as adaptive response. It is observed in... (Review)
Review
The ability of a cell, tissue, or organism to better resist stress damage by prior exposure to a lesser amount of stress is known as adaptive response. It is observed in all organisms in response to a number of different cytotoxic agents. One of these agents, oxidative stress, is known to induce an adaptive response in bacteria that is accompanied by the induction of many proteins. De novo protein synthesis is required for adaptive response to oxidative and other types of stress, indicating that newly synthesized protective proteins are necessary for adaptation. Adaptive response to oxidative stress also has been observed in mammalian cells. Several studies suggest it is necessary to first preexpose mammalian cells to a somewhat toxic oxidative stress in order to observe significant resistance to a subsequent highly lethal dose of oxidant. Cross-resistance of oxidatively stressed cells to other toxic agents including gamma- and X-irradiation, heat shock, aldehydes, heavy metals, MNNG, N-ethylmaleimide, and heme also has been reported. Understanding oxidant adaptive response in more detail and identifying the protective proteins involved may prove to be of clinical benefit.
Topics: Adaptation, Physiological; Animals; Escherichia coli; Eukaryotic Cells; Humans; Oxidants; Oxidative Stress
PubMed: 7705299
DOI: 10.1289/ehp.94102s1025 -
Kidney International. Supplement Feb 2001Considerable evidence has accumulated that chronic uremia is associated with a multifactorial immunoinflammatory syndrome, which occurs early in the course of renal... (Review)
Review
Considerable evidence has accumulated that chronic uremia is associated with a multifactorial immunoinflammatory syndrome, which occurs early in the course of renal failure, is accentuated with the progression of uremia, and culminates in maintenance dialysis therapy. We previously described the presence of a circulating oxidized plasma protein named advanced oxidation protein products (AOPPs). Beyond evidence that AOPPs represent an exquisite marker of oxidative stress, their role(s) in the pathophysiology of chronic renal failure and dialysis-related complications might be of great importance. Regarding the mechanisms of generation of AOPP, we underscore the importance of the chlorinated oxidants, previously solely considered as microbicidal agents, in the generation of AOPP. Indeed, AOPPs appear to act as true inflammatory mediators since they are able to trigger the oxidative burst in neutrophils as well as in monocytes. Thus, it is hypothesized that the AOPPs, which arise from the reaction between chlorinated oxidants and plasma proteins, constitute a new molecular basis for the deleterious activity of oxidants, and they could be considered to be true mediators of the proinflammatory effect of oxidative stress in uremia.
Topics: Antioxidants; Biomarkers; Humans; Inflammation Mediators; Kidney Failure, Chronic; Oxidants; Oxidation-Reduction; Oxidative Stress; Phagocytes; Proteins
PubMed: 11168994
DOI: 10.1046/j.1523-1755.2001.59780108.x -
Molecules (Basel, Switzerland) May 2022The leaves of are polyphenol-rich traditional medicines used to treat inflammation-related diseases. The present study aimed to optimise the solvent for the effective...
The leaves of are polyphenol-rich traditional medicines used to treat inflammation-related diseases. The present study aimed to optimise the solvent for the effective recovery of active leaf components through simple direct extraction and verify the biological effects of the selected extract in a model of human neutrophils ex vivo. The extracts were comprehensively standardised, and forty-one individual polyphenols, representing salicylates, catechins, procyanidins, phenolic acids, and flavonoids, were identified by UHPLC-PDA-ESI-MS. The chosen methanol-water (75:25, /) extract (ME) was obtained with the highest extraction yield and total phenolic levels (397.9 mg/g extract's dw), including 98.9 mg/g salicylates and 299.0 mg/g non-salicylate polyphenols. In biological tests, ME revealed a significant and dose-dependent ability to modulate pro-oxidant and pro-inflammatory functions of human neutrophils: it strongly reduced the ROS level and downregulated the release of pro-inflammatory cytokines and tissue remodelling enzymes, especially IL-1β and elastase 2, in cells stimulated by MLP, LPS, or MLP + cytochalasin B. The extracts were also potent direct scavengers of in vivo relevant oxidants (O, OH, and HO) and inhibitors of pro-inflammatory enzymes (cyclooxygenase-2, hyaluronidase, and lipoxygenase). The statistically significant correlations between the tested variables revealed the synergic contribution of individual polyphenols to the observed effects and indicated them as useful active markers for the standardisation of the extract/plant material. Moreover, the safety of ME was confirmed in cytotoxicity tests. The obtained results might partially explain the ethnomedicinal application of leaves and support the usage of the standardised leaf extract in the adjuvant treatment of oxidative stress and inflammation-related chronic diseases.
Topics: Gaultheria; Humans; Hydrogen Peroxide; Inflammation; Neutrophils; Oxidants; Plant Extracts; Polyphenols; Reactive Oxygen Species; Salicylates
PubMed: 35630834
DOI: 10.3390/molecules27103357 -
Free Radical Biology & Medicine Jul 2008Oxidants are produced as a by-product of aerobic metabolism, and organisms ranging from prokaryotes to mammals have evolved with an elaborate and redundant complement of... (Review)
Review
Oxidants are produced as a by-product of aerobic metabolism, and organisms ranging from prokaryotes to mammals have evolved with an elaborate and redundant complement of antioxidant defenses to confer protection against oxidative insults. Compelling data now exist demonstrating that oxidants are used in physiological settings as signaling molecules with important regulatory functions controlling cell division, migration, contraction, and mediator production. These physiological functions are carried out in an exquisitely regulated and compartmentalized manner by mild oxidants, through subtle oxidative events that involve targeted amino acids in proteins. The precise understanding of the physiological relevance of redox signal transduction has been hampered by the lack of specificity of reagents and the need for chemical derivatization to visualize reversible oxidations. In addition, it is difficult to measure these subtle oxidation events in vivo. This article reviews some of the recent findings that illuminate the significance of redox signaling and exciting future perspectives. We also attempt to highlight some of the current pitfalls and the approaches needed to advance this important area of biochemical and biomedical research.
Topics: Amino Acids; Animals; Gene Expression Regulation; Humans; Hydrogen Peroxide; Oxidants; Oxidation-Reduction; Signal Transduction
PubMed: 18423411
DOI: 10.1016/j.freeradbiomed.2008.03.011 -
Journal of Nanobiotechnology Mar 2017Engineered nanomaterials (ENMs) are key drivers for the development of highly sophisticated new technologies. As all new attainments, the rapidly increasing used of ENMs... (Review)
Review
Engineered nanomaterials (ENMs) are key drivers for the development of highly sophisticated new technologies. As all new attainments, the rapidly increasing used of ENMs raise concerns about their safety for the environment and humans. There is growing evidence showing that if engineered nanomaterials are released into the environment, there is a possibility that they could cause harm to aquatic microorganisms. Among the divers effects triggering their toxicity the ability of ENMs to generate reactive oxygen species (ROS) capable of oxidizing biomolecules is currently considered a central mechanism of toxicity. Therefore, development of sensitive tools for quantification of the ROS generation and oxidative stress are highly sought. After briefly introducing ENMs-induced ROS generation and oxidative stress in the aquatic microorganisms (AMOs), this overview paper focuses on a new optical biosensor allowing sensitive and dynamic measurements of HO in real-time using multiscattering enhanced absorption spectroscopy. Its principle is based on sensitive absorption measurements of the heme protein cytochrome c whose absorption spectrum alters with the oxidation state of constituent ferrous Fe and ferric Fe. For biological applications cytochrome c was embedded in porous random media resulting in an extended optical path length through multiple scattering of light, which lowers the limit of detection to a few nM of HO. The sensor was also integrated in a microfluidic system containing micro-valves and sieves enabling more complex experimental conditions. To demonstrate its performance, abiotic absorption measurements of low concentrations of dye molecules and 10 nm gold particles were carried out achieving limits of detection in the low nM range. Other biologically relevant reactive oxygen species can be measured at sub-μM concentrations, which was shown for glucose and lactate through enzymatic reactions producing HO. In ecotoxicological investigations HO excreted by aquatic microorganisms exposed to various stressors were measured. Pro-oxidant effects of nano-TiO and nano-CuO towards green alga Chlamydomonas reinhardtii were explored in various exposure media and under different light illuminations. Dynamics of Cd induced effects on photosynthetic activity, sensitisation and recovery of cells of C. reinhardtii was also studied.
Topics: Biosensing Techniques; Chlamydomonas reinhardtii; Copper; Equipment Design; Hydrogen Peroxide; Lab-On-A-Chip Devices; Nanoparticles; Oxidants; Oxidative Stress; Titanium; Water Pollutants, Chemical
PubMed: 28270155
DOI: 10.1186/s12951-017-0253-x -
Free Radical Biology & Medicine 1997Redox (oxidation-reduction) reactions regulate signal transduction. Oxidants such as superoxide, hydrogen peroxide, hydroxyl radicals, and lipid hydroperoxides (i.e.,... (Review)
Review
Redox (oxidation-reduction) reactions regulate signal transduction. Oxidants such as superoxide, hydrogen peroxide, hydroxyl radicals, and lipid hydroperoxides (i.e., reactive oxygen species) are now realized as signaling molecules under subtoxic conditions. Nitric oxide is also an example of a redox mediator. Reactive oxygen species induce various biological processes such as gene expression by stimulating signal transduction components such as Ca(2+)-signaling and protein phosphorylation. Various oxidants increase cytosolic Ca2+; however, the exact origin of Ca2+ is controversial. Ca2+ may be released from the endoplasmic reticulum, extracellular space, or mitochondria in response to oxidant-influence on Ca2+ pumps, channels, and transporters. Alternatively, oxidants may release Ca2+ from Ca2+ binding proteins. Various oxidants stimulate tyrosine as well as serine/threonine phosphorylation, and direct stimulation of protein kinases and inhibition of protein phosphatases by oxidants have been proposed as mechanisms. The oxidant-stimulation of the effector molecules such as phospholipase A2 as well as the activation of oxidative stress-responsive transcription factors may also depend on the oxidant-mediated activation of Ca(2+)-signaling and/or protein phosphorylation. In addition to the stimulation of signal transduction by oxidants, the observations that ligand-receptor interactions produce reactive oxygen species and that antioxidants block receptor-mediated signal transduction led to a proposal that reactive oxygen species may be second messengers for transcription factor activation, apoptosis, bone resorption, cell growth, and chemotaxis. Physiological significance of the role of biological oxidants in the regulation of signal transduction as well as the mechanisms of the oxidant-stimulation of signal transduction are discussed.
Topics: Animals; Calcium; Humans; Oxidants; Phosphorylation; Reactive Oxygen Species; Receptors, Cell Surface; Second Messenger Systems; Signal Transduction; Stimulation, Chemical
PubMed: 8958153
DOI: 10.1016/s0891-5849(96)00275-4 -
Biomolecules Jun 2023Numerous chemical probes have been used to measure or image oxidative, nitrosative and related stress induced by free radicals in biology and biochemistry. In many... (Review)
Review
Numerous chemical probes have been used to measure or image oxidative, nitrosative and related stress induced by free radicals in biology and biochemistry. In many instances, the chemical pathways involved are reasonably well understood. However, the rate constants for key reactions involved are often not yet characterized, and thus it is difficult to ensure the measurements reflect the flux of oxidant/radical species and are not influenced by competing factors. Key questions frequently unanswered are whether the reagents are used under 'saturating' conditions, how specific probes are for particular radicals or oxidants and the extent of the involvement of competing reactions (e.g., with thiols, ascorbate and other antioxidants). The commonest-used probe for 'reactive oxygen species' in biology actually generates superoxide radicals in producing the measured product in aerobic systems. This review emphasizes the need to understand reaction pathways and in particular to quantify the kinetic parameters of key reactions, as well as measure the intracellular levels and localization of probes, if such reagents are to be used with confidence.
Topics: Reactive Oxygen Species; Oxidation-Reduction; Free Radicals; Superoxides; Oxidants; Antioxidants; Coloring Agents; Oxidative Stress
PubMed: 37509077
DOI: 10.3390/biom13071041 -
IUBMB Life 2007The decomposition of lipid hydroperoxides (LOOH) into peroxyl radicals is a potential source of singlet molecular oxygen ((1)O(2)) in biological systems. Recently, we... (Review)
Review
The decomposition of lipid hydroperoxides (LOOH) into peroxyl radicals is a potential source of singlet molecular oxygen ((1)O(2)) in biological systems. Recently, we have clearly demonstrated the generation of (1)O(2) in the reaction of lipid hydroperoxides with biologically important oxidants such as metal ions, peroxynitrite and hypochlorous acid. The approach used to unequivocally demonstrate the generation of (1)O(2) in these reactions was the use of an isotopic labeled hydroperoxide, the (18)O-labeled linoleic acid hydroperoxide, the detection of labeled compounds by HPLC coupled to tandem mass spectrometry (HPLC-MS/MS) and the direct spectroscopic detection and characterization of (1)O(2) light emission. Using this approach we have observed the formation of (18)O-labeled (1)O(2) by chemical trapping of (1)O(2) with anthracene derivatives and detection of the corresponding labeled endoperoxide by HPLC-MS/MS. The generation of (1)O(2) was also demonstrated by direct spectral characterization of (1)O(2) monomol light emission in the near-infrared region (lambda = 1270 nm). In summary, our studies demonstrated that LOOH can originate (1)O(2). The experimental evidences indicate that (1)O(2) is generated at a yield close to 10% by the Russell mechanism, where a linear tetraoxide intermediate is formed in the combination of two peroxyl radicals. In addition to LOOH, other biological hydroperoxides, including hydroperoxides formed in proteins and nucleic acids, may also participate in reactions leading to the generation (1)O(2). This hypothesis is currently being investigated in our laboratory.
Topics: Cell Membrane; DNA; Hydrogen Peroxide; Lipid Peroxides; Molecular Structure; Oxidants; Proteins; Singlet Oxygen
PubMed: 17505972
DOI: 10.1080/15216540701242508