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Articoli di riviste sul tema "Free radical"

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Autore: Grafiati

Pubblicato: 4 giugno 2021

Ultima modifica: 6 settembre 2023

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1

Yañez Jaramillo, Lina M., Joy H. Tannous e Arno de Klerk. "Persistent Free Radicals in Petroleum". Processes 11, n. 7 (11 luglio 2023): 2067. http://dx.doi.org/10.3390/pr11072067.

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The persistent free radical content in petroleum is of the order 1018 spins/g (1 μmol/g), with higher and lower values found depending on origin and in different distillation fractions. The field of persistent free radicals in petroleum was reviewed with the aim of addressing and explaining apparent inconsistencies between free radical persistence and reactivity. The macroscopic average free radical concentration in petroleum is persistent over geological time, but individual free radical species in petroleum are short-lived and reactive. The persistent free radical concentration in petroleum can be explained in terms of a dynamic reaction equilibrium of free radical dissociation and association that causes a finite number of species at any given time to be present as free radicals. Evidence to support this description are observed changes in free radical concentration related to change in Gibbs free energy when the bulk liquid properties are changed and responsiveness of free radical concentration to dynamic changes in temperature. Cage effects, solvent effects, steric protection, and radical stabilization affect free radical reaction rate but do not explain the persistent free radical concentration in petroleum. The difference between persistent free radicals in straight-run petroleum and converted petroleum is that straight-run petroleum is an equilibrated mixture, but converted petroleum is not at equilibrium and the free radical concentration can change over time. Based on the limited data available, free radicals in straight-run petroleum appear to be part of the compositional continuum proposed by Altgelt and Boduszynski. Persistent free radical species are partitioned during solvent classification of whole oil, with the asphaltenes (n-alkane insoluble) fraction having a higher concentration of persistent free radicals than maltenes (n-alkane soluble) fraction. Attempts to relate persistent free radical concentration to petroleum composition were inconclusive.

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2

Silaev, Michael M. "Free-Radical Nonbranched-Chain Oxidation of Hydrogen". International Journal of Innovative Research in Computer Science & Technology 6, n. 5 (settembre 2018): 91–98. http://dx.doi.org/10.21276/ijircst.2018.6.5.1.

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3

Stevanovic, Jelka, Suncica Borozan, Slavoljub Jovic e Igor Ignjatovic. "Physiology of free radicals". Veterinarski glasnik 65, n. 1-2 (2011): 95–107. http://dx.doi.org/10.2298/vetgl1102095s.

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Free radicals imply that every atom, molecule, ion, group of atoms, or molecules with one or several non-paired electrons in outer orbital. Among these are: nitrogenoxide (NO?), superoxide-anion-radical (O2?-), hydroxyl radical (OH?), peroxyl radical (ROO?), alcoxyl radical (RO?) and hydroperoxyl radical (HO2?). However, reactive oxygen species also include components without non-paired electrons in outer orbital (so-called reactive non-radical agents), such as: singlet oxygen (1O2), peroxynitrite (ONOO-), hydrogen-peroxide (H2O2), hypochloric acid (eg. HOCl) and ozone (O3). High concentrations of free radicals lead to the development of oxidative stress which is a precondition for numerous pathological effects. However, low and moderate concentrations of these matter, which occur quite normally during cell metabolic activity, play multiple significant roles in many reactions. Some of these are: regulation of signal pathways within the cell and between cells, the role of chemoattractors and leukocyte activators, the role in phagocytosis, participation in maintaining, changes in the position and shape of the cell, assisting the cell during adaption and recovery from damage (e.g.caused by physical effort), the role in normal cell growth, programmed cell death (apoptosis) and cell ageing, in the synthesis of essential biological compounds and energy production, as well as the contribution to the regulation of the vascular tone, actually, tissue vascularization.

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4

Kim, Eun-Kyung, e Mi Ryeong Song. "Factors Influencing the Level of Oxygen Free Radicals in Female Nursing Students". Global Journal of Health Science 11, n. 7 (15 maggio 2019): 1. http://dx.doi.org/10.5539/gjhs.v11n7p1.

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This study was conducted to investigate the levels of oxygen free radicals and related health factors in 201 female nursing students. The questionnaire was completed by the participants and their oxygen free radical levels were measured by urine test. In this study, an oxygen free radical analyzer was used to measure oxygen free radical levels. The oxygen free radical analyzer analyzes the amount of oxygen free radicals in the body by measuring urinary malondialdehyde (MDA). To determine factors associated with oxygen free radical levels, multiple regression tests were conducted. Of the participants, 89.6% exhibited normal levels of oxygen free radicals and 10.4% had elevated levels. In this study, the factors that affected oxygen free radical levels were eating habit (β = .20, p =. 003), fatigue (β = .20, p = .004), and detox necessity (β = .18, p = .006). In order to lower oxygen free radical levels of female nursing students, the areas of eating habit, fatigue, and detox must receive increased focus.

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5

Horgan, John. "Free Radical". Scientific American 262, n. 5 (maggio 1990): 40–44. http://dx.doi.org/10.1038/scientificamerican0590-40.

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6

Silaev, Michael M. "KINETIC EQUATIONS FOR RADICAL-CHAIN OXIDATION INVOLVING PROCESS-INHIBITING ALKYL (OR HYDRO)TETRAOXYL FREE RADICAL". American Journal of Applied Sciences 05, n. 06 (30 giugno 2023): 29–48. http://dx.doi.org/10.37547/tajas/volume05issue06-07.

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The derivation of kinetic equations for the oxidation processes by the free-radical nonbranched-chain mechanism is shown. This derivation is based on the proposed reaction scheme for the initiated addition of free radicals to the multiple bond of the molecular oxygen includes the addition reaction of the peroxyl free radical to the oxygen molecule to form the tetraoxyl free radical. This reaction competes with chain propagation reactions through a reactive free radical. The chain evolution stage in this scheme involves a few of free radicals, one of which – alkyl(or hydro)tetraoxyl – is relatively low-reactive and inhibits the chain process by shortening of the kinetic chain length. The rate equations (containing one to three parameters to be determined directly) are deduced using the quasi-steady-state treatment. These kinetic equations were used to describe the γ-induced nonbranched-chain processes of free-radical oxidation of liquid o-xylene at 373 K and hydrogen dissolved in water containing various amounts of oxygen at 296 K. The ratios of rate constants of competing reactions and rate constants of addition reactions to the molecular oxygen are defined. In these processes the oxygen with the increase of its concentration begins to act as an oxidation autoinhibitor (or an antioxidant), and the rate of peroxide formation as a function of the dissolved oxygen concentration has a maximum. It is shown that a maximum in these curves arises from the competition between hydrocarbon (or hydrogen) molecules and dioxygen for reacting with the emerging peroxyl 1:1 adduct radical. From the energetic standpoint possible nonchain pathways of the free-radical oxidation of hydrogen and the routes of ozone decay via the reaction with the hydroxyl free radical in the upper atmosphere (including the addition yielding the hydrotetraoxyl free radical, which can be an intermediate in the sequence of conversions of biologically hazardous UV radiation energy) were examined. The energetics of the key radical-molecule gas-phase reactions is considered.

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7

Adrian, Gerild, Edi Suryanto e Defny S. Wewengkang. "AKTIVITAS PENANGKAL RADIKAL BEBAS DARI FRAKSI KULIT KAYU SAGU BARUK (Arenga microcarpha Beccari)". PHARMACON 10, n. 1 (24 febbraio 2021): 762. http://dx.doi.org/10.35799/pha.10.2021.32777.

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ABSTRACTThis study aims to determine the antioxidant activity and free radical antidote from fraction of bark sago baruk (Arenga microcarpha Beccari). This study initiated by extracting the powder of bark sago baruk using the maceration method for 3 days with ethanol 80%. The extract then partitioned using a series of solvent such as petroleum ether, ethyl acetate, buthanol, aquadest. The results showed that the ethyl acetate fraction had the highest free radical antidote content followed by the aquadest fraction, buthanol fraction, petroleum ether fraction. The content of free radical antidote respectively was 86,25%; 66,30%; 65,32%; 43,43%. Based on this study, the ethyl acetate fraction was the best fraction can act as an antidote to free radicals better than other fractions. Keywords: Bark sago baruk, fraction, free radical antidote ABSTRAKPenelitian ini bertujuan untuk menentukan Aktivitas penangkal radikal bebas dari fraksi kulit kayu sagu baruk (Arenga microcarpha beccari). Penelitian ini dimulai dengan mengekstraksi serbuk kulit kayu sagu baruk menggunakan cara maserasi selama 3 hari dengan pelarut etanol 80%. Ekstrak kemudian dipartisi menggunakan pelarut petroleum eter, etil asetat, butanol, dan aquades. kemudian ditentukan aktivitas antioksidan dan penangkal radikal bebas. Hasilnya menunujukan bahwa fraksi etil asetat memiliki kandungan penangkal radikal bebas tertinggi diikuti fraksi aquades, fraksi butanol, dan fraksi petroleum eter. Kandungan penangkal radikal bebas berturut-turut adalah 86,25%; 66,30%; 65,32%; 43,43%. Berdasarkan penelitian ini, dapat disimpulkan bahwa fraksi etil asetat dapat berperan sebagai penangkal radikal bebas lebih baik dibandingkan dengan fraksi lainnya. Kata Kunci: Kulit Kayu Sagu Baruk, Fraksi, Penangkal Radikal Bebas

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8

Mikayil Aliyev, Mirza, Ulduz Yunis Safarova e Shafiqa Jahangir Jafarova. "CHARACTERISTICS AND THERAPEUTIC EFFECTS OF THE NOVEL FREE RADICAL SCAVENGER – EDARAVONE". NATURE AND SCIENCE 04, n. 05 (28 dicembre 2020): 17–20. http://dx.doi.org/10.36719/2707-1146/05/17-20.

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Edaravone is the first free radical scavenger which approved clinically and has an ability to decrease the level of free radicals in cells. Edaravone is a strong antioxidant, which can protect different cells (e.g. endothelial cells) against damage by ROS by inhibiting the lipoxygenase metabolism of arachidonic acid, by trapping hydroxyl radicals, by increasing prostacyclin production, by inhibiting alloxan-induced lipid peroxidation, etc. Because of that, Edaravone is used in treatment of diseases which are associated with oxidative stress. Key words: edaravone, free radical, antioxidant, neuroprotective agent, oxidative stress

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9

Jonsson, M., J. Lind, T. Reitberger, T. E. Eriksen e G. Merenyi. "Free radical combination reactions involving phenoxyl radicals". Journal of Physical Chemistry 97, n. 31 (agosto 1993): 8229–33. http://dx.doi.org/10.1021/j100133a018.

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10

Reimer, Keith A., Masaru Tanaka, Charles E. Murry, Vincent J. Richard e Robert B. Jennings. "Evaluation of Free Radical Injury in Myocardium". Toxicologic Pathology 18, n. 4a (gennaio 1990): 470–80. http://dx.doi.org/10.1177/0192623390004part_105.

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Abundant evidence now is available that free radicals are produced in excess when myocardium is reperfused following an episode of ischemia and that free radicals can injure myocytes and endothelial cells. Free radicals may contribute to either reversible or irreversible manifestations of cell injury from ischemia and reperfusion. Several investigators have observed that postischemic contractile dysfunction (myocardial stunning) can be attenuated by a variety of anti-free radical therapies, and there seems to be general agreement that free radical injury contributes to stunning. Whether free radicals are an important cause of lethal myocyte injury (“lethal reperfusion injury”) remains controversial. Using similar interventions and animal models, both positive and negative results have been reported from a growing number of studies done to test the effect of anti-free radical therapies on infarct size. Proposed explanations include differences in: 1) dose of drug and onset or duration of treatment, 2) duration of occlusion or reperfusion, 3) methods of measuring infarct size or area at risk, and 4) failure of some studies to control for baseline variation in the major determinants of infarct size, e.g., collateral blood flow. At present, none of these explanations seems sufficient to resolve the question.

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11

Davydov, Evgeniy, Georgiy Pariiskii, Iryna Gaponova, Tatyana Pokholok e Gennady Zaikov. "Polymers in polluted atmosphere. Free radical and ion-radical conversions initiated by nitrogen oxides". Chemistry & Chemical Technology 2, n. 1 (15 marzo 2008): 33–45. http://dx.doi.org/10.23939/chcht02.01.033.

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Nitric oxide, nitrogen dioxide, nitrogen trioxide as well as dimers of nitrogen dioxide are reactive initiators of radical transformations of macromolecules and modifying reactants for polymers. Features of the initiation mechanism determining the composition of molecular and radical products in polymers under the action of nitrogen oxides are discussed.

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12

Zhao, Zizhen, Chen Fu, Yuping Zhang e Ailing Fu. "Dimeric Histidine as a Novel Free Radical Scavenger Alleviates Non-Alcoholic Liver Injury". Antioxidants 10, n. 10 (27 settembre 2021): 1529. http://dx.doi.org/10.3390/antiox10101529.

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Non-alcoholic liver injury (NLI) is a common disease worldwide. Since free radical damage in the liver is a crucial initiator leading to diseases, scavenging excess free radicals has become an essential therapeutic strategy. To enhance the antioxidant capacity of histidine, we synthesized a protonated dimeric histidine, H-bihistidine, and investigated its anti-free radical potential in several free-radical-induced NLI. Results showed that H-bihistidine could strongly scavenge free radicals caused by H2O2, fatty acid, and CCl4, respectively, and recover cell viability in cultured hepatocytes. In the animal model of nonalcoholic fatty liver injury caused by high-fat diet, H-bihistidine reduced the contents of transaminases and lipids in serum, eliminated the liver’s fat accumulation, and decreased the oxidative damage. Moreover, H-bihistidine could rescue CCl4-induced liver injury and recover energy supply through scavenging free radicals. Moreover, liver fibrosis prepared by high-fat diet and CCl4 administration was significantly alleviated after H-bihistidine treatment. This study suggests a novel nonenzymatic free radical scavenger against NLI and, potentially, other free-radical-induced diseases.

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13

Davies, M. J., S. Fu e R. T. Dean. "Protein hydroperoxides can give rise to reactive free radicals". Biochemical Journal 305, n. 2 (15 gennaio 1995): 643–49. http://dx.doi.org/10.1042/bj3050643.

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Proteins damaged by free-radical-generating systems in the presence of oxygen yield relatively long-lived protein hydroperoxides. These hydroperoxides have been shown by e.p.r. spectroscopy to be readily degraded to reactive free radicals on reaction with iron(II) complexes. Comparison of the observed spectra with those obtained with free amino acid hydroperoxides had allowed identification of some of the protein-derived radical species (including a number of carbon-centred radicals, alkoxyl radicals and a species believed to be the CO2 radical anion) and the elucidation of novel fragmentation and rearrangement processes involving amino acid side chains. In particular, degradation of hydroperoxide functions on the side chain of glutamic acid is shown to result in decarboxylation at the side-chain carboxy group via the formation of the CO2 radical anion; the generation of an identical radical from hydroperoxide groups on proteins suggests that a similar process occurs with these molecules. In a number of cases these fragmentation and rearrangement reactions give rise to further reactive free radicals (R., O2-./HO2., CO2-.) which may act as chain-carrying species in protein oxidations. These studies suggest that protein hydroperoxides are capable of initiating further radical chain reactions both intra- and inter-molecularly, and provide information on some of the fundamental mechanisms of protein alteration and side-chain fragmentation.

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14

Zhong, Sabilla, Andreas Hafner, Christoph Hussal, Martin Nieger e Stefan Bräse. "Metal-free radical perfluoroalkylation of (hetero)arenes". RSC Advances 5, n. 9 (2015): 6255–58. http://dx.doi.org/10.1039/c4ra13430c.

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15

OTSUKA, TOMONORI. "RADICAL FREE MERGER". ENGLISH LINGUISTICS 34, n. 1 (2017): 34–68. http://dx.doi.org/10.9793/elsj.34.1_34.

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16

Jenkins, Robert R. "Free Radical Chemistry". Sports Medicine 5, n. 3 (marzo 1988): 156–70. http://dx.doi.org/10.2165/00007256-198805030-00003.

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17

Wilcox, Kate. "Free Radical Shift". Scientific American 300, n. 5 (maggio 2009): 20–22. http://dx.doi.org/10.1038/scientificamerican0509-20.

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18

Chambers, Richard D., Anwar H. S. Gilani, Alan F. Gilbert, John Hutchinson e Richard L. Powell. "Free-radical chemistry". Journal of Fluorine Chemistry 106, n. 1 (ottobre 2000): 53–67. http://dx.doi.org/10.1016/s0022-1139(00)00288-8.

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19

Porter, Ned A., David R. Magnin e Bruce T. Wright. "Free radical macrocyclization". Journal of the American Chemical Society 108, n. 10 (maggio 1986): 2787–88. http://dx.doi.org/10.1021/ja00270a066.

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20

Liochev, Stefan I. "Free radical paradoxes". Free Radical Biology and Medicine 65 (dicembre 2013): 232–33. http://dx.doi.org/10.1016/j.freeradbiomed.2013.06.027.

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21

Carrington, Alan. "A FREE RADICAL". Annual Review of Physical Chemistry 52, n. 1 (ottobre 2001): 1–13. http://dx.doi.org/10.1146/annurev.physchem.52.1.1.

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22

Lurie, D. J. "Free radical imaging". British Journal of Radiology 74, n. 885 (settembre 2001): 782–84. http://dx.doi.org/10.1259/bjr.74.885.740782.

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23

Nagendrappa, G. "An appreciation of free radical chemistry 6. Experiments involving free radicals". Resonance 10, n. 9 (settembre 2005): 79–84. http://dx.doi.org/10.1007/bf02896323.

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24

Salvemini, Daniela, e Regina Botting. "Modulation of platelet function by free radicals and free-radical scavengers". Trends in Pharmacological Sciences 14, n. 2 (febbraio 1993): 36–42. http://dx.doi.org/10.1016/0165-6147(93)90028-i.

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Karl, Oettl, Joachim Greilberger e Gilbert Reibnegger. "Modulation of Free Radical Formation by Pterin Derivatives". Pteridines 15, n. 3 (agosto 2004): 97–101. http://dx.doi.org/10.1515/pteridines.2004.15.3.97.

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Abstract All classes of pterins, fully reduced tetrahydropterins, aromatic pterins and dihydropterins have been investigated upon their effects on radical mediated reactions. Meanwhile all these classes were shown to act as both, proand antioxidants by a number of different methods including chemical, biochemical and biological systems. From reduced pterins radicals including oxygen-, nitrogen- and pterin-radicals arc formed enzymatically and non-enzymatically, reduced pterins react with free radicals and serve as reductive agents. All classes of pterins may interfere with enzymes involved in radical formation. Upon the diversity of possibilities the net effect of a particular compound is a question of the experimental settings and the physiological relevant role often remains obscure.

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26

Wu, Yuh-Wern, Hsu-Ting Huang, Yi-Jing Chen e Jyh-Ferng Yang. "Free radical SH2′ reaction mechanism study by comparing free radical SH2′ reaction with free radical addition reaction". Tetrahedron 62, n. 25 (giugno 2006): 6061–64. http://dx.doi.org/10.1016/j.tet.2006.03.106.

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Matsugo, Seiichi, Masashi Mizuno e Tetsuya Konishi. "Free Radical Generating and Scavenging Compounds as a New Type of Drug". Current Medicinal Chemistry 2, n. 4 (dicembre 1995): 763–90. http://dx.doi.org/10.2174/092986730204220224092844.

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Abstract: Recently, the free radical investigations cover a broad field of research related to chemistry, biology, medicine and biochemistry. One of the reasons for this is that the free radicals play crutial roles in many pathogenic disorders, typically carcinogenesis. So, in this sense it is very important to elucidate the precise mechanism of action of free radicals in vivo from the aspect of tumor necrosis. Indeed, many drugs have been extensively studied in relation to free radicals in recent years. These studies can be divided into two categories one of which emphasizes the advantageous side of free radicals, while the other emphasizes the toxic aspects of free radicals. In tis review article, we will discuss four major studies related free radical studies based on the chemical standpoint of view. Frist we will introduce the recent advances of radical generating drugs such as bleomycin and some ene-diyne natural products in the medicinal field. Second, we will introduce the possible use of free radical generating compounds as a condidate of the new-type of drug. Third, we will show the protective effects and importance of some recent advances in antioxidants research, which show the potentiality of natural antioxidants as the protective or therapeutic medicine for free radical deseases. Finally, we will introduce some recent progress in the gene-regulation studies by the antioxidants and show our ideas for the future application for this concept in the medicinal fields.

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Murphy, John A. "Free radicals in synthesis. Clean reagents affording oxidative or reductive termination". Pure and Applied Chemistry 72, n. 7 (1 gennaio 2000): 1327–34. http://dx.doi.org/10.1351/pac200072071327.

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Neurotoxic organotin reagents currently play a key role in radical chemistry. As a result, this is an important area for development of new clean replacement reactions. The pharmaceutical industry in particular has had to avoid use of radical methodology for the formation of carbon_carbon bonds for this reason. With the current dawn in green chemistry, a host of new clean radical methods is beginning to flourish. Our aim has been to develop new nontoxic methodology for carbon_carbon bond formation by radical chemistry, which would provide either reductive termination (giving a hydrogen atom to the ultimate radical, as happens with tributyltin hydride), or oxidative functionalization, installing a useful polar group at the site of the ultimate radical. Two methods for effecting radical reactions in an environmentally friendly way are presented: (i) The tetrathiafulvalene (TTF)-mediated radical-polar crossover reaction converts arenediazonium salts to aryl radicals, which have sufficient lifetime to cyclize onto alkenes—the resulting alkyl radicals couple with TTF+• to afford sulfonium salts which, in turn, undergo solvolysis to alcohols, ethers or amides. The method provides the key step in a synthesis of (±)-aspidospermidine. (ii) Hypophosphite salts and hypophosphorous acid, on the other hand, form C_C bonds with reductive termination. These economical reagents afford radicals efficiently, starting from aryl iodides, alkyl bromides, and alkyl iodides, and give very easy separation of products from by-products.

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De Schutter, Coralie, Emmanuel Pfund e Thierry Lequeux. "Radical conjugate addition of ambiphilic fluorinated free radicals". Tetrahedron 69, n. 29 (luglio 2013): 5920–26. http://dx.doi.org/10.1016/j.tet.2013.05.006.

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Yuan, Ningning, Wenqing Wang, Ziye Wu, Sheng Chen, Gengwen Tan, Yunxia Sui, Xinping Wang, Jun Jiang e Philip P. Power. "A boron-centered radical: a potassium-crown ether stabilized boryl radical anion". Chemical Communications 52, n. 86 (2016): 12714–16. http://dx.doi.org/10.1039/c6cc06918e.

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Li, Guoxiang, Zhongyang Luo, Wenbo Wang e Jianmeng Cen. "A Study of the Mechanisms of Guaiacol Pyrolysis Based on Free Radicals Detection Technology". Catalysts 10, n. 3 (5 marzo 2020): 295. http://dx.doi.org/10.3390/catal10030295.

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In order to understand the reaction mechanism of lignin pyrolysis, the pyrolysis process of guaiacol (o-methoxyphenol) as a lignin model compound was studied by free radical detection technology (electron paramagnetic resonance, EPR) in this paper. It was proven that the pyrolysis reaction of guaiacol is a free radical reaction, and the free radicals which can be detected mainly by EPR are methyl radicals. This paper proposes a process in which four free radicals (radicals 1- C6H4(OH)O*, radicals 5- C6H4(OCH3)O*, methyl radicals, and hydrogen radicals) are continuously rearranged during the pyrolysis of guaiacol.

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West, Robert, Kerim Samedov, Amitabha Mitra, Paul W. Percival, Jean-Claude Brodovitch, Graeme Langille, Brett M. McCollum et al. "Germanium-centered free radicals studied by muon spin spectroscopy". Canadian Journal of Chemistry 92, n. 6 (giugno 2014): 508–13. http://dx.doi.org/10.1139/cjc-2013-0427.

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Transverse-field muon spin rotation (TF-μSR) spectra have been recorded for free radicals formed by positive muon irradiation of nine different divalent germanium compounds. Muon-electron hyperfine coupling constants (Aμ) were determined from the spectra and compared with values predicted from density functional theory molecular orbital (DFT-MO) calculations on the muoniated radicals formed by muonium addition to the germanium atom. The muon hyperfine constants for germylenes containing N–Ge bonds are generally quite large, from 593 to 942 MHz, indicating strong interaction between the muon and the unpaired electron in these radicals. The radical derived from one of the germylenes exhibited a significantly lower muon hyperfine constant, suggesting that in this case the muoniated germyl radical undergoes a coupling reaction to form a digermanyl radical, which is what is detected by μSR.

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Jarco, Sylwia, Barbara Pilawa e Paweł Ramos. "Free Radical Scavenging Activity of Infusions of Different Medicinal Plants for Use in Obstetrics". Plants 10, n. 10 (26 settembre 2021): 2016. http://dx.doi.org/10.3390/plants10102016.

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An X-band (9.3 GHz) electron paramagnetic resonance (EPR) spectroscopy was used to examine the free radical scavenging activity of the following infusions, which were nonirradiated and exposed to UVA: root of Asparagus racemosus and herbs of Mitchella repens, Cnicus benedictus L., Galega officinalis L., and Eupatorium cannabinum L. The plant materials for obstetrics applications were chosen for analysis. The aims of these studies were to compare the free radical scavenging ability of the tested infusions and to determine the influence of UVA irradiation of the plant materials on interactions of these infusions with free radicals. Both the magnitude and kinetics of the interactions of the infusions with the model DPPH free radicals were examined. The ability to quench the free radicals for the examined plant infusions increases in the following order: Asparagus racemosus (root) < Mitchella repens (herb) < Cnicus benedictus L. (herb) < Galega officinalis L. (herb) < Eupatorium cannabinum L. (herb). The analyzed infusions differ in the kinetics of the interactions with free radicals. The fastest interactions with free radicals characterize the infusions of Galega officinalis L. herb and Eupatorium cannabinum L. herb. The infusion of Mitchella repens herb interacts with free radicals in the slowest way. UVA radiation reduces the antioxidant interactions of all tested infusions, especially the infusion of Eupatorium cannabinum L. herb, which should be protected against UVA radiation during storage. The weakest decrease of free radical scavenging activity was observed for the infusion of the root of Asparagus racemosus exposed to UVA radiation. UVA radiation affected the speed of the free radical interactions of the infusions, depending on the type of plant materials. EPR spectroscopy is useful to examine the free radical scavenging activity of plant infusions, which is helpful to find effective antioxidants for applications in obstetrics and their optimal storage conditions.

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34

Kalaiyarasi, D., V. Manobharathi e S. Mirunalini. "Capsaicin in hot chili peppers as a potent free radical scavenger: An in vitro approach". Research Journal of Biotechnology 17, n. 4 (25 marzo 2022): 68–75. http://dx.doi.org/10.25303/1704rjbt6875.

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In humans, countless chronic conditions are connected with the accumulation of free radicals. Antioxidants can scavenge free radicals and reduce their effect. The hunt for natural antioxidants of plant provenance becomes an urgent primary concern. So, the present study was to investigate the antioxidant and free radical scavenging activity of Capsaicin by using various in vitro assays such as 1,1-diphenyl-2-picrylhydrazyl free radical (DPPH), 2,2′-azino-bis(3- ethylbenzthiazoline-6-sulfonic acid) (ABTS●+), hydroxyl radical, superoxide anion, hydrogen peroxide, nitric oxide and reducing power. The findings from this study indicated that Capsaicin exhibited significant inhibition of free radical which was calculated as IC50 value compared with standard ascorbic acid. IC50 values of capsaicin and ascorbic acid were found to be 44.12μg/mL and 42.52μg/mL in DPPH radical assay, 39.89μg/mL and 37.75μg/mL in ABTS●+ radical assay, 43.65μg/mL and 48.33μg/mL in hydroxyl radical assay, 39.79μg/mL and 42.16μg/mL in superoxide anion radical assay, 31.37μg/mL and 30.90μg/mL in hydrogen peroxide radical assay, 43.30μg/mL and 42.45μg/mL in nitric oxide radical assay and 39.33μg/mL and 38.79 μg/mL in reducing power assay respectively. Therefore, capsaicin might be a good plant-based pharmaceutical product recommended as a potential antioxidant for various oxidative degenerative diseases and often serve as an effective radical scavenger or blocker.

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Nugraheni, Tiyas Putri, Vivin Rosvita e Husnun Khairunnisa Pratiwi. "UJI AKTIVITAS PENANGKAPAN RADIKAL BEBAS DPPH OLEH EKSTRAK ETANOL DAUN PISANG TANDUK (MUSA PARADISIACA VAR. FORMATYPICA) DAN DAUN PISANG CAVENDISH (MUSA PARADISIACA VAR. SAPIENTUM)". Indonesia Jurnal Farmasi 2, n. 1 (6 aprile 2023): 69. http://dx.doi.org/10.26751/ijf.v2i1.415.

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AbstractHas done research about free radical scavenging activity of ethanolic extract Musa paradisiaca var formatypica and Musa paradisiaca var sapientum leaf. Banana leaf contain phenolic compunds, flavonoids, alkaloids, tannin, and saponin as a free radical scavenging.Extracts were prepared by maceration method using ethanol 70% as solvent. DPPH free radical scavenging activity was performed by spectrophotometry visible to extracts with quercetin as the comparison. The free radical scavenging activity was expressed by percent reduction and ES50.Study result showed that ethanol extract of banana leaf and Cavendish leaf containing flavonoids, polyphenols, tannins, saponins, terpenoids and had antioxidant activity also DPPH free radical scavenging activity. The ES50 value ethanol extract of banana leaf is 104.36 (µg / ml), ethanol extract of Cavendish leaf is 157.36 (µg / ml), whereas quercetin is 2.86 (µg / ml).Statistical analysis result showed a significant difference between percent of free radical scavenging activity of quercetin, banana leaf extract and Cavendish leaf extract.Keywords: Free radical, antioxidant, extract banana leaf, extract cavendish leaf AbstrakTelah dilakukan penelitian tentang aktivitas penangkapan radikal bebas oleh ekstrak etanol daun pisang Tanduk dan daun pisang Cavendish. Daun pisang mengandung golongan senyawa fenolik, flavonoid, alkaloid, tannin, dan saponin yang berpotensi sebagai penangkal radikal bebas.Ekstrak dibuat dengan metode maserasi menggunakan pelarut 70%. Uji penangkapan radikal bebas DPPH dilakukan secara spektrofotometri visibel terhadap ekstrak dengan pembanding kuersetin. Aktivitas penangkapan radikal bebas dinyatakan sebagai persen peredaman dan ES50.Hasil penelitian menunjukkan bahwa ekstrak etanol daun pisang Tanduk dan ekstrak etanol daun pisang Cavendish mengandung senyawa flavonoid, polifenol, tanin, saponin, terpenoid, serta mempunyai aktivitas sebagai antioksidan dan penangkap radikal bebas DPPH. Ekstrak etanol daun pisang Tanduk mempunyai nilai ES50 sebesar 104,36 (µg/ml), ekstrak etanol daun pisang Cavendish memiliki nilai ES50 sebesar 157,36 (µg/ml), sedangkan standar kuersetin mempunyai nilai ES50 sebesar 2,86 (µg/ml).Hasil analisis statistik menunjukkan adanya perbedaan yang bermakna antara persen penangkapan radikal bebas kuersetin, ekstrak daun pisang Tanduk, dan ekstrak daun pisang Cavendish.Kata Kunci: Radikal bebas, antioksidan, ekstrak daun pisang tanduk, ekstrak daun pisang cavendish

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36

Ionita, Petre. "The Chemistry of DPPH· Free Radical and Congeners". International Journal of Molecular Sciences 22, n. 4 (3 febbraio 2021): 1545. http://dx.doi.org/10.3390/ijms22041545.

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Abstract (sommario):

Since the discovery in 1922 of 2,2-diphenyl-1-(2,4,6-trinitrophenyl) hydrazyl stable free radical (DPPH·), the chemistry of such open-shell compounds has developed continuously, allowing for both theoretical and practical advances in the free radical chemistry area. This review presents the important, general and modern aspects of the chemistry of hydrazyl free radicals and the science behind it.

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37

ROTA, Cristina, P. David BARR, V. Martha MARTIN, F. Peter GUENGERICH, Aldo TOMASI e P. Ronald MASON. "Detection of free radicals produced from the reaction of cytochrome P-450 with linoleic acid hydroperoxide". Biochemical Journal 328, n. 2 (1 dicembre 1997): 565–71. http://dx.doi.org/10.1042/bj3280565.

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The ESR spin-trapping technique was employed to investigate the reaction of rabbit cytochrome P-450 1A2 (P450) with linoleic acid hydroperoxide. This system was compared with chemical systems where FeSO4 or FeCl3 was used in place of P450. The spin trap 5,5ʹ-dimethyl-1-pyrroline N-oxide (DMPO) was employed to detect and identify radical species. The DMPO adducts of hydroxyl, O2-•, peroxyl, methyl and acyl radicals were detected in the P450 system. The reaction did not require NADPH-cytochrome P-450 reductase or NADPH. The same DMPO-radical adducts were detected in the FeSO4 system. Only DMPO-•OH radical adduct and carbon-centred radical adducts were detected in the FeCl3 system. Peroxyl radical production was completely O2-dependent. We propose that polyunsaturated fatty acids are initially reduced to form alkoxyl radicals, which then undergo intramolecular rearrangement to form epoxyalkyl radicals. Each epoxyalkyl radical reacts with O2, forming a peroxyl radical. Subsequent unimolecular decomposition of this peroxyl radical eliminates O2-• radical.

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38

Murrell, G. A. C., M. J. O. Francis e L. Bromley. "Modulation of fibroblast proliferation by oxygen free radicals". Biochemical Journal 265, n. 3 (1 febbraio 1990): 659–65. http://dx.doi.org/10.1042/bj2650659.

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The major unexplained phenomenon in fibrotic conditions is an increase in replicating fibroblasts. In this report we present evidence that oxygen free radicals can both stimulate and inhibit proliferation of cultured human fibroblasts, and that fibroblasts themselves release superoxide (O2.-) free radicals. Fibroblasts released O2.- in concentrations which stimulated proliferation, a finding confirmed by a dose-dependent inhibition of proliferation by free radical scavengers. Oxygen free radicals released by a host of agents may thus provide a very fast, specific and sensitive trigger for fibroblast proliferation. Prolonged stimulation may result in fibrosis, and agents which inhibit free radical release may have a role in the prevention of fibrosis.

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39

Merkley, Nadine, Paul C. Venneri e John Warkentin. "Cyclopropanation of benzylidenemalononitrile with dialkoxycarbenes and free radical rearrangement of the cyclopropanes". Canadian Journal of Chemistry 79, n. 3 (1 marzo 2001): 312–18. http://dx.doi.org/10.1139/v01-017.

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Thermolysis of 2-cinnamyloxy-2-methoxy-5,5-dimethyl-Δ3-1,3,4-oxadiazoline (1a) and the analogous 2-benzyloxy-2-methoxy compound (1b) at 110°C, in benzene containing benzylidenemalononitrile, afforded products of apparent regiospecific addition of methoxycarbonyl and cinnamyl (or benzyl) radicals to the double bond. When the thermolysis of 1a was run with added TEMPO, methoxycarbonyl and cinnamyl radicals were captured. Thermolysis of the 2,2-dibenzyloxy analogue (1c) in the presence of benzylidenemalononitrile gave an adduct that is formally the product of addition of benzyloxycarbonyl and benzyl radicals to the double bond. In this case, a radical addition mechanism could be ruled out, because the rate constant for decarboxylation of benzyloxycarbonyl radicals is very large. A mechanism that fits all of the results is predominant cyclopropanation of benzylidenemalononitrile by the dialkoxycarbenes derived from the oxadiazolines, in competition with fragmentation of the carbenes to radical pairs. The cyclopropanes so formed then undergo homolytic ring-opening to the appropriate diradicals. Subsequent β-scission of the diradicals to afford radical pairs, and coupling of those pairs, gives the final products. Thus, both carbene and radical chemistry are involved in the overall processes.Key words: cyclopropane, dialkoxycarbene, β-scission, oxadiazoline, radical.

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40

North, J. A., A. A. Spector e G. R. Buettner. "Cell fatty acid composition affects free radical formation during lipid peroxidation". American Journal of Physiology-Cell Physiology 267, n. 1 (1 luglio 1994): C177—C188. http://dx.doi.org/10.1152/ajpcell.1994.267.1.c177.

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Lipid-derived free radicals generated from intact human U937 monocytes exposed to iron-induced oxidative stress were detected by electron paramagnetic resonance (EPR) with the spin trap alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone (POBN). Lipid radical formation was enhanced when the cells were enriched with n-3 or n-6 polyunsaturated fatty acids. Computer simulation indicated that at least two POBN spin adducts were formed, having spectral characteristics consistent with carbon-centered radicals (aN = 15.9 G and aH = 2.6 G; aN = 15.1 G and aH = 2.8 G). These alkyl radicals are probably formed by beta-scission of alkoxyl radicals. POBN spin adduct formation correlated with ethane generation. Addition of ascorbate to the assay medium greatly increased the radical signal intensity. Although radical generation was cell dependent and POBN spin adducts were observed in cell homogenates, the adducts formed by the intact cells were detected only in the extracellular medium. These findings indicate that the extent of lipid radical formation in response to oxidative stress can be influenced by changes in the polyunsaturated fatty acid composition of the cell lipids and suggest the possibility that carbon-centered lipi radicals may interact with extracellular structures.

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Nikolić-Kokić, Aleksandra, Duško Blagojević e Mihajlo Spasić. "Complexity of free radical Metabolism in human Erythrocytes". Journal of Medical Biochemistry 29, n. 3 (1 luglio 2010): 189–95. http://dx.doi.org/10.2478/v10011-010-0018-7.

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Abstract (sommario):

Complexity of free radical Metabolism in human ErythrocytesThe auto-oxidation of oxyhaemoglobin to methaemoglobin generating superoxide anion radical (O2.-) represents the main source of free radicals in the erythro-cytes. Hydrogen peroxide is produced by O2.-dismutation or originates from the circulation. Human erythrocytes are also exposed to the prooxidative actions of nitric oxide (NO) from circulation. Free radicals that may induce reactions with direct dangerous consequences to erythrocytes are also preceded by the reaction of O2.-and NO producing peroxynitrite. In physiological settings, erythrocytes show a self-sustaining activity of antioxidative defence (AD) enzymes, such as: superoxide dismutase (SOD, EC 1.11.16), catalase (CAT, EC 1.11.1.6), glutathione peroxidase (GSHPx, EC 1.11.1.9) and glutathione reductase (GR, EC 1.6.4.2), as well as low molecular weight antioxidants: glutathione and vitamins E and C. Their coordinate actions protect the erythrocyte's bio-macromolecules from free radical-mediated damage. Since there is node novosynthesis of AD enzymes in mature erythrocytes, their defence capacity is limited. Free radicals influence antioxidative enzymes capacities and relative share of particular components in the whole antioxidative system. Therefore, by measuring changes in the activity of individual AD components, as well as their interrelations by statistical canonical discriminant methods, valuable data about the complexity, overall relations and coordinated actions in the AD system in erythrocytes and its relevance for systemic effects can be acquired.

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42

Brent, Jeffrey A., e Barry H. Rumack. "Role of free radicals in toxic hepatic injury I. free radical biochemistry". Journal of Toxicology: Clinical Toxicology 31, n. 1 (gennaio 1993): 139–71. http://dx.doi.org/10.3109/15563659309000383.

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43

AOYAGI, Kazumasa, e Mitsuharu NARITA. "Symposium on free radicals and diseases. Free radical toxicity in renal disease." Nihon Naika Gakkai Zasshi 79, n. 9 (1990): 1230–33. http://dx.doi.org/10.2169/naika.79.1230.

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44

Cai, Yu-Jun, Jin-Qiu Dai, Jian-Guo Fang, Lan-Ping Ma, Li-Fen Hou, Li Yang e Zhong-Li Liu. "Antioxidative and free radical scavenging effects of ecdysteroids from Serratula strangulata". Canadian Journal of Physiology and Pharmacology 80, n. 12 (1 dicembre 2002): 1187–94. http://dx.doi.org/10.1139/y02-152.

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Abstract (sommario):

The antioxidative and free radical scavenging effects of four ecdysteroids, 20-hydroxyecdysone (E1), 25-deoxy-11,20-dihydroxyecdysone (E2), 24-(2-hydroxyethyl)-20-hydroxyecdysone (E3), and 20-hydroxyecdysone-20,22-monoacetonide (E4), isolated from the Chinese herbSerratula strangulata have been investigated in vitro. These ecdysteroids could protect human erythrocytes against oxidative hemolysis induced by a water-soluble azo initiator 2,2'-azobis(2-amidinopropane hydrochloride) (AAPH). They could also inhibit the peroxidation of rat liver microsomes induced by hydroxyl radicals, as monitored by the formation of thiobarbituric acid reactive substances (TBARS), and prevent radical-induced decrease of membrane fluidity as determined by fluorescence polarization. They reacted with galvinoxyl radicals in homogeneous solution, and the pseudo-first-order rate constants were determined spectrophotometrically by following the disappearance of galvinoxyl radicals. Compounds E1 and (or) E3 were the most active in both antioxidative and radical-scavenging reactions.Key words: ecdysteroid, Serratula strangulata, free radical, erythrocyte, lipid peroxidation, antioxidant.

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45

Rahman, Arif, Abd Malik e Aktsar Roskiana Ahmad. "SKRINING FITOKIMIA DAN UJI AKTIVITAS ANTIOKSIDAN EKSTRAK ETANOLIK BUAH BUNI (Antidesma bunius (L.) SPRENG)". Jurnal Fitofarmaka Indonesia 3, n. 2 (5 luglio 2016): 159–63. http://dx.doi.org/10.33096/jffi.v3i2.497.

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Abstract (sommario):

Free radicals play a role in the occurrence of various degenerative diseases that require free-radical scavengers or antioxidants. Buni fruit (Antidesma bunius (L.) Spreng) has the bioactive components are Anthocyanins (flavonoids) that serves to the free radicals. This study aimed to measure the antioxidant activity of theethanol extract contained 70% fruit Buni obtained by using the method of nitric oxide. Simplicia buni macerated dried fruit with 70% ethanol. Extracts were obtained in the test antioxidant activity against nitric oxide radicals. The antioxidant activity against free radical absorbance measured by means of UV-Vis spectrophotometry at a wavelength of 546 nm and calcul ated IC50 values. The results shows that the fruit buni has potential as a free radical with IC50 value of 2.28 µg/mL and a comparison of quercetin with IC50 value of 5.88 µg/mL.

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Mitrohina, Natal'ya. "Oxidative stress in animals: role in oncogenesis from pathomorphologist view". Russian veterinary journal 2020, n. 5 (25 novembre 2020): 27–30. http://dx.doi.org/10.32416/2500-4379-2020-5-27-30.

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Abstract (sommario):

Oxidative stress is a pathological accumulation of free radicals that contribute to the launch of intracellular damaging action mechanisms. Free radical is an atom possessing free or missing electron, and seeking to restore the lost electron, taking it from other molecules ― as a result a new free radical is formed. The mechanism is chain reaction-based. Hypoxia acts as an additional stimulus to the appearance of oxygen free radicals. Cell hypoxia develops following any type of cell damage: mechanical, bacteriological, chemical, etc. Cell hypoxia inevitably leads to the development of an inflammatory reaction, which is followed by the formation of oxygen free radicals and, as a result, by oxidative stress development.

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Pinet, Sandra, Mathieu Pucheault, Virginie Liautard e Mégane Debiais. "Radical Metal-Free Borylation of Aryl Iodides". Synthesis 49, n. 21 (29 maggio 2017): 4759–68. http://dx.doi.org/10.1055/s-0036-1588431.

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Abstract (sommario):

A simple metal-free borylation of aryl iodides mediated by a fluoride sp2–sp3 diboron adduct is described. The reaction conditions are compatible with various functional groups. Electronic effects of substituents do not affect the borylation while steric hindrance does. The reaction proceeds via a radical mechanism in which pyridine serves to stabilize the boryl radicals, generated in situ.

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48

G, Savitha, Vishnupriya V e Surapaneni Krishnamohan. "IN VITRO ANTIOXIDANT CAPACITY AND FREE RADICAL SCAVENGING ACTIVITIES OF CARDIOSPERMUM HALICACABUM LINN." Asian Journal of Pharmaceutical and Clinical Research 11, n. 7 (7 luglio 2018): 421. http://dx.doi.org/10.22159/ajpcr.2018.v11i7.25044.

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Abstract (sommario):

Objective: Free radicals and oxidants are produced in the body during normal cellular metabolism and exposure to pollutions and ionizing radiations. They exert beneficial and harmful effects to the human body. Harmful effects of these radicals are destroyed by either antioxidants of our body in situ or antioxidants which are supplied through foods. Hence, the aim of this present study is to assess the antioxidant and free radical scavenging capacity of the easily available edible plant Cardiospermum halicacabum Linn. (Mudakathan keerai).Methods: Antioxidant and free radical scavenging activities of the aerial parts extract of C. halicacabum was determined by 2,2-diphenyl-1- picrylhydrazyl (DPPH) radical scavenging assay, 2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical scavenging assay, ferrous ion chelating assay, nitric oxide (NO) radical scavenging assay, superoxide radical scavenging assay, hydroxyl radical scavenging assay, and lipid peroxidation assay.Results: Remarkable free radical scavenging potential was observed in the ethanolic extract of C. halicacabum with IC50 values on all tested radicals, namely DPPH (IC50=34.06 μg/ml), ABTS (IC50=21.45 μg/ml), ferrous ion chelating (IC50=19.56 μg/ml), NO (IC50=25.16 μg/ml), superoxide (IC50=35.16 μg/ml), hydroxyl (IC50=28.56 μg/ml), and lipid peroxidation (IC50=33.12 μg/ml). The results revealed that ethanolic extract of C. halicacabum Linn. has significant antioxidant activity.Conclusion: The present study suggested that the aerial part extract of C. halicacabum serves as a good source of natural antioxidants.

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Girma, Mitiku, e Alex I. Smirnov. "Wound-induced Free-radical Formation in Corn Seedlings". HortScience 30, n. 4 (luglio 1995): 897C—897. http://dx.doi.org/10.21273/hortsci.30.4.897c.

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Abstract (sommario):

Recent studies performed at the Univ. of Sheffield (Sheffield, England) have established a correlation between the onset of senescence and the loss of viability in plants with a development of stable free-radicals that can be observed by Electron Paramagnetic Resonance (EPR) spectroscopy. We explored the possibility of free-radical formation following root injury of corn seedlings (Zea mays L.). Free radical signals were detected by EPR spectroscopy at 9.5 GHz. In all cases, we observed a single-line free-radical signal (g value ≈2.004) superimposed with six-line EPR spectrum from Mn2 + ions naturally present in the plant tissues. We determined a consistent increase in the intensity of single-line EPR signal after inducing root injury. This signal presumably is attributed to a quinone-derived radical and, as speculated, is associated with stressed respiratory transport chains. Based on our results, we suggest that free-radical reactions can be induced by root injury. Furthermore, an appearance of free-radical signal in the root may serve as an indication of a stress, natural and induced. If the precursors of observed free-radical signal can be determined, this will provide better insight on free-radical processes in plants followed by an injury. This work used the resources of the Illinois EPR Research Center (NIH P4 1 -RR0 1811).

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Flitter, W. D., e R. P. Mason. "The spin trapping of pyrimidine nucleotide free radicals in a Fenton system". Biochemical Journal 261, n. 3 (1 agosto 1989): 831–39. http://dx.doi.org/10.1042/bj2610831.

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Abstract (sommario):

The reaction of the hydroxyl radical, generated by a Fenton system, with pyrimidine deoxyribonucleotides was investigated by using the e.s.r. technique of spin trapping. The spin trap t-nitrosobutane was employed to trap secondary radicals formed by the reaction of the hydroxyl radical with these nucleotides. The results presented here show that hydroxyl-radical attack on thymidine, 2-deoxycytidine 5-monophosphate and 2-deoxyuridine 5-monophosphate produced nucleotide-derived free radicals. The results indicate that .OH radical attack occurs predominantly at the carbon-carbon double bond of the pyrimidine base. The e.s.r. studies showed a good correlation with previous results obtained by authors who used x- or gamma-ray irradiation to generate the hydroxyl radical. A thiobarbituric acid assay was also used to monitor the damage produced to the nucleotides by the Fenton system. These results showed qualitative agreement with the spin-trapping studies.

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