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Articoli di riviste sul tema "Free radicals (Chemistry)"

Autore: Grafiati

Pubblicato: 4 giugno 2021

Ultima modifica: 29 luglio 2024

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1

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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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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2

Nagendrappa, G. "An appreciation of free radical chemistry Part 4. Free radicals in atmospheric chemistry". Resonance 10, n. 7 (luglio 2005): 61–72. http://dx.doi.org/10.1007/bf02867108.

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3

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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4

[Sbreve]imkovic, Ivan. "FREE RADICALS IN WOOD CHEMISTRY". Journal of Macromolecular Science, Part C: Polymer Reviews 26, n. 1 (febbraio 1986): 67–80. http://dx.doi.org/10.1080/07366578608081969.

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5

Halliwell, Barry. "The Chemistry of Free Radicals". Toxicology and Industrial Health 9, n. 1-2 (gennaio 1993): 1–21. http://dx.doi.org/10.1177/0748233793009001-203.

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6

Pryor, W. A. "Free radicals in organic chemistry". Free Radical Biology and Medicine 21, n. 2 (gennaio 1996): 253–54. http://dx.doi.org/10.1016/0891-5849(96)90038-6.

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7

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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8

Lemaire, M. T. "Recent developments in the coordination chemistry of stable free radicals". Pure and Applied Chemistry 76, n. 2 (1 gennaio 2004): 277–93. http://dx.doi.org/10.1351/pac200476020277.

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Several advances in the coordination chemistry of stable free-radical species over the past six years are documented in this review article. Specifically, a number of recent reports focused on the coordination chemistry of chelating nitroxide ligands are highlighted, with an emphasis on enhanced magnetic or optical properties in these complexes. Furthermore, very intriguing recent magnetic and optical studies with one-dimensional nitroxide chain complexes (new "Glauber" chains and chiral magnets) are also discussed. The verdazyls are another family of stable radicals whose coordination chemistry was literally unexplored prior to 1997. A summary of recent reports discussing metal-verdazyl coordination complexes is also presented, followed by an eye to the future of stable radical design and the coordination chemistry of these interesting molecules.

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9

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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10

Van Lente, Frederick. "Free Radicals". Analytical Chemistry 65, n. 12 (15 giugno 1993): 374–77. http://dx.doi.org/10.1021/ac00060a601.

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11

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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12

Hamilton, R. J., C. Kalu, E. Prisk, F. B. Padley e H. Pierce. "Chemistry of free radicals in lipids". Food Chemistry 60, n. 2 (ottobre 1997): 193–99. http://dx.doi.org/10.1016/s0308-8146(96)00351-2.

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13

Lazar, M., J. Rychly, V. Klimo, P. Pelikan e L. Valko. "Free radicals in chemistry and biology". Free Radical Biology and Medicine 11, n. 2 (gennaio 1991): 233. http://dx.doi.org/10.1016/0891-5849(91)90175-3.

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14

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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15

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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16

Nagendrappa, G. "An appreciation of free radical chemistry part 5: Free radicals in organic synthesis". Resonance 10, n. 8 (agosto 2005): 80–90. http://dx.doi.org/10.1007/bf02866748.

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17

Nagendrappa, G. "An appreciation of free radical chemistry 3. Free radicals in diseases and health". Resonance 10, n. 4 (aprile 2005): 65–74. http://dx.doi.org/10.1007/bf02834649.

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18

Sethi, Kavleen Kaur, Gaurav Singh, Abhishek Sinha e Haider Iqbal. "An Understanding of Antioxidants and Oral Lesions". Dental Journal of Indira Gandhi Institute of Medical Sciences 2 (14 novembre 2023): 123–29. http://dx.doi.org/10.25259/djigims_5_2023.

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The study of free radical chemistry has received a lot of attention recently. Our bodies produce free radicals, reactive oxygen and nitrogen species, and reactive nitrogen species as a result of a variety of endogenous processes, exposure to various physicochemical circumstances, or pathological conditions. For optimum physiological function, free radicals and antioxidants must coexist in balance. Oxidative stress results when the body’s defenses against free radicals are overpowered. As a result, free radicals damage lipids, proteins, and Deoxyribonucleic acid (DNA) and cause a variety of human disorders. Therefore, using antioxidants from an external source can help to manage this oxidative damage. Recently, it has been suggested that synthetic antioxidants like butylated hydroxytoluene and butylated hydroxyanisole are harmful to human health. Thus, in recent years, research into natural substances with antioxidative action has been more focused.

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19

Lu, Keding, Song Guo, Zhaofeng Tan, Haichao Wang, Dongjie Shang, Yuhan Liu, Xin Li, Zhijun Wu, Min Hu e Yuanhang Zhang. "Exploring atmospheric free-radical chemistry in China: the self-cleansing capacity and the formation of secondary air pollution". National Science Review 6, n. 3 (19 luglio 2018): 579–94. http://dx.doi.org/10.1093/nsr/nwy073.

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Abstract Since 1971, it has been known that the atmospheric free radicals play a pivotal role in maintaining the oxidizing power of the troposphere. The existence of the oxidizing power is an important feature of the troposphere to remove primary air pollutants emitted from human beings as well as those from the biosphere. Nevertheless, serious secondary air-pollution incidents can take place due to fast oxidation of the primary pollutants. Elucidating the atmospheric free-radical chemistry is a demanding task in the field of atmospheric chemistry worldwide, which includes two kinds of work: first, the setup of reliable radical detection systems; second, integrated field studies that enable closure studies on the sources and sinks of targeted radicals such as OH and NO3. In this review, we try to review the Chinese efforts to explore the atmospheric free-radical chemistry in such chemical complex environments and the possible link of this fast gas-phase oxidation with the fast formation of secondary air pollution in the city-cluster areas in China.

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20

Bisht, Rekha. "Antioxidants: a brief review". Journal of Drug Delivery and Therapeutics 8, n. 6-s (15 dicembre 2018): 373–76. http://dx.doi.org/10.22270/jddt.v8i6-s.2116.

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The field of free radical chemistry has gained a great deal of attention in recent years. Free radicals reactive oxygen species generated by our body by various endogenous systems leads to various pathological conditions. A balance between free radicals and antioxidants is prerequisite for proper physiological function. Oxidative stress caused by generation of free radicals adversely alters lipids, proteins, and DNA and provokes a number of human ailments. Oxidative stress can be managed by using external sources of antioxidants. Synthetic antioxidants such as butylated hydroxytoluene and butylated hydroxyanisole have recently been reported to be harmful for human health. Thus, the search for effective, nontoxic natural compounds with antioxidant activity has been escalated in recent years. The present review provides a brief overview on antioxidants and natural sources of antioxidants in the management of human diseases. Keywords: free radical, Oxidative stress, antioxidants,

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21

Constable, Edwin C., e Catherine E. Housecroft. "Before Radicals Were Free – the Radical Particulier of de Morveau". Chemistry 2, n. 2 (20 aprile 2020): 293–304. http://dx.doi.org/10.3390/chemistry2020019.

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Today, we universally understand radicals to be chemical species with an unpaired electron. It was not always so, and this article traces the evolution of the term radical and in this journey, monitors the development of some of the great theories of organic chemistry.

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22

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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23

Dunne, Jacqueline, Alexis Caron, Patrick Menu, Abdu I. Alayash, Paul W. Buehler, Michael T. Wilson, Radu Silaghi-Dumitrescu, Beatrice Faivre e Chris E. Cooper. "Ascorbate removes key precursors to oxidative damage by cell-free haemoglobin in vitro and in vivo". Biochemical Journal 399, n. 3 (13 ottobre 2006): 513–24. http://dx.doi.org/10.1042/bj20060341.

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Haemoglobin initiates free radical chemistry. In particular, the interactions of peroxides with the ferric (met) species of haemoglobin generate two strong oxidants: ferryl iron and a protein-bound free radical. We have studied the endogenous defences to this reactive chemistry in a rabbit model following 20% exchange transfusion with cell-free haemoglobin stabilized in tetrameric form [via cross-linking with bis-(3,5-dibromosalicyl)fumarate]. The transfusate contained 95% oxyhaemoglobin, 5% methaemoglobin and 25 μM free iron. EPR spectroscopy revealed that the free iron in the transfusate was rendered redox inactive by rapid binding to transferrin. Methaemoglobin was reduced to oxyhaemoglobin by a slower process (t1/2=1 h). No globin-bound free radicals were detected in the plasma. These redox defences could be fully attributed to a novel multifunctional role of plasma ascorbate in removing key precursors of oxidative damage. Ascorbate is able to effectively reduce plasma methaemoglobin, ferryl haemoglobin and globin radicals. The ascorbyl free radicals formed are efficiently re-reduced by the erythrocyte membrane-bound reductase (which itself uses intra-erythrocyte ascorbate as an electron donor). As well as relating to the toxicity of haemoglobin-based oxygen carriers, these findings have implications for situations where haem proteins exist outside the protective cell environment, e.g. haemolytic anaemias, subarachnoid haemorrhage, rhabdomyolysis.

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24

Hideg, K. "Book Review, Free Radicals in Organic Chemistry". Synthesis 1996, n. 03 (marzo 1996): 419–22. http://dx.doi.org/10.1055/s-1996-4206.

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25

Bergendi, L', L. Beneš, Z. Ďuračková e M. Ferenčik. "Chemistry, physiology and pathology of free radicals". Life Sciences 65, n. 18-19 (ottobre 1999): 1865–74. http://dx.doi.org/10.1016/s0024-3205(99)00439-7.

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26

Janzen, Edward G., e Dale E. Nutter. "Spin Trapping Chemistry of Iminyl Free Radicals". Magnetic Resonance in Chemistry 35, n. 2 (febbraio 1997): 131–40. http://dx.doi.org/10.1002/(sici)1097-458x(199702)35:2<131::aid-omr23>3.0.co;2-3.

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27

Ferradini, Christiane, e Jean-Paul Jay-Gerin. "La radiolyse de l'eau et des solutions aqueuses : historique et actualité". Canadian Journal of Chemistry 77, n. 9 (1 settembre 1999): 1542–75. http://dx.doi.org/10.1139/v99-162.

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Experiments showing that water is decomposed by the action of high-energy radiations date back to the first days of the discovery of radioactivity, a century ago. On the occasion of this anniversary, we have attempted to give a comprehensive account of the radiation chemistry of water and its solutions since its origin, with special emphasis on the various physical and chemical stages that led to the present state of this science. To this aim, we describe the effect of different intervening factors on the molecular and radical yields, including dissolved solute concentration, pH, radiation intensity (or dose rate), type and energy of the radiation, presence of oxygen, temperature, phase, and pressure. We also discuss briefly the chemical behavior of the free radicals produced in radiolyzed aqueous solutions. A good, albeit incomplete, description of the phenomena is obtained that leads to various perspectives concerning, on the one hand, the development of this science and, on the other hand, its potential for applications.Key words : radical chemistry, dilution curve, water, hydrated electron, hydroxyl and superoxide radicals, free radicals, radiolysis, chain reactions, molecular and radical yields, cell survival, linear energy transfer.

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28

Abedinzadeh, Z. "Sulfur-centered reactive intermediates derived from the oxidation of sulfur compounds of biological interest". Canadian Journal of Physiology and Pharmacology 79, n. 2 (1 febbraio 2001): 166–70. http://dx.doi.org/10.1139/y00-085.

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Sulphur compounds play a central role in the structure and activity of many vital systems. In the living cell, sulfur constitutes an essential part of the defense against oxidative damage and is transformed into a variety of sulfur free radical species. Many studies of the chemistry of sulfur-centered radicals using pulse radiolysis and photolysis techniques to detect and measure the kinetics of these radicals have been published and reviewed. This paper discusses the present state of research on the formation and reactivity of certain sulfur-centered radicals [RS·, RSS·, RS·+, (RSSR)·+] and their implications for biological systems.Key words: sulfur-centered radicals, thiylradicals, sulfur-centered radical cation, cation radicals.

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29

Emmerson, K. M., N. Carslaw, D. C. Carslaw, J. D. Lee, G. McFiggans, W. Bloss, T. Gravestock et al. "Free radical modelling studies during the UK TORCH Campaign in summer 2003". Atmospheric Chemistry and Physics Discussions 6, n. 5 (18 ottobre 2006): 10523–65. http://dx.doi.org/10.5194/acpd-6-10523-2006.

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Abstract. The Tropospheric ORganic CHemistry experiment (TORCH) took place during the heatwave of summer 2003 at Writtle College, a site 2 miles west of Chelmsford in Essex and 25 miles north east of London. The experiment was one of the most highly instrumented to date. A combination of a large number of days of simultaneous, collocated measurements, a consequent wealth of model constraints and a highly detailed chemical mechanism, allowed the atmospheric chemistry of this site to be studied in detail. The concentrations of the hydroxyl radical, the hydroperoxy radical and the sum of peroxy radicals, were measured between 25 July and 31 August using laser-induced fluorescence at low pressure and the peroxy radical chemical amplifier techniques. The concentrations of the radical species were predicted using a zero-dimensional box model based on the Master Chemical Mechanism version 3.1, which was constrained with the observed concentrations of relatively long-lived species. The model included a detailed parameterisation to account for heterogeneous loss of hydroperoxy radicals onto aerosol particles. Quantile-quantile plots were used to assess the model performance in respect of the measured radical concentrations. On average, measured hydroxyl radical concentrations were over-predicted by 24%. Modelled and measured hydroperoxy radical concentrations agreed very well, with the model over-predicting on average by only 7%. The sum of peroxy radicals was under-predicted when compared with the respective measurements by 22%. OH initiation was dominated by the reactions of excited oxygen atoms with water, nitrous acid photolysis and the ozone reaction with alkene species. Photolysis of aldehyde species was the main initiation route for HO2 and RO2. Termination, under all conditions, primarily involved reactions with NOx for OH and heterogeneous chemistry on aerosol surfaces for HO2. The OH chain length varied between 2 and 8 cycles, the longer chain lengths occurring before and after the most polluted part of the campaign. Peak local ozone production of 17 ppb hr−1 occurred on 3 and 5 August, signifying the importance of local chemical processes to ozone production on these days. On the whole, agreement between model and measured radicals is good, giving confidence that our understanding of atmospheres influenced by nearby urban sources is adequate.

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30

Emmerson, K. M., N. Carslaw, D. C. Carslaw, J. D. Lee, G. McFiggans, W. J. Bloss, T. Gravestock et al. "Free radical modelling studies during the UK TORCH Campaign in Summer 2003". Atmospheric Chemistry and Physics 7, n. 1 (12 gennaio 2007): 167–81. http://dx.doi.org/10.5194/acp-7-167-2007.

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Abstract (sommario):

Abstract. The Tropospheric ORganic CHemistry experiment (TORCH) took place during the heatwave of summer 2003 at Writtle College, a site 2 miles west of Chelmsford in Essex and 25 miles north east of London. The experiment was one of the most highly instrumented to date. A combination of a large number of days of simultaneous, collocated measurements, a consequent wealth of model constraints and a highly detailed chemical mechanism, allowed the atmospheric chemistry of this site to be studied in detail. Between 25 July and 31 August, the concentrations of the hydroxyl radical and the hydroperoxy radical were measured using laser-induced fluorescence at low pressure and the sum of peroxy radicals was measured using the peroxy radical chemical amplifier technique. The concentrations of the radical species were predicted using a zero-dimensional box model based on the Master Chemical Mechanism version 3.1, which was constrained with the observed concentrations of relatively long-lived species. The model included a detailed parameterisation to account for heterogeneous loss of hydroperoxy radicals onto aerosol particles. Quantile-quantile plots were used to assess the model performance in respect of the measured radical concentrations. On average, measured hydroxyl radical concentrations were over-predicted by 24%. Modelled and measured hydroperoxy radical concentrations agreed very well, with the model over-predicting on average by only 7%. The sum of peroxy radicals was under-predicted when compared with the respective measurements by 22%. Initiation via OH was dominated by the reactions of excited oxygen atoms with water, nitrous acid photolysis and the ozone reaction with alkene species. Photolysis of aldehyde species was the main route for initiation via HO2 and RO2. Termination, under all conditions, primarily involved reactions with NOx for OH and heterogeneous chemistry on aerosol surfaces for HO2. The OH chain length varied between 2 and 8 cycles, the longer chain lengths occurring before and after the most polluted part of the campaign. Peak local ozone production of 17 ppb hr−1 occurred on 3 and 5 August, signifying the importance of local chemical processes to ozone production on these days. On the whole, agreement between model and measured radicals is good, giving confidence that our understanding of atmospheres influenced by nearby urban sources is adequate.

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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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32

Brodovitch, Jean-Claude, Brenda Addison-Jones, Khashayar Ghandi, Iain McKenzie, Paul W. Percival e Joachim Schüth. "Free radicals formed by H(Mu) addition to fluoranthene". Canadian Journal of Chemistry 81, n. 1 (1 gennaio 2003): 1–6. http://dx.doi.org/10.1139/v02-191.

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Abstract (sommario):

Muonium has been used as an H atom analogue to investigate the free radicals formed by H addition to the polyaromatic hydrocarbon fluoranthene. There are nine unique carbons in the molecule, but only five radicals were detected. Muon and proton hyperfine constants were determined by transverse field µSR and µLCR, respectively, and compared with calculated values. All signals were assigned to radicals formed by Mu addition to C-H sites. There is no evidence for addition to the tertiary carbons at ring junctions.Key words: muonium, fluoranthene, free radical, hyperfine constants.

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Tomaszewski, MJ, J. Warkentin e NH Werstiuk. "Free-Radical Chemistry of Imines". Australian Journal of Chemistry 48, n. 2 (1995): 291. http://dx.doi.org/10.1071/ch9950291.

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Aryl radicals bearing an aldimino functional group as part of an ortho substituent cyclized by addition to C and/or N of the imino group. When the choice was between 5-exo closure to C and 6-endo closure to N, the former predominated. However, 6-endo closure to C predominated over 5-exo cyclization to N in isomeric imines. Absolute values of cyclization rate constants were determined and an explanation for the unusual 6-endo preference is offered. Chiral induction in 6-endo cyclization to C of an aldimine from D-glyceraldehyde acetonide was observed, and its sense was determined.

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34

Elliot, A. John, Shahsultan Padamshi e Jana Pika. "Free-radical redox reactions of uranium ions in sulphuric acid solutions". Canadian Journal of Chemistry 64, n. 2 (1 febbraio 1986): 314–20. http://dx.doi.org/10.1139/v86-053.

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The radiolytic reduction of uranyl ions in degassed sulphuric acid solutions containing various organic solutes was studied. It was shown that while ĊOOH, CO2−, and α-hydroxy-alkyl radicals reduced uranyl ions, the β-hydroxy-alkyl radicals and those derived from gluconic acid could not affect the reduction. The oxidation of uranium(IV) by hydrogen peroxide at pH 0.7 involves hydroxyl radicals in a chain mechanism but at pH 2.0 the oxidation proceeds by a non-radical reaction pathway. From the enhancement of the rate of oxidation of uranium(IV) by oxygen in the presence of 2-propanol, a mechanism involving the perhydroxyl radical, which reconciles earlier published data on kinetics and oxygen tracer studies, is proposed for the oxygen-uranium(IV) reactions.

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35

Tkáč, Alexander, e Eva Hanušovská. "Reactivity of Free Radicals Generated from Neurotransmitters Studied by Electron Spin Resonance Spectroscopy". Collection of Czechoslovak Chemical Communications 69, n. 11 (2004): 2081–90. http://dx.doi.org/10.1135/cccc20042081.

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Free phenoxy radicals derived from catecholamine-type neurotransmitters (dopamine, noradrenaline, adrenaline) σ-coordinated to Co(III) chelates were generated by the reaction of π-coordinated tert-butylperoxy radicals with the neurotransmitters in non-polar solvent at ambient temperature. The ESR signals of the formed complexes are split into the basic octet line resulting from the interaction of the unpaired electron of the phenoxy radical with the 59Co nucleus (I = 7/2). Increasing the polarity of the solution starts the decomplexation and the liberated phenoxy radicals of the neurotransmitters disappear by recombination or by H-abstraction from the added antioxidant. When vitamin E is added to the system, only the ESR signal of the stable α-tocopheroxy radicals is detectable. Similarly, in the presence of the antiarrhytmic drug Stobadine, only the signal of the corresponding nitrogen-centred radical is seen. In the presence of both antioxidants, rapid H-transfer occurs from vitamin E to the Stobadine radicals.

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36

K. Koltover, Vitaly. "Free Radical Timer of Aging: from Chemistry of Free Radicals to Systems Theory of Reliability". Current Aging Science 10, n. 1 (5 gennaio 2017): 12–17. http://dx.doi.org/10.2174/1874609809666161009220822.

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37

Koltover, Vitaly K. "Free Radical Theory of Aging: From Chemistry of Free Radicals to Reliability of Biological Systems". Free Radical Biology and Medicine 76 (novembre 2014): S33—S34. http://dx.doi.org/10.1016/j.freeradbiomed.2014.10.448.

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38

Tkáč, Alexander. "Alternating reactivity of free radicals coordinated to chelated transition metals and to hemoproteins". Collection of Czechoslovak Chemical Communications 53, n. 10 (1988): 2429–46. http://dx.doi.org/10.1135/cccc19882429.

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Abstract (sommario):

The mean lifetime of free radicals increases by coordination to transition metals of chelates including hemoproteins (hemoglobin, cytochrome c, catalase), when the radical generation proceeds in non-polar media in temperature range of physiological ones (290-310 K). In polar media (water, methyl- or ethylalcohol, pyridine), or in the presence of effective ligating agents (e.g. bases of nucleic acids), or at slightly elevated temperatures the intermediately stabilized oxygen centred radicals are liberated from the complex and the original high reactivity of the free radical is renewed. It is assumed that in this way sterically unhindered free radicals derived from chemical carcinogens with alternating reactivity could be transported through the microheterogeneous cell matrix.

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39

Crich, David, e Qingwei Yao. "Free radical chemistry of nucleosides and nucleotides. Ring opening of C4′-radicals". Tetrahedron 54, n. 3-4 (gennaio 1998): 305–18. http://dx.doi.org/10.1016/s0040-4020(97)10262-9.

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40

Kostka, Peter. "Free radicals (nitric oxide)". Analytical Chemistry 67, n. 12 (15 giugno 1995): 411–16. http://dx.doi.org/10.1021/ac00108a023.

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41

Shahzad, Asif, Shoukat Hussain, Nazima Anwar, Abdul Karim, Ume Aeman e Muhammad Javid Iqbal. "An overview of free Radicals & antioxidants and its Deletenous actions." FRONTIERS IN CHEMICAL SCIENCES 2, n. 2 (31 dicembre 2021): 147–64. http://dx.doi.org/10.52700/fcs.v2i2.32.

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Abstract (sommario):

In modern years, there has been a large dealing of work toward the area of free radical chemistry. Free radicals reactive oxygen species and reactive nitrogen species are create by our body by various endogenic systems, influence to different physio chemical conditions or unhealthy states. A balance between free radicals and antioxidants is necessary for proper physiological function. If free radicals overwhelm the body's ability to modulate them, a condition known as oxidative stress ensues. Free radicals thus unfavorable alter lipids, proteins, and DNA and activate a number of human diseases. Hence application of external source of antioxidants can assist in coping this oxidative stress. Synthetic antioxidants such as butylated hydroxytoluene and butylated hydroxyanisole have recently been reported to be dangerous for human health. The present review provides a brief overview on oxidative stress mediate cellular damages and role of dietary antioxidants as functional foods in the organization of human diseases. We need to take balance diet which provide much more antioxidants to lower risks of health and run to life longer.The purpose of this review is that we want awareness related to sources of antioxidants from plants and highlight the studies of antioxidants and free radicals which provide prove for maintaining healthy aging. Key words: antioxidant, free radicals, aging, oxidative stress. Graphically Abstract;

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42

Cherkasov, Artem R., M. Jonsson, Vladimir I. Galkin e Rafael A. Cherkasov. "Correlation analysis in the chemistry of free radicals". Russian Chemical Reviews 70, n. 1 (31 gennaio 2001): 1–22. http://dx.doi.org/10.1070/rc2001v070n01abeh000574.

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43

Mason, T. J. "Free radicals and ultrasound in chemistry and medicine". Ultrasonics Sonochemistry 1, n. 2 (1994): S131—S132. http://dx.doi.org/10.1016/1350-4177(94)90011-6.

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44

YOSHIKAWA, TOSHIKAZU. "Chemistry of active enzymes and free radicals and organism. 4. Active oxygen, free radicals and diseases." Kagaku To Seibutsu 37, n. 7 (1999): 475–81. http://dx.doi.org/10.1271/kagakutoseibutsu1962.37.475.

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45

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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46

Mathew, Lukose, Emmanuel Y. Osei-Twum e John Warkentin. "Thermolysis of α-hydroperoxyalkyl diazenes. Spin trapping of radical intermediates and spin trapping kinetics". Canadian Journal of Chemistry 69, n. 9 (1 settembre 1991): 1398–402. http://dx.doi.org/10.1139/v91-206.

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Abstract (sommario):

α-Hydroperoxyalkyl diazenes (Me2C(OOH)N=NR, 1, R = CH2CF3, CH2CH2OMe, CH(Me)2, CMe3, CH2Ph, Ph, CH2CH2OPh, and c-C3H5CD2) decompose in benzene, at 50 °C or less, by a mechanism involving free radical (R•) intermediates. The radicals were trapped with 1-methyl-4-nitroso-3,5-diphenylpyrazole, 2, to afford spin adducts (nitroxyls) that were observed by ESR spectroscopy. When the solvent was ethyl vinyl ether, radicals from 1 (R = CH2CH2OPh) were trapped by the solvent and the adduct radicals so formed were spin trapped by 2. These observations support free radical mechanisms for thermolysis of 1 and for the hydroxyalkylations that occur when 1 are decomposed in solutions containing enol ethers or other unsaturated substrates. The ring-opening of cyclopropylmethyl radicals (cpm) to 3-butenyl radicals was used to estimate the rate constant for radical trapping by 2. For cpm the rate constant is given by log kcpm = (10.7 ± 0.4) − (3.9 ± 0.5)/θ where θ = 2.3 RT kcal mol−1. At 25 °C, the spin trapping rate constant has the value 6.9 × 107 M−1 s−1. Key words: hydroperoxyalkyl diazenes; radicals, spin trapping; spin trapping, rate constant.

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47

Lüring, Ulrich, e André Kirsch. "Imidyl Radicals – Free-Radical Addition ofN1-Bromoimides to Alkenes". Chemische Berichte 126, n. 5 (maggio 1993): 1171–78. http://dx.doi.org/10.1002/cber.19931260517.

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48

Aliaga, Carolina, e Eduardo A. Lissi. "Comparison of the free radical scavenger activities of quercetin and rutin An experimental and theoretical study". Canadian Journal of Chemistry 82, n. 12 (1 dicembre 2004): 1668–73. http://dx.doi.org/10.1139/v04-151.

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Abstract (sommario):

Natural radical scavengers have recently received considerable interest owing to the role of free radicals in causing oxidative stress in living organisms. Flavonoids constitute one of the most important families of molecules with antioxidant activities, a characteristic associated with the presence in their structure of hydroxyl groups bound to aromatic rings. Quercetin is a potent antioxidant whose high reactivity could be associated with the presence of the OH group in the C ring. To address the role of this group in quercetin's free radical scavenging capacity, we have carried out experimental determinations and theoretical calculations regarding the reactivity of quercetin and rutin. The reactivity of both compounds towards free radicals was assessed employing the radical anion 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonate) and peroxyl radicals. These measurements indicate that quercetin is more reactive and has more reactive centers than rutin, suggesting that the extra OH group located in the C ring could directly contribute to reactivity of quercetin. This conclusion is in agreement with the evaluation of local reactivity indexes, such as the Fukui function.Key words: quercetin, rutin, antioxidant activity, ABTS, peroxyl radicals, Fukui function, local reactivity index.

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49

Kircher, Raphael, Sarah Mross, Hans Hasse e Kerstin Münnemann. "Functionalized Controlled Porous Glasses for Producing Radical-Free Hyperpolarized Liquids by Overhauser DNP". Molecules 27, n. 19 (28 settembre 2022): 6402. http://dx.doi.org/10.3390/molecules27196402.

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Abstract (sommario):

Overhauser dynamic nuclear polarization (ODNP) can be used as a tool for NMR signal enhancement and happens on very short time scales. Therefore, ODNP is well suited for the measurement of fast-flowing samples, even in compact magnets, which is beneficial for the real-time monitoring of chemical reactions or processes. ODNP requires the presence of unpaired electrons in the sample, which is usually accomplished by the addition of stable radicals. However, radicals affect the nuclear relaxation times and can hamper the NMR detection. This is circumvented by immobilizing radicals in a packed bed allowing for the measurement of radical-free samples when using ex situ DNP techniques (DNP build-up and NMR detection happen at different places) and flow-induced separation of the hyperpolarized liquid from the radicals. Therefore, the synthesis of robust and chemically inert immobilized radical matrices is mandatory. In the present work, this is accomplished by immobilizing the radical glycidyloxy-tetramethylpiperidinyloxyl with a polyethyleneimine (PEI) linker on the surface of controlled porous glasses (CPG). Both the porosity of the CPGs and also the size of the PEI-linker were varied, resulting in a set of distinct radical matrices for continuous-flow ODNP. The study shows that CPGs with PEI-linkers provide robust, inert and efficient ODNP matrices.

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50

Bognár, Balázs, Györgyi Úr, Cecília Sár, Olga H. Hankovszky, Kálmán Hideg e Tamás Kálai. "Synthesis and Application of Stable Nitroxide Free Radicals Fused with Carbocycles and Heterocycles". Current Organic Chemistry 23, n. 4 (22 maggio 2019): 480–501. http://dx.doi.org/10.2174/1385272823666190318163321.

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Abstract (sommario):

Stable nitroxide free radicals have traditionally been associated with 2,2,6,6- tetramethylpiperidine-1-oxyl (TEMPO) or its 4-substituted derivatives as relatively inexpensive and readily accessible compounds with limited possibilities for further chemical modification. Over the past two decades, there has been a resurgence of interest in stable free radicals with proper functionalization tuned for various applications. The objective of this review is to present recent results with synthetic methodologies to achieve stable nitroxide free radicals fused with aromatic carbocycles and heterocycles. There are two main approaches for accessing stable nitroxide free radicals fused with arenes, e.g., isoindoline- like nitroxides: further functionalization and oxidation of phthalimide or inventive functionalization of pyrroline nitroxide key compounds. The latter also offers the constructions of versatile heterocyclic scaffolds (furan, pyrrole, thiophene, 1,2-thiazole, selenophene, pyrazole, pyrimidine, pyridine, pyridazine, 1,5-benzothiazepine) that are fused with pyrroline or tetrahydropyridine nitroxide rings. The possible applications of these new stable nitroxide free radicals, such as covalent spin labels and noncovalent spin probes of proteins and nucleic acids, profluorescent probes, building blocks for construction of dual active drugs and electroactive materials, and substances for controlled free radical polymerization, are discussed.

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