Artykuły w czasopismach na temat „Radicals”
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Ngai, Ming-Yu, Arghya Banerjee i Zhen Lei. "Acyl Radical Chemistry via Visible-Light Photoredox Catalysis". Synthesis 51, nr 02 (12.12.2018): 303–33. http://dx.doi.org/10.1055/s-0037-1610329.
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Visible-light photoredox catalysis enables easy access to acyl radicals under mild reaction conditions. Reactive acyl radicals, generated from various acyl precursors such as aldehydes, α-keto acids, carboxylic acids, anhydrides, acyl thioesters, acyl chlorides, or acyl silanes, can undergo a diverse range of synthetically useful transformations, which were previously difficult or inaccessible. This review summarizes the recent progress on visible-light-driven acyl radical generation using transition-metal photoredox catalysts, metallaphotocatalysts, hypervalent iodine catalysts or organic photocatalysts.1 Introduction2 The Scope of This Review3 Aldehydes as a Source of Acyl Radicals4 α-Keto Acids as a Source of Acyl Radicals5 Carboxylic Acids as a Source of Acyl Radicals6 Anhydrides as a Source of Acyl Radicals7 Acyl Thioesters as a Source of Acyl Radicals8 Acyl Chlorides as a Source of Acyl Radicals9 Acyl Silanes as a Source of Acyl Radicals10 Conclusions and Future Outlook
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Taniguchi, Tsuyoshi. "Recent Advances in Reactions of Heteroatom-Centered Radicals". Synthesis 49, nr 16 (26.07.2017): 3511–34. http://dx.doi.org/10.1055/s-0036-1588481.
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Heteroatom-centered radicals show versatile reactivity and offer useful synthetic methods in organic chemistry. The development of new approaches for forming heteroatom-centered radicals has recently expanded the practicality of radical chemistry for synthesis. This review focuses on recent advances in reactions of representative heteroatom-centered radicals.1 Introduction2 Group 17 Elements: Chlorine and Bromine Radicals3 Group 15 and Group 16 Elements3.1 Nitrogen- and Oxygen-Centered Radicals3.2 Phosphorus- and Sulfur-Centered Radicals3.3 Other Radicals4 Group 14 Elements: Silicon-Centered Radicals5 Group 13 Elements: Boron-Centered Radicals6 Conclusion
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Monika, Monika, i Sermadurai Selvakumar. "Recent Developments in Direct C–H Functionalization of Quinoxalin-2(1H)-ones via Radical Addition Processes". Synthesis 51, nr 22 (24.09.2019): 4113–36. http://dx.doi.org/10.1055/s-0037-1611910.
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This review article covers the recent developments in direct C–H functionalization of quinoxalin-2(1H)-one derivatives via radical additions at the C3 position. Reaction types have been categorized depending on the kind of radical used, with representative examples and insightful mechanistic details provided.1 Introduction2 Reactions with Alkyl Radicals3 Reactions with Acyl Radicals4 Reactions with Aryl Radicals5 Reactions with Perfluoroalkyl Radicals6 Reactions with Alkoxycarbonyl Radicals7 Reactions with Nitrogen Radicals8 Reactions with Oxygen Radicals9 Reactions with Phosphorus Radicals10 Conclusion
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Bao, Xiazhen, Jun Li, Wei Jiang i Congde Huo. "Radical-Mediated Difunctionalization of Styrenes". Synthesis 51, nr 24 (10.10.2019): 4507–30. http://dx.doi.org/10.1055/s-0039-1690987.
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Styrene, an extremely important compound in the chemical industry, is mainly produced by the dehydrogenation or oxidative dehydrogenation of ethylbenzene. Transformation of this raw organic material to more useful fine organic chemicals is a very significant topic. Recently, the radical difunctionalization of styrene has become a powerful and efficient tool for organic synthesis. This strategy can introduce two substituents into a styrene molecule in one step via addition to the C=C bond, enhancing the molecular complexity in a single operation with good selectivity and wide functional group compatibility.1 Introduction2 C-Centered Radicals3 CF3 and Other Polyfluoroalkyl Radicals4 N-Centered Radicals5 P-Centered Radicals6 O-Centered Radicals7 S-Centered Radicals8 Other-Atom-Centered Radicals9 Conclusion and Perspective
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de Bruin, Bas, i Colet te Grotenhuis. "Radical-type Reactions Controlled by Cobalt: From Carbene Radical Reactivity to the Catalytic Intermediacy of Reactive o-Quinodimethanes". Synlett 29, nr 17 (19.07.2018): 2238–50. http://dx.doi.org/10.1055/s-0037-1610204.
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In this account, we summarize our recent efforts in the fields of ‘open-shell organometallic chemistry’ and ‘metalloradical catalysis’. We focus in particular on the use of so-called ‘carbene radicals’ for the synthesis of a variety of useful synthons for organic chemistry. We further show that unexpected reactivity arises from catalytic synthesis of unusual o-quinone methide and o-quinodimethane intermediates that undergo subsequent rearrangements to uncommon products.1 Introduction2 General (Fischer-Type) Carbene and Nitrene Reactivity and Their Relation to Carbene and Nitrene Radical Reactivity3 Carbene and Nitrene (Radical) Precursors4 Formation and Intrinsic Radical-Type Reactivity of Carbene and Nitrene Radicals5 Types of Cobalt Catalysts Used in Reactions Involving Carbene and Nitrene Radicals6 Applications of Cobalt-Catalyzed Ring-Closure Reactions via Carbene Radicals7 Intermediacy of o-Quinone Methide and o-Quidodimethanes in Carbene Ring-Closing Reactions8 Conclusion
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Sands, A. D. "Radicals and one-sided ideals". Proceedings of the Royal Society of Edinburgh: Section A Mathematics 103, nr 3-4 (1986): 241–51. http://dx.doi.org/10.1017/s0308210500018898.
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The correspondence between radicals of associative rings and A-radicals is studied. It is shown that corresponding to each A-radical there is an interval of radicals and that each radical belongs to exactly one such interval. The question of the nature of the radical of a one-sided ideal is considered. It is shown that the radicals such that the radical of a one-sided ideal is always a one-sided ideal are those which contain their associated A-radicals. Radicals such that the radical of a one-sided ideal always equals the intersection of a left ideal and a right ideal are described, as are those A-radicals such that every associated radical has this property.
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Seath, Ciaran P., i Nathan T. Jui. "Intermolecular Reactions of Pyridyl Radicals with Olefins via Photoredox Catalysis". Synlett 30, nr 14 (24.04.2019): 1607–14. http://dx.doi.org/10.1055/s-0037-1611527.
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Pyridines are valuable motifs in a number of bioactive and functional molecules. The chemoselective functionalization of these structures from stable and widely available starting materials is a meaningful goal. We have demonstrated selective formation of pyridyl radicals at any position (2-, 3-, 4-pyridyl), through the action of a reducing photoredox catalyst. These radicals readily engage alkenes to deliver high-value products. Alteration of the reaction medium has enabled the use of a diverse range of alkene subtypes in a highly divergent and chemoselective manner.1 Introduction2 Minisci-Type Pyridine Alkylation3 An Alternate Approach – Reductive Radical Formation4 Conjugate Addition of Pyridyl Radicals5 Radical Hydroarylation of Neutral and Rich Olefins6 Solvent-Based Chemoselectivity7 Summary and Outlook
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Das, Suresh, i Clemens von Sonntag. "The Oxidation of Trimethylamine by OH Radicals in Aqueous Solution, as Studied by Pulse Radiolysis, ESR, and Product Analysis. The Reactions of the Alkylamine Radical Cation, the Aminoalkyl Radical, and the Protonated Aminoalkyl Radical". Zeitschrift für Naturforschung B 41, nr 4 (1.04.1986): 505–13. http://dx.doi.org/10.1515/znb-1986-0418.
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Hydroxyl radical reactions with trimethylamine in aqueous solution lead to the formation of the aminoalkyl radical (CH3)2NCH2 (A) and its conjugated acid (CH3)2HN+CH2 (AH+) as well as to the alkylamine radical cation (CH3)3N+(N+). These radicals are transform ed into each other by hydrolytic reactions, e.g.[xxx]Radicals AH+ are more acidic (pKa ≈ 3.6) than the radicals N+(pKa ≈ 8.0). Consequently, N+ predom inate over AH+ under quasi equilibrium conditions (e.g. in the presence of phosphate buffer) and are the only species observed by ESR in acid solutions. Reacting with the protonated amine. OH radicals abstract hydrogen at nitrogen and at carbon with comparable ease. Reaction of OH radicals with the free amine may initially also generate N+, beside H-abstraction at carbon. Radicals A’ absorb more strongly at 260 nm (ε = 3390 dm3mol-1cm-1) than the radical cation N+(ε = 950 dm3mol-1cm-1). Radical A' has reducing properties whereas radicals AH+ and N+ have oxidizing properties and hence can be monitored with p-nitroacetophenone (the reducing radicals), and Fe(CN)64- , N ,N'-tetramethyl-p-phenylenediamine and 2,2'-azinobis-(3-ethyl-benzthiazoline- 6-sulphonate) (the oxidizing radicals). These radicals mainly (≥ 85 % ) disproportionate. one of the products being formaldehyde
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Chow, Yuan L., i Richard A. Perry. "Chemistry of amidyl radicals: intramolecular reactivities of alkenyl amidyl radicals". Canadian Journal of Chemistry 63, nr 8 (1.08.1985): 2203–10. http://dx.doi.org/10.1139/v85-362.
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Amidyl radicals possessing Δ4,5, Δ5,6, and Δ6,7 double bonds were generated from the photodecomposition of nitrosamides and chloramides and the products were identified. Dichotomies of amidyl radical reactivities were discovered and compared with published kinetic rate constants. In complete reversal to intermolecular reactivities, intramolecularly the alkenyl amidyl radicals preferentially add to the double bonds rather than abstract a C-5 hydrogen even if it is allylic. In intramolecular competition, amidyl radicals add to an acyl side chain double bond more efficiently than to an alkyl one; this is just the opposite to intramolecular H-abstraction of amidyl radicals. Taken together with the published results, it is established that, in intramolecular attacks of double bonds, amidyl radicals selectively undergo the propia-addition to generate an exo-cyclic radical rather than the longa-addition to an endo-cyclic radical: this rule should replace the old one that amidyl radicals preferentially cyclize to form five-membered rings if choices are available.
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Li, Guoxiang, Zhongyang Luo, Wenbo Wang i Jianmeng Cen. "A Study of the Mechanisms of Guaiacol Pyrolysis Based on Free Radicals Detection Technology". Catalysts 10, nr 3 (5.03.2020): 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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Marnett, Lawrence J., i Allan L. Wilcox. "The chemistry of lipid alkoxyl radicals and their role in metal-amplified lipid peroxidation". Biochemical Society Symposia 61 (1.11.1995): 65–72. http://dx.doi.org/10.1042/bss0610065.
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Reaction of polyunsaturated fatty acid hydroperoxides with metal complexes generates lipid alkoxyl radicals and metal-oxo complexes. Lipid alkoxyl radicals are presumed to be the species responsible for metal-amplified lipid peroxidation because of the chemical analogy of simple organic alkoxyl radicals to the hydroxyl radical. However, polyunsaturated fatty acid alkoxyl radicals exhibit a rich and diverse chemistry that is dominated by intramolecular cyclization to epoxyallylic radicals. Studies described herein demonstrate that the equilibrium between cyclization and ring-opening of epoxyallylic radicals lies overwhelmingly toward cyclization. Thus lipid alkoxyl radicals have a steady-state concentration that is so low that their contribution to metal-amplified lipid peroxidation is insignificant. In fact, the species responsible for metal amplification of lipid peroxidation appears to be the epoxyperoxyl radical formed by coupling the epoxyallylic radical to molecular oxygen.
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Xu, Fei, Wanni Yu, Rui Gao, Qin Zhou, Qingzhu Zhang i Wenxing Wang. "Dioxin Formations from the Radical/Radical Cross-Condensation of Phenoxy Radicals with 2-Chlorophenoxy Radicals and 2,4,6-Trichlorophenoxy Radicals". Environmental Science & Technology 44, nr 17 (wrzesień 2010): 6745–51. http://dx.doi.org/10.1021/es101794v.
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Kajiwara, Atsushi. "Characterizations of radicals formed in radical polymerizations and transfer reactions by electron spin resonance spectroscopy". Pure and Applied Chemistry 90, nr 8 (28.08.2018): 1237–54. http://dx.doi.org/10.1515/pac-2018-0401.
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Abstract Electron spin resonance (ESR, aka electron paramagnetic resonance, EPR) investigations have been conducted on radicals formed during radical polymerizations and provide a detailed characterization of the active radical species. Active propagating radicals can be observed during actual radical polymerizations by ESR/EPR. The chain lengths of the observed radicals were estimated by a combination of atom transfer radical polymerization (ATRP) and ESR/EPR. The structures of the chain end radicals were determined by analysis of the ESR/EPR spectra. An increase in the dihedral angles between terminal p-orbital of radical and Cβ–H bonds was observed with increasing chain lengths of methacrylate polymers. Radical transfer reactions were observed during radical polymerization of acrylates. A combination of ATRP and ESR/EPR clarified a 1,5-hydrogen shift mechanism of the radical transfer reactions using model adamantyl acrylate radicals. Penultimate unit effects were also observed. Time-resolved ESR/EPR (TR ESR) spectroscopy clarified the initiation processes of an alternating copolymerization of styrene with maleic anhydride and the copolymerization of styrene with 1,3-butadiene. Several unsolved problems in conventional radical polymerization processes have been clarified using combinations of ATRP with ESR/EPR and TR ESR. Characterization of the radicals in radical polymerizations using various ESR techniques would definitely provide interesting and useful information on conventional radical polymerizations.
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Nakazawa, H., K. Ichimori, Y. Shinozaki, H. Okino i S. Hori. "Is superoxide demonstration by electron-spin resonance spectroscopy really superoxide?" American Journal of Physiology-Heart and Circulatory Physiology 255, nr 1 (1.07.1988): H213—H215. http://dx.doi.org/10.1152/ajpheart.1988.255.1.h213.
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A recent study has indicated that the generation of an oxygen radical in freeze-clamped myocardium on reperfusion can be directly demonstrated using electron-spin resonance spectroscopy (ESR). However, the results need to be analyzed with caution, since artifactual radicals are misleading problems common to this method. To test whether that reported superoxide is truly the biologically existing radical or an artifactual radical, we performed experiments using isolated, perfused rat and rabbit hearts and open-chest canine hearts subjected to ischemia/reperfusion. Radicals were freeze trapped at 77 degrees K, and ESR measurements were made. The ESR spectra exhibited four free radicals. Among these, two radicals which had been previously claimed as superoxide and a nitrogen-centered radical were shown as mechanically yielded artifactual radicals. These were produced by pulverization of the frozen sample. In artifact-free samples, superoxide could not be detected. The radicals native to the myocardium were identified as coenzyme Q10-. and another radical the species of which remains unclear.
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Birkenmeier, Gary F., i Richard Wiegandt. "Essential covers and complements of radicals". Bulletin of the Australian Mathematical Society 53, nr 2 (kwiecień 1996): 261–66. http://dx.doi.org/10.1017/s000497270001697x.
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We show that a radical has a semisimple essential cover if and only if it is hereditary and has a complement in the lattice of hereditary radicals. In 1971 Snider gave a full description of supernilpotent radicals which have a complement. Recently Beidar, Fong, Ke, and Shum have determined radicals with semisimple essential covers. Using their results, we are able to provide a lower radical representation of complemented subidempotent radicals. This completes Snider's description of hereditary complemented radicals.
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Koppenol, W. H. "Names for inorganic radicals (IUPAC Recommendations 2000)". Pure and Applied Chemistry 72, nr 3 (1.01.2000): 437–46. http://dx.doi.org/10.1351/pac200072030437.
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Introduction: Knowledge of the properties and reactivities of stable inorganic radicals was obtained decades ago through gas-phase studies of various oxides of halogens, sulfur, and nitrogen. More recently, pulse radiolysis and flash photolysis techniques developed in the 1960s made it possible to study short-lived radicals, such as hydrated electrons, hydrogen atoms, and hydroxyl radicals. Because of the high time-resolution of these techniques, absorption spectra and redox properties of these inorganic radicals could be determined. The interest in radicals increased when it was shown that superoxide, or dioxide(1-), is formed in vivo. The discovery that in aerobic organisms enzymes catalyze the disproportionation of this radical resulted in new areas of research, such as radical biology and radicals in medicine. Interest in simple radicals was further boosted most recently by the remarkable observation that the radical nitrogen monoxide is formed enzymatically from the amino acid arginine. Radicals are important in a variety of catalytic processes and in the atmospheric gas and liquid phases; furthermore, a substantial number of inorganic radicals have been observed in interstellar gas clouds.Contents:1. Introduction 2. Definitions 3. Nomenclature 3.1. Introduction 3.2. Coordination nomenclature 3.2.1. Selection of the central atom3.2.2. Radicals with net charges 3.2.3. Attached atoms or groups of atoms 3.2.4. The radical dot 3.2.5. Examples 3.3. Substitutive nomenclature
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Danylchenko, P. Yu. "Criminological typology of radical criminals among sentenced to imprisonment". Law and Safety 88, nr 1 (29.03.2023): 146–56. http://dx.doi.org/10.32631/pb.2023.1.13.
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The article is devoted to the study of radical criminals among those sentenced to imprisonment. The purpose of the article is to provide a criminological typological characteristic of criminal radicals among those sentenced to imprisonment. The following tasks have been solved to achieve this goal: 1) to define the typological criteria for the division of criminal radicals among those sentenced to imprisonment; 2) to identify the relevant criminological types according to the criteria; 3) to identify and describe the signs of criminological types of criminal radicals among those sentenced to imprisonment.
It has been proposed that 7 typological personal criteria should be used in scientific use and practical criminal prevention activities: by nature, by the direction of criminal and radical actions, by the contextual element of personal radicalisation, by the source of radical attitude, by the peculiarities of the radical’s predicate state, by the existential content of criminal and radical behaviour, and by the dominant social and role feature. According to them, 22 criminological types (including subtypes) of criminal radicals among convicts were identified. The author describes the key criminologically significant features of each type. The integrated typological characteristics of radical criminals among convicts give grounds to note that most of them can be correlated with an initiative, aggressive, rational-conformist, collectivist radical of an inclusive type.
Both the initial diagnostic work of the relevant units and officials of the quarantine, diagnostic and distribution sectors of correctional colonies, as well as the further work of social and psychological work inspectors, should be aimed at identifying and recording these features. It has been argued that this information should also be taken into account when organising and carrying out operational work among prisoners in order to block the development of motivations for radical actions in a timely manner and to stop the tendencies of radicalisation among prisoners.
It has been noted that the proposed typology of criminal radicals in penitentiary institutions is not closed, exhaustive, and can be supplemented with other criteria and types depending on the researcher's target setting and a specific applied request in the field of prevention of criminal radical manifestations in penitentiary institutions.
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FRANCE-JACKSON, H. "ON BAD SUPERNILPOTENT RADICALS". Bulletin of the Australian Mathematical Society 85, nr 2 (15.12.2011): 271–74. http://dx.doi.org/10.1017/s0004972711003066.
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AbstractA supernilpotent radical α is called bad if the class π(α) of all prime and α-semisimple rings consists of the one-element ring 0 only. We construct infinitely many bad supernilpotent radicals which form a generalization of Ryabukhin’s example of a supernilpotent nonspecial radical. We show that the family of all bad supernilpotent radicals is a sublattice of the lattice of all supernilpotent radicals and give examples of supernilpotent radicals that are not bad.
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TUMURBAT, S., i H. FRANCE-JACKSON. "ON PRIME-LIKE RADICALS". Bulletin of the Australian Mathematical Society 82, nr 1 (2.03.2010): 113–19. http://dx.doi.org/10.1017/s0004972709001129.
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AbstractA radical γ is prime-like if, for every prime ring A, the polynomial ring A[x] is γ-semisimple. In this paper, we study properties of prime-like radicals. In particular, we give necessary and sufficient conditions for a radical γ containing the prime radical β to be prime-like. This allows us to easily find distinct special radicals that coincide on simple rings and on polynomial rings, which answers a question put by Ferrero. It also allows us to reformulate a long-standing open problem of Gardner in terms of prime-like radicals.
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Beidar, Konstantin I., i K. Trokanová-Salavová. "Additive radicals". Czechoslovak Mathematical Journal 39, nr 4 (1989): 659–73. http://dx.doi.org/10.21136/cmj.1989.102342.
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Vergely, Catherine, i Rochette Luc. "Forgotten Radicals in Biology". International Journal of Biomedical Science 4, nr 4 (15.12.2008): 255–59. http://dx.doi.org/10.59566/ijbs.2008.4255.
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Redox reactions play key roles in intra- and inter-cellular signaling, and in adaptative processes of tissues towards stress. Among the major free radicals with essential functions in cells are reactive oxygen species (ROS) including superoxide anion (O2-), hydroxyl radical (OH) and reactive nitrogen species (RNS) such as nitric oxide (NO). In this article, we review the forgotten and new radicals with potential relevance to cardiovascular pathophysiology. Approximately 0.3% of O2- present in cytosol exists in its protonated form: hydroperoxyl radical (HO2). Water (H2O) can be split into two free radicals: OH and hydrogen radical (H). Several free radicals, including thiyl radicals (RS) and nitrogen dioxide (NO2) are known to isomerize double bonds. In the omega-6 series of poly-unsaturated fatty acids (PUFAs), cis-trans isomerization of γ-linolenate and arachidonate catalyzed by RS has been investigated. Evidence is emerging that hydrogen disulphide (H2S) is a signaling molecule in vivo which can be a source of free radicals. The Cu-Zn superoxide dismutase (SOD) enzyme can oxidize the ionized form of H2S to hydro-sulphide radical: HS. Recent studies suggest that H2S plays an important function in cardiovascular functions. Carbonate radical, which can be formed when OH reacts with carbonate or bicarbonate ions, is also involved in the activity of Cu-Zn-SOD. Recently, it has been reported that carbonate anion were potentially relevant oxidants of nucleic acids in physiological environments. In conclusion, there is solid evidence supporting the formation of many free radicals by cells leading which may play an important role in their homeostasis.
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Liu, Youjia, Malgorzata Biczysko i Nigel W. Moriarty. "A radical approach to radicals". Acta Crystallographica Section D Structural Biology 78, nr 1 (1.01.2022): 43–51. http://dx.doi.org/10.1107/s2059798321010809.
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Nitroxide radicals are characterized by a long-lived spin-unpaired electronic ground state and are strongly sensitive to their chemical surroundings. Combined with electron paramagnetic resonance spectroscopy, these electronic features have led to the widespread application of nitroxide derivatives as spin labels for use in studying protein structure and dynamics. Site-directed spin labelling requires the incorporation of nitroxides into the protein structure, leading to a new protein–ligand molecular model. However, in protein crystallographic refinement nitroxides are highly unusual molecules with an atypical chemical composition. Because macromolecular crystallography is almost entirely agnostic to chemical radicals, their structural information is generally less accurate or even erroneous. In this work, proteins that contain an example of a radical compound (Chemical Component Dictionary ID MTN) from the nitroxide family were re-refined by defining its ideal structural parameters based on quantum-chemical calculations. The refinement results show that this procedure improves the MTN ligand geometries, while at the same time retaining higher agreement with experimental data.
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Wisniak, Jaime. "Auguste Laurent. Radical and radicals". Educación Química 20, nr 2 (kwiecień 2009): 166–75. http://dx.doi.org/10.1016/s0187-893x(18)30023-5.
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Yañez Jaramillo, Lina M., Joy H. Tannous i Arno de Klerk. "Persistent Free Radicals in Petroleum". Processes 11, nr 7 (11.07.2023): 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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Nauser, Thomas, Willem H. Koppenol i Janusz M. Gebicki. "The kinetics of oxidation of GSH by protein radicals". Biochemical Journal 392, nr 3 (6.12.2005): 693–701. http://dx.doi.org/10.1042/bj20050539.
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Current studies provide evidence that proteins are initial targets of ROS (reactive oxygen species) in biological systems and that the damaged proteins can in turn damage other cell constituents. This study was designed to test the possibility that protein radicals generated by ROS can oxidize GSH and assess the probability of this reaction in vivo by measurement of the rate constant of this reaction. Lysozyme radicals were generated by hydroxyl and azide radicals in steady-state gamma ray radiolysis. In the absence of dioxygen, a range of protein carbon-centred amino acid radicals were produced by the hydroxyl radicals, and defined tryptophan radicals by the azide radicals. In the presence of dioxygen, each carbon-centred radical was converted to a protein peroxyl radical. Each of the peroxyl radicals was able to oxidize a molecule of GSH, regardless of its location in the protein. The peroxyl radicals were 10 and 20 times more effective GSH oxidants than the carbon-centred radicals produced randomly in the lysozyme, or the defined tryptophan lysozyme radicals respectively. We obtained for the first time the rate constant of reaction between a protein free-radical and GSH. Lysozyme tryptophan carbon radicals generated by nanosecond pulse radiolysis and flash photolysis oxidized GSH with a rate constant of (1.05±0.05)×105 M−1·s−1. Overall, the results are consistent with the hypothesis that protein radicals may be important intermediates in the pathway linking oxidative stress and damage in living organisms and emphasize the strongly enhancing role of dioxygen in this process.
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Folkes, Lisa K., Silvina Bartesaghi, Madia Trujillo, Peter Wardman i Rafael Radi. "Radiolysis Studies of Oxidation and Nitration of Tyrosine and Some Other Biological Targets by Peroxynitrite-Derived Radicals". International Journal of Molecular Sciences 23, nr 3 (4.02.2022): 1797. http://dx.doi.org/10.3390/ijms23031797.
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The widespread interest in free radicals in biology extends far beyond the effects of ionizing radiation, with recent attention largely focusing on reactions of free radicals derived from peroxynitrite (i.e., hydroxyl, nitrogen dioxide, and carbonate radicals). These radicals can easily be generated individually by reactions of radiolytically-produced radicals in aqueous solutions and their reactions can be monitored either in real time or by analysis of products. This review first describes the general principles of selective radical generation by radiolysis, the yields of individual species, the advantages and limitations of either pulsed or continuous radiolysis, and the quantitation of oxidizing power of radicals by electrode potentials. Some key reactions of peroxynitrite-derived radicals with potential biological targets are then discussed, including the characterization of reactions of tyrosine with a model alkoxyl radical, reactions of tyrosyl radicals with nitric oxide, and routes to nitrotyrosine formation. This is followed by a brief outline of studies involving the reactions of peroxynitrite-derived radicals with lipoic acid/dihydrolipoic acid, hydrogen sulphide, and the metal chelator desferrioxamine. For biological diagnostic probes such as ‘spin traps’ to be used with confidence, their reactivities with radical species have to be characterized, and the application of radiolysis methods in this context is also illustrated.
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ZHDANOV, R. I. "ChemInform Abstract: Nitroxyl Radicals and Non-Radical Reactions of Free Radicals". ChemInform 24, nr 31 (20.08.2010): no. http://dx.doi.org/10.1002/chin.199331310.
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Nakashima, Nobuaki, i Keitaro Yoshihara. "Oscillator Strengths of the Ultraviolet Bands of Hot and Relaxed Methallyl, Allyl, and Methyl Radicals". Laser Chemistry 7, nr 2-4 (1.01.1987): 177–96. http://dx.doi.org/10.1155/lc.7.177.
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Absorption spectra of methallyl, allyl, and methyl radicals were measured in the ArF laser flash photolysis of halogenated methanes and olefins, and 2-methyl-1-butene. Broad absorption spectra were detected immediately after excitation, indicating that the radicals carried high internal energy (called “hot” radicals here). The spectra were sharpened with time due to collisions with foreign gases and finally reached equilibrium (spectra in relaxed states). The oscillator strengths (f) of methallyl and allyl radicals were found to remain about the same for hot and relaxed states. The values (f) in the relaxed states were determined with errors of ±10% to be 0.14 for the methallyl radical, 0.26 for the allyl radical, and 1.57 × 10−2 (including the partition function) for the methyl radical. The molar extinction coefficients of the allylic radicals were 1.4–1.8 times as great as ones previously reported. Rate constants of collisional relaxation by nitrogen were discussed for seven hot radicals and molecules. Larger species gave greater rate constants. The hot methyl radical relaxed with a rate constant of 1.0 × 107s−1 in the presence of 760 Torr of nitrogen, while for the trimethylallyl radical it was 20 times as great as that of the methyl radical.
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FRANCE-JACKSON, H. "ON α-LIKE RADICALS". Bulletin of the Australian Mathematical Society 84, nr 1 (16.06.2011): 111–15. http://dx.doi.org/10.1017/s0004972711002231.
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AbstractA radical ρ is called prime-like if for every prime ring A, the polynomial ring A[x] is ρ-semisimple. Let α be a radical satisfying the polynomial equation α(A[x])=(α(A))[x] for every ring A. A radical γ is called α-like if for every α-semisimple ring A, the polynomial ring A[x] is γ-semisimple. In this paper, we study properties of α-like radicals. We show that α-likeness is a generalization of prime-likeness and extend some results concerning prime-like radicals. This allows us easily to find distinct special radicals which coincide on simple rings and on polynomial rings, which answers a question put by Ferrero.
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Luo, Jie, Xiao-Fan Rong, Yu-Yuan Ye, Wen-Zhen Li, Xiao-Qiang Wang i Wenjing Wang. "Research Progress on Triarylmethyl Radical-Based High-Efficiency OLED". Molecules 27, nr 5 (1.03.2022): 1632. http://dx.doi.org/10.3390/molecules27051632.
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Perchlorotrityl radical (PTM), tris (2,4,6-trichlorophenyl) methyl radical (TTM), (3,5-dichloro-4-pyridyl) bis (2,4,6 trichlorophenyl) methyl radical (PyBTM), (N-carbazolyl) bis (2,4,6-trichlorophenyl) methyl radical (CzBTM), and their derivatives are stable organic radicals that exhibit light emissions at room temperature. Since these triarylmethyl radicals have an unpaired electron, their electron spins at the lowest excited state and ground state are both doublets, and the transition from the lowest excited state to the ground state does not pose the problem of a spin-forbidden reaction. When used as OLED layers, these triarylmethyl radicals exhibit unique light-emitting properties, which can increase the theoretical upper limit of the OLED’s internal quantum efficiency (IQE) to 100%. In recent years, research on the luminescent properties of triarylmethyl radicals has attracted increasing attention. In this review, recent developments in these triarylmethyl radicals and their derivatives in OLED devices are introduced.
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Brown, CE, AG Neville, DM Rayner, KU Ingold i J. Lusztyk. "Kinetic and Spectroscopic Studies on Acyl Radicals in Solution by Time-Resolved Infrared Spectroscopy". Australian Journal of Chemistry 48, nr 2 (1995): 363. http://dx.doi.org/10.1071/ch9950363.
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A number of acyl radicals, RĊ=O, have been generated in hexane or di -t-butyl peroxide as solvent at room temperature by 308 nm laser flash photolysis, and their spectroscopic and kinetic properties have been examined by time-resolved infrared spectroscopy. The C=O stretching frequencies for the RĊ=O radicals are found to be higher than those of the corresponding aldehydes, RCHO, by between 108 and 128 cm-1, an effect attributed to a higher C=O bond order in the radicals. For the RĊ=O radicals some typical values of vC =O are: CH3Ċ=O, 1864 cm-1; (CH3)3CĊ=O, 1848 cm-1; and C6H5Ċ=O, 1828 cm-1, while the corresponding acylperoxyl radicals, RC(O)OO, formed by reaction with oxygen have vC =O values of 1838, 1840 and 1820 cm-1, respectively. The acyl radicals exhibit a reactivity towards a variety of substrates that is roughly comparable to that of simple alkyl radicals. For reactions of the benzoyl radical some typical rate constants/M-1 s-1 are: CCl4, 6.0x104; C6H5SH, 4.8×107; CCl3Br, 2.2×108; Tempo, 1.1×109; and oxygen, 1.8×109. Alkanoyl radicals have a rather similar reactivity to benzoyl. The propanoyl radical reacts with tributyltin deuteride with a rate constant of 3×105 M-1s-1. The hex-5-enoyl radical undergoes a 5-exo-trig cyclization to form the 2-oxocyclopentylmethyl radical with a rate constant of 2.2×105 s-1, a value which is almost identical to that for cyclization of the hex-5-enyl radical. It is hoped that our kinetic data will prove useful in the planning of organic synthetic strategies which involve acyl radical chemistry.
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Shukla, D., N. P. Schepp, N. Mathivanan i L. J. Johnston. "Generation and spectroscopic and kinetic characterization of methoxy-substituted phenoxyl radicals in solution and on paper". Canadian Journal of Chemistry 75, nr 12 (1.12.1997): 1820–29. http://dx.doi.org/10.1139/v97-615.
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A number of methoxy-substituted phenoxyl radicals have been generated and characterized by laser flash photolysis techniques in solution and on paper. The radicals have been produced by three routes in solution: hydrogen abstraction from phenols by tert-butoxyl radical, photolysis of α-aryloxyacetophenones, and direct excitation of phenols. Most of the phenoxyl radicals studied have a characteristic absorption near 400 nm; the ortho-substituted radicals have an additional broad absorption in the visible in non-hydroxylic solvents (e.g., 650 nm for 2-methoxyphenoxyl radical). The relative intensities of the 400 nm and the long-wavelength bands vary with substitution pattern and solvent, with the long wavelength band being much weaker in hydroxylic solvents. Direct excitation of phenols provides an alternate source of phenoxyl radicals in some cases. However, for 4-methoxyphenol there are overlapping absorptions due to triplet phenol and phenol radical cation, both of which absorb in the 400–460 nm region. The 4-methoxyphenol radical cation is formed in a biphotonic process and decays by deprotonation to give the phenoxyl radical. The 4-methoxyphenoxyl radical can also be generated on paper from either the ketone or phenol precursor and decays with complex kinetics that depend on the precursor loading and laser intensity. There is no evidence for the formation of significant amounts of long-lived ketone or phenol triplets on paper. The decay kinetics for the phenoxyl radical are modified by the addition of the radical scavenger dithioerythritol. The results indicate both static and dynamic components to the radical scavenging process. The generation of phenoxyl radicals on paper in the presence and absence of scavengers provides the basis for the development of a new method for screening potential photoyellowing inhibitors and understanding their mode of action. Keywords: phenoxyl radicals, paper photoyellowing, laser flash photolysis, triplets, radical cations.
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Abedinzadeh, Z. "Sulfur-centered reactive intermediates derived from the oxidation of sulfur compounds of biological interest". Canadian Journal of Physiology and Pharmacology 79, nr 2 (1.02.2001): 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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Lankin, V. Z., O. I. Shadyro, K. B. Shumaev, K. B. Shumaev, A. K. Tikhaze i A. A. Sladkova. "Non-Enzymatic Methylglyoxal Formation From glucose Metabolites and Generation of Superoxide Anion Radical During Methylglyoxal-Dependent Cross-Links Reaction". Journal of Antioxidant Activity 1, nr 4 (25.09.2019): 33–45. http://dx.doi.org/10.14302/issn.2471-2140.jaa-19-2997.
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The paper explores the formation of a-oxoaldehydes during the interaction of glucose metabolites with hydroxyl or alkoxyl radicals. Hydroxyl radicals were generated under radiolysis of aqueous solutions, and alkoxyl radicals (t-BuO) were obtained in the model system tert-butyl hydroperoxide/Fe2+. High-performance liquid chromatography revealed that methylglyoxal was one of the organic products resulting from t-BuO-induced transformations of fructose-1,6-bisphosphate under hypoxic conditions. The interaction of lysine and methylglyoxal one of the main targets of a-oxoaldehydes in proteins was also studied. As chemiluminescence and EPR spectroscopy demonstrated, this reaction generates a methylglyoxal anion radical, a cation-radical of methylglyoxal dialkylamine and a superoxide anion radical. EPR signal of methylglyoxal-derived free radicals was observed in hypoxia, whereas only the trace amounts of these free radicals were recorded in the aerated reaction medium.
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Ho, Connie Suk-Han, Ting-Ting Ng i Wing-Kin Ng. "A “Radical” Approach to Reading Development in Chinese: The Role of Semantic Radicals and Phonetic Radicals". Journal of Literacy Research 35, nr 3 (wrzesień 2003): 849–78. http://dx.doi.org/10.1207/s15548430jlr3503_3.
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Two studies investigating the significance of radical knowledge in Chinese reading development are reported in this paper. Study 1 examined the semantic radical knowledge of 20 Grade 1, 20 Grade 3, and 20 Grade 5 Chinese children in Hong Kong. It was found that various types of semantic radical knowledge, including the position and semantic category of semantic radicals, correlated significantly with Chinese word reading and sentence comprehension. Study 2 examined phonetic radical knowledge with another three groups of 20 Chinese children in Grades 1, 3, and 5 respectively. It was found that various measures of phonetic radical knowledge, including the function and sound value of phonetic radicals, correlated significantly with Chinese word reading. These studies found that, developmentally, the children started acquiring the knowledge of character structure, position, semantic category, and sound value of radicals from about Grade 1. However, they did not understand that the function of semantic radicals is to provide meaning cues in reading until Grade 3. The authors concluded that the radical is an important orthographic processing unit in reading development in Chinese.
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Davies, M. J., i T. F. Slater. "Studies on the photolytic breakdown of hydroperoxides and peroxidized fatty acids by using electron spin resonance spectroscopy. Spin trapping of alkoxyl and peroxyl radicals in organic solvents". Biochemical Journal 240, nr 3 (15.12.1986): 789–95. http://dx.doi.org/10.1042/bj2400789.
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Spin trapping using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) has been used to detect and distinguish between the carbon-centred, alkoxyl, and peroxyl radicals produced during the photolytic decomposition of hydroperoxides. Photolysis of tert-butyl and cumene hydroperoxides, and peroxidized fatty acids, in toluene, with low levels of u.v. light, is shown to lead to the initial production of alkoxyl radicals by homolysis of the oxygen-oxygen bond. Subsequent reaction of these radicals with excess hydroperoxide leads, by hydrogen abstraction, to the production of peroxyl radicals that can be detected as their corresponding adducts with the spin trap. Subsequent breakdown of these adducts produces alkoxyl radicals and a further species that is believed to be the oxidized spin-trap radical 5,5-dimethyl-1-pyrrolidone-2-oxyl. No evidence was obtained at low hydroperoxide concentrations, with either the cumene or lipid alkoxyl radicals, for the occurrence of beta-scission reactions; the production of low levels of carbon-centred radicals is believed to be due to the alternative reactions of hydrogen abstraction, ring closure, and/or 1,2 hydrogen shifts. Analogous experiments with 3,3,5,5-tetramethyl-1-pyrroline N-oxide (TMPO) led only to the trapping of alkoxyl radicals with no evidence for peroxyl radical adducts, this is presumably due to a decreased rate of radical addition because of increased steric hindrance.
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ZEE, Jolanda Van der. "Formation of peroxide- and globin-derived radicals from the reaction of methaemoglobin and metmyoglobin with t-butyl hydroperoxide: an ESR spin-trapping investigation". Biochemical Journal 322, nr 2 (1.03.1997): 633–39. http://dx.doi.org/10.1042/bj3220633.
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The reaction of human methaemoglobin and horse metmyoglobin with t-butyl hydroperoxide (t-BuOOH) was investigated with the ESR spin-trapping technique. With the spin trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO) the formation of peroxyl, alkoxyl and methyl radicals derived from t-BuOOH could be detected. The relative contributions of these radicals were determined at various DMPO concentrations by computer simulation. From these data it could be concluded that the alkoxyl radical was the initial radical produced, which indicates that the hydroperoxide is cleaved homolytically. Further investigations, with the nitroso spin trap 2-methyl-2-nitrosopropane (MNP), showed the formation of globin-centred radicals. Non-specific proteolysis of the MNP adducts revealed isotropic three-line spectra, which means that the radical adducts were centred on a tertiary carbon with no bonds to a hydrogen or nitrogen. Comparison with MNP adducts of several amino acids indicated that in methaemoglobin the radical adduct was most probably located on a valine residue. With metmyoglobin the same adduct was obtained, whereas an additional adduct could be assigned to a tyrosyl radical. These protein radicals most probably resulted from hydrogen abstraction by the metal–oxo species, formed by heterolytic cleavage of the hydroperoxide. These results therefore show that homolytic cleavage of the hydroperoxide leads to the formation of peroxide-derived radicals, whereas concurrent heterolytic cleavage results in protein-derived radicals.
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BIRKENMEIER, GARY F., HENRY E. HEATHERLY i ENOCH K. S. LEE. "SPECIAL RADICALS FOR NEAR-RING". Tamkang Journal of Mathematics 27, nr 4 (12.10.2020): 281–88. http://dx.doi.org/10.5556/j.tkjm.27.1996.3956.
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The concept of a special radical for near-rings has been treated in several nonequivalent, but related, ways in the recent literature. We use the version due to K. Kaarli to establish that various prime radicals and the nil radical are special radicals on the class A of all near-rings which satisfy an extended version of the Andrunakievich Lemma. Since A includes all d.g. near-rings—and much more—these results significantly extend results previously obtained by Kaarli and by Groenewald. We also obtain special radical results for the Jacobson type radicals 30 and 3 1 , albeit on less extensive classes. Examples are given which illustrate and delimit the theory developed.
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Han, Zhen Xing, Bing Wu, Ian Brown, Mark Beck i Srini Raghavan. "Detection of HO2•/O2•- Radicals Formed in Aqueous Solutions Irradiated with Megasonic Waves Using a Cavitation Threshold (CT) Cell Set-Up". Solid State Phenomena 219 (wrzesień 2014): 170–73. http://dx.doi.org/10.4028/www.scientific.net/ssp.219.170.
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Acoustic cavitation, especially transient cavitation, in solutions is accompanied by a number of physical and chemical effects. Due to high temperature and pressure conditions inside bubbles at their collapse, excitation of various species as well as formation of radicals occurs in solution [1-4]. Water molecules excited by megasonic irradiation typically dissociate to hydrogen and hydroxyl radicals (H• and OH•) [5]. The hydroxyl radical is a strong oxidant while the hydrogen radical has reducing properties. In presence of O2 in the solution, H• reacts with O2 to form hydroperoxyl (HO2•) radicals, which act as a reducing as well as a (weak) oxidizing agent [6]. Dissociation of hydroperoxyl radicals result in the formation of superoxide anion radicals (O2•-) as follows [6]:
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Yan, Xu, Lihua Zhang, Qian Liu, Guan Wang, Xiaofei Liu i Wantai Yang. "A novel radical polymerization system initiated by a redox reaction with NHPI and xanthone". Polym. Chem. 8, nr 41 (2017): 6356–61. http://dx.doi.org/10.1039/c7py01329a.
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A novel redox reaction system consisting of xanthone (XT) andN-hydroxyphthalimide (NHPI) for radical polymerization is developed where NHPI and XT experience a one-electron-transfer reaction, which produces two kinds of radicals, PINO radicals and cycloketyl (CK) radicals.
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Walton, John, i Ffrancon Williams. "The Games Radicals Play: Special Issue on Free Radicals and Radical Ions". Molecules 20, nr 2 (9.02.2015): 2831–34. http://dx.doi.org/10.3390/molecules20022831.
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Sueishi, Yoshimi, Daisuke Yoshioka, Shigeru Oowada, Nobuyuki Endoh, Shunji Kohri, Hirotada Fujii, Masashi Shimmei i Yashige Kotake. "Is the Oxygen Radical Absorbance Capacity (ORAC) Method a Peroxyl-radical Scavenging Assay?" Zeitschrift für Physikalische Chemie 224, nr 06 (1.07.2010): 921–28. http://dx.doi.org/10.1524/zpch.2010.5536.
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AbstractThe oxygen radical absorbance capacity (ORAC) method employs a water soluble azo-radical initiator, AAPH (2,2’-azobis(2-amidinopropane) dihydrochloride) as a free radical generator, by which the fluorescent probe fluorescein is damaged to result in the loss of fluorescence. Antioxidants can protect the probe from the damage and the degree of protection is quantified. Because AAPH has been used as a lipid-peroxidation reagent, “oxygen radical” in ORAC is generally accepted as peroxyl radicals; however, in the present spin trapping experiments using a newly developed spin trap, CYPMPO, there was no indication of peroxyl-radical formation in AAPH decomposition in aqueous media. These spin trapping studies demonstrated that alkoxyl (RO·) radical adduct was the sole product of AAPH decomposition. In contrast, alkyl-peroxyl (ROO·) radical was spin-trapped during the decomposition of a lipid soluble azo-radical initiator AIBN (azobis(isobutyronitrile)) in non-aqueous media. We speculate that alkyl-peroxyl radicals are short-lived in water, rapidly converted into alkoxyl radicals. Although the possibility that ORAC method monitors peroxyl-radical scavenging activity cannot be completely eliminated, spin trapping evidence strongly indicates that ORAC method is a scavenging capacity assay for alkoxyl radicals.
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Saran, Manfred, Christa Michel i Wolf Bors. "Radical Functions in vivo: A Critical Review of Current Concepts and Hypotheses". Zeitschrift für Naturforschung C 53, nr 3-4 (1.04.1998): 210–27. http://dx.doi.org/10.1515/znc-1998-3-411.
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Abstract Most of the basic knowledge about radical reactions comes from radiation chemical studies in vitro. In view of the rapidly increasing knowledge on radical reaction in vivo, it is important to reconcile the fundamental physico-chemical reaction characteristics of radicals with the need to explain their alleged biological effects. Severe problems in the understanding of their in vivo action remain unsolved. An example is phagocytosis, which seems to be a paradigm of a ‘deleterious’ radical process. The exact mechanism is not clear; so it is an open question whether the intruder is eventually killed by radicals (like OH) or by endproducts of radical reactions (like H2O2 and/or HOCl). It is even more difficult to understand signalling by radicals: owing to their chemical nature they are ‘unspecifically’ reacting species -they with draw or add electrons-and thus their reactions are governed by redox-properties. Since all radicals have different redox characteristics and different molecular shapes, the usual key-and-keyhole picture for molecular interaction does not apply, as there, is no reactive site conceivable which has the property of reacting with radicals ‘specifically. Our intent in this article is: (i) to briefly review some fundamental characteristics of in vitro radical reactions, (ii) to extrapolate from this to the conditions in vivo, and (iii) to discuss current hypotheses concerning the redox-regulation of cellular signalling. This leads us to the tentative conclusion that radicals per se must be tolerated by the cell and do not threaten its life, if they stay below a certain concentration limit. The main biologi cal implication of radical-reactions seems to be that the cell derives signals from the balance of oxidative versus reductive processes and that radicals may interact with pathways of intra-and intercellular communication.
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Wang, Degui, Heinz-Peter Schuchmann i Clemens von Sonntag. "Phenylalanine: Its ˙OH and SO4˙⁻-Induced Oxidation and Decarboxylation. A Pulse Radiolysis and Product Analysis Study". Zeitschrift für Naturforschung B 48, nr 6 (1.06.1993): 761–70. http://dx.doi.org/10.1515/znb-1993-0610.
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Phenylamine has been oxidized by radiolytically generated hydroxyl and sulfate radicals, the ensuing intermediates and their reactions have been studied by pulse radiolysis and product analysis in the absence and presence of oxidants such as Fe(CN)63- and O2. Upon OH radical attack, hydroxycyclohexadienyl-type radicals are mainly formed while Η-abstraction reactions can be neglected. In the presence of Fe(CN)63- these radicals are for the most part oxidized to the corresponding tyrosines (80%), except for the ipso-OH-adduct radicals (≈ 20%). It is concluded that ˙OH-addition is almost random, but with a slight avoidance of the metaposition relative to the ortho-, para- and ipso-positions. Oxygen adds reversibly to the OH-adduct radicals (kf = 1.8 × 108 dm3 mol-1 s-1, kr = 5.4 × 104 s-1). In this case, tyrosine formation occurs by HO2˙-elimination. However, due to side reactions, tyrosine formation only reaches 52% of the OH radical yield. The tyrosine yield drops to 10% in the absence of an oxidant.Upon SO4˙⁻-attack, decarboxylation becomes a major process (33% of SO4˙⁻) alongside the production of tyrosines (43%). Here, with Fe(CN)63- as the oxidant the formation of p-Tyr (18.5%) and m-Tyr (16.5%) is preferred over o-Tyr formation (8.5%). It is believed that in analogy to other systems a radical cation is formed immediately upon SO4˙⁻-attack which either reacts with water under the formation of hydroxycyclohexadienyl-type (“OH-adduct”) radicals, or decarboxylates after intramolecular electron transfer. The radical cation can also arise indirectly through H+-catalysed water elimination from the ˙OH-adduct radicals. At pH 2 and a dose rate of 0.0046 Gy s-1 CO2 formation matches the OH radical yield when ˙OH is the attacking radical. Below pH 2, G(CO2) decreases with falling pH. This indicates the occurrence of another, unimolecular, pathway under these conditions competing effectively with decarboxylation. This appears to be a relatively slow deprotonation reaction of the carboxylprotonated phenylalanine radical cation which gives rise to the benzyl-type radical.
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Kozmon, Stanislav, i Igor Tvaroška. "DFT Study on 3-Substituted Tetrahydropyran-2-yl Radicals". Collection of Czechoslovak Chemical Communications 71, nr 10 (2006): 1453–69. http://dx.doi.org/10.1135/cccc20061453.
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A series of tetrahydropyran-2-yl radical (1) analogs was studied using density functional theory (DFT) to model conformational behavior of glycopyranosyl radicals. Calculations of the structure and stability of the 4C1, 1C4, B2,5, O,3B, and 4H3 ring conformers for tetrahydropyran-2-yl radical (1) and for 3-fluoro- (2, 7), 3-hydroxy- (3, 8), 3-methoxy- (4, 9), 3-acetoxy- (5, 10), and 3-(benzyloxy)tetrahydropyran-2-yl (6, 11) derivatives showed that conformational behavior of the 3-substituted radicals depends on both the electronic character and orientation of the C3 substituent. The calculations show that radical 1 is slightly pyramidal and exists as an equilibrium mixture of the 4C1 and 1C4 conformers. Substituents at the C3 position force 2-11 radicals to adopt a chair conformation with the substituent in the axial orientation. Thus radicals 2-6 prefer the 1C4 conformer though there are several ring conformers in equilibrium whereas for radicals 7-11 the 4C1 conformer predominates. The calculated preferences are consistent with available ESR data. These results provide further support for the importance of quasi-homoanomeric interactions on stability of anomeric radicals.
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Mathew, Lukose, Emmanuel Y. Osei-Twum i John Warkentin. "Thermolysis of α-hydroperoxyalkyl diazenes. Spin trapping of radical intermediates and spin trapping kinetics". Canadian Journal of Chemistry 69, nr 9 (1.09.1991): 1398–402. http://dx.doi.org/10.1139/v91-206.
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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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Too, Pei Chui, Ya Lin Tnay i Shunsuke Chiba. "Copper-catalyzed aerobic aliphatic C–H oxygenation with hydroperoxides". Beilstein Journal of Organic Chemistry 9 (25.06.2013): 1217–25. http://dx.doi.org/10.3762/bjoc.9.138.
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We report herein Cu-catalyzed aerobic oxygenation of aliphatic C–H bonds with hydroperoxides, which proceeds by 1,5-H radical shift of putative oxygen-centered radicals (O-radicals) derived from hydroperoxides followed by trapping of the resulting carbon-centered radicals with molecular oxygen.
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Han, Zhen Xing, Srini Raghavan i Mark Beck. "Estimation of the Generation Rate of H· Radicals in a Megasonic Field Using an Electrochemical Technique". Solid State Phenomena 314 (luty 2021): 181–85. http://dx.doi.org/10.4028/www.scientific.net/ssp.314.181.
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Radical formation and detection in aqueous solutions under acoustic irradiation are important during wet cleaning processes in semiconductor industries. Oxidizing radicals such as hydroxyl and hydroperoxyl radicals have been widely studied and characterized using fluorescence and chemiluminescence methods. Hydrogen radicals, which are strongly reducing in nature, have not received much attention. In this study, the rate of hydrogen radical generation in a megasonic field (0.93 MHz) was measured using an electrochemical technique. Specifically, the method is based on the reduction of cupric ions to cuprous chloride complex by the hydrogen radicals in the presence of an excess of chloride ions. This is followed by chronoamperometric determination of the oxidation of cuprous chloride complex back to cupric ions. Hydrogen radical generation rate was measured at different megasonic power densities.
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Ilić-Georgijević, Emil. "On graded special radicals of graded rings". Journal of Algebra and Its Applications 17, nr 06 (23.05.2018): 1850109. http://dx.doi.org/10.1142/s0219498818501098.
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In this paper, a graded ring is a ring which is the direct sum of a family of its additive subgroups indexed by a nonempty set under the assumption that the product of homogeneous elements is again homogeneous. We study graded special radicals and special radicals of graded rings, but which contain the corresponding Jacobson radicals. There are two versions of this graded radical, which we name the graded over-Jacobson and the large graded over-Jacobson radical. We establish several characterizations of the graded over-Jacobson radical of a graded ring and also prove that the largest homogeneous ideal contained in the corresponding classical radical of a graded ring coincides with the large graded over-Jacobson radical of that ring.
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Ohmi, H., K. Ichihara i Y. Abiko. "Role of oxygen radicals in canine myocardial metabolic derangement during regional ischemia". American Journal of Physiology-Heart and Circulatory Physiology 262, nr 2 (1.02.1992): H553—H561. http://dx.doi.org/10.1152/ajpheart.1992.262.2.h553.
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To clarify the role of oxygen radicals in the development of myocardial injury during ischemia, production of lipid peroxides mediated by oxygen radicals was determined in in vivo dogs subjected to regional ischemia and reperfusion. Myocardial injury was assessed by derangement in energy and carbohydrate metabolism caused by ischemia and reperfusion. The production of lipid peroxides mediated by oxygen radicals considerably increased not only during reperfusion after ischemia but also during ischemia. Removal of oxygen radicals by administration of radical scavengers [recombinant human superoxide dismutase + catalase or N-(2-mercaptopropionyl)glycine] completely prevented the increase in production of lipid peroxides during ischemia. However, the radical scavengers did not attenuate the myocardial energy and carbohydrate metabolic derangements caused by ischemia and reperfusion after ischemia. These results suggest that significant amounts of oxygen radicals are generated during ischemia as well as during reperfusion and that the oxygen radicals and subsequent lipid peroxidation are not major factors in development of myocardial injury during either ischemia or reperfusion after ischemia.