Articoli di riviste: "Hydroxyle radical"

1

Zylber, Jean, Nicole Zylber, Daniel Lefort, Christiane Ferradini e Bernard Hickel. "Régiosélectivité de la réaction des radicaux hydroxyle et hydroxy-2 propyle-2 avec l'hypoxanthine". Canadian Journal of Chemistry 66, n. 2 (1 febbraio 1988): 283–87. http://dx.doi.org/10.1139/v88-048.

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The reactivity of [Formula: see text] and (CH3)2ĊOH radicals with hypoxanthine was studied under comparable γ-irradiation conditions. A difference in regioselectivity of attack by the electrophilic [Formula: see text] radical and the nucleophilic (CH3)2ĊOH radical is observed, the latter leading in 70% yield to a C-8 substituted product. The rate constants of the addition of the radical to hypoxanthine were determined by pulse radiolysis to be k = 1.4 × 108 M−1 s−1 in acid medium, and in neutral medium k = 7 × 105 M−1 s−1. The much more reactive [Formula: see text] radical leads essentially to degradation products arising, interalia, from attack on C-2 (resulting in the formation of xanthine, which disappears rapidly), while attack at C-8, approximately three times less rapid, leads to the6,8-diketo purine, which does not undergo further reactions and thus accumulates in the medium. [Journal translation]

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Gallard, H., J. De Laat e B. Legube. "Étude comparative de la vitesse de décomposition de H2O2 et de l'atrazine par les systèmes Fe(III)/H2O2, Cu(II)/H2O2 et Fe(III)/Cu(II)/H2O2". Revue des sciences de l'eau 12, n. 4 (12 aprile 2005): 713–28. http://dx.doi.org/10.7202/705374ar.

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Cette étude a eu pour objectif de comparer les vitesses de décomposition du peroxyde d'hydrogène et d'oxydation de l'atrazine par les systèmes catalytiques Fe(III)/H2O2, Cu(II)/H2O2, et Fe(III)/Cu(II)/H2O2. Les expériences ont été réalisées à pH 3,0, à une température de 25,0 (± 0,2) °C, en milieu perchlorate, en présence et en absence d'oxygène dissous. L'étude comparative a confirmé que les vitesses de décomposition de H2O2 et d'oxydation de l'atrazine sont beaucoup plus lentes en présence de Cu(II) qu'en présence de Fe(III) et l'addition de Cu(II) augmente l'efficacité du système Fe(III)/H2O2. Pour nos conditions expérimentales ([composé organique]o < 1 µM) les expériences de cinétique compétitive, réalisées avec des solutions aqueuses contenant trois composés organiques (atrazine, 1,2,4-trichlorobenzène, 2,5-dichloronitrobenzène), ont montré que le radical hydroxyle représente la principale espèce responsable de l'oxydation des composés organiques. Les résultats ont également mis en évidence la formation très rapide d'un composé entre Cu(II) et H2O2 (étude spectrophotométrique) et ont montré l'importance de la concentration en oxygène dissous sur les vitesses globales de décomposition de H2O2 et de l'atrazine par les systèmes Cu(II)/H2O2 et Fe(III)/Cu(II)/H2O2.

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Zheng, Cheng-Dong, Gang Li, Hu-Qiang Li, Xiao-Jing Xu, Jin-Ming Gao e An-Ling Zhang. "DPPH-Scavenging Activities and Structure-Activity Relationships of Phenolic Compounds". Natural Product Communications 5, n. 11 (novembre 2010): 1934578X1000501. http://dx.doi.org/10.1177/1934578x1000501112.

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Thirty-eight phenolic compounds (including 31 flavonoids) were examined for their DPPH radical-scavenging activities, and structure-activity relationships were evaluated. Specifically, the presence of an Ortho-dihydroxyl structure in phenolics is largely responsible for their excellent antiradical activity. 3-Hydroxyl was also essential to generate a high radical-scavenging activity. An increasing number of hydroxyls on flavones with a 3′,4′-dihydroxyl basic structure, the presence of a third hydroxyl group at C-5′, a phloroglucinol structure, glycosylation and methylation of the hydroxyls, and some other hydroxyls, for example 5-, and 7-hydroxyl in ring A, decreased the radical-scavenging activities of flavonoids and other phenolics.

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Rhim, Tae-Jin, Hee-Sun Jeong, Young-Jin Kim, Doo-Young Kim, Young-Ju Han, Hae-Yon Kwon e Ki-Rok Kwon. "A study on the comparison of antioxidant effects among cultivated ginseng, and cultivated wild ginseng extracts -Using the measurement of superoxide and hydroxy radical scavenging activities-". Journal of Korean Institute of Herbal Acupuncture 12, n. 2 (30 giugno 2009): 7–12. http://dx.doi.org/10.3831/kpi.2009.12.2.007.

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Choi, Jeong-Hwan, Dong-Hun Shin, Hye-Bin Kim, Jong-Gook Kim e Kitae Baek. "One-step Oxidation of Total Organic Carbon, Total Nitrogen, and Total Phosphorous using Wet Chemical Oxidation". Journal of Korean Society of Environmental Engineers 42, n. 12 (31 dicembre 2020): 603–9. http://dx.doi.org/10.4491/ksee.2020.42.12.603.

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Objective:This study proposed the simultaneous multi-oxidation of total organic carbon, total nitrogen, and total phosphorous using modified wet chemical oxidation method.Methods:The multi oxidation process was based on the dual radical system with sulfate and hydroxyl radicals. The sodium persulfate (Na2S2O8) and sodium hydroxide (NaOH) were activated at 40℃ and UV irradiation with 254 nm to generate the sulfate radical and hydroxyl radical. The organic matters were oxidized by the dual radicals, and TOC, TN, and TP values were compared with the control group.Results and Discussion:The dual radical system oxidized organic carbon to carbon dioxide effectively, and the TOC values were similar to the value obtained from the high-temperature combustion technique. However, the residual persulfate after oxidation process interfered the absorbance for TN and inhibit the complexation in TP measurement. The residual persulfate was effectively converted to sulfate by longer heating and UV irradiation, and the interferences were more sensitive to reaction temperature than UV irradiation time. As a result, a higher temperature condition was more effective and enhanced the applicability of multi-oxidation.Conclusions:The multi oxidation of TOC, TN, and TP was demonstrated by wet chemical oxidation, and the proposed method is expected to secure the sample and reduce the analytic time. However, the more suitable condition to enhance the accuracy of TOC, TN, and TP in the multi-oxidation system should be studied further.

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Vrecko, Karoline, e Gilbert Reibnegger. "Influence of 7,8 Dihydroneopterin and Hyperoxia on Neurite Growth and Tyrosine Hydroxylase Activity of PC 12 Cells". Pteridines 13, n. 3 (agosto 2002): 94–99. http://dx.doi.org/10.1515/pteridines.2002.13.3.94.

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Abstract The influence of dihydroneopterin on tyrosine hydroxylase activity in PC 12 cells was investigated under normoxic and hyperoxic conditions, and with or without iron ions in the incubation medium. Low dihydroneopterin concentrations as well as hyperoxia increase tyrosine hydroxylase activity. Due to a too vigorous radical formation, high dihydroneopterin concentrations lead to a decrease of tyrosine hydroxylation in normoxic state and even more strongly in hyperoxic state. Similar depression of tyrosine hydroxylase activity was seen after addition of iron ions, which can form hydroxyl radicals by a Fenton type reaction. As higher iron concentrations in combination with dihydroneopterin do not suppress tyrosine hydroxylase activity completely, we conclude that dihydroneopterin and iron ions react with each other resulting in neutralisation of their effects. In conclusion, 7,8 dihydroneopterin can modulate tyrosine hydroxylase activity and its effects are dependent on concentration of oxygen as well as presence or absence of iron ions.

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7

Duwe, A. K., J. Werkmeister, J. C. Roder, R. Lauzon e U. Payne. "Natural killer cell-mediated lysis involves an hydroxyl radical-dependent step." Journal of Immunology 134, n. 4 (1 aprile 1985): 2637–44. http://dx.doi.org/10.4049/jimmunol.134.4.2637.

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Abstract The role of oxygen radicals in lysis of K562 target cells by human natural killer (NK) cells was determined by addition of scavengers of these free radicals. Lysis was greatly reduced under hypoxic conditions. Superoxide dismutase and cytochrome c, scavengers of superoxide anions, and catalase and scavengers of hypochlorite had no effect on lysis. Of 15 hydroxyl radical scavengers tested, 13 inhibited lysis. These were not toxic, because cell morphology and spontaneous chromium release were not affected and preculture with scavengers was not inhibitory. These scavengers differed widely in structure, but degree of inhibition of lysis correlated with their rate constants (k) for reaction with hydroxyl radical (k vs log inhibitor concentration required to decrease lysis by 50%: r = -0.9202, p less than 0.001), showing that inhibition was due to inactivation of the hydroxyl radical. Target cell binding was not reduced at concentrations that inhibited lysis. Inhibitors of the lipoxygenase pathway also decreased lysis, suggesting this pathway to be the source of hydroxyl radicals. In view of the reported requirements for hydroxyl radical-mediated lipid peroxidation for optimal secretory activity in a number of cell types, it appears that the generation of hydroxyl radicals by NK cells is required for delivery of cytotoxic factors.

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8

Gebicka, L., e J. L. Gebicki. "Scavenging of oxygen radicals by heme peroxidases." Acta Biochimica Polonica 43, n. 4 (31 dicembre 1996): 673–78. http://dx.doi.org/10.18388/abp.1996_4463.

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The reactions of two heme peroxidases, horseradish peroxidase and lactoperoxidase and their compounds II (oxoferryl heme intermediates, Fe(IV) = O or ferric protein radical Fe(III)R.) and compounds III (resonance hybrids [Fe(III)-O2-. Fe(II)-O2] with superoxide radical anion generated enzymatically or radiolytically, and with hydroxyl radicals generated radiolytically, were investigated. It is suggested that only the protein radical form of compound II of lactoperoxidase reacts with superoxide, whereas compound II of horseradish peroxidase, which exists only in oxoferryl form, is unreactive towards superoxide. Compound III of the investigated peroxidases does not react with superoxide. The lactoperoxidase activity loss induced by hydroxyl radicals is closely related to the loss of the ability to form compound I (oxoferryl porphyrin pi-cation radical, Fe(IV) = O(Por+.) or oxoferryl protein radical Fe(IV) = O(R.)). On the other hand, the modification of horseradish peroxidase induced by hydroxyl radicals has been reported to cause also restrictions in substrate binding (Gebicka, L. & Gebicki, J.L., 1996, Biochimie 78, 62-65). Nevertheless, it has been found that only a small fraction of hydroxyl radicals generated homogeneously does inactivate the enzymes.

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9

Bi, Yong Guang, e Chun Chun Liu. "Study on Scavenging Free Radical Activity with Polysaccharides Materials in Chuanxiong Based on Composite Properties of Biomaterials". Advanced Materials Research 583 (ottobre 2012): 244–47. http://dx.doi.org/10.4028/www.scientific.net/amr.583.244.

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By using spectrophotometric detection of the Chuanxiong polysaccharides on the free radical scavenging. The results show that the Chuanxiong polysaccharides on DPPH radical, hydroxyl radical (HO•) and superoxide anion radical (•) clearance. Scavenging ability with the the Chuanxiong polysaccharide concentration increased, and showed the dose-effect relationship. Concentration of 2.0mg/mL when DPPH radicals clear the rate of 35.61%, while the rate of hydroxyl radicals and superoxide anion radical scavenging, clear the rate of 57.78% and 57.14%. Chuanxiong polysaccharide is an ideal natural antioxidants and good prospects for the development of biomedical composites.

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10

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

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

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11

Carlsson, Magnus, David Stenman, Gábor Merényi e Torbjörn Reitberger. "A comparative study on the degradation of cotton linters induced by carbonate and hydroxyl radicals generated from peroxynitrite". Holzforschung 59, n. 2 (1 febbraio 2005): 132–42. http://dx.doi.org/10.1515/hf.2005.020.

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Abstract Carbonate (CO3 •−) and hydroxyl (HO•) radicals were chemically produced in cotton linter suspensions using peroxynitrite as a radical precursor. Both radicals could degrade cotton linters, as shown by viscosity and GPC-SEC measurements. As evidenced by the viscosity measurements, the presence of oxygen during the cotton linter treatments slightly increased cellulose degradation by both radicals. For the carbonate radical, more than 90% of the viscosity losses could be recovered by reductive NaBH4 treatment before measuring the viscosity, whereas only approximately 40% of the viscosity was recovered after hydroxyl radical degradation and subsequent NaBH4 treatment. This indicates that carbonate radicals mainly abstract H-atoms adjacent to hydroxyl groups, i.e., at C2, C3 and C6. This intramolecular selectivity may reflect a polar effect, whereby hydrogen atom abstractions from these positions are favoured. In addition, abstraction at C6 would be sterically and statistically favoured.

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Haire, D. Larry, Yashige Kotake e Edward G. Janzen. "An EPR/ENDOR study of aminoxyls (nitroxides) capable of intramolecular bonding: hydroxyalkyl radical spin adducts of nitrones". Canadian Journal of Chemistry 66, n. 8 (1 agosto 1988): 1901–11. http://dx.doi.org/10.1139/v88-307.

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A comparison of the effect of solvent and 13C labeling (of the radical addend) on the EPR (electron paramagnetic resonance) spectra of hydroxyalkyl vs. alkyl radical adducts of α-phenyl-N-tert-butyl nitrone (PBN) and 5,5-dimethyl-1-pyrroline-1-oxide (DMPO) has been investigated. The solution ENDOR spectra in toluene and in ethanol are the first examples studied of aminoxyls with hydroxyl substituents in close proximity to the free radical centre. Diastereomeric mixtures of hydroxyalkyl radical adducts are clearly resolved by ENDOR spectroscopy. Conformations of these radicals have been assigned based on the 1H and 13C hyperfine splittings (HFS's) and by differential optimum ENDOR temperatures. Definitive assignments of carbon-centered radical adducts of DMPO and PBN are shown to be feasible by monitoring the β-13C HFS's of the radical addend. Long-range γ-H HFS's from the added radical group can be observed when the deuterated spin trap PBN-d14 is used. The production of 13C labeled hydroxyalkyl adducts of nitrones (e.g., DMPO–13CH2OH, from the reaction of hydroxyl radicals with added 13CH3OH) is shown to be useful as an improved EPR spectroscopic method for the verification of the presence of hydroxyl radicals.

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Zuofa Zhang, Jie Jin e Liangen Shi. "Antioxidant Properties of Ethanolic Extract from Ramulus mori (Sangzhi)". Food Science and Technology International 15, n. 5 (ottobre 2009): 435–44. http://dx.doi.org/10.1177/1082013209350277.

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The antioxidant properties and total phenolic contents of four fractions of ethanolic extract from Ramulus mori were examined. Various experimental models including superoxide radical, hydroxyl radical, 1,1-diphenyl-2-picrylhydrazyl radicals (DPPH) scavenging activity, metal chelating activity, and reducing power were used for characterization of their antioxidant activity. The four fractions showed various degrees of efficacy in each assay in a dose-dependent manner. The third fraction with the highest amount of total phenolics was the most potent antioxidant in all assays used. In addition, the most powerful compound (oxyresveratrol) was isolated and identified followed by on-line HPLC method and characterized by different spectral analysis. Oxyresveratrol exhibited impressive antioxidant activities in scavenging the superoxide radical, hydroxide radical, and DPPH. On the basis of the results obtained, Ramulus mori may serve as a potential source of natural antioxidant due to its significant antioxidant activity and oxyresveratrol may be the most powerful antioxidant in ethanolic extracts of Ramulus mori.

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Utsumi, Hideo, Sang-Kuk Han e Kazuhiro Ichikawa. "Enhancement of hydroxyl radical generation by phenols and their reaction intermediates during ozonation". Water Science and Technology 38, n. 6 (1 settembre 1998): 147–54. http://dx.doi.org/10.2166/wst.1998.0247.

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Generation of hydroxyl radicals, one of the major active species in ozonation of water was directly observed with a spin-trapping/electron spin resonance (ESR) technique using 5,5-dimethyl-1-pyrrolineN-oxide (DMPO) as a spin-trapping reagent. Hydroxyl radical were trapped with DMPO as a stable radical, DMPO-OH. Eighty μM of ozone produced 1.08 X 10-6M of DMPO-OH, indicating that 1.4% of •OH is trapped with DMPO. Generation rate of DMPO-OH was determined by ESR/stopped-flow measurement. Phenol derivatives increased the amount and generation rate of DMPO-OH, indicating that phenol derivatives enhance •OH generation during ozonation of water. Ozonation of 2,3-, 2,5-, 2,6-dichlorophenol gave an ESR spectra of triplet lines whose peak height ratio were 1:2:1. ESR parameters of the triplet lines agreed with those of the corresponding dichloro-psemiquinone radical. Ozonation of 2,4,5- and 2,4,6-trichlorophenol gave the same spectra as those of 2,5- and 2,6-dichlorophenol, respectively, indicating that a chlorine group in p-position is substituted with a hydroxy group during ozonation. Amounts of the radical increased in an ozone-concentration dependent manner and were inhibited by addition of hydroxyl radical scavengers. These results suggest that p-semiquinone radicals are generated from the chlorophenols by hydroxyl radicals during ozonation. The p-semiquinone radicals were at least partly responsible for enhancements of DMPO-OH generation.

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Aditya, Manashi, e Soumen Bhattacharjee. "Foliar anti-diabetic and antioxidant potential of a promising accession of Amaranthus hypochondriacus L.: GC-MS based evidences". Journal of Phytopharmacology 7, n. 2 (10 aprile 2018): 121–26. http://dx.doi.org/10.31254/phyto.2018.7204.

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The present study makes an effort to investigate the foliar neutraceutical potential of a promising green accession of a seed amaranth (Amaranthus hypochondriacus, accession no. IC94661) based on anti-lipid peroxidation property, reducing power, metal chelating activity, hydroxyl radical scavenging property, antidiabetic factor and GC-MS based identification of hydroxyl containing phytochemicals. Methanol and aqueous fractions possessed exhibited better anti-lipid peroxidation, reducing, hydroxyl radical scavenging, and metal chelating properties in the experimental accession. Estimation of anti-diabetic factors from the young leaf extract also revealed significantly high α-glucosidase and α- amylase inhibition properties. When GC-MS study was carried out, it exhibited presence of several hydroxyls containing phytochemicals in the accession, some of which are having antioxidant properties. Taken as a whole, the data not only provide evidence of rich sources of marker antioxidant properties but also the availability of several phytochemicals with hydroxyls, in support of its rich pharmaceutical potential

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Wang, Rui, Chen-Loung Chen e Josef S. Gratzl. "Ozonation of pine kraft lignin in alkaline solution. Part 1: Ozonation, characterization of kraft lignin and its ozonated preparations". Holzforschung 58, n. 6 (1 ottobre 2004): 622–30. http://dx.doi.org/10.1515/hf.2004.116.

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Abstract Pine kraft lignin was purified to obtain a kraft lignin preparation (KL) with weight average molecular mass (Mw) of 5500. The KL was then ozonated with an ozone-air stream containing 2–2.5% of ozone in 0.1 M sodium hydroxide solution to prepare ozonated kraft lignin preparations with ozone consumption of 10, 25, 30 and 40% per KL; Oz-10-KL, Oz-25-KL, Oz-30-KL and Oz-40-KL, respectively. The pH of reaction mixture was decreased with increasing ozone consumption, while the carboxylic acid content and the Mw of resulting ozonated lignins increase with increasing ozone consumption. The KL and its ozonated preparations were then characterized by elemental composition, functional group analysis, molecular mass distribution and nitrobenzene-K4MnO4 oxidation. The results showed that the KL extensively undergoes oxidative cleavage of both side chains and aromatic moieties without decrease in the Mw as well as dehydrogenationive coupling of phenolic degraded fragments by active oxygen radical species, such as hydroperoxyl and hydroxyl radicals. The formation of these active oxygen radical species are produced by way of a series of reactions initiated by the reaction of ozone with hydroxide anions at pH range of 12.4–10.5, producing superoxide (-O2•) and hydroperoxyl (HOO•) radicals.

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Tong, Hua, Yan Fang Liu, Hongyan Yan, Chunxu Jiang, Feng Gao, Zemin Mei, Kun Hong, Xiaocui Yang e Zuocheng Wang. "Theoretical investigation of the chiral transition of serine and the roles of water, hydroxyl radical and hydroxide ion". New Journal of Chemistry 43, n. 31 (2019): 12340–50. http://dx.doi.org/10.1039/c9nj01796h.

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Venkatachalapathi, A., Abdul Kaffoor H e S. Paulsamy. "In vitro antioxidant activity and polyphenol estimation of methanolic fruit extract of Carissa spinarum L." Journal of Ayurvedic and Herbal Medicine 3, n. 3 (30 settembre 2017): 122–26. http://dx.doi.org/10.31254/jahm.2017.3304.

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Antioxidant property of methanolic fruit extract of the medicinal tree species, Carissa spinarum was evaluated by studying the contents of total phenolics, tannins and flavonoids, free radical scavenging activity using 1,1-diphenyl-2- picryl hydrozyl (DPPH), hydroxyl radical scavenging activity, reducing power activity, ABTS•+ assay and metal chelating activity. The results of the study revealed that both the parts studied were found to have potent antioxidant activity against DPPH, hydroxyl and ABTS•+ radicals with the IC50 value of 88.98 for methanolic fruit extract for DPPH radicals and 849.70 for hydroxyl radicals. Therefore methanolic fruit extract of C. spinarum can be considered as a new potential source of natural antioxidants for pharmaceutical industries.

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Siriwardhana, Nalin, K. W. Lee, Y. J. Jeon, S. H. Kim e J. W. Haw. "Antioxidant Activity of Hizikia fusiformis on Reactive Oxygen Species Scavenging and Lipid Peroxidation Inhibition". Food Science and Technology International 9, n. 5 (ottobre 2003): 339–46. http://dx.doi.org/10.1177/1082013203039014.

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Water and organic extracts (diethyl ether, chloroform, ethyl acetate, acetone, ethanol and methanol) obtained from Hizikia fusiformis were screened on reactive oxygen species (ROS) scavenging assays (1,1-diphenyl-2-picrylhydrazyl (DPPH), superoxide anion, hydrogen peroxide and hydroxyl radical) and lipid peroxidation (inhibition of linoleic acid oxidation) inhibitory assays. Water, methanol and ethanol extracts showed significant ROS radical scavenging activities. Water extracts showed high scavenging activities on hydrogen peroxide (around 76%) and DPPH radicals (around 75%) while it presented a moderate scavenging activity on hydroxyl radicals (around 54%). Comparatively higher ROS scavenging activities were recorded in hydroxyl radical and DPPH scavenging assays. DPPH radical scavenging activities were well correlated with the polyphenolic content. ROS scavenging and lipid peroxidation inhibition activities indicated that H. fusiformis might be a valuable natural antioxidative source containing both water and fatsoluble antioxidative components.

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Wasselin-Trupin, V., G. Baldacchino e B. Hickel. "Détection des radicaux OH et O2 issus de la radiolyse de l'eau par chimiluminescence résolue en temps". Canadian Journal of Physiology and Pharmacology 79, n. 2 (1 febbraio 2001): 171–75. http://dx.doi.org/10.1139/y00-090.

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A new method for the detection of low concentrations of hydroxyl and superoxide radicals, formed by water radiolysis, is described in this article. The method used is the time resolved chemiluminescence. It has been performed with an electron beam delivered by a Febetron 707 accelerator. This method allows to measure hydroxyl and superoxide radical concentrations in a large range of concentrations, between 105 and 108 M.Key words: chemiluminescence, pulse radiolysis, hydroxyl radical, superoxyde radical.[Traduit par la Rédaction]

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Lankin, V. Z., O. I. Shadyro, K. B. Shumaev, K. B. Shumaev, A. K. Tikhaze e 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, n. 4 (25 settembre 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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Diaz-Uribe, Carlos, William Vallejo e Cesar Quiñones. "Physical-Chemical Study of Anthracene Selective Oxidation by a Fe(III)-Phenylporhyrin Derivative". International Journal of Molecular Sciences 21, n. 1 (5 gennaio 2020): 353. http://dx.doi.org/10.3390/ijms21010353.

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In this work, we studied the anthracene oxidation by hydroxyl radicals. Hydroxyl radical was generated by reaction of 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin Fe (III) (TPPFe) with hydrogen peroxide under visible radiation at a nitrogen atmosphere. The TPPFe was synthesized by Adler Method followed by metal complexation with Fe (III) chloride hexahydrate. Hydroxyl radical was detected by fluorescence emission spectroscopy and we studied kinetic of anthracene selective oxidation by hydroxyl radicals through the differential method. The TPPFe was characterized by UV-Vis spectrophotometry, Dynamic Light Scattering (DLS) and Scanning Electron Microscopy (SEM) measurements. The results indicated that TPPFE was compound by micro-particles with a size distribution of around 2500 nm. Kinetic results showed that the apparent rate constant for the oxidation of anthracene increased exponentially on as temperature increases, furthermore, the activation energy for the Anthracene oxidation by hydroxyl radicals under visible irradiation was 51.3 kJ/mol. Finally, anthraquinone was the main byproduct generated after oxidation of anthracene by TPP-Fe under visible irradiation.

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Gonzalez, Teresa, Franck Peiretti, Catherine Defoort, Patrick Borel e Roland Govers. "2′,7′-dichlorofluorescin-based analysis of Fenton chemistry reveals auto-amplification of probe fluorescence and albumin as catalyst for the detection of hydrogen peroxide". Biochemical Journal 477, n. 24 (18 dicembre 2020): 4689–710. http://dx.doi.org/10.1042/bcj20200602.

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Fluorophore 2′,7′-dichlorofluorescin (DCF) is the most frequently used probe for measuring oxidative stress in cells, but many aspects of DCF remain to be revealed. Here, DCF was used to study the Fenton reaction in detail, which confirmed that in a cell-free system, the hydroxyl radical was easily measured by DCF, accompanied by the consumption of H2O2 and the conversion of ferrous iron into ferric iron. DCF fluorescence was more specific for hydroxyl radicals than the measurement of thiobarbituric acid (TBA)-reactive 2-deoxy-D-ribose degradation products, which also detected H2O2. As expected, hydroxyl radical-induced DCF fluorescence was inhibited by iron chelation, anti-oxidants, and hydroxyl radical scavengers and enhanced by low concentrations of ascorbate. Remarkably, due to DCF fluorescence auto-amplification, Fenton reaction-induced DCF fluorescence steadily increased in time even when all ferrous iron was oxidized. Surprisingly, the addition of bovine serum albumin rendered DCF sensitive to H2O2 as well. Within cells, DCF appeared not to react directly with H2O2 but indirect via the formation of hydroxyl radicals, since H2O2-induced cellular DCF fluorescence was fully abolished by iron chelation and hydroxyl radical scavenging. Iron chelation in H2O2-stimulated cells in which DCF fluorescence was already increasing did not abrogate further increases in fluorescence, suggesting DCF fluorescence auto-amplification in cells. Collectively, these data demonstrate that DCF is a very useful probe to detect hydroxyl radicals and hydrogen peroxide and to study Fenton chemistry, both in test tubes as well as in intact cells, and that fluorescence auto-amplification is an intrinsic property of DCF.

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24

Wang, Ying, Anni B. Hougaard, Wilhelm Paulander, Leif H. Skibsted, Hanne Ingmer e Mogens L. Andersen. "Catalase Expression Is Modulated by Vancomycin and Ciprofloxacin and Influences the Formation of Free Radicals in Staphylococcus aureus Cultures". Applied and Environmental Microbiology 81, n. 18 (6 luglio 2015): 6393–98. http://dx.doi.org/10.1128/aem.01199-15.

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ABSTRACTDetection of free radicals in biological systems is challenging due to their short half-lives. We have applied electron spin resonance (ESR) spectroscopy combined with spin traps using the probes PBN (N-tert-butyl-α-phenylnitrone) and DMPO (5,5-dimethyl-1-pyrrolineN-oxide) to assess free radical formation in the human pathogenStaphylococcus aureustreated with a bactericidal antibiotic, vancomycin or ciprofloxacin. While we were unable to detect ESR signals in bacterial cells, hydroxyl radicals were observed in the supernatant of bacterial cell cultures. Surprisingly, the strongest signal was detected in broth medium without bacterial cells present and it was mitigated by iron chelation or by addition of catalase, which catalyzes the decomposition of hydrogen peroxide to water and oxygen. This suggests that the signal originates from hydroxyl radicals formed by the Fenton reaction, in which iron is oxidized by hydrogen peroxide. Previously, hydroxyl radicals have been proposed to be generated within bacterial cells in response to bactericidal antibiotics. We found that whenS. aureuswas exposed to vancomycin or ciprofloxacin, hydroxyl radical formation in the broth was indeed increased compared to the level seen with untreated bacterial cells. However,S. aureuscells express catalase, and the antibiotic-mediated increase in hydroxyl radical formation was correlated with reducedkatAexpression and catalase activity in the presence of either antibiotic. Therefore, our results show that inS. aureus, bactericidal antibiotics modulate catalase expression, which in turn influences the formation of free radicals in the surrounding broth medium. If similar regulation is found in other bacterial species, it might explain why bactericidal antibiotics are perceived as inducing formation of free radicals.

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25

Chen, Yuan, Yingqi Mi, Jingjing Zhang, Fang Dong, Qing Li, Naiyun Ji e Zhanyong Guo. "Radical Scavenging Activities of Novel Cationic Inulin Derivatives". Polymers 10, n. 12 (22 novembre 2018): 1295. http://dx.doi.org/10.3390/polym10121295.

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Many saccharides are attractive targets for biomaterial applications, due to their abundance, biocompatibility, and biodegradability. In this article, a synthesis process of 6-N-substituted cationic inulin derivatives, including 6-pyridyl-6-deoxyinulin bromide (PIL), 6-(2-amino-pyridyl)-6-deoxyinulin bromide (2APIL), 6-(3-amino-pyridyl)-6-deoxyinulin bromide (3APIL), 6-(4-amino-pyridyl)-6-deoxyinulin bromide (4APIL), 6-(2,3-diamino-pyridyl)-6-deoxyinulin bromide (2,3DAPIL), 6-(3,4-diamino-pyridyl)-6-deoxyinulin bromide (3,4DAPIL), and 6-(2,6-diamino-pyridyl)-6-deoxyinulin bromide (2,6DAPIL) was described. The C6-OH of inulin was first activated by PPh3/N-bromosuccinimide (NBS) bromination. Then, pyridine and different kinds of amino-pyridine groups (different position and different numbers of amino) were grafted onto inulin, respectively, via nucleophilic substitution. Then, we confirmed their structure by Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance (NMR) spectroscopy. After this, their radical scavenging activities against hydroxyl radical and diphenylpicryl phenylhydrazine (DPPH) radical were tested in vitro. Each derivative showed a distinct improvement in radical scavenging activity when compared to inulin. The hydroxyl-radical scavenging effect decreased in the following order: 3APIL > PIL > 3,4DAPIL > 4APIL > 2,3DAPIL > 2,6DAPIL > 2APIL. Amongst them, 3APIL revealed the most powerful scavenging effect on hydroxyl radicals, as well as DPPH radicals. At 1.6 mg/mL, it could completely eliminate hydroxyl radicals and could clear 65% of DPPH radicals. The results also showed that the steric hindrance effect and the substitute position of the amino group had an effect on the radical scavenging activity. Moreover, the application prospects of inulin derivatives as natural antioxidant biomaterials are scientifically proven in this paper.

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26

J, Mancini-Filho. "Natural Antioxidants and Tissue Inflammation". Bioequivalence & Bioavailability International Journal 7, n. 2 (4 luglio 2023): 1–3. http://dx.doi.org/10.23880/beba-16000203.

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The phenolic compounds present in food cover a wide range of structures that have different biological properties. Highlighting its antioxidant properties and the presence mainly of spices, herbs and other foods. Some compounds present in spices can be listed for their antioxidant activity, such as: cloves have eugenol, pinene in their composition, cinnamon also has eugenol, limonene, pinene, catechins and other phenolic compounds in their composition, anise has pinene, rutin, apigenin, oregano has apigenin, quercecin, rosmarinic, caffeic, p-coumaric acids, and others. Rosemary presents the carnosic, rosmarinic, caffeic and hydroxycinnamic. The tissue inflammatory process normally starts with the presence of free radicals that are associated with the oxidative process activated by reactive oxygen species represented by peroxides, superoxide ion, presence of hydroxyl radical, singlet oxygen, among others. The highlighted phenolic compounds have in their structure one or more hydroxyls that have the property of donating a hydrogen atom to free radical structures, which can block the triggering of the oxidative process and thus inflammation.

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27

Li, Mengqi, Fuminori Yoneyama, Nayu Toshimitsu, Takeshi Zendo, Jiro Nakayama e Kenji Sonomoto. "Lethal Hydroxyl Radical Accumulation by a Lactococcal Bacteriocin, Lacticin Q". Antimicrobial Agents and Chemotherapy 57, n. 8 (3 giugno 2013): 3897–902. http://dx.doi.org/10.1128/aac.00638-13.

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ABSTRACTThe antimicrobial mechanism of a lactococcal bacteriocin, lacticin Q, can be described by the toroidal pore model without any receptor. However, lacticin Q showed different degrees of activity (selective antimicrobial activity) against Gram-positive bacteria even among related species. The ability of lacticin Q to induce pore formation in liposomes composed of lipids from different indicator strains indicated that its selective antimicrobial activity could not be attributed only to membrane lipid composition. We investigated the accumulation of deleterious hydroxyl radicals after exposure to lacticin Q as a contributing factor to cell death in the indicator strains. When lacticin Q of the same concentration as the MIC or minimum bactericidal concentration was added to the indicator cultures, high levels of hydroxyl radical accumulation were detected. Treatment with hydroxyl radical scavengers, thiourea and 2,2′-bipyridyl, decreased the levels of hydroxyl radical accumulation and recovered cell viability. These results suggest that, with or without pore formation, the final antimicrobial mechanism of lacticin Q is the accumulation of hydroxyl radicals, which varies by strain, resulting in the selective antimicrobial activity of lacticin Q.

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28

Han, Zhen Xing, Bing Wu, Ian Brown, Mark Beck e 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 (settembre 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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29

Tumbas, Vesna, Gordana Cetkovic, Sonja Djilas, Jasna Canadanovic-Brunet, Jelena Vulic, Zeljko Knez e Mojca Skerget. "Antioxidant activity of mandarin (Citrus reticulata) peel". Acta Periodica Technologica, n. 41 (2010): 195–203. http://dx.doi.org/10.2298/apt1041195t.

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Mandarin peel, a waste product coming from juice production, was extracted by conventional extraction with 70% acetone. Content of flavonoids in mandarin peel extract (MPE) was determined by HPLC. Hesperidin was the most dominant flavonoid. Free radical scavenging activity of MPE on stable DPPH radicals and reactive hydroxyl radicals was also evaluated. EC50 value determined in spectrophotometrical DPPH radical assay was 0.179 mg/ml, while this value in ESR spin trapping hydroxyl radical assay was 0.415 mg/ml. Also, MPE showed protective effects in stabilising sunflower oil during accelerated storage. The results indicated that mandarin peel can be a valuable source of natural antioxidants.

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30

Mojovic, Milos, Ivan Spasojevic, Mirjana Vuletic, Zeljko Vucinic e Goran Bacic. "An EPR spin-probe and spin-trap study of the free radicals produced by plant plasma membranes". Journal of the Serbian Chemical Society 70, n. 2 (2005): 177–86. http://dx.doi.org/10.2298/jsc0502177m.

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Plant plasma membranes are known to produce superoxide radicals, while the production of hydroxyl radical is thought to occur only in the cell wall. In this work it was demonstrated using combined spin-trap and spin-probe EPR spectroscopic techniques, that plant plasma membranes do produce superoxide and hydroxyl radicals but by kinetically different mechanisms. The results show that superoxide and hydroxyl radicals can be detected by DMPO spin-trap and that the mechanisms and location of their production can be differentiated using the reduction of spin-probes Tempone and 7-DS. It was shown that the mechanism of production of oxygen reactive species is NADH dependent and diphenylene iodonium inhibited. The kinetics of the reduction of Tempone, combined with scavengers or the absence of NADH indicates that hydroxyl radicals are produced by a mechanism independent of that of superoxide production. It was shown that a combination of the spin-probe and spin-trap technique can be used in free radical studies of biological systems, with a number of advantages inherent to them.

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31

Rudziński, Krzysztof J., e Rafał Szmigielski. "Aqueous Reactions of Sulfate Radical-Anions with Nitrophenols in Atmospheric Context". Atmosphere 10, n. 12 (9 dicembre 2019): 795. http://dx.doi.org/10.3390/atmos10120795.

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Nitrophenols, hazardous environmental pollutants, react promptly with atmospheric oxidants such as hydroxyl or nitrate radicals. This work aimed to estimate how fast nitrophenols are removed from the atmosphere by the aqueous-phase reactions with sulfate radical-anions. The reversed-rates method was applied to determine the relative rate constants for reactions of 2-nitrophenol, 3-nitrophenol, 4-nitrophenol, 2,4-dinitrophenol, and 2,4,6-trinitrophenol with sulfate radical-anions generated by the autoxidation of sodium sulfite catalyzed by iron(III) cations at ~298 K. The constants determined were: 9.08 × 108, 1.72 × 109, 6.60 × 108, 2.86 × 108, and 7.10 × 107 M−1 s−1, respectively. These values correlated linearly with the sums of Brown substituent coefficients and with the relative strength of the O–H bond of the respective nitrophenols. Rough estimation showed that the gas-phase reactions of 2-nitrophenol with hydroxyl or nitrate radicals dominated over the aqueous-phase reaction with sulfate radical-anions in deliquescent aerosol and haze water. In clouds, rains, and haze water, the aqueous-phase reaction of 2-nitrophenol with sulfate radical-anions dominated, provided the concentration of the radical-anions was not smaller than that of the hydroxyl or nitrate radicals. The results presented may be also interesting for designers of advanced oxidation processes for the removal of nitrophenol.

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32

Kozlov, Andrey V., Sabzali Javadov e Natascha Sommer. "Cellular ROS and Antioxidants: Physiological and Pathological Role". Antioxidants 13, n. 5 (14 maggio 2024): 602. http://dx.doi.org/10.3390/antiox13050602.

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Reactive oxygen species (ROS) are highly reactive oxygen derivatives that include free radicals such as superoxide anion radical (O2•−) and hydroxyl radical (HO•), as well as non-radical molecules hydrogen peroxide (H2O2), peroxynitrite (ONOO−), and hypochlorous acid (HOCl) [...]

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33

Ragnar, M., T. Eriksson e T. Reitberger. "Detection of Radicals Generated by Strong Oxidants in Acidic Media". Holzforschung 53, n. 3 (10 maggio 1999): 285–91. http://dx.doi.org/10.1515/hf.1999.048.

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Summary A new method to study superoxide and hydroxyl radicals in aqueous solution in the pH range 1 to 6 is described and critically evaluated. The method primarily detects superoxide, which reacts with tetranitromethane (TNM) by reductive cleavage. The strongly coloured nitroform anion (ε350nm = 15000M−1 cm−1) formed, is easily measured in a spectrophotometer or in a stopped-flow equipment. Hydroxyl radicals are measured indirectly. In a first step the hydroxyl radical reacts with iso-propyl alcohol to give acetone and superoxide. The superoxide formed is then in a second step detected with TNM. The TNM-method was primarily designed to monitor the radical formation under ozone bleaching conditions, but it is also applicable in acidic hydrogen peroxide.

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34

Cho, Min, Hyenmi Chung, Wonyong Choi e Jeyong Yoon. "Different Inactivation Behaviors of MS-2 Phage and Escherichia coli in TiO2 Photocatalytic Disinfection". Applied and Environmental Microbiology 71, n. 1 (gennaio 2005): 270–75. http://dx.doi.org/10.1128/aem.71.1.270-275.2005.

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ABSTRACT Despite a wealth of experimental evidence concerning the efficacy of the biocidal action associated with the TiO2 photocatalytic reaction, our understanding of the photochemical mechanism of this particular biocidal action remains largely unclear. It is generally accepted that the hydroxyl radical (Ã¯Â¿Â½OH), which is generated on the surface of UV-illuminated TiO2, plays the main role. However, our understanding of the exact mode of action of the hydroxyl radical in killing microorganisms is far from complete, and some studies report that other reactive oxygen species (ROS) (H2O2 and O2Ã¯Â¿Â½−, etc.) also play significant roles. In particular, whether hydroxyl radicals remain bound to the surface or diffuse into the solution bulk is under active debate. In order to examine the exact mode of action of ROS in inactivating the microorganism, we tested and compared the levels of photocatalytic inactivation of MS-2 phage and Escherichia coli as representative species of viruses and bacteria, respectively. To compare photocatalytic microbial inactivation with the photocatalytic chemical degradation reaction, para-chlorobenzoic acid, which rapidly reacts with a hydroxyl radical with a diffusion-limited rate, was used as a probe compound. Two different hydroxyl radical scavengers, tert-butanol and methanol, and an activator of the bulk phase hydroxyl radical generation, Fe2+, were used to investigate their effects on the photocatalytic mode of action of the hydroxyl radical in inactivating the microorganism. The results show that the biocidal modes of action of ROS are very different depending on the specific microorganism involved, although the reason for this is not clear. It seems that MS-2 phage is inactivated mainly by the free hydroxyl radical in the solution bulk but that E. coli is inactivated by both the free and the surface-bound hydroxyl radicals. E. coli might also be inactivated by other ROS, such as O2Ã¯Â¿Â½− and H2O2, according to the present results.

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35

Zocoler, Analice Martins Daleffi, Andréia Cristina Conegero Sanches, Ingrid Albrecht e João Carlos Palazzo de Mello. "Antioxidant capacity of extracts and isolated compounds from Stryphnodendron obovatum Benth". Brazilian Journal of Pharmaceutical Sciences 45, n. 3 (settembre 2009): 443–52. http://dx.doi.org/10.1590/s1984-82502009000300009.

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Abstract (sommario):

The extract from stem bark of Stryphnodendron obovatum Benth. was chromatographed on a Sephadex® LH-20 column, and yielded nine compounds: gallic acid (GA), p-hydroxybenzoic acid (PHB), gallocatechin (GC), epigallocatechin (EPG), 4'-O-methylgallocatechin (MGC), epigallocatechin-(4β→8)-epigallocatechin (EPEP), epigallocatechin-(4β→8)-gallocatechin (EPGC), robinetinidol-(4α→8)-gallocatechin (ROGC) and robinetinidol-(4β→8)-epigallocatechin (ROEP). Evaluation of the antioxidant capacity in vitro by the methods of DPPH free radical (IC50; μg/mL) and reduction of the phosphomolybdenum complex (RAC) gave the following results, respectively: crude extract 4.52 and 0.8242; ethyl-acetate fraction 4.04 and 0.9537; aqueous fraction 5.58 and 0.9275. The crude extract and ethyl-acetate fraction were shown to possess an antioxidant capacity comparable to that of vitamin C (4.93 and 1.0). The values obtained by the DPPH free-radical method for the isolated compounds were IC50 (μM): GA=8.89; PHB=10.12; GC=16.46; EPG=13.20; MGC=21.00; EPEP=6.89; EPGC=4.91; ROGC=7.78 and ROEP=6.20. Vitamin C and trolox showed 30.11 and 30.10, respectively. Dimers showed greater activity in scavenging free radicals, possibly related to the number of hydroxyls. However, compounds without a hydroxyl at position 5 of the A-ring (5-deoxy-proanthocyanidins) did not change the antioxidant activity of the DPPH free radical, as evaluated here for the first time. Among the monomers, there appeared to be a direct relationship in scavenging of free radicals because of the stereochemistry of the compounds. The presence of a methyl radical on the B-ring significantly reduced the scavenging of free radicals of gallocatechin. All compounds showed greater scavenging of radicals than vitamin C and trolox, and these two compounds showed no significant difference from each other.

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Raja, Boobalan, e Kodukkur Pugalendi. "Evaluation of antioxidant activity of Melothria maderaspatana in vitro". Open Life Sciences 5, n. 2 (1 aprile 2010): 224–30. http://dx.doi.org/10.2478/s11535-010-0005-5.

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AbstractIn this study, an aqueous extract of leaves from Melothria maderaspatana was tested for in vitro antioxidant activity. Free radical scavenging assays, such as hydroxyl radical, hydrogen peroxide, superoxide anion radical and 2,2-diphenyl-1-picryl hydrazyl (DPPH), 2,2’-azinobis-(3-ethyl-enzothiazoline-6-sulfonic acid) (ABTS) radical scavenging, and reducing power assay, were studied. The extract effectively scavenged hydroxyl radical, hydrogen peroxide and superoxide anion radicals. It also scavenged DPPH and ABTS radicals. Furthermore, it was found to have reducing power. All concentrations of leaf extract exhibited free radical scavenging and antioxidant power, and the preventive effects were in a dose-dependent manner. The antioxidant activities of the above were compared to standard antioxidants such as butylated hydroxytoluene (BHT), ascorbic acid, and α-tocopherol. The results obtained in the present study indicate that the M. maderaspatana extract could be considered a potential source of natural antioxidant.

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37

Taiwo, F. A., H. J. Powers, E. Nakano, H. R. Griffiths e D. F. Nugent. "Free radical reactions in atherosclerosis; An EPR spectrometry study". Spectroscopy 20, n. 2 (2006): 67–80. http://dx.doi.org/10.1155/2006/474183.

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The copper catalysed oxidation of homocysteine has been studied by electron paramagnetic resonance (EPR) spectroscopy and spin trapping techniques to determine the nature of free radical species formed under varying experimental conditions. Three radicals; thiyl, alkyl and hydroxyl were detected with hydroxyl being predominant. A reaction mechanism is proposed involving Fenton chemistry. Inclusion of catalase to test for intermediate generation of hydrogen peroxide showed a marked reduction in amount of hydroxyl radical generated. In contrast, the addition of superoxide dismutase showed no significant effect on the level of hydroxyl radical formed. Enhanced radical formation was observed at higher levels of oxygen, an effect which has consequences for differential oxygen levels in arterial and venous systems. Implications are drawn for a higher incidence of atherosclerotic plaque formation in arteries versus veins.

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38

Derwent, Richard G. "Representing Organic Compound Oxidation in Chemical Mechanisms for Policy-Relevant Air Quality Models under Background Troposphere Conditions". Atmosphere 11, n. 2 (7 febbraio 2020): 171. http://dx.doi.org/10.3390/atmos11020171.

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This intercomparison has taken thirteen chemical mechanisms and compared how they treat VOC oxidation and degradation and its relationship to the photochemical formation of ozone and hydroxyl radicals. Here, we have looked in some detail at the incremental responses of hydroxyl radicals to incremental additions of a range of organic compounds under conditions appropriate to the background atmosphere. Most of the time, with most organic compounds and most chemical mechanisms, incremental additions of an organic compound led to depletion of hydroxyl radical concentrations. The chemical mechanisms studied demonstrated increasingly negative incremental hydroxyl radical reactivities with increasing carbon numbers for the alkanes ethane, propane and n-butane. Hydroxyl radical incremental reactivities for the simple alkenes, ethylene and propylene, were reasonably consistent across the chemical mechanisms studied. However, this consistent representation did not extend to trans but-2-ene, where reactivity estimates spanned a range of a factor of five. Incremental reactivities were reasonably well-defined for isoprene which was encouraging in view of its importance to background tropospheric chemistry. The most serious discrepancies emerging from this study were found with the aromatics toluene and o-xylene, and with the Master Chemical Mechanism and these are discussed in some detail.

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39

Rao, Ashwathanarayana. "STUDY ON ANTIOXIDANT AND CYTOTOXIC PROPERTIES OF OLEA DIOICA ROXB. CRUDE EXTRACT AND ITS PURE COMPOUND COLLECTED FROM WESTERN GHATS, KARNATAKA, INDIA." Asian Journal of Pharmaceutical and Clinical Research 10, n. 2 (1 febbraio 2017): 356. http://dx.doi.org/10.22159/ajpcr.2017.v10i2.15727.

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Introduction: Olea dioica Roxb. an important medicinal tree plants used by local siddha tribes, belongs to the family Oleaceae. The parts such asleaves, bark, root, and fruits used in the traditional medicine to cure skin diseases, rheumatism, fever, and cancer.Objectives: The anti-oxidant experiment by metal chelating activity, superoxide radicals, hydroxyl radical, 2,2-diphenyl-2-picrylhydrazyl radicals,2,2-azino-bis(3-ethylbenzothiazoline)-6-sulfonic acid radical scavenging assays with in vitro cytotoxicity was tested using trypan blue dye exclusiontechnique and 3-(4, 5 dimethylthiazole-2yl)-2, 5-diphenyltetrazolium bromide assay was conducted.Results: Anti-oxidant experiments revealed that the bark ethanolic extract of the O. dioica plant parts has excellent radical scavenging activity and itsextracted pure compound, Benzene ethanol, 4-hydroxy-alcohol, showed excellent radical scavenging activity higher than the standards used. In vitrocytotoxicity experiments revealed that bark ethanolic extract has excellent cytotoxicity activity and its pure compound benzene-ethanol, 4-hydroxyalcoholalso showed excellentactivitywhichis comparablewith the standardcurcumin.Conclusion: O. dioica bark could be exploited as a valuable source of antioxidant and cytotoxic agent for pharmaceutical industry.Keywords: Olea dioica Roxb, Metal chelating, Superoxide radicals, Hydroxyl radical, 2,2-diphenyl-2-picrylhydrazyl radicals, 2,2-azinobis(3-ethylbenzothiazoline)-6-sulfonic acid radical scavenging,Trypan blue, 3-(4,5dimethylthiazole-2yl)-2,5-diphenyltetrazolium bromide assay, Benzeneethanol, 4-hydroxy-alcohol.

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40

Puntarulo, S., e A. I. Cederbaum. "Effect of oxygen concentration on microsomal oxidation of ethanol and generation of oxygen radicals". Biochemical Journal 251, n. 3 (1 maggio 1988): 787–94. http://dx.doi.org/10.1042/bj2510787.

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Abstract (sommario):

The iron-catalysed production of hydroxyl radicals, by rat liver microsomes (microsomal fractions), assessed by the oxidation of substrate scavengers and ethanol, displayed a biphasic response to the concentration of O2 (varied from 3 to 70%), reaching a maximal value with 20% O2. The decreased rates of hydroxyl-radical generation at lower O2 concentrations correlates with lower rates of production of H2O2, the precursor of hydroxyl radical, whereas the decreased rates at elevated O2 concentrations correlate with lower rates (relative to 20% O2) of activity of NADPH-cytochrome P-450 reductase, which reduces iron and is responsible for redox cycling of iron by the microsomes. The oxidation of aniline or aminopyrine and the cytochrome P-450/oxygen-radical-independent oxidation of ethanol also displayed a biphasic response to the concentration of O2, reaching a maximum at 20% O2, which correlates with the dithionite-reducible CO-binding spectra of cytochrome P-450. Microsomal lipid peroxidation increased as the concentration of O2 was raised from 3 to 7 to 20% O2, and then began to level off. This different pattern of malondialdehyde generation compared with hydroxyl-radical production probably reflects the lack of a role for hydroxyl radical in microsomal lipid peroxidation. These results point to the complex role for O2 in microsomal generation of oxygen radicals, which is due in part to the critical necessity for maintaining the redox state of autoxidizable components of the reaction system.

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Huang, Chenkun, Qiuyue Chen, Shengqiang Li e Jian Wang. "The Detection Methods of Hydroxyl Radical: A Review". E3S Web of Conferences 375 (2023): 03009. http://dx.doi.org/10.1051/e3sconf/202337503009.

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Abstract (sommario):

Hydroxyl radical (·OH) can rapidly react with biological macromolecules, organic and inorganic substances on account of its strong oxidizing property, so it is widely used in sewage treatment, chemiluminescence analysis, biological macromolecule modification and other fields. The strengthening effect of Hydrodynamic cavitation on chemical reactions depends on the number of free radicals initiated by cavitation. These free radicals are highly reactive and react rapidly with pollutants and other species in wastewater. Therefore, the systematic summary of detection methods of hydroxyl radical and the description of its advantages and disadvantages can provide technical support for scientific researchers, and guides the research in the future.

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42

Shao, Youxiang, Hua Hou e Baoshan Wang. "Theoretical study of the mechanisms and kinetics of the reactions of hydroperoxy (HO2) radicals with hydroxymethylperoxy (HOCH2O2) and methoxymethylperoxy (CH3OCH2O2) radicals". Phys. Chem. Chem. Phys. 16, n. 41 (2014): 22805–14. http://dx.doi.org/10.1039/c4cp02747g.

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43

Hale, W. B., B. Turner e J. T. LaMont. "Oxygen radicals stimulate guinea pig gallbladder glycoprotein secretion in vitro". American Journal of Physiology-Gastrointestinal and Liver Physiology 253, n. 5 (1 novembre 1987): G627—G630. http://dx.doi.org/10.1152/ajpgi.1987.253.5.g627.

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In several animal models of cholelithiasis, and in humans with gallstones, hypersecretion of gallbladder mucin is observed. This study was undertaken to determine the effect of oxygen radicals on guinea pig gallbladder glycoprotein secretion in organ culture. Mucosal explants were incubated with [3H]glucosamine hydrochloride to label glycoproteins, then exposed to oxygen radicals generated by chelated ferric iron and ascorbic acid. Marked stimulation of glycoprotein release was observed after a 30-min exposure to the oxygen radical-generating system, and the effect was inhibited by mannitol. The stimulatory effect of hydroxyl radical was not accompanied by leakage of intracellular lactate dehydrogenase. Parallel experiments with human granulocytes activated with f-Met-Leu-Phe and coincubated with gallbladder explants revealed similar results. These results indicate that oxygen radicals, especially the hydroxyl radical (OH.), are capable of stimulating rapid release of mucous-type glycoproteins from gallbladder epithelium.

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44

Jiang, Feng, Jiansha Gao e Di Lang. "Photocatalytic Selective Degradation of Catechol and Resorcinol on the TiO2 with Exposed {001} Facets: Roles of Two Types of Hydroxyl Radicals". Catalysts 12, n. 4 (29 marzo 2022): 378. http://dx.doi.org/10.3390/catal12040378.

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Photocatalytic studies on contaminant degradation in water suspension generally suggest that the degradation reaction mainly takes place on the surface of the photocatalysts rather than in the water phase. The mechanism of selective degradation is often difficult to distinguish concerning the contribution of adsorption and radical selectivity. This study is thus designed to investigate the roles of two types of hydroxyl radicals, adsorbed hydroxyl radical (·OHa) and free hydroxyl radical (·OHf), on the selective degradation of catechol (CT) and resorcinol (RE). CT and RE are significantly different in adsorption on a TiO2 photocatalyst with a highly exposed {001} facet. CT can be selectively degraded by TiO2 and was highly correlated with adsorption. Free radical quenching experiment results showed that the degradation of CT can be identified as the combined effect of both ·OHa and ·OHf, while the degradation of RE was mainly due to the ·OHf. Electron paramagnetic resonance coupled with spin trapping agents was used to detect the relative concentration of hydroxyl radicals in all the photocatalytic degradation processes. After a series analysis, we proposed that the mechanism of selective degradation mainly depends on the concentration of ·OHf for the pollutant molecules with weak adsorption on the catalyst surface.

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Xu, Li Ping, e Xin Wang. "Evaluation the Effect of Anti-Oxidation of Chondroitin Sulfate". Advanced Materials Research 989-994 (luglio 2014): 793–96. http://dx.doi.org/10.4028/www.scientific.net/amr.989-994.793.

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Study of the antioxidant activity of chondroitin sulfate extracted from chicken cartilage. The total antioxidant capacity, inhibition the capacity of anti-superoxide anion, hydroxyl radical, anti-liposome and Alkyl radical was determined, respectively; the effect of the anti-oxidation of chondroitin sulfate was observed. The result indicated that chondroitin sulfate had the strong elimination ability to the five free radicals. The ability of total antioxidant the values of scavenging activities of the maximum inhibition rate to anti-superoxide anion, hydroxyl radical, anti-liposome and alkyl radical was 30.56 U/mL, 97.74%, 80.69% ,48.05% and 78.57%, respectively.

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Moore, Peter W., Jordan P. Hooker, Athanasios Zavras, George N. Khairallah, Elizabeth H. Krenske, Paul V. Bernhardt, Gina Quach, Evan G. Moore, Richard A. J. O'Hair e Craig M. Williams. "Hydroxyl Radicals via Collision-Induced Dissociation of Trimethylammonium Benzyl Alcohols". Australian Journal of Chemistry 70, n. 4 (2017): 397. http://dx.doi.org/10.1071/ch16602.

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The hydroxyl radical is a well known reactive oxygen species important for interstellar, atmospheric, and combustion chemistry in addition to multiple biochemical processes. Although there are many methods to generate the hydroxyl radical, most of these are inorganic based, with only a few originating from organic precursor molecules. Reported herein is the observation that trimethylammonium benzyl alcohols and their corresponding deuterated isotopologues act as a good source of hydroxyl and deuteroxyl radicals in the gas-phase under collision-induced dissociation (CID) conditions. Attempts to replicate this chemistry in the condensed phase are described.

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Bratishko, Kristina Aleksandrovna, Mariya Vladimirovna Zykova, Vladimir Vladimirovich Ivanov, Evgeniy Evgen'yevich Buyko, Larisa Aleksandrovna Drygunova, Irina Vasil'yevna Perminova e Mikhail Valer'yevich Belousov. "PEAT HUMIC ACIDS – PROSPECTIVE BIOLOGICALLY ACTIVE SUBSTANCES WITH ANTIOXIDANT ACTIVITY FOR THE DEVELOPMENT OF PROTECTIVE AGENTS". chemistry of plant raw material, n. 1 (16 marzo 2021): 287–98. http://dx.doi.org/10.14258/jcprm.2021018784.

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A present study was carried out to investigate the antioxidant activity (AOA) of humic acids (HA) isolated by sodium hydroxide and sodium pyrophosphate from nine peat species of the Tomsk region different by botanical composition, degree of decomposition and ash content. All HA samples had shown the AOA in the study. As the results of four research methods, it was found that HAs are highly effective in inhibiting the free ABTS•+ radical cation, superoxide anion radical O2-•, hydroxyl radical HO•, and are able to bind Fe2+ in a wide range of concentrations. The activity of HAs in different tests was not equal between samples; HAs isolated by sodium hydroxide have had a higher AOA in inhibition of the superoxide anion–radical O2-• in the model reaction compared to HAs isolated by sodium pyrophosphate within the same peat species. In the study of iron binding activity, an inverse relationship was observed. In the model reactions of the free ABTS•+ radical cation and the hydroxyl radical HO• inhibition, a comparable level of activity was registered between the HA samples isolated by different solutions. Such an uneven distribution of the activity between various HA samples can be explained by the unequal chemical parameters of their structure, which depend on their origin and method of isolation. Using of such classical antioxidants with an established mechanism of action as comparison drugs, as a water-soluble analogue of tocopherol - "Trolox", a water-soluble antioxidant – ascorbic acid, a classic chelator – ethylenediaminetetraacetic acid (EDTA), a classic trap of a hydroxyl radical – mannitol, it is possible to conclude that the investigated HAs are effective antioxidants belonging to the groups of proton donors and complexing agents.

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Cheng, Peng, Guodong Feng, Chang Sun, Wenjing Xu, Ji-Hu Su, Wenfu Yan e Jihong Yu. "An efficient synthetic route to accelerate zeolite synthesis via radicals". Inorganic Chemistry Frontiers 5, n. 9 (2018): 2106–10. http://dx.doi.org/10.1039/c8qi00441b.

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Hadjimitova, Vera, Trayko Traykov, Milka Mileva e Stefan Ribarov. "Effect of Some Psychotropic Drugs on Luminol - Dependent Chemiluminescence Induced by O2–, •OH, HOCl". Zeitschrift für Naturforschung C 57, n. 11-12 (1 dicembre 2002): 1066–71. http://dx.doi.org/10.1515/znc-2002-11-1220.

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We studied antioxidant activity of six neuroleptics (chlorpromazine, levomepromazine, promethazine, trifluoperazine and thioridazine) and two antidepressants (imipramine and amitriptyline) in the range of concentration of 10−7−10−4 м. We applied luminol-dependent chemiluminescence to test the ability of these drugs to scavenge the biologically relevant oxygen-derived species: hydroxyl radical, superoxide radical, hypochlorous acid in vitro. We found that the phenothiazines were powerful scavengers of hydroxyl and superoxide radicals. Chlorprothixene, amitriptyline and imipramine had no scavenge activity to the superoxide radical. All drugs showed a moderate scavenger effect on hypochloric anion.

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50

McArdle, A., J. van der Meulen, G. L. Close, D. Pattwell, H. Van Remmen, T. T. Huang, A. G. Richardson, C. J. Epstein, J. A. Faulkner e M. J. Jackson. "Role of mitochondrial superoxide dismutase in contraction-induced generation of reactive oxygen species in skeletal muscle extracellular space". American Journal of Physiology-Cell Physiology 286, n. 5 (maggio 2004): C1152—C1158. http://dx.doi.org/10.1152/ajpcell.00322.2003.

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Abstract (sommario):

Contractions of skeletal muscles produce increases in concentrations of superoxide anions and activity of hydroxyl radicals in the extracellular space. The sources of these reactive oxygen species are not clear. We tested the hypothesis that, after a demanding isometric contraction protocol, the major source of superoxide and hydroxyl radical activity in the extracellular space of muscles is mitochondrial generation of superoxide anions and that, with a reduction in MnSOD activity, concentration of superoxide anions in the extracellular space is unchanged but concentration of hydroxyl radicals is decreased. For gastrocnemius muscles from adult (6–8 mo old) wild-type ( Sod2+/+) mice and knockout mice heterozygous for the MnSOD gene ( Sod2+/-), concentrations of superoxide anions and hydroxyl radical activity were measured in the extracellular space by microdialysis. A 15-min protocol of 180 isometric contractions induced a rapid, equivalent increase in reduction of cytochrome c as an index of superoxide anion concentrations in the extracellular space of Sod2+/+ and Sod2+/- mice, whereas hydroxyl radical activity measured by formation of 2,3-dihydroxybenzoate from salicylate increased only in the extracellular space of muscles of Sod2+/+ mice. The lack of a difference in increase in superoxide anion concentration in the extracellular space of Sod2+/+ and Sod2+/- mice after the contraction protocol supported the hypothesis that superoxide anions were not directly derived from mitochondria. In contrast, the data obtained suggest that the increase in hydroxyl radical concentration in the extracellular space of muscles from wild-type mice after the contraction protocol most likely results from degradation of hydrogen peroxide generated by MnSOD activity.

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