Articoli di riviste: "Free radicals (Chemistry) – Analysis"

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

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Cherkasov, A. R., M. Jonsson, V. I. Galkin e R. A. Cherkasov. "ChemInform Abstract: Correlation Analysis in the Chemistry of Free Radicals". ChemInform 32, n. 29 (25 maggio 2010): no. http://dx.doi.org/10.1002/chin.200129286.

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Liu, Yuyan, Xiaoyong Liu, Hongping Liu, Yuanqing Guo, Guangming Huang, Jieli Lin, Hui Gao e Chuanxi Duan. "Spectroscopic analysis of asymmetric top free radicals". Science in China Series B: Chemistry 44, n. 1 (febbraio 2001): 7–16. http://dx.doi.org/10.1007/bf02879730.

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Simándi, László I. "Analysis of free radicals in biological systems". Reaction Kinetics & Catalysis Letters 59, n. 2 (novembre 1996): 383–84. http://dx.doi.org/10.1007/bf02068138.

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Das, Suresh, e 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, n. 4 (1 aprile 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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SANO, HIROAKI. "Chemistry and biology of active oxygens and free radicals. 2. Analyses of active oxygens and free radicals." Kagaku To Seibutsu 37, n. 5 (1999): 328–33. http://dx.doi.org/10.1271/kagakutoseibutsu1962.37.328.

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Doi, Naoki, Yasushi Sasai, Yukinori Yamauchi, Tetsuo Adachi, Masayuki Kuzuya e Shin-ichi Kondo. "Kinetic analysis of mechanoradical formation during the mechanolysis of dextran and glycogen". Beilstein Journal of Organic Chemistry 13 (19 giugno 2017): 1174–83. http://dx.doi.org/10.3762/bjoc.13.116.

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A detailed electron spin resonance (ESR) analysis of mechanically induced free radicals (mechanoradicals) formation of glucose-based polysaccharides, dextran (Dx) and glycogen (Gly) was performed in comparison with amylose mechanoradicals. The ESR spectra of the samples mechanically fractured at room temperature were multicomponent. The radical concentration of Dx and Gly mechanoradicals gradually decreased during vibratory milling after reaching the maximum value. Although the molecular weight of Dx or the particle diameter of Gly steeply diminished until reaching the each maximum value of radical concentration, after that the molecular weight or the particle diameter slowly decreased. These results suggested that Dx and Gly mechanoradicals might be more unstable than amylose radicals possessing an intramolecular helical structure due to the branched structure.

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Akhter, Parveen, Uzma Ashiq, Rifat A. Jamal, Zara Shaikh, Mohammad Mahroof-Tahir, Mehreen Lateef e Rooma Badar. "Chemistry, Alpha-glucosidase and Radical Scavenging Properties of Uranyl(VI) Hydrazide Complexes". Medicinal Chemistry 15, n. 8 (18 novembre 2019): 923–36. http://dx.doi.org/10.2174/1573406415666190213101044.

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Background: Antioxidant, anti-inflammatory, antiviral and antitumoral activities among others are essential characteristics in the development of novel therapeutic compounds. Acid hydrazides can form complexation with certain metal ions that positively enhance these biological characteristics. Objective: Five new complexes of uranium with hydrazide ligands were synthesized at room temperature. Methods: Methods: The characterization was done by spectroscopic methods (ESI-Mass, IR, 1H-NMR, 13CNMR), CHN analysis and conductivity measurements. Metal complexes along with their respective ligands were further screened for their antioxidant (DPPH, superoxide and nitric oxide free radicals) properties and enzyme inhibition (α-glucosidase) activities. Results: Elemental and spectral data indicate octahedral geometry around uranyl (UO2 2+) species. Magnetic moments indicate the diamagnetic nature of uranyl(VI) ion in the complex in solid state. IC50 values showed potential antioxidant behavior of uranyl complexes demonstrating interesting structure-activity relationships. In general, hydrazide ligands were not active against superoxide and nitric oxide radicals while varying degree of results were observed against DPPH radical whereas all uranyl-complexes showed promising radical scavenging activities against all of them. Promising inhibitory potential was displayed by UO2 +2 hydrazide complexes against α- glucosidases whereas free hydrazide ligands were inactive. Conclusion: Structure function relationship demonstrates that the nature of ligand, position of substituent, electronic and steric effects are significant factors affecting the radical scavenging and enzyme inhibition activities of the compounds.

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Zhang, Yong-Kang, Dao-Hui Lu e Guang-Zhi Xu. "Synthesis and Plane Selective Spin Trapping of a Novel Trap 5,5-Dimethyl-3-(2-ethoxycarbonylethyl)-1-pyrroline N-oxide". Zeitschrift für Naturforschung B 45, n. 7 (1 luglio 1990): 1075–83. http://dx.doi.org/10.1515/znb-1990-0729.

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A novel cyclic nitrone spin trap 5,5-dimethyl-3-(2-ethoxycarbonylethyl)-1-pyrroline N-oxide has been prepared and its ability to trap a series of transient free radicals has been investigated. This nitrone scavenges free radicals to give persistent nitroxides, e.g., the half life-times of hydroxyl radical adducts and tert-butoxy radical adducts in benzene >30 min, and the life-time of acetyl adducts >60 min. The EPR spectrum of 2,2-dimethyl-4-(3-hydroxypropyl)pyrrolidinyl-1-oxyl aminoxyl shows that the hyperfine splitting constants of twoβ-hydrogens are equal to 14.58 G and 23.29 G respectively, i.e., the two β-hydrogens are not magnetically equivalent. Radical addition to the nitrone is probably plane selective affording only one of the two possible geometric isomer pairs of the spin adduct nitroxides. The trans approach mechanism is proposed through configuration and conformation analysis.

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Prior, Ronald L., e Guohua Cao. "Analysis of Botanicals and Dietary Supplements for Antioxidant Capacity: A Review". Journal of AOAC INTERNATIONAL 83, n. 4 (1 luglio 2000): 950–56. http://dx.doi.org/10.1093/jaoac/83.4.950.

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Abstract Free radicals and other reactive species are considered to be important causative factors in the development of diseases of aging such as cancer and cardiovascular diseases. This relationship has led to considerable interest in assessing the antioxidant capacity of foods and botanicals and other nutritional antioxidant supplements. The use of the oxygen radical absorbance capacity (ORAC) assay as a tool for antioxidant assessment is described and proposed as a method for comparing botanical sources and for standardizing nutritional supplements. The free radical or oxidant source is important and direct comparisons cannot be made between procedures that use different sources. The ORAC procedure uses 2,2′-azobis(2-amidinopropane) dihydrochloride as a peroxyl radical source, which is relevant to biological systems because the peroxyl radical is the most abundant free radical. Other oxidant sources (hydroxyl radical and Cu++) can also be used to characterize antioxidants in botanicals. Phenolics or polyphenolics are responsible for most of the antioxidant capacity in fruits, vegetables, and most botanical antioxidant supplements. Although little is known about the absorption and metabolism of these components, improvement in the in vivo antioxidant status has been observed in human subjects following consumption of antioxidant botanicals. The ORAC method provides a basis from which to establish appropriate dietary intakes that might impact health outcomes.

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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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CHENG, Y., L. LI, Z. MENG, A. HOU, Y. WU e L. TENG. "Component Analysis and Free Radicals Scavenging Activity of Physalis alkekengi L. Polysaccharide". Chemical Research in Chinese Universities 24, n. 2 (marzo 2008): 167–70. http://dx.doi.org/10.1016/s1005-9040(08)60034-3.

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Hug, Gordon L., Krzysztof Bobrowski, Dariusz Pogocki, Bronislaw Marciniak, Christian Schöneich e Gerald Hörner. "Factor analysis of transient spectra. Free radicals in cyclic dipeptides containing methionine". Research on Chemical Intermediates 35, n. 4 (aprile 2009): 431–42. http://dx.doi.org/10.1007/s11164-009-0044-6.

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Ponec, Robert, Štěpán Krupička e Milan Hájek. "MO analysis of chemically interacting systems. Reaction of hydrogen abstraction by free radicals". Collection of Czechoslovak Chemical Communications 52, n. 3 (1987): 547–54. http://dx.doi.org/10.1135/cccc19870547.

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The charge and spin transfer accompanying the process of the exchange of the bonds in the reaction of hydrogen abstraction by free radicals was examined in terms of intermolecular population analysis. The results obtained enable a qualitative discussion of the role of polar and steric effects in this reaction.

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NIETO-GALAN, AGUSTÍ. "Free radicals in the European periphery: ‘translating’ organic chemistry from Zurich to Barcelona in the early twentieth century". British Journal for the History of Science 37, n. 2 (24 maggio 2004): 167–91. http://dx.doi.org/10.1017/s0007087404005436.

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In 1915, after acquiring first-hand knowledge of the new free radical chemistry at the Swiss Federal Institute of Technology (ETH) in Zurich, Antonio García Banús (1888–1955) became professor of organic chemistry at the University of Barcelona and created his own research group, which was to last from 1915 until 1936. He was a gifted teacher and a prolific writer who attempted to introduce international scientific standards into his local environment. This paper analyses the bridges that Banús built between the experimental culture of organic chemistry at the ETH and the University of Barcelona. It presents a case study which aims to provide new historical data for the general analysis of groups who conducted their work in the European periphery.

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Kleimeyer, James A., e Joel M. Harris. "Monitoring the Formation and Decay of Transient Photosensitized Intermediates Using Pump-Probe UV Resonance Raman Spectroscopy. II: Kinetic Modeling and Multidimensional Least-Squares Analysis". Applied Spectroscopy 57, n. 4 (aprile 2003): 448–53. http://dx.doi.org/10.1366/00037020360625998.

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Analysis of transient excited-state Raman spectra is a challenging spectroscopic measurement since transient spectral features are often overlapped with dominant ground-state and solvent bands. In the previous manuscript, resolution of component Raman spectra from the time-resolved amine quenching of excited-triplet benzophenone was accomplished using self-modeling curve resolution, a model-free factor analysis technique that relies on correlation in the data along a changing composition dimension. The results are consistent with the production of diphenylketyl radicals by H-atom abstraction from the amine and subsequent free-radical decay by recombination reactions. A kinetic model for this chemistry is developed in the present work, based on the observed Raman scattering data and the structures of product species confirmed by mass spectral analysis. The model is applied to the analysis of the time-dependent Raman scattering data using multidimensional least-squares methods, and it yielded well-resolved spectra of benzophenone excited-triplet states, diphenyl ketyl radical, and the solvent and ground-state precursors. The best-fit kinetic parameters agree well with the time-dependent triplet-state and ketyl-radical concentration profiles.

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Jiang, Ying, Likun Xue, Rongrong Gu, Mengwei Jia, Yingnan Zhang, Liang Wen, Penggang Zheng et al. "Sources of nitrous acid (HONO) in the upper boundary layer and lower free troposphere of the North China Plain: insights from the Mount Tai Observatory". Atmospheric Chemistry and Physics 20, n. 20 (26 ottobre 2020): 12115–31. http://dx.doi.org/10.5194/acp-20-12115-2020.

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Abstract. Nitrous acid (HONO) is a significant precursor of atmospheric “detergent” OH radicals and plays a vital role in tropospheric chemistry. The current knowledge about daytime HONO sources is incomplete, and its impact on the tropospheric radical chemistry has not been fully quantified. Existing observational studies of HONO were mostly conducted at the surface, with few efforts focusing on the high-elevation atmosphere. In order to better understand the characteristics and sources of HONO in the upper boundary layer and lower free troposphere, two intensive field observations were carried out at the summit of Mt. Tai (1534 m a.s.l.), the peak of the North China Plain (NCP), in winter 2017 and spring 2018. HONO showed moderate concentration levels (average ± standard deviation: 0.15±0.15 and 0.13±0.15 ppbv), with maximum values of 1.14 and 3.23 ppbv in winter and spring, respectively. Diurnal variation patterns with broad noontime maxima and lower nighttime concentrations were observed during both campaigns, which is distinct from most of the previous studies at the ground level. The Lagrangian particle dispersion model (LPDM, WRF-FLEXPART v3.3) simulations indicated the combined effects of the planetary boundary layer evolution and valley breeze on the daytime HONO peak. A photostationary state (PSS) analysis suggested a strong unknown daytime HONO source with production rates of 0.45±0.25 ppb h−1 in winter and 0.64±0.49 ppb h−1 in spring. Correlation analysis supported the important role of photo-enhanced heterogeneous conversion of NO2 to HONO on the aerosol surface at this high-elevation site. HONO photolysis is the predominant primary source of OH radical and plays a major role in the radical chemistry at Mt. Tai. The model only considering a homogenous HONO source predicted much lower levels of the HOx radicals and atmospheric oxidation capacity than the model constrained with measured HONO data. This study sheds light on the characteristics, sources, chemistry, and impacts of HONO in the upper boundary layer and lower free troposphere in the NCP region.

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Laird, Ellen R., e William L. Jorgensen. "Computer assisted analysis of reactions involving organic free radicals and diradicals". Journal of Chemical Information and Modeling 30, n. 4 (1 novembre 1990): 458–66. http://dx.doi.org/10.1021/ci00068a018.

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Shoaf, Antony R., Ali U. Shaikh, Raymond D. Harbison e Oscar Hinojosa. "Extraction and analysis of superoxide free radicals (·O−2) from whole mammalian liver". Journal of Bioluminescence and Chemiluminescence 6, n. 2 (aprile 1991): 87–96. http://dx.doi.org/10.1002/bio.1170060206.

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Barclay, L. RC, M. C. Basque e M. R. Vinqvist. "Singlet-oxygen reactions sensitized on solid surfaces of lignin or titanium dioxide: Product studies from hindered secondary amines and from lipid peroxidation". Canadian Journal of Chemistry 81, n. 6 (1 giugno 2003): 457–67. http://dx.doi.org/10.1139/v02-199.

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Product analyses and kinetic methods were used to determine the role of singlet oxygen in lignin-catalyzed oxidations of organic substrates. Method A used the ESR analysis of nitroxide radicals formed by singlet oxygen (Type II) on 2,2,6,6-tetramethylpiperidine, 1, or tetramethylpiperidone, 2. Method B used HPLC analysis of the 9- and 13-linoleate chain hydroperoxides formed on oxidation of methyl linoleate to distinguish free-radical peroxidation (Type I) from singlet-oxygen oxidation (Type II) on the basis of different cis,trans (kinetic) to trans,trans (thermodynamic) product ratios. Applications of method A to solid dispersions of lignin or titanium dioxide (TiO2, a known singlet-oxygen sensitizer) indicated singlet-oxygen reactions. In addition to the nitroxide triplet, irradiation of lignin produces a persistent broad signal in the solid attributed to phenoxyl radicals. Benzophenone and 3,5-di-tert-butyl-ortho-benzoquinone, 5, coated on silica gel were used as models to compare the effects of irradiating such compounds on the products and kinetics of methyl linoleate oxidation. Benzophenone acted as an initiator, giving free-radical peroxidation, whereas 5 or lignin coated with methyl linoleate acted as singlet-oxygen sensitizers, according to both product studies (method B) and the kinetic order in oxygen consumption during UV photolysis. Photolysis of phase-separated sensitizer (TiO2 or lignin) and substrate (methyl linoleate) resulted in typical singlet-oxygen products. These results indicate that singlet oxygen plays a significant role in the photo-yellowing of high-lignin-content wood pulps. Key words: lignin, singlet oxygen, mechanism, peroxidation, products.

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Sikandar, Aatika, Mengyue Zhang, Yuanyuan Wang, Xiaofeng Zhu, Xiaoyu Liu, Haiyan Fan, Yuanhu Xuan, Lijie Chen e Yuxi Duan. "Mycochemical Screening and Analysis, Antioxidant Activity, and Biochemical Composition of Fermentation Strain Snef1216 (Penicillium chrysogenum)". Journal of Analytical Methods in Chemistry 2020 (30 marzo 2020): 1–8. http://dx.doi.org/10.1155/2020/3073906.

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Antioxidants are the radical scavengers that inhibit peroxidation and other free-radical processes, which in return safeguard different organisms from various diseases attributed to radical reactions. Synthetic antioxidants inhibit free radicals, but they also have harmful side effects. However, mycochemicals of natural fungal origin are safe and best substitutes for harmful synthetic chemical antioxidants. The prime objectives of the study include appropriate qualitative and quantitative mycochemical screening, antioxidant potential, and chemical composition of Snef1216 (Penicillium chrysogenum). The study has used aluminium chloride colourimetric method, Folin–Ciocalteu reagent assay, and DPPH (1,1-diphenyl-1-picrylhydrazyl) for analysis of total flavonoid content and phenol content and antioxidant activity, respectively. However, the presence of biologically active compounds was screened through gas chromatography-mass spectrometry (GC-MS). Quantitative analysis demonstrated the existence of flavonoids, glycosides, flavones, saponins, phenols, and catecholic tannins excluding alkaloids, terpenoids, steroids, and gallic tannins. The outcomes exposed total flavonoid content and phenolic content in P. chrysogenum were 85.31 ± 1.23 mg·QE/g and 135.77 ± 1.14 mg·GAE/g, respectively. Snef1216 (P. chrysogenum) displayed the highest free-radical scavenging activity with 63.86% inhibition of DPPH. The analysis confirms that Snef1216 (P. chrysogenum) is an alternative source of natural antioxidants. The obtained data have provided the foundation for its use in agricultural, environmental, and pharmaceutical industries.

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Söylemez, Nazlı, Ebru Yabaş, Serap Şahin Bölükbaşı e Mustafa Sülü. "Antioxidant activities of the new tetrasubstituted metal-free, Zn(II) and Co(II) monophthalocyanines". Journal of Porphyrins and Phthalocyanines 22, n. 01n03 (gennaio 2018): 233–42. http://dx.doi.org/10.1142/s1088424618500190.

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4-[(4′-(Tert-butyl)phenoxy)phenoxy]phthalonitrile 1 has been prepared by the reaction of 4-(4-nitrophenoxy)phthalonitrile with 4-tertiarylbutylphenole. 4-((4′-tert-butyl)phenoxy)phenoxy tetrasubstituted metal-free 2, zinc(II) 3 and cobalt(II) 4 phthalocyanines have been prepared by tetramerization of compound 1. The synthesized phthalocyanines showed high solubility in common organic solvents such as CHCl[Formula: see text]. All compounds were characterized by elemental analysis and [Formula: see text]H-NMR, [Formula: see text]C-NMR, UV-vis, IR spectra. Aggregation behaviors of these compounds have been investigated in different solvents (CHCl[Formula: see text], THF, DMF and DMSO) and different concentrations in CHCl[Formula: see text]. The in vitro antioxidant activities of phthalocyanine compounds 2, 3 and 4 were evaluated in a series of assays involving DPPH radicals, hydroxyl radicals, superoxide radicals, singlet oxygen and hydrogen peroxide. Antioxidant activity of compound 2was found to be higher than that of compounds 3 and 4.

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Xue, L. K., T. Wang, H. Guo, D. R. Blake, J. Tang, X. C. Zhang, S. M. Saunders e W. X. Wang. "Sources and photochemistry of volatile organic compounds in the remote atmosphere of western China: results from the Mt. Waliguan Observatory". Atmospheric Chemistry and Physics Discussions 13, n. 5 (2 maggio 2013): 11745–88. http://dx.doi.org/10.5194/acpd-13-11745-2013.

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Abstract. The chemistry of the natural atmosphere and the influence by long-range transport of air pollution are key issues in the atmospheric sciences. Here we present two intensive field measurements of volatile organic compounds (VOCs) in late spring and summer of 2003 at Mt. Waliguan (WLG, 36.28° N, 100.90° E, 3816 m a.s.l.), a baseline station in the northeast part of Qinghai-Tibetan Plateau. Most VOC species exhibited higher concentrations in late spring than in summer. A typical diurnal variation was observed with higher nighttime levels, in contrast to results from other mountainous sites. Five different air masses were identified from backward trajectory analysis showing distinct VOC speciation. Air masses originating from the central Eurasian continent contained the lowest VOC levels compared to the others that were impacted by anthropogenic emissions from China and the Indian sub-continent. The data were compared with the TRACE-P (Transport and Chemical Evolution over the Pacific) data to examine the inflow and outflow of air pollution over the China sub-continent. The results show that the free troposphere over China may be affected by the inflow from the Eurasian continent in spring, and the emissions in China may not have a significant influence on the free tropospheric outflow. A photochemical box model based on the Master Chemical Mechanism (version 3.2) and constrained by a full suite of measurements was developed to probe the photochemistry of atmosphere at WLG. Our results show net ozone production from in-situ photochemistry during both late spring and summer. Oxidation of nitric oxide (NO) by the hydroperoxyl radical (HO2) dominates the ozone production relative to the oxidation by the organic peroxy radicals (RO2), and the ozone is primarily destroyed by photolysis and reactions with the HOx(HOx = OH + HO2) radicals. Ozone photolysis is the predominant primary source of radicals (ROx = OH + HO2 + RO2), followed by the photolysis of oxygenated VOCs and hydrogen peroxides. The radical losses are governed by the self and cross reactions among the radicals. The findings can provide insights into the background chemistry and the impacts of pollution transport on the pristine atmosphere over the Eurasian continent.

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Qu, Hong-jie, Lang Yuan, Cai-xin Jia, Hai-tao Yu e Hui Xu. "DFT Investigation of Hydrogen Atom Abstraction from NHC-Boranes by Methyl, Ethyl and Cyanomethyl Radicals—Composition and Correlation Analysis of Kinetic Barriers". Molecules 25, n. 19 (1 ottobre 2020): 4509. http://dx.doi.org/10.3390/molecules25194509.

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Understanding the hydrogen atom abstraction (HAA) reactions of N-heterocyclic carbene (NHC)-boranes is essential for extending the practical applications of boron chemistry. In this study, density functional theory (DFT) computations were performed for the HAA reactions of a series of NHC-boranes attacked by •CH2CN, Me• and Et• radicals. Using the computed data, we investigated the correlations of the activation and free energy barriers with their components, including the intrinsic barrier, the thermal contribution of the thermodynamic reaction energy to the kinetic barriers, the activation Gibbs free energy correction and the activation zero-point vibrational energy correction. Furthermore, to describe the dependence of the activation and free energy barriers on the thermodynamic reaction energy or reaction Gibbs free energy, we used a three-variable linear model, which was demonstrated to be more precise than the two-variable Evans–Polanyi linear free energy model and more succinct than the three-variable Marcus-theory-based nonlinear HAA model. The present work provides not only a more thorough understanding of the compositions of the barriers to the HAA reactions of NHC-boranes and the HAA reactivities of the substrates but also fresh insights into the suitability of various models for describing the relationships between the kinetic and thermodynamic physical quantities.

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Zhang, X., Z. M. Chen, S. Z. He, W. Hua, Y. Zhao e J. L. Li. "Peroxyacetic acid in urban and rural atmosphere: concentration, feedback on PAN-NO<sub>x</sub> cycle and implication on radical chemistry". Atmospheric Chemistry and Physics Discussions 9, n. 5 (26 ottobre 2009): 22581–617. http://dx.doi.org/10.5194/acpd-9-22581-2009.

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Abstract. Peroxyacetic Acid (PAA) is one of important atmospheric organic peroxides, which have received increasing attention for their potential contribution to the oxidation capacity of the troposphere and the formation of secondary aerosols. We report here that, for the first time, a series of data for atmospheric PAA concentrations at urban and rural sites, from five field campaigns carried out in China in summer 2006, 2007 and 2008. For these five measurements, daytime mean PAA concentrations on sunlit days were 0.02–0.14 ppbv with a maximum level of ~1 ppbv. The various meteorological and chemical parameters influencing PAA concentrations were examined using the Principal Factor Analysis. This statistical analysis shows that the local photochemical production was the major source of PAA, and its concentration increased with increasing temperature, solar radiation and ozone but decreased with increasing NOx (NO and NO2), CO, SO2, and relative humidity. Based on the dataset, several issues are highlighted in this study: (i) because PAA is a product from the photochemical oxidation of some specific volatile organic compounds (VOCs) that lead to acetyl peroxy radicals, the importance of various VOCs with respect to the PAA formation is therefore ranked using the incremental reactivity method. (ii) The contribution of PAN thermal degradation to PAA formation under conditions of different NOx concentrations is estimated based on the chemical kinetics analysis. The result shows that PAN seems to play an important role in the formation of PAA when the NO/NO2 concentration ratio was less than 0.2 and PAA would correspondingly have feedback on the PAN-NOx cycle. (iii) PAA and other peroxides, such as methyl hydroperoxide (MHP) and H2O2, usually exhibited a similar asymmetric shape typically shifted to the afternoon. However, at a high SO2 level, H2O2 showed a profile different from those of MHP and PAA. The combination of linear regression and chemical kinetics analysis reveals that a possible unknown pathway results in the significant removal of H2O2 and the extent of H2O2 undergoing this pathway needs a further study. (iv) Considering that PAA is the reservior of free radicals, its fate is expected to have an effect on the free radical budget in the atmosphere. A box model based on the CBM-IV mechanism has been performed to access its influence on the radical budget. We suggest that the detailed information on PAA in the atmosphere is of importance to better understand the free radical chemistry.

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Zhang, X., Z. M. Chen, S. Z. He, W. Hua, Y. Zhao e J. L. Li. "Peroxyacetic acid in urban and rural atmosphere: concentration, feedback on PAN-NO<sub>x</sub> cycle and implication on radical chemistry". Atmospheric Chemistry and Physics 10, n. 2 (25 gennaio 2010): 737–48. http://dx.doi.org/10.5194/acp-10-737-2010.

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Abstract. Peroxyacetic acid (PAA) is one of the most important atmospheric organic peroxides, which have received increasing attention for their potential contribution to the oxidation capacity of the troposphere and the formation of secondary aerosols. We report here, for the first time, a series of data for atmospheric PAA concentrations at urban and rural sites, from five field campaigns carried out in China in summer 2006, 2007 and 2008. For these five measurements, daytime mean (08:00–20:00 LT) PAA concentrations on sunlit days were 21.4–148.0 pptv with a maximum level of ~1 ppbv. The various meteorological and chemical parameters influencing PAA concentrations were examined using Principal Factor Analysis. This statistical analysis shows that the local photochemical production was the major source of PAA, and its concentration increased with increasing temperature, solar radiation and ozone but decreased with increasing NOx (NO and NO2), CO, SO2, and relative humidity. Based on the dataset, several issues are highlighted in this study: (i) Because PAA is a product from the photochemical oxidation of some specific volatile organic compounds (VOCs) that lead to acetyl peroxy radicals, the importance of various VOCs with respect to the PAA formation is therefore ranked using the incremental reactivity method. (ii) The contribution of PAN thermal degradation to PAA formation under conditions of different NOx concentrations is estimated based on the chemical kinetics analysis. The result shows that PAN seems to play an important role in the formation of PAA when the NO/NO2 concentration ratio was less than 0.2 and PAA would correspondingly have feedback on the PAN-NOx cycle. (iii) PAA and other peroxides, such as methyl hydroperoxide (MHP) and H2O2, usually exhibited a similar asymmetric shape typically shifted to the afternoon. However, under some conditions, H2O2 diurnal cycle was out of phase with MHP and PAA. The combination of linear regression and kinetics analysis indicate that the formation and removal processes of H2O2 may be different from those of MHP and PAA. (iv) Considering that PAA is the reservior of free radicals, its fate is expected to have an effect on the free radical budget in the atmosphere. A box model based on the CBM-IV mechanism has been performed to access its influence on the radical budget. We suggest that the detailed information on PAA in the atmosphere is of importance to better understand the free radical chemistry.

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Ramirez, Dario C., Sandra E. Gomez-Mejiba, Jean T. Corbett, Leesa J. Deterding, Kenneth B. Tomer e Ronald P. Mason. "Cu,Zn-superoxide dismutase-driven free radical modifications: copper- and carbonate radical anion-initiated protein radical chemistry". Biochemical Journal 417, n. 1 (12 dicembre 2008): 341–53. http://dx.doi.org/10.1042/bj20070722.

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Abstract (sommario):

The understanding of the mechanism, oxidant(s) involved and how and what protein radicals are produced during the reaction of wild-type SOD1 (Cu,Zn-superoxide dismutase) with H2O2 and their fate is incomplete, but a better understanding of the role of this reaction is needed. We have used immuno-spin trapping and MS analysis to study the protein oxidations driven by human (h) and bovine (b) SOD1 when reacting with H2O2 using HSA (human serum albumin) and mBH (mouse brain homogenate) as target models. In order to gain mechanistic information about this reaction, we considered both copper- and CO3•− (carbonate radical anion)-initiated protein oxidation. We chose experimental conditions that clearly separated SOD1-driven oxidation via CO3•− from that initiated by copper released from the SOD1 active site. In the absence of (bi)carbonate, site-specific radical-mediated fragmentation is produced by SOD1 active-site copper. In the presence of (bi)carbonate and DTPA (diethylenetriaminepenta-acetic acid) (to suppress copper chemistry), CO3•− produced distinct radical sites in both SOD1 and HSA, which caused protein aggregation without causing protein fragmentation. The CO3•− produced by the reaction of hSOD1 with H2O2 also produced distinctive DMPO (5,5-dimethylpyrroline-N-oxide) nitrone adduct-positive protein bands in the mBH. Finally, we propose a biochemical mechanism to explain CO3•− production from CO2, enhanced protein radical formation and protection by (bi)carbonate against H2O2-induced fragmentation of the SOD1 active site. Our present study is important for establishing experimental conditions for studying the molecular mechanism and targets of oxidation during the reverse reaction of SOD1 with H2O2; these results are the first step in analysing the critical targets of SOD1-driven oxidation during pathological processes such as neuroinflammation.

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28

Staniczek, Jakub, Żaneta Jastrzębska-Stojko e Rafał Stojko. "Biological Activity of Propolis Ointment with the Addition of 1% Nanosilver in the Treatment of Experimentally-Evoked Burn Wounds". Polymers 13, n. 14 (14 luglio 2021): 2312. http://dx.doi.org/10.3390/polym13142312.

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Abstract (sommario):

The main objective of this study was to assess the pharmacological efficacy of ointments containing 1% propolis and 1% nanosilver, compared to the conventional treatment of burn wounds. In the evaluation of the results, we used clinical observation of scars, microbiological examinations, pathomorphological examinations, and analysis of free radicals. The analysis of the experiment results concerning the therapeutic effectiveness of the propolis ointment revealed its wide-ranging antibacterial action (against Gram-positive and Gram-negative bacteria). The 1% propolis ointment was found to accelerate neoangiogenesis and epithelialization, have a positive effect on the healing of burn wounds, improve the cosmetic look of scars, and have no side-effects. The analysis of free radicals in burn wounds showed impressive activity of the 1% nanosilver ointment in the reduction of free radicals. No synergism of pharmacological activity of propolis and nanosilver was shown. A comparative evaluation of the acquired research material allows us to provide a favorable opinion on the topical treatment of burn wounds with 1% propolis. The obtained results show that the 1% propolis ointment reduces healing time, offers antimicrobial action, and has a positive effect on the normal process of scar formation.

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29

GOLOVIN, A. V., D. A. PONOMAREV e V. V. TAKHISTOV. "THERMOCHEMISTRY OF ORGANIC, HETEROORGANIC, AND INORGANIC MOLECULES AND THEIR FRAGMENTS: "QUANTUM-CHEMICAL CALCULATIONS OF THERMOCHEMICAL PARAMETERS: MOLECULES AND THEIR FRAGMENTS"". Journal of Theoretical and Computational Chemistry 09, supp01 (gennaio 2010): 125–53. http://dx.doi.org/10.1142/s0219633610005529.

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Abstract (sommario):

Analysis of theoretical enthalpies of formation for about 300 molecules and their fragments (free radicals, biradicals, and ions) was performed to show that the results of semiempirical, DFT, and ab initio methods must be taken with great caution. A brief review of the authors' alternative empirical methodologies for calculation of enthalpies of formation for molecules (enthalpic shift procedure) and free radicals (enthalpies of isodesmic reactions) is given.

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30

Saghafi, Homeira, e Morteza Vahedpour. "Atmospheric reactions of glyoxal with NO2 and NH2 radicals: Hydrogen abstraction mechanism and natural bond orbital analysis". Progress in Reaction Kinetics and Mechanism 44, n. 2 (maggio 2019): 187–209. http://dx.doi.org/10.1177/1468678319848880.

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Abstract (sommario):

Glyoxal can be important in atmospheric chemistry in terms of its ability to convert to secondary organic aerosols. In this study, the glyoxal-breaking reaction by two atmospheric active radicals, NO2 and NH2, has been investigated at the B3LYP and M06-2X levels in connection with 6-311++G(d,p) basis set. The formation of the most stable adducts from glyoxal with NO2/NH2 radical requires two hydrogen atom transfers. The accuracy of the predicted mechanisms in describing the hydrogen transfers was confirmed by atoms-in-molecules calculations and natural bond orbital analysis. The calculated results predict that hydrogen transfer process in both reactions at the M06-2X level is favourable from the kinetic and thermodynamic points of view. In the natural bond orbital analysis, the stabilization energy, E(2), delocalization corrections, at the B3LYP level is much higher than the same results at the M06-2X level (nearly twice). The activation thermodynamic parameters show that the first steps of the two reactions have lower barrier energy than the second steps. The Gibbs free energy values estimate that adducts of both the reactions at the mentioned method are spontaneous. The whole reaction of glyoxal + NH2 is more favourable than the whole reaction of glyoxal + NO2. The rate constants were calculated for the mentioned pathways using transition state theory for bimolecular steps and the fitted equations are reported.

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31

Skeva, Elina, e Stella Girousi. "A study of the antioxidative behavior of phenolic acids, in aqueous herb extracts, using a dsDNA biosensor". Open Chemistry 10, n. 4 (1 agosto 2012): 1280–89. http://dx.doi.org/10.2478/s11532-012-0051-0.

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Abstract (sommario):

AbstractElectrochemical DNA biosensors are promising tools for the fast, inexpensive and simple in vitro analysis for the determination of free radicals and antioxidants. High concentrations of antioxidants in such compounds as phenolic acids and plant extracts, act as free radical terminators which reduce the effect of the oxidative dam-age on DNA. The electrochemical behavior of three representative phenolic acids, caffeic acid, gallic acid and trolox were studied by cyclic voltammetry. Moreover, the determination of the above antioxidants under the optimized conditions (scan rate, deposition potential and time) using differential pulse voltammetry was also investigated. In vitro studies focused on their antioxidative effect were performed by adsorptive transfer stripping voltammetry and dsDNA biosensor. Using Fenton’s system, with FeSO4 and H2O2 was chosen as a strong oxidative system. This biosensor was applied as a screening antioxidant test in order to estimate the antioxidant capacity of aqueous herb extracts.

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32

Carter, Jennifer, Michael H. Fenwick, Wen-wei Huang, Vladimir V. Popik e Thomas T. Tidwell. "Addition of the nitroxyl radical TEMPO to 1-naphthylketene: formation of an unusual adduct". Canadian Journal of Chemistry 77, n. 5-6 (1 giugno 1999): 806–9. http://dx.doi.org/10.1139/v99-043.

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Abstract (sommario):

1-Naphthylketene (2), generated by thermal Wolff-rearrangement, is trapped in situ by 2,2,6,6-tetramethylpiridinyloxy radical (TEMPO, TO·) to form the adduct 1-naphthCH(OT)CO2T (4), whose structure is confirmed by an X-ray determination. The 1H NMR spectrum of 4 displays three CH3 groups with very high field chemical shifts (δ 0.10-0.47), and this is attributed to the location of these groups in the shielding region above the π system of the naphthyl ring. At -40°C, doubling of most of the 1H NMR signals occurs, and this is attributed to a freezing out of two conformations differing by rotation around the naphthylCH bond.Key words: ketene, TEMPO, restricted rotation, 1H NMR, conformational analysis, free radicals.

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33

Li, Xican, Xiaojian Ouyang, Minshi Liang e Dongfeng Chen. "Comparative Analysis of Radical Adduct Formation (RAF) Products and Antioxidant Pathways between Myricetin-3-O-Galactoside and Myricetin Aglycone". Molecules 24, n. 15 (30 luglio 2019): 2769. http://dx.doi.org/10.3390/molecules24152769.

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Abstract (sommario):

The biological process, 3-O-galactosylation, is important in plant cells. To understand the mechanism of the reduction of flavonol antioxidative activity by 3-O-galactosylation, myricetin-3-O-galactoside (M3OGa) and myricetin aglycone were each incubated with 2 mol α,α-diphenyl-β-picrylhydrazyl radical (DPPH•) and subsequently comparatively analyzed for radical adduct formation (RAF) products using ultra-performance liquid chromatography coupled with electrospray ionization quadrupole time-of-flight tandem mass spectrometry (UPLC-ESI-Q-TOF-MS) technology. The analyses revealed that M3OGa afforded an M3OGa–DPPH adduct (m/z 873.1573) and an M3OGa–M3OGa dimer (m/z 958.1620). Similarly, myricetin yielded a myricetin–DPPH adduct (m/z 711.1039) and a myricetin–myricetin dimer (m/z 634.0544). Subsequently, M3OGa and myricetin were compared using three redox-dependent antioxidant analyses, including DPPH•-trapping analysis, 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide radical (PTIO•)-trapping analysis, and •O2 inhibition analysis. In the three analyses, M3OGa always possessed higher IC50 values than those of myricetin. Conclusively, M3OGa and its myricetin aglycone could trap the free radical via a chain reaction comprising of a propagation step and a termination step. At the propagation step, both M3OGa and myricetin could trap radicals through redox-dependent antioxidant pathways. The 3-O-galactosylation process, however, could limit these pathways; thus, M3OGa is an inferior antioxidant compared to its myricetin aglycone. Nevertheless, 3-O-galactosylation has a negligible effect on the termination step. This 3-O-galactosylation effect has provided novel evidence that the difference in the antioxidative activities of phytophenols exists at the propagation step rather than the termination step.

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34

Chaubey, Ankita, e Ashok K. Dubey. "Chemistry and Antioxidant Potential of Phytoconstituents from Aegle Marmelos Fruit-Shell". Current Drug Metabolism 21, n. 7 (5 novembre 2020): 525–33. http://dx.doi.org/10.2174/1389200221666200711161056.

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Abstract (sommario):

Background: Oxidative stress is among the main causes of metabolic disorders. Hence, there is a need to discover potent antioxidants for therapeutic applications. Objective: The objective of this study has been to investigate the phytoconstituents of the methanolic extract of the hard shell of Aegle marmelos fruit and their antioxidant potential. Methods: Methanolic extract was fractionated using different solvents by liquid-liquid extraction. Characterization of the phytoconstituents was done by using phytochemical tests and GC-MS analysis. The free radical scavenging activity, total reducing power, lipid peroxidation inhibition and cell protection assays against oxidative stress were performed with methanolic extract and its fractions. Results: Therapeutically significant class of compounds, for example, polyphenols, glycosides and sterols were revealed in the hard-shell extract. Differential separation of compounds was achieved by liquid-liquid extraction using different solvents. Six compounds: 4-Hydroxybenzeneacetic acid; 5-Oxo-pyrrolidine-2-carboxylic acid methyl ester; 1-[3-Methyl-3-Butenyl] Pyrrolidine; Trans-sinapyl alcohol; 5-[Hydroxymethyl]-2-furaldehyde and 2,4- Dihydroxy-2,5-dimethyl-3[2H]-furan-3-one, identified in the fruit-shell extract, are being reported for the first time from this plant. Strong antioxidant potential of the extract was evident from efficient scavenging of free radicals. The extract also conferred protection to yeast cells against oxidative damage. Conclusion: Results showed that the hard shell of the Aegle marmelos fruit was a potent source for antioxidant compounds, which can be developed for therapeutic applications in the control and management of metabolic diseases.

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35

Maimulyanti, Askal, Anton Restu Prihadi e Iwan Safrudin. "Chemical Composition, Phytochemical Screening and Antioxidant Activity of Acmella uliginosa (Sw.) Cass Leaves". Indonesian Journal of Chemistry 16, n. 2 (13 marzo 2018): 162. http://dx.doi.org/10.22146/ijc.21160.

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Abstract (sommario):

Acmella uliginosa (Sw.) Cass is widely used in traditional medicine and used in the treatment of many diseases. Extraction of component in leaves of Acmella uliginosa used methanol, ethyl acetate and n-hexane solvent. The percentage yield of extract from the leaves in methanol, ethyl acetate and n-hexane were 6.50, 0.49, and 0.66, respectively. Analysis of component in various extracts of Acmella uliginosa (Sw.) Cass leaves used Gas Chromatography-Mass Spectrometry (GC-MS). The various classes of phytochemicals were identified from fractions of methanolic leaves extract by GC-MS. Qualitative analysis of phytochemical constituents in methanol, ethyl acetate and n-hexane extract were tannins, flavonoids, saponin, alkaloid and steroid. Antioxidant activity of Acmella uliginosa leaves from Indonesia was carried out by using 1,1,diphenyl-2-picryl-hydrazine (DPPH) free radical scavenging assay. The IC50 of three extract was calculated. A comparative study determined that Acmella uliginosa in ethyl acetate extract showed the highest antioxidant potential (IC50 = 28.09 µg/mL) compared to methanol extract (IC50 = 44.31 µg/mL) and n-hexane extract (181.23 µg/mL) against DPPH free radicals.

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Elbayomi, Smaher M., Haili Wang, Tamer M. Tamer e Yezi You. "Enhancement of Antioxidant and Hydrophobic Properties of Alginate via Aromatic Derivatization: Preparation, Characterization, and Evaluation". Polymers 13, n. 15 (2 agosto 2021): 2575. http://dx.doi.org/10.3390/polym13152575.

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Abstract (sommario):

The preparation of bioactive polymeric molecules requires the attention of scientists as it has a potential function in biomedical applications. In the current study, functional substitution of alginate with a benzoyl group was prepared via coupling its hydroxyl group with benzoyl chloride. Fourier transform infrared spectroscopy indicated the characteristic peaks of aromatic C=C in alginate derivative at 1431 cm−1. HNMR analysis demonstrated the aromatic protons at 7.5 ppm assigned to benzoyl groups attached to alginate hydroxyl groups. Wetting analysis showed a decrease in hydrophilicity in the new alginate derivative. Differential scanning calorimetry and thermal gravimetric analysis showed that the designed aromatic alginate derivative demonstrated higher thermo-stability than alginates. The aromatic alginate derivative displayed high anti-inflammatory properties compared to alginate. Finally, the in vitro antioxidant evaluation of the aromatic alginate derivative showed a significant increase in free radical scavenging activity compared to neat alginate against DPPH (2,2-diphenyll-picrylhydrazyl) and ABTS free radicals. The obtained results proposed that the new alginate derivative could be employed for gene and drug delivery applications.

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37

Roheem, Fatimah, Siti Mat Soad, Qamar Ahmed, Syed Ali Shah, Jalifah Latip e Zainul Zakaria. "Evaluation of the Enzyme Inhibitory and Antioxidant Activities of Entada spiralis Stem Bark and Isolation of the Active Constituents". Molecules 24, n. 6 (13 marzo 2019): 1006. http://dx.doi.org/10.3390/molecules24061006.

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Abstract (sommario):

Digestive enzymes and free radical inhibitors are used to prevent complications resulting from diabetes. Entada spiralis (family Leguminosae), which is a well-known medicinal plant in herbal medicine due to its various traditional and medicinal applications, was studied. Crude extracts were successively obtained from the stem bark using petroleum ether, chloroform and methanol as extracting solvents. The antioxidant activity of all the extracts, fractions and isolated compounds were estimated using 2,2-diphenyl-1-picrylhydrazyl (DPPH), β-carotene and 2,2′-azinobis(-3-ethylbenzothiazine-6-sulfonic acid) (ABTS) assays, while digestive enzymes inhibitory activity was assessed using α-amylase and α-glucosidase inhibitory methods. Structure elucidation of pure compounds was achieved through different spectroscopic analysis methods. Fractionation and purification of the most active methanol extract resulted in the isolation of a ferulic ester namely; (e)-hexyl 3-(4-hydroxy-3-methoxyphenyl) acrylate (FEQ-2) together with five known phenolic constituents, identified as kaempferol (FEQ-3), 5,4′-dihydroxy-3,7,3′-trimethoxyflavone (FEQ-2), gallic acid (FEQ-5), (+)-catechin (FEQ-7) and (−)-epicatechin (FEQ-8). FEQ-5 exhibited the strongest antioxidant and enzyme inhibitory activities followed by FEQ-3 and FEQ-4. FEQ-2 also displayed potent free radical scavenging activity with IC50 values of 13.79 ± 2.13 (DPPH) and 4.69 ± 1.25 (ABTS) µg/mL, respectively. All other compounds were found active either against free radicals or digestive enzymes.

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Bernardi, Fernando, Andrea Bottoni e Jaques Fossey. "Quantitative PMO Analysis of a Free Radical Reaction Pathway". Bulletin des Sociétés Chimiques Belges 91, n. 5 (1 settembre 2010): 365. http://dx.doi.org/10.1002/bscb.19820910524.

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39

Chang, Mian, Peiyuan Li e Liping Yang. "Simulation and analysis of free radical branching copolymerization kinetics". Science in China Series B: Chemistry 41, n. 2 (aprile 1998): 162–67. http://dx.doi.org/10.1007/bf02877802.

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40

Popa, Cristina, Mihai Patachia, Stefan Banita e Dan Constantin Dumitras. "Exertion in Kangoo Jumps Aerobic: Evaluation and Interpretation Using Spectroscopic Technique Determinations". Journal of Spectroscopy 2013 (2013): 1–6. http://dx.doi.org/10.1155/2013/602434.

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Abstract (sommario):

Laser photoacoustic spectroscopy (LPAS) is growing quickly in its applications to real world problems—one of the problems is to prevent obesity—being a candidate technology for breath analysis applications. The ongoing paper is aiming to investigate the evaluation of oxidative stress in womens practicing Kangoo Jumps (KJ) aerobics. Because it is not possible to directly measure free radicals in the body, we approach that by measuring the by-products (breath ethylene) that result from free radical reactions. We found out that the mixture of exhaled breath in women's after the KJ exercises contains low concentration of ethylene compared to the exhaled breath of the women before the start of exercise program. This result can add valuable information to the contribution to reduce the generation of prooxidants during and after KJ aerobics.

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Shoaib, Mohammad, Syed Wadood Ali Shah, Niaz Ali, Ismail Shah, Muhammad Naveed Umar, Shafiullah, Muhammad Ayaz, Muhammad Nawaz Tahir e Sohail Akhtar. "In VitroEnzyme Inhibition Potentials and Antioxidant Activity of Synthetic Flavone Derivatives". Journal of Chemistry 2015 (2015): 1–7. http://dx.doi.org/10.1155/2015/516878.

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Abstract (sommario):

Free radicals are produced by an important chemical process known as oxidation that in turn initiates chain reactions to damage the cells and originate oxidative stress. Flavones have got special position in research field of natural and synthetic organic chemistry due to their biological capabilities as antioxidant. The antioxidants are known to possess extensive biological effects that include antiviral, antibacterial, anti-inflammatory, antithrombotic, and vasodilatory activities. The simple flavone (F1) and substituted flavone derivatives (F2–F5) have been synthesized fromo-hydroxyacetophenone and benzaldehyde derivatives in good yield. The structures have been established by different spectroscopic techniques like1H NMR,13C NMR, IR, and elemental analysis. Antioxidant profile of these compounds was established using DPPH and H2O2free radical scavenging assay. The findings showed that halogenated flavones showed more enzyme inhibitions and antioxidant activities than simple flavones and are potential candidates for the treatment of wide range of diseases.

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Kozik, Violetta, Krystyna Jarzembek, Agnieszka Jędrzejowska, Andrzej Bąk, Justyna Polak, Mariola Bartoszek e Katarzyna Pytlakowska. "Investigation of Antioxidant Activity of Pomegranate Juices by Means of Electron Paramagnetic Resonance and UV-Vis Spectroscopy". Journal of AOAC INTERNATIONAL 98, n. 4 (1 luglio 2015): 866–70. http://dx.doi.org/10.5740/jaoacint.sge4-kozik.

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Abstract (sommario):

Abstract Pomegranate fruit (Punica granatum L.) is a source of numerous phenolic compounds, and it contains flavonoids such as anthocyanins, anthocyanidins, cyanidins, catechins and other complexes of flavonoids, ellagitannins, and hydrolyzed tannins. Pomegranate juice shows antioxidant, antiproliferative, and anti-atherosclerotic properties. The antioxidant capacity (TEAC) of the pomegranate juices was measured using electron paramagnetic resonance (EPR) spectroscopy and 1,1-diphenyl-2-picrylhydrazyl (DPPH•) as a source of free radicals, and the total phenolic (TP) content was measured using UV-Vis spectroscopy. All the examined pomegranate juices exhibited relatively high antioxidant properties. The TEAC values determined by means of EPR spectroscopy using Trolox (TE) as a free radical scavenger were in the range of 463.12 to 1911.91 μmol TE/100 mL juice. The TP content measured by the Folin-Ciocalteu method, using gallic acid (GA) as a free radical scavenger, widely varied in the investigated pomegranate juice samples and ranged from 1673.62 to 5263.87 mg GA/1 L juice. The strongest antioxidant properties were observed with the fresh pomegranate juices obtained from the fruits originating from Israel, Lebanon, and Azerbaijan. Correlation analysis of numerical data obtained by means of EPR spectroscopy (TEAC) and UV-Vis spectroscopy (TP) gave correlation coefficient (r) = 0.90 and determination coefficient (r2) = 0.81 (P <0.05).

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Pallag, Annamaria, Tunde Jurca, Vasile Sirbu, Ana Honiges e Claudia Jurca. "Analysis of the Amount of Polyphenols, Flavonoids and Assessment of the Antioxidant Capacity of Frozen Fruits". Revista de Chimie 69, n. 2 (15 marzo 2018): 445–48. http://dx.doi.org/10.37358/rc.18.2.6124.

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Abstract (sommario):

The data from literature shows that frozen vegetal products preserve their nutritional qualities for a long time. Fruits have a high content of substances with antioxidant capacity in the body. There are many recent studies demonstrating the importance of antioxidant substances in neutralizing free radicals in the human body. In this study there were analysed phenolic compounds and flavonoids in eight different species of fruits, belonging to three families. The antioxidant capacity of the extracts was evaluated by: CUPRAC assay, ABTS method and FRAP method. Our results show that the studied fruits represent rich sources of compounds with antioxidant capacity.

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Joseph, Anu Mary, K. N. Madhusoodhanan, Rosamma Alex e Benny George. "STABLE FREE RADICAL–ASSISTED MECHANICAL DEVULCANIZATION OF CARBON BLACK–FILLED NATURAL RUBBER VULCANIZATES". Rubber Chemistry and Technology 91, n. 2 (1 aprile 2018): 469–91. http://dx.doi.org/10.5254/rct.18.81633.

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Abstract (sommario):

ABSTRACT The issue of recombining of the radicals formed from cross-link scission and the consequent reformation of once-cleaved cross-links during mechanical devulcanization of carbon black–filled NR vulcanizates was investigated in a two-roll mill by the addition of the stable free radical 4-hydroxy-TEMPO (4HT), formerly 4-hydroxy-2, 2, 6, 6-tetramethylpiperidine-N-oxyl free radical. The effect of concentration of 4HT (0–6 pounds per hundred of rubber [phr]) and the effect of cure system, that is, conventional, semi-efficient (EV), and EV, used for vulcanization of the original sample on the efficiency of devulcanization were determined from the residual cross-link density of the gel part of the devulcanized rubber and the percent devulcanization, and further from revulcanizate properties. Chemical probe analysis of the devulcanized sample disclosed that (i) mechanical shearing predominantly breaks the majority cross-link type that decides the associated percent devulcanization; (ii) shear-induced chain-shortening reactions of polysulfidic cross-links occur at ambient conditions, increasing the absolute value of monosulfidic links irrespective of the significant reduction in total cross-link density due to cross-link scission; (iii) re–cross-linking of once cleaved bonds is being arrested in the presence of 4HT, thereby increasing the percent devulcanization. Both the bond energy of the cross-link type to be cleaved and the recombining capacity of the broken cross-links seem to play a decisive role in percent devulcanization, and the probable mechanism involved is suggested.

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Qi, Xuyao, Haibo Xue, Haihui Xin e Ziming Bai. "Quantum chemistry calculation of reaction pathways of carboxyl groups during coal self-heating". Canadian Journal of Chemistry 95, n. 8 (agosto 2017): 824–29. http://dx.doi.org/10.1139/cjc-2017-0176.

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Abstract (sommario):

During coal self-heating, reactions of carboxyl groups feature in the evolution of the spontaneous combustion of coal. However, their elementary reaction pathways during this process still have not been revealed. This paper selected the Ar–CH2–COOH as a typical carboxyl group containing structure for the analysis of the reaction pathways and enhancement effect on the coal self-heating process by quantum chemistry calculations. The results indicate that the hydrogen atoms in carboxyl groups are the active sites, which undergo the oxidation process and self-reaction process during coal self-heating. They both have two elementary reactions, namely (i) the hydrogen abstraction of –COOH by oxygen and the decarboxylation of the –COO· free radical and (ii) the hydrogen abstraction of –COOH and its pyrolysis. The total enthalpy change and activation energy of the oxidation process are 76.93 kJ/mol and 127.85 kJ/mol, respectively, which indicate that this process is endothermic and will occur at medium temperatures. For the hydrogen abstraction of –COOH by hydrocarbon free radicals, the thermal parameters are 53.53 kJ/mol and 56.13 kJ/mol, respectively, which has the same thermodynamic properties as the oxidation process. However, for the pyrolysis, the thermal parameters are –42.53 kJ/mol and 493.68 kJ/mol, respectively, and is thus exothermic and would not occur until the coal reaches high temperatures. They affect heat accumulation greatly, generate carbon dioxide, and provide new active centers for enhancing the coal self-heating process. The results would be helpful for further understanding of the coal self-heating mechanism.

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Clarke, Jennifer L., Irida Kastrati, Linda J. Johnston e Gregory RJ Thatcher. "Photochemical reactions of thiols with organic nitrates Oxygen atom transfer via a thionitrate". Canadian Journal of Chemistry 84, n. 4 (1 aprile 2006): 709–19. http://dx.doi.org/10.1139/v06-056.

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Nitroglycerin is an organic nitrate that has been used in the clinical treatment of angina for 130 years, yet important details of its mechanism of action remain unanswered. The biological activity of nitrates suggests that they are bioactivated to NO via a three-electron reduction. The involvement of free or bound protein thiols in this reduction has often been proposed. To examine the involvement of thiyl radicals in such a process, the photochemical generation of benzenethiyl radical from thiol and disulfide precursors was studied in the presence of isopropyl nitrate. Analysis of reaction products and kinetics led to the conclusion that photolysis of the nitrate to NO2 dominated the observed photochemistry. Formation of sulfonothioate and NO as products, and trapping of NO2 by 4-chlorophenol, indicated a mechanism involving oxygen atom transfer from N to S via a thionitrate intermediate. The results of the study did not indicate a rapid reaction between thiyl radical and organic nitrate. Despite weak nitrate absorption of light >300 nm and a relatively high BDE for homolysis to give NO2, the photochemistry under thiyl-generating conditions was driven by nitrate photolysis to NO2. A novel nitrate, containing a phenyl disulfanyl group linked to nitrate groups, did not undergo photolysis to NO2 or generate sulfonothioate, but did yield NO. These observations suggest that reaction between thiyl radicals and nitrates leading to NO release is a viable pathway, but it is subservient to other competing reactions, such as photolysis, in the case of IPN, and reaction with thiolate, in the case of the novel nitrate.Key words: nitrate, photolysis, thiyl radical, nitrogen dioxide, nitric oxide.

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47

Heming, Martin, Emil Roduner, Bruce D. Patterson, Walter Odermatt, Jörg Schneider, Hanspeter Baumeler, Hugo Keller e Ilija M. Savić. "Detection of muonated free radicals through the effects of avoided level crossing. Theory and analysis of spectra". Chemical Physics Letters 128, n. 1 (luglio 1986): 100–106. http://dx.doi.org/10.1016/0009-2614(86)80154-3.

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48

Bilici, Ali, İbrahim Halil Geçibesler e İsmet Kaya. "Enzymatic synthesis of 5-amino quinoline oligomers and evaluation of their free radical scavenging activity". Canadian Journal of Chemistry 95, n. 1 (gennaio 2017): 7–15. http://dx.doi.org/10.1139/cjc-2016-0210.

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The compound 5-aminoquinoline (AQ) was treated with horseradish peroxidase (HRP) and H2O2 in a reaction medium containing a dioxane:phosphate buffer mixture (70:30). Products (OAQ) with a degree of polymerization ranging from 4 to 12 were obtained. 1H NMR, FTIR, UV–vis, SEM, TG–DTA, DSC, XRD analysis, and conductivity measurements were conducted for characterization of OAQ. Compared with a monomer, OAQ showed higher thermal stability. After heating to 1000 °C, 46% of the initial weight of the OAQ remained. The antioxidant efficiencies of the monomer and oligomer were evaluated by the typical spectrophotometric method such as the bleaching of 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals. OAQ showed improved DPPH activity compared with the AQ monomer.

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49

Barzegar, Abolfazl, e Rogaie Rezaei-Sadabady. "Stepwise sequential analysis of stable multiradicals formation in polyphenolic myricetin active OH groups throughout the antioxidant process to scavenge free radicals". Journal of Molecular Structure 1146 (ottobre 2017): 635–43. http://dx.doi.org/10.1016/j.molstruc.2017.06.011.

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50

Hawrył, Anna, Mirosław Hawrył, Agnieszka Hajnos-Stolarz, Jagoda Abramek, Anna Bogucka-Kocka e Łukasz Komsta. "HPLC Fingerprint Analysis with the Antioxidant and Cytotoxic Activities of Selected Lichens Combined with the Chemometric Calculations". Molecules 25, n. 18 (19 settembre 2020): 4301. http://dx.doi.org/10.3390/molecules25184301.

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The aim of this study was to evaluate the ability of multivariate techniques to predict antioxidant and cytotoxic activity of the selected lichens from the chromatographic data. A simple and reproducible HPLC-DAD technique has been used to obtain the chromatographic fingerprint profiles. Reversed phase high performance liquid chromatography (RP-HPLC) linear gradient system with methanol, water and phosphoric acid (V) (pH 2.3) as the mobile phase was used (50 min). Principal Component Analysis (PCA) has been applied to the evaluation of the phytochemical similarity between studied samples, especially between the same species collected in various places of Poland (Cetraria islandica (L.) Ach., CI, Cladina mitis Sandst., CM, Hypogymnia physodes (L.) Nyl., HP). The ability to scavenge free radicals was evaluated using 2,2-diphenyl-1-picrylhydrazyl (DPPH) and ferric reducing antioxidant power (FRAP) methods and the total phenolic content was determined by Folin-Ciocalteu (F-C) test. In the case of DPPH % of inhibition was higher for selected species (Pseudevernia furfuracea (L.) Zopf, H. physodes in comparison to the literature data. The FRAP test showed that the H. physodes extract had higher ability to scavenge free radical in comparison to Cladonia furcata (Huds.) Schrader and Evernia prunastri (L.) Ach., whereas P. furfuracea extract showed higher ability than C. islandica. The high content of phenolics in P. furfuracea and H. physodes confirms their high antioxidant activity. The cytotoxic activity of studied extracts was tested by cell culture method using the human HL-60 / MX2 acute CKL-22 (CRL-2257) promyelocytic leukemia tumor cell line. The lowest values of IC50 [µg∙mL−1] were obtained for: H. physodes (HP1)—99.4; C. digitate—122.6; H. physodes (HP)—136.5, C. subulata—142.6; C. mitis—180.2.

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