The Experts below are selected from a list of 19476 Experts worldwide ranked by ideXlab platform
Catherine Riceevans - One of the best experts on this subject based on the ideXlab platform.
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34 screening of dietary carotenoids and carotenoid rich fruit extracts for antioxidant activities applying 2 2 azinobis 3 ethylenebenzothiazoline 6 sulfonic acid Radical Cation decolorization assay
Methods in Enzymology, 1999Co-Authors: Nicoletta Fellegrini, Roberta Ke, Min Yang, Catherine RiceevansAbstract:Publisher Summary This chapter discusses the screening of dietary carotenoids and carotenoid-rich fruit extracts for antioxidant activities applying 2, 2'-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) Radical Cation decolorization assay. The decolorization of the ABTS Radical Cation is an efficient, accurate assay for screening the antioxidant activities of lipophilic substances and food extracts. The inhibitory response of the Radical Cation is proportional to the antioxidant concentration, and the time point selected (2.5 min) for the analysis explains that this is an ideal measuring point when the reaction is complete. Results for the carotenoids are of the same order as previously reported data using alternative systems for generating the ABTS .+ Radical Cation. It is essential to examine the relative bioavailability, absorption, and hypoactivity of dietary carotenoids and flavonoids/phenolics to understand the importance of these diverse nutritional components in the maintenance of health and disease prevention. The chapter concludes with a discussion of trolox reference standard for relative antioxidant activities.
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factors influencing the antioxidant activity determined by the abts Radical Cation assay
Free Radical Research, 1997Co-Authors: Nicholas J Miller, Catherine RiceevansAbstract:(1997). Factors Influencing the Antioxidant Activity Determined by the ABTS•+ Radical Cation Assay. Free Radical Research: Vol. 26, No. 3, pp. 195-199.
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factors influencing the antioxidant activity determined by the abts Radical Cation assay
Free Radical Research, 1997Co-Authors: Nicholas J Miller, Catherine RiceevansAbstract:Abstract This study introduces a simple direct antioxidant assay, based on the reduction of the ABTS.+ Radical Cation, and compares it with the myoglobin/ABTS.+ assay. The methods give closely similar results, establishing that the antioxidants studied to date in the latter assay act by scavenging the ABTS.+ Radical Cation and not by inhibiting its formation through reduction of ferryl myoglobin or reaction with H2O2.
Andrzej Rajca - One of the best experts on this subject based on the ideXlab platform.
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Radical Cation and neutral Radical of aza thia 7 helicene with somo homo energy level inversion
Journal of the American Chemical Society, 2016Co-Authors: Ying Wang, Maren Pink, Suchada Rajca, Hui Zhang, Arnon Olankitwanit, Andrzej RajcaAbstract:We report a relatively persistent, open-shell aza-thia[7]helicene with cross-conjugated electron-rich π-system. The singly occupied molecular orbital (SOMO) energy levels of both Radical Cation and neutral Radical of the [7]helicene are below the highest occupied molecular orbital (HOMO) energy levels, thereby violating the Aufbau principle. The aza-thia[7]helicene is prepared from β-hexathiophene by a three-step one-pot reaction, in which the pyrrole ring is constructed by two consecutive C–N bond formations. Chemical oxidation converts the helicene to its Radical Cation, while in the presence of base (Cs2CO3), the oxidation gives neutral aminyl Radical, likely via proton dissociation from the aminium Radical Cation with a low pKa. Reaction of the aza-thia[7]helicene with NaH provides the corresponding anion, which shows characteristic cyclic voltammetry wave at anodic peak potential Epa ≈ +0.2 V. Chemical oxidation of the anion with ferrocenium hexafluorophosphate at room temperature gives persistent ne...
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Radical Cation and Neutral Radical of Aza-thia[7]helicene with SOMO–HOMO Energy Level Inversion
2016Co-Authors: Ying Wang, Maren Pink, Suchada Rajca, Hui Zhang, Arnon Olankitwanit, Andrzej RajcaAbstract:We report a relatively persistent, open-shell aza-thia[7]helicene with cross-conjugated electron-rich π-system. The singly occupied molecular orbital (SOMO) energy levels of both Radical Cation and neutral Radical of the [7]helicene are below the highest occupied molecular orbital (HOMO) energy levels, thereby violating the Aufbau principle. The aza-thia[7]helicene is prepared from β-hexathiophene by a three-step one-pot reaction, in which the pyrrole ring is constructed by two consecutive C–N bond formations. Chemical oxidation converts the helicene to its Radical Cation, while in the presence of base (Cs2CO3), the oxidation gives neutral aminyl Radical, likely via proton dissociation from the aminium Radical Cation with a low pKa. Reaction of the aza-thia[7]helicene with NaH provides the corresponding anion, which shows characteristic cyclic voltammetry wave at anodic peak potential Epa ≈ +0.2 V. Chemical oxidation of the anion with ferrocenium hexafluorophosphate at room temperature gives persistent neutral aminyl Radical. Structure of the aza-thia[7]helicene is supported by NMR, IR, X-ray crystallography, and cyclic voltammetry. The Radical Cation and neutral Radical are characterized by EPR and UV–vis-NIR spectroscopies. DFT computations of the Radical Cation and neutral Radical predict the SOMO–HOMO energy level inversion, which is supported experimentally by electrochemical data for the Radical Cation
Catherine A. Rice-evans - One of the best experts on this subject based on the ideXlab platform.
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Antioxidant activity applying an improved ABTS Radical Cation decolorization assay
Free Radical Biology and Medicine, 1999Co-Authors: Roberta Re, Catherine A. Rice-evans, Anna Proteggente, Ananth Pannala, Nicoletta Pellegrini, Min YangAbstract:A method for the screening of antioxidant activity is reported as a decolorization assay applicable to both lipophilic and hydrophilic antioxidants, including flavonoids, hydroxycinnamates, carotenoids, and plasma antioxidants. The pre-formed Radical monoCation of 2,2'-azinobis-(3- ethylbenzothiazoline-6-sulfonic acid) (ABTS·+) is generated by oxidation of ABTS with potassium persulfate and is reduced in the presence of such hydrogen-donating antioxidants. The influences of both the concentration of antioxidant and duration of reaction on the inhibition of the Radical Cation absorption are taken into account when determining the antioxidant activity. This assay clearly improves the' original TEAC assay (the ferryl myoglobin/ABTS assay) for the determination of antioxidant activity in a number of ways. First, the chemistry involves the direct generation of the ABTS Radical monoCation with no involvement of an intermediary Radical. Second, it is a decolorization assay; thus the Radical Cation is pre-formed prior to addition of antioxidant test systems, rather than the generation of the Radical taking place continually in the presence of the antioxidant. Hence the results obtained with the improved system may not always be directly comparable with those obtained using the original TEAC assay. Third, it is applicable to both aqueous and lipophilic systems.
Ying Wang - One of the best experts on this subject based on the ideXlab platform.
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Radical Cation and neutral Radical of aza thia 7 helicene with somo homo energy level inversion
Journal of the American Chemical Society, 2016Co-Authors: Ying Wang, Maren Pink, Suchada Rajca, Hui Zhang, Arnon Olankitwanit, Andrzej RajcaAbstract:We report a relatively persistent, open-shell aza-thia[7]helicene with cross-conjugated electron-rich π-system. The singly occupied molecular orbital (SOMO) energy levels of both Radical Cation and neutral Radical of the [7]helicene are below the highest occupied molecular orbital (HOMO) energy levels, thereby violating the Aufbau principle. The aza-thia[7]helicene is prepared from β-hexathiophene by a three-step one-pot reaction, in which the pyrrole ring is constructed by two consecutive C–N bond formations. Chemical oxidation converts the helicene to its Radical Cation, while in the presence of base (Cs2CO3), the oxidation gives neutral aminyl Radical, likely via proton dissociation from the aminium Radical Cation with a low pKa. Reaction of the aza-thia[7]helicene with NaH provides the corresponding anion, which shows characteristic cyclic voltammetry wave at anodic peak potential Epa ≈ +0.2 V. Chemical oxidation of the anion with ferrocenium hexafluorophosphate at room temperature gives persistent ne...
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Radical Cation and Neutral Radical of Aza-thia[7]helicene with SOMO–HOMO Energy Level Inversion
2016Co-Authors: Ying Wang, Maren Pink, Suchada Rajca, Hui Zhang, Arnon Olankitwanit, Andrzej RajcaAbstract:We report a relatively persistent, open-shell aza-thia[7]helicene with cross-conjugated electron-rich π-system. The singly occupied molecular orbital (SOMO) energy levels of both Radical Cation and neutral Radical of the [7]helicene are below the highest occupied molecular orbital (HOMO) energy levels, thereby violating the Aufbau principle. The aza-thia[7]helicene is prepared from β-hexathiophene by a three-step one-pot reaction, in which the pyrrole ring is constructed by two consecutive C–N bond formations. Chemical oxidation converts the helicene to its Radical Cation, while in the presence of base (Cs2CO3), the oxidation gives neutral aminyl Radical, likely via proton dissociation from the aminium Radical Cation with a low pKa. Reaction of the aza-thia[7]helicene with NaH provides the corresponding anion, which shows characteristic cyclic voltammetry wave at anodic peak potential Epa ≈ +0.2 V. Chemical oxidation of the anion with ferrocenium hexafluorophosphate at room temperature gives persistent neutral aminyl Radical. Structure of the aza-thia[7]helicene is supported by NMR, IR, X-ray crystallography, and cyclic voltammetry. The Radical Cation and neutral Radical are characterized by EPR and UV–vis-NIR spectroscopies. DFT computations of the Radical Cation and neutral Radical predict the SOMO–HOMO energy level inversion, which is supported experimentally by electrochemical data for the Radical Cation
V A Starodub - One of the best experts on this subject based on the ideXlab platform.
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first hybrid Radical Cation salts with halogen substituted iron bis dicarbollide anions synthesis structure properties
Journal of Organometallic Chemistry, 2017Co-Authors: Olga N. Kazheva, V I Bregadze, Andrey V Kravchenko, V A Starodub, Irina D Kosenko, Grigorii G Alexandrov, Denis M Chudak, I A Lobanova, L I Buravov, Svetlana G ProtasovaAbstract:Abstract New Radical-Cation salts based on bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF or ET) were synthesized: (ЕТ)2[8,8′-Br2-3,3′-Fe(1,2-C2B9H10)2] (1) and (ЕТ)[8,8′-I2-3,3′-Fe(1,2-C2B9H10)2] (2). Their crystal structures were studied by X-ray analysis, electroconducting and magnetic properties were measured in a wide temperature range. Salts (1) and (2) appeared to be the first Radical-Cation salts with [8,8′-I2-3,3′-Fe(1,2-C2B9H10)2]- and [8,8′-Br2-3,3′-Fe(1,2-C2B9H10)2]- anions, respectively. In the literature [8,8′-I2-3,3′-Fe(1,2-C2B9H10)2]- and [8,8′-Br2-3,3′-Fe(1,2-C2B9H10)2]- anions are presented for the first time. Salts (1) and (2) were found to be paramagnetic. Their room temperature conductivities were 2 and 1·10−6 Ohm−1cm−1, respectively.
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tetrathiafulvalene based Radical Cation salts with transition metal bis dicarbollide anions
CrystEngComm, 2015Co-Authors: V I Bregadze, Olga N. Kazheva, O A Dyachenko, Andrey V Kravchenko, Igor B Sivaev, V A StarodubAbstract:Radical Cation salts based on derivatives of tetrathiafulvalene and sandwiched transition metal bis(dicarbollide) anions are of great interest in the development of new molecular conducting materials. The data on their synthesis, crystal structure, and electrical and magnetic properties were reviewed. The effect of various substituents in the metallacarborane anion on the structure and physical properties of their tetrathiafulvalene-based Radical Cation salts was analyzed. Relationships between the crystal structure and properties of the tetrathiafulvalene-based Radical Cation salts containing sandwiched transition metal bis(1,2-dicarbollide) anions are discussed.
