The oxygen radical absorbance capacity (ORAC) method was used to detect the antiperoxyradical ability of organoselenium compounds: selenophene and its derivative, 2-amino-4,5,6,7-tetrahydro-1-selenophene-3-carbonitrile (ATSe); while as a comparison, the sulfur-containing analogue of selenophene—thiophene and its derivative—2-amino-4,5,6,7-tetrahydro-1-thiophene-3-carbonitrile (ATS)—was selected. Cyclic voltammetry (CV), differential pulse voltammetry (DPV) and squarewave voltammetry (SWV) methods were used to determine the redox characteristics of organoselenium and organosulfur compounds. The antiradical activity and capacity of the studied compounds were also measured by using stable radical 2,2ʹ-diphenyl-1-picrylhydrazyl (DPPH). Detected anodic peaks of the oxidation of selenophene, thiophene and their derivatives in CV, DPV and SWV in the interval of −1200 ÷ (+1600) mV potentials in regard to the Ag/Ag+ medium of acetonitrile prove the presence of antiperoxyradical activity in regard to oxidizers, i.e., peroxyradicals. The chemical mechanism of the antiperoxyradical ability of selenophene, thiophene and their organic derivatives is proposed.
Absolute rate constants (k eff ) for the chemical reactions of Cu(II) 2 (3,5-di-iso-propylsalicylate) 4 (H 2 O) 3 , Cu(II) 2 (3,5-di-tert-butylsalicylate) 4 , Cu(II) 2 (3,5-di-tert-butylsalicylate) 4 (H 2 O) 4 , Cu(II) 2 (3,5-dimethylsalicylate) 4 (H 2 O) 3 , Cu(II) 2 (3-ethylsalicylate) 4 (H 2 O), Cu(II) 2 (3-phenylsalicylate) 4 , and Cu(II)(3,5-di-iso-propylsalicylate) 2 (pyridine) 2 with tertbutylperoxyl radical were determined using kinetic electron paramagnetic resonance measurements in 10% toluene in the hexane medium at temperatures ranging from −63 • C to 2 • C. These antioxidant (AO) chelates were ranked by their reactivity as follows:Cu(II)(3,5-di-isopropylsalicylate) 2 (pyridine) 2 at 20 • C. Differential pulse voltammetry was used to determine redox behavior of these chelates in CH 2 Cl 2 . Two types of salicylic OH groups were detected in these Cu(II) salicylates, characterized by the presence or absence of AO reactivity. One of them REACTIVITY OF SUBSTITUTED COPPER(II) SALICYLATES WITH TERT-BUTYLPEROXYL RADICAL 57was coordinate covalently bonded to Cu(II) via the oxygen atoms of the salicylic OH groups, displaying oxidation peak potentials in the range from +650 to 970 mV versus Ag/Ag + . The second type was intramolecularly hydrogen bonded to carboxylate oxygens, with an oxidation peak potential in the range from +1100 to 1200 mV versus Ag/Ag + . It was concluded that nonhydrogen-bonded salicylic OH groups are responsible for the antiperoxyl radical reactivity of these chelates, while neither Cu(II) nor salicylate ligands displayed reactivity with peroxyl radical. It has been established in this research that axially bonded electron pair donors such as pyridine and water decrease H-donating reactivity of Cu(II) salicylates by promoting the formation of intramolecular hydrogen bonding between the salicylic OH hydrogen atoms and carboxylate oxygen atoms in the salicylic ligands. Dependences of log k eff at 20 • C and the anodic oxidation potential (E pa ) for the salicylic OH group on the difference between symmetric and asymmetric stretching frequencies of carboxylate groups (in Fourier transform infrared spectra) for the substituted Cu(II) salicylates were determined. C 2009 Wiley Periodicals, Inc. Int J Chem Kinet 42: [56][57][58][59][60][61][62][63][64][65][66][67] 2010
ethylenediaminonickel(II), and N,N -bis(salicylidene)ethylenediaminoaquacobalt(II), as well as (R,R)-(-)-N,N -bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediamine, were kinetically examined as antioxidants in the scavenging of tert-butylperoxyl radical (tert-butylOO • ). Absolute rate constants and corresponding Arrhenius parameters were determined for reactions of tert-butylOO• with these chelates in the temperature range −52.5 to −11 • C. High reactivity of tert-butylOO• with Mn(III) and Co(II) salicylidene Schiff base chelates was established using a kinetic electron paramagnetic resonance method. These salicylidene Schiff base chelates react in a 1:1 stoichiometric fashion with tert-butylOO
Chemical mechanisms of antioxidant and electron donating function of the hypothalamic proline-rich polypeptides have been clarified on the molecular level. The antioxidant-chelating property of Galarmin and Gx-NH(2) was established by their capability to inhibit copper(II) dichloride catalyzed H(2)O(2) decomposition, thus preventing formation of HO(*) and HOO(*) radicals. The antiradical activity of Galarmin and Gx-NH(2) was determined by their ability to react with 2,2-diphenyl-1-picrylhydrazyl radical applying differential pulse voltammetry and UV-Vis spectrophotometry methods. Galarmin manifest antiradical activity towards 2,2-diphenyl-1-picrylhydrazyl radical, depending on the existence of phenolic OH group in tyrosine residue at the end of the molecule. The presence of antiradical activity and reduction properties of Galarmin are confirmed by the existence of an oxidation specific peak in voltammograms made by differential pulse voltammetry at E ( composite function) = 0.795 V vs. Ag/Ag(+) aq.
The hybrid molecule phenylthiazolidine derivatives and probucol were kinetically examined as antioxidants (AOs) in scavenging tert‐butylperoxyl radical (t‐BuOO•) with comparable to the reference AO, butylated hydroxytoluene (BHT). The anti‐t‐BuOO• reactivity of phenylthiazolidine derivatives and probucol was established using the direct kinetic electron paramagnetic resonance (EPR) technique with pulse reactant injection. Absolute values of the bimolecular reaction rate constants and antiradical capacities of the studied compounds were measured from −63 to 0°C. The main antiperoxylradical sites of the compounds under study were revealed.High removal ability of t‐BuOO• by (2‐(4‐hydroxyphenyl)thiazolidine), 4‐[thiazolidin‐2‐yl]benzene‐1,2‐diol, 2‐(4‐hydroxyphenyl)thiazolidine‐4‐carboxylic acid and probucol was connected with the reaction of hydrogen atom abstraction from phenolic OH group.Weaker antiperoxylradical reactivity of 2‐phenylthiazolidine was connected with the slower reaction of hydrogen atom abstraction from benzylic C–H bond in reference to nitrogen and sulfur atoms compared with the phenolic OH group. It is found that sulfide groups had much weaker participation in antiperoxylradical reactivity of the studied compounds. It is concluded that removal of alkylperoxyl radicals by oxidizable phenylthiazolidine derivatives and probucol may partially account for biological activity of their compounds.
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