Home About us Contact
|
Home About us Contact | ||
|
|
||
Chain-breaking Antioxidant (chain-breaking + antioxidant)
Selected AbstractsNatural polyphenols as chain-breaking antioxidants during methyl linoleate peroxidationEUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 8 2010Ivan Tichonov Abstract A technique based on monitoring oxygen consumption was applied to study 11 natural and model polyphenols (PP, QH2) as well as four typical monophenolics as a chain-breaking antioxidant during the controlled chain oxidation of methyl linoleate (ML) in bulk at 37°C. The antioxidant activities of QH2 were characterized by two parameters: the rate constant k1 for reaction of QH2 with the peroxy radical : (i) QH2,+,,,,,+,LOOH and the stoichiometric factor of inhibition, f, which shows how many kinetic chains may be terminated by one molecule of QH2. The rate constant k1 were reduced significantly by factor of 4 ,28 as compared to these determined during the oxidation of styrene in bulk; the effect was typically more pronounced for catechol derivatives than for pyrogallol derivatives. At the same time, f for QH2 was found to be close to two independent of the number of active OH groups, similar to that determined earlier during the inhibited oxidation of styrene. The formation of H bond between OH group of QH2 and carboxyl group of ML is suggested as a reason for reducing effect of ML on k1. Practical applications: This work reports rate constants for the reaction of lipid peroxyl radical with phenolics and stoichiometric coefficient of inhibition, which characterize the antioxidant activity (AOA) of 15 natural and model PP, QH2 during the controlled peroxidation of ML. The reactivity of PP, QH2 during the oxidation of ML is routinely lower than the reactivity during the oxidation of non-polar model hydrocarbons. This information may be useful to estimate the AOA of natural PP, QH2 in real systems of practical significance including plant oils, fats, food-stuffs, biological objects, and similar. [source] The chain-breaking antioxidant activity of phenolic compounds with different numbers of O-H groups as determined during the oxidation of styreneINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 2 2009Ivan Tikhonov The technique based on monitoring oxygen consumption was applied to test 18 polyphenols (PP) and model phenolics as a chain-breaking antioxidant during the oxidation of styrene initiated by 2,2,-azobis(2,4-dimethylvaleronitril) at 37°C. The chain-breaking capability of PP was characterized by two parameters: the rate constant k1 for the reaction of antioxidants with the peroxy radical produced from styrene and the stoichiometric coefficient of inhibition, f, which shows how many kinetic chains are terminated by one molecule of PP. Rate constants k1 × 105 (in M,1 s,1) were found to be 10 (catechol), 27 (pyrogallol), 34 (3,6-di-tert-Bu-catechol), 4.3 (protocatechic acid), 12 (gallic acid), 15 (caffeic acid), <0.01 (chrysin), 1.3 (kaempferol), 19 (quercetin), 5.3 (baicalein), 16 (epicatechin), 32 (epigallocatechin), 9.0 (dihydroquercetin), 3.3 (resveratrol), and 16 (nordihydroguaiaretic acid). The value of k1 increases when going from one to two and three adjacent O-H groups in a benzene ring (catechol and pyrogallol derivatives, respectively). At the same time, two O-H groups in metaposition in a A-ring of flavonoids actually do not participate in the inhibition. For the majority of PP, f is near to 2 independent of the number of OH groups. The correlation of k1 with the structure of PP and the OH bond dissociation enthalpy has been discussed. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 41: 92,100, 2009 [source] Self-sensitized Photodegradation of Membrane-bound Protoporphyrin Mediated by Chain Lipid Peroxidation: Inhibition by Nitric Oxide with Sustained Singlet Oxygen DamagePHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 2 2005Magdalena Niziolek ABSTRACT In the presence of exciting light, iron and reductants, the singlet oxygen (1O2)-generating sensitizer protoporphyrin IX (PpIX) induces free radical lipid peroxidation in membranes, but gradually degrades in the process. We postulated that NO, acting as a chain-breaking antioxidant, would protect PpIX against degradation and consequently prolong its ability to produce 1O2. This idea was tested by irradiating PpIX-containing liposomes (LUVs) in the presence of iron and ascorbate, and monitoring the cholesterol hydroperoxides 5,-OOH and 7,/,-OOH as respective 1O2 and free radical reporters. 5,-OOH accumulation, initially linear with light fluence, slowed progressively after prolonged irradiation, whereas 7,/,-OOH accumulation only accelerated after an initial lag. The active, but not spent, NO donor spermine NONOate (0.4 mM) virtually abolished 7,/,-OOH buildup as well as 5,-OOH slowdown. Increasing membrane phospholipid unsaturation hastened the onset of rapid chain peroxidation and 5,-OOH slowdown. Accompanying the 5,-OOH effect was a steady decrease in 1O2 quantum yield and PpIX fluorescence at 632 nm, both of which were inhibited by NO. An NO-inhibitable decay of PpIX fluorescence was also observed during dark incubation of 5,-OOH-bearing LUVs with iron and ascorbate, confirming a link between chain peroxidation and PpIX loss. By protecting PpIX in irradiated membranes, NO might select for and prolong purely 1O2 -mediated damage. Supporting this was our observation that 1O2 -mediated photoinactivation of a nonmembrane target, lactate dehydrogenase, slowed concurrently with 5,-OOH accumulation and that spermine NONOate prevented this. Thus, NO not only protected membrane lipids against PpIX-sensitized free radical damage, but PpIX itself, thereby extending its 1O2 -generating lifetime. Consistent findings were obtained using porphyrin-sensitized COH-BR1 cells. These previously unrecognized effects of NO could have important bearing on 5-aminolevulinate-based photodynamic therapy in which PpIX is metabolically deposited in tumor cells. [source] Natural polyphenols as chain-breaking antioxidants during methyl linoleate peroxidationEUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 8 2010Ivan Tichonov Abstract A technique based on monitoring oxygen consumption was applied to study 11 natural and model polyphenols (PP, QH2) as well as four typical monophenolics as a chain-breaking antioxidant during the controlled chain oxidation of methyl linoleate (ML) in bulk at 37°C. The antioxidant activities of QH2 were characterized by two parameters: the rate constant k1 for reaction of QH2 with the peroxy radical : (i) QH2,+,,,,,+,LOOH and the stoichiometric factor of inhibition, f, which shows how many kinetic chains may be terminated by one molecule of QH2. The rate constant k1 were reduced significantly by factor of 4 ,28 as compared to these determined during the oxidation of styrene in bulk; the effect was typically more pronounced for catechol derivatives than for pyrogallol derivatives. At the same time, f for QH2 was found to be close to two independent of the number of active OH groups, similar to that determined earlier during the inhibited oxidation of styrene. The formation of H bond between OH group of QH2 and carboxyl group of ML is suggested as a reason for reducing effect of ML on k1. Practical applications: This work reports rate constants for the reaction of lipid peroxyl radical with phenolics and stoichiometric coefficient of inhibition, which characterize the antioxidant activity (AOA) of 15 natural and model PP, QH2 during the controlled peroxidation of ML. The reactivity of PP, QH2 during the oxidation of ML is routinely lower than the reactivity during the oxidation of non-polar model hydrocarbons. This information may be useful to estimate the AOA of natural PP, QH2 in real systems of practical significance including plant oils, fats, food-stuffs, biological objects, and similar. [source] | ||||||||||