Electron spin resonance spectra of radical intermediates in the oxidation of ascorbic acid and related substances

Chromate is an established human carcinogen. There have been many studies of the reactivity of chromate aimed at improving understanding of chromate toxicity. In the present paper a number of conclusions of these studies are reviewed and considered in the light of new results obtained in our laboratories. A number of hypotheses are considered; it is concluded, however, that it is impossible to reconcile the generation of strand breaks by chromate during its reduction by glutathione with any simple mechanism involving the generation of DNA lesions by free hydroxyl radicals. Kinetic, spin-trapping, and competition kinetic studies, based on a strand-breaking assay, are reported in support of this conclusion. -Environ Health Perspect 1 02(Suppl 3):3-10 (1994).

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“…The situation is further complicated for ascorbic acid by the stability of the ascorbic acid radical anion (45,46).…”

Section: Mehanisms Ofreductonsmentioning

confidence: 99%

Chemical Models Important in Understanding the Ways in Which Chromate Can Damage DNA

O’Brien

Kortenkamp

1994

Environmental Health Perspectives

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“…In a 1 mM aqueous sodium ascorbate solution (pH = 7.6, pKa of AH2 = 4.2 [29]) there exists, in equilibrium with AH-and A, an ESR detectable concentration of A'- [10,28]. (AH2 = ascorbic acid, AH-= ascorbate anion, A = dehydroascorbic, and A'-= ascorbate free radical, pKa = -0.45 [28].…”

Section: Resultsmentioning

confidence: 99%

“…(AH2 = ascorbic acid, AH-= ascorbate anion, A = dehydroascorbic, and A'-= ascorbate free radical, pKa = -0.45 [28]. )…”

Section: Resultsmentioning

confidence: 99%

Hydrogen peroxide and hydroxyl radical formation by methylene blue in the presence of ascorbic acid

Buettner¹,

Bannister²

1984

Radiat Environ Biophys

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Summary.Using ESR we have demonstrated the formation of the ascorbate free radical from sodium ascorbate, methylene blue and light. In oxygen uptake experiments we have observed the production of hydrogen peroxide while spin trapping experiments have revealed the iron catalyzed production of the hydroxyl free radical in this system. The presence of this highly reactive radical suggests that it could be the radical that initiates free radical damage in this photodynamic system.

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“…It has been established that L-ascorbic acid 1 (vitamin C) is readily oxidized in aqueous solution to a relatively stable radical whose controversial 1, the non-enzymatic systems, formation of the structure has been determined by esr spectroscopy ascorbate free radical may involve either an elec- (3). he ascorbic acid radicals generated in non-tron-transfer process and/or a molecular eliminaaqueous and aprotic solvents have also been re-tion process.…”

Section: Introductionmentioning

confidence: 99%

An electron spin resonance and time-resolved CIDEP study of the oxidation of ascorbic acid by pyruvic acid, duroquinone, and vitamin K₁

Depew¹,

Adeleke²,

Wan³

1981

Can. J. Chem.

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. Can. J. Chem. 59,2708 (1981).The photooxidation of vitamin C by pyruvic acid and its derivatives, duroquinone, and vitamin K, is systematically studied by the combined esr and time-resolved CIDEP technique. Because of the unique property of the triplet pyruvic acid which is different from that of the duroquinone triplet, the choice of these model systems allowed the CIDEP observations of the initial polarization of the ascorbate radical anion and its counter primary radical in either the enhanced absorptive or the emissive mode. The results demonstrate the efficient photooxidation of vitamin C by the triplet vitamin K, and that the latter triplet possesses similar properties as the triplet quinones. In the photooxidation system involving vitamin C and pyruvic acid, the adjustment of the pH ofthe aqueous solution afforded an opportunity to observe the photochemical reaction between two anions, the pyruvate anion and the ascorbate anion. Arguments were made in favor of an electron transfer mechanism for the oxidation of vitamin C by triplet vitamin K, but against the electron transfer mechanism for the oxidation of vitamin C by triplet pyruvate anion. T, values of the primary radicals estimated from their CIDEP transient responses at low microwave power are reported and it was suggested that the hydrogenbonding capacity of the ascorbate radical anion in water does not contribute significantly to the relative difference of Ti's between itself and the counter pyruvic ketyl radical.M. CATHERINE DEPEW, BABATUNDE B. ADELEKE et JEFFREY K. S. WAN. Can. J. Chem. 59,2708 (1981). En faisant appel la rpe combinke a la technique de PEDIC resolue en fonction du temps, on Ctudie systkmatiquement la photooxydation de la vitamine C par l'acide pyruvique et ses derives, par la duroquinone et par la vitamine K,. Compte tenu de la propriete unique du triplet de I'acide pyruvique qui est differente de celle du triplet de la duroquinone, le choix de ces modeles permet des observations de PEDIC de la polarisation initiale de I'anion radical ascorbate et de son radical primaire oppose lors de I'absorption ou de I'emission. Les resultats demontrent I'efficacite de la photooxydation de la vitamine C par le triplet de la vitamine K, et que le dernier triplet possede des propriCtCs identiques a celles du triplet des quinones. Dans la photooxydation qui implique la vitamine C et I'acide pyruvique, I'ajustement du pH de la solution aqueuse fournit I'opportunitk d'observer la reaction photochimique entre deux anions, I'anion pyruvate et I'anion ascrobate. On suggere un mecanisme par transfec d'tlectrons pour I'oxydation de la vitamine C par le triplet de la vitamine K,, mais on n'admet pas ce mecanisme dans le cas de I'oxydation de la vitamine C par le triplet de I'anion pyruvate. On rapporte les valeurs de T, des radicaux primaires evalues a partir de leurs reponses intermediaires en PEDIC en microondes de faible puissance, et on suggere que la capacite en liaison hydrogenes de I'anion radical ascorbate dans I'eau ne contribue pas de f a~o ...

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Electron spin resonance spectra of radical intermediates in the oxidation of ascorbic acid and related substances

Cited by 241 publications

References 1 publication

Chemical Models Important in Understanding the Ways in Which Chromate Can Damage DNA

Chemical Models Important in Understanding the Ways in Which Chromate Can Damage DNA

Hydrogen peroxide and hydroxyl radical formation by methylene blue in the presence of ascorbic acid

An electron spin resonance and time-resolved CIDEP study of the oxidation of ascorbic acid by pyruvic acid, duroquinone, and vitamin K₁

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Electron spin resonance spectra of radical intermediates in the oxidation of ascorbic acid and related substances

Cited by 241 publications

References 1 publication

Chemical Models Important in Understanding the Ways in Which Chromate Can Damage DNA

Chemical Models Important in Understanding the Ways in Which Chromate Can Damage DNA

Hydrogen peroxide and hydroxyl radical formation by methylene blue in the presence of ascorbic acid

An electron spin resonance and time-resolved CIDEP study of the oxidation of ascorbic acid by pyruvic acid, duroquinone, and vitamin K1

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An electron spin resonance and time-resolved CIDEP study of the oxidation of ascorbic acid by pyruvic acid, duroquinone, and vitamin K₁