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'Dehydroascorbic Acid' in keywords
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1982 (1)
1981 (1)
1977 (1)
1Author    WernerH. Kalus, WilliamG. FilbyRequires cookie*
 Title    Is there an Equilibrium between A scorbic and Dehydroascorbic Acids?  
 Abstract    The previously reported interaction between ascorbate monoanion and dehydroascorbic acid yielding semidehy-droascorbic acid has been shown to be therm odynam ically unfeasible and non-existent. N o evidence for radical for­ mation in the reinvestigation o f the reaction using ESR spectroscopy under careful exclusion o f air could be found. Our results show that the detection o f the free radical in earlier studies resulted from the reaction of ascorbate with traces of oxygen and/o r metals. 
  Reference    Z. Naturforsch. 36c, 1088—1090 (1981); received May 19 1981 
  Published    1981 
  Keywords    Ascorbic Acid, Dehydroascorbic Acid, Redox Potential, Free Radical, ESR 
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 TEI-XML for    default:Reihe_C/36/ZNC-1981-36c-1088_n.pdf 
 Identifier    ZNC-1981-36c-1088_n 
 Volume    36 
2Author    Helmut Sapper, Sa-Ouk Kang, H Ans-H Elm, Ut Paul, W. Olfgang, Lohm AnnRequires cookie*
 Title    The Reversibility of the Vitamin C Redox System: Electrochemical Reasons and Biological Aspects  
 Abstract    The biological efficacy o f vitamin C depends on its redox abilities as given by the relations between ascorbic acid, semidehydroascorbic acid, and dehydroascorbic acid. It is shown by means of proton magnetic resonance spectroscopy that the enzymatic (by ascorbate oxidase) as well as non-enzymatic (by iodine) oxidation o f ascorbic acid is, in principle, reversible despite the hydration and structural changes during the formation o f dehydroascorbic acid. The strong redox activity o f semidehydroascorbic acid which results in a fast disproportionation to ascorbic acid and dehydroascorbic acid is inferred from an inversion o f the electrochemical potentials o f the vitamin C redox system. The capacity o f this is maintained by a fast reduction o f dehydro­ ascorbic acid e.g. by reduced glutathione, preventing its delactonization and further degradation. 
  Reference    Z. Naturforsch. 37c, 942 (1982); received May 19/July 20 1982 
  Published    1982 
  Keywords    Vitamin C, Dehydroascorbic Acid, Glutathione, Ascorbate Oxidase, NM R Spectroscopy 
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 TEI-XML for    default:Reihe_C/37/ZNC-1982-37c-0942.pdf 
 Identifier    ZNC-1982-37c-0942 
 Volume    37 
3Author    Rudolf MatuschRequires cookie*
 Title    Reduktone und Reduktonate, I Das Redoxpaar Dehydroascorbinsäure-Ascorbinsäure und ihre Anionen Reductones and Reductonates, I The Redox Pair Dehydroascorbic Acid-Ascorbic Acid and Anions  
 Abstract    On the basis of NMR spectroscopy (X H and 1 3 C) it can be shown that in water, dimethyl-sulfoxide and p-dioxane only the tautomer 1 of L-ascorbic acid is found in a measurable amount. Upon formation of the mono-anion l a deprotonation occurs on the hydroxyl group attached to C-3; in addition the hydroxyl group on C-2 is deprotonated in case of the di-anion lb . Both anions do not open the lactone ring. After oxidation with iodine in aqueous solution only the dimer of dehydroascorbic acid is detected. This is hydrolized with a half-life of three hours to the monomeric dehydro ascorbic acid dihydrate 7. In dimethylsulfoxide the oxidation rate is decreased, and therefore the formation of the monomeric non-hydratized dehydroascorbic acid 10 can be monitored. This undergoes ringclosure relatively fast to give the half-ketal 13, the reaction of which via 14 leads to the optical active dimeric dehydroascorbic acid 6 . The L-ascorbic acid acetonide 15 is oxidised by iodine to 16 which undergoes racemization via the enol 17 to give 18. This forms an equilibrium with compound 19. 
  Reference    (Z. Naturforsch. 32b, 562—568 [1977]; eingegangen am 17. Dezember 1976) 
  Published    1977 
  Keywords    Ascorbic Acid, Dehydroascorbic Acid, Dimeric Dehydroascorbic Acid, Dehydroascorbic Acid-dihydrate, Dehydroascorbic Acid-acetonide 
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 TEI-XML for    default:Reihe_B/32/ZNB-1977-32b-0562.pdf 
 Identifier    ZNB-1977-32b-0562 
 Volume    32