Showing papers on "Dehydroascorbic acid published in 1977"

Physiological role of dehydroascorbic acid.

Abstract: Dehydroascorbic acid is present in insignificant amounts in plant and animal tissue but appears in considerable amounts under various physiological and pathological conditions. It is found increased: in blood of patients suffering from infectious diseases; in blood and tissues of thyrotoxic patients; in blood after injection of thyroxin, corticotropin and cortisone. In all the above conditions there is concomitant decrease in L-ascorbic acid and glutathione values of blood and tissues. Dehydroascorbic acid, however, disappears after continued administration of a high dose of ascorbic acid. The accumulation of dehydroascorbic acid seems to be an indication of ascorbic acid deficiency. The extreme sensitivity of the ascorbate system to physiological changes is suggestive of a major biochemical role for this redox system. Accumulated evidences indicate that dehydroascorbic acid possible control cell division.

Determination of vitamin c (l-ascorbic acid and dehydroascorbic acid) in food by manual and automated photometric methods

Abstract: L-ascorbic acid (AA) plus dehydroascorbic acid (DHAA) in foods were determined manually and with an automated sample processor according to the principles of the 2,4-dinitrophenylhydrazine method of Pelletier [J. Lab. & Clin. Med. (1968), 72: 674] for biological materials but with modifications that rendered the methods simpler and applicable to foods. These methods eliminated interference from reductones (arising from sugars during food processing) and of diketogulonic acid (a product of the oxidation of DHAA). Sucrose in a concentration 30,000 times that of AA did not affect the vitamin C assay values. Fructose and glucose, in concentrations respectively 417 and 1668 times that of AA, increased the vitamin C values by only 2–3%. Since a higher range of concentrations of fructose and glucose together gave rather constant increase (8%) in vitamin C values, possible interference from the sugars in noncitrus fruits was eliminated by incorporating a mixture of these sugars in the solutions of standards and samples. Comparisons of vitamin C values in food between the proposed procedures and a modification of the widely used method of Roe [J. Biol. Chem. (1961b) 236: 1611] showed agreement (±5%) for 70% of the foods analyzed. Values were approximately 10% lower by the proposed procedures in the remaining samples. These differences were attributed to the greater specificity of the new methods. Precision of the new procedures was generally within a coefficient of variation of 6% and values (mean of 4 assays on different days) obtained with an automatic sample processor and with manual analyses agreed within 3%.

Effects of metal ions and flavonoids on the oxidation of ascorbic acid.

Abstract: Effects of metal ions and flavonoids on the oxidatio of ascorbic acid (I) have been investigated polarographically in the acetate buffer solution of pH 5.4. since I gives a diffusion-controlled anodic wave due to a two-electron oxidation to form dehydroascorbic acid, the rate of the oxidation of I can be followed by measuring the change in the limiting current of I with time. The rate of the oxidation of I was enhanced by the presence of some metal ions. Among them, the effect of copper (II) was especially pronounced. Such the fact can be explained on the basis of the formation of a coordinative linkage between metal and ascorbate ions and the reducibility of metal ions. Contrary to this, flavonoids exhibited an inhibition effect on the copper (II)-catalyzed oxidation of I. The effect became more marked in the order of 3-hydroxyflavone

Semiautomated method for the fluorometric determination of total vitamin C in food products.

Abstract: A simple method employing simultaneous extraction and oxidation has been developed for the semiautomated determination of ascorbic and dehydroascorbic acids in food products. Recovery studies were conducted on ready-to-eat breakfast cereals and both fresh and canned fruits and vegetables, with average recoveries of 101, 100, and 102%, respectively. Reproducibility data were generated showing a relative standard deviation of 3.5%. The automated method was compared with the manual AOAC fluorometric method and with indophenol titration; correlation coefficients were 0.9960 and 0.9926, respectively. The hydrolysis product of dehydroascorbic acid, 2,3-diketogulonic acid, a reported interference in this method, was prepared and shown not to form an interfering fluorescent derivative.

[On the mechanism of ascorbic acid induced methemoglobin reduction of human erythrocytes (author's transl)].

Abstract: Ascorbic acid and dehydroascorbic acid penetrate the human erythrocyte membrane. In vitro methemoglobin is reduced nonenzymatically by both substances in concentrations of 10(-2) M to 10(-3) M. Dehydroascorbic acid is reduced nonenzymatically to ascorbic acid by GSH, even with low GSH-content of erythrocytes. Under physiological conditions ascorbic acid induced methemoglobin reduction is far less important than reduction by the NADH dependent methemoglobin reductase system. In methemoglobinemic conditions caused by toxic effects or by congenital methemoglobin reductase deficiency treatment with ascorbic acid is possible. However, critically increased methemoglobin content of the blood higher than 30% makes therapy with methylene blue necessary.

Pyrazines in the reaction of l-dehydroascorbic acid with ammonia and glycine

Abstract: Volatile reaction products of L-dehydroascorbic acid with ammonia and glycine were isolated from alkaline solutions, separated by gas-liquid chromatography and identified by comparison of their gas chromatographic retention and mass spectral data with those of authentic compounds. Five alkylpyrazines were positively identified: methyl-; 2,5-dimethyl-; trimethyl-; 2,5-dimethyl-3-ethyl-; and tetramethyl-pyrazine.

Compartmentation of redox metabolites in the anterior eye segment

Abstract: In bovine corneal epithelium, stroma, and aqueous humor the levels of ascorbic acid (ASC) and dehydroascorbic acid (DHA) were investigated. Two methods were used, the photometric assay with 2,6-dichlorophenolindophenol and the formation of osazone by 2,4-dinitrophenylhydrazine. The ASC levels in the corneal epithelium and aqueous humor were found to be in the millimolar range, the ASC/DHA ratio being about 10. The stromal ASC and DHA levels were much lower, with a ratio of 0.7. ASC and DHA had similar levels and ratios to those of reduced and oxidized glutathione (GSH/GSSG) reported in the literature. In the corneal epithelium the redox ratio of glutathione was higher than that of ascorbic acid. Therefore, glutathione was supposed to reduce dehydroascorbic acid.

Ređuktone 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 (1H and 13C) it can be shown that in water, dimethylsulfoxide and p-dioxane only the tautomer 1 of L-ascorbic acid is found in a measurable amount. Upon formation of the mono-anion la 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 1b. 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.

Detection composite for ascorbic acid* method and element for the detection

Abstract: Ascorbic acid in a sample such as blood serum is quantitatively assayed by converting the ascorbic acid to dehydroascorbic acid with ascorbic acid oxidase and reacting the dehydroascorbic with a coupling substance such as phenylenediamine to produce a detectable product. The ascorbic acid oxidase and coupling substance can be combined to form a reagent composition which can be incorporated into integral multilayer elements to form a test element.

Investigation of the mechanism of ascorbic acid radical formation and destruction

Abstract: 1. ESR signals for the dehydroascorbic acid radical-anions (D−) resulting from the interaction of AA with aqua ions and mono- and bis-α,α′-dipiridyl (dipy) complexes of Cu2+ have been recorded in a streaming system. 2. An expression for the rate of generation of D− has been obtained, the mechanism of destruction of radicals had been established, and rate constants for the reaction of D− with Cu2, Cu2+dipy2, and Cu+ have been determined. 3. Study has been made of the affect of acetonitrile on formation and destruction of radicals.