- Variation in ascorbic acid oxidation routes in H2O2 and cupric ion solution as determined by GC/MS
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Recent reports have suggested that ascorbic acid protects low-density lipoprotein from peroxide-induced oxidation, but does not protect and may actually function as a prooxidant in the presence of cupric ions. However, dehydroascorbic acid, (the first oxidation product of ascorbic acid) has been shown to protect low-density lipoprotein from cupric ion oxidation but not peroxide-induced oxidation. We have examined the degradation of ascorbic acid, uniformly labeled [13C6]ascorbic acid, and [6,6-2H2]ascorbic acid in hydrogen peroxide and cupric ion solutions using gas chromatography/mass spectrometry to determine products and routes of oxidation using different oxidant sources. We have found that hydrogen peroxide leads to the formation of a six-carbon product with a mass increment of 32 (a double oxygen addition) relative to ascorbic acid, consistent with the oxidation sequence of ascorbic acid (mass 176) going to dehydroascorbic acid (mass 174) to 2,3-diketogulonic acid (mass 192) to 2,3-diketo-4,5,5,6-tetrahydroxyhexanoic acid (mass 208). Cupric ion solutions, on the other hand, do not appear to induce significant amounts of 2,3-diketo-4,5,5,6-tetrahydroxyhexanoic acid but rather lead to the formation of a threo-hexa-2,4-dienoic acid lactone (mass 174) as the major six-carbon species. These data suggest that different oxidation stresses lead to solutions containing different ascorbic acid oxidation products. These ascorbic acid-derived species could, in turn, interact differently with other substances in the aqueous environment, including free metal ions and low-density lipoprotein. This may help explain previous reports showing divergent protective effects of ascorbic acid and dehydroascorbic acid on low-density lipoprotein when different oxidation methods are used.
- Deutsch, John C.,Santhosh-Kumar,Hassell, Kathryn L.,Kolhouse, J. Fred
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- Generation of hydrogen peroxide and hydroxyl radical resulting from oxygen-dependent oxidation of l-ascorbic acid via copper redox-catalyzed reactions
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The generation of hydrogen peroxide (H2O2) and hydroxyl radical (HO?) during the oxidation of l-ascorbic acid (l-AA) by oxygen with copper as a catalyst was investigated to set up the O2/Cu/l-AA process with benzoic acid (BA) as a probe reagent. The high concentration of H2O2 that is generated undergoes an intramolecular two-electron transfer and is further activated by the intermediate cuprous copper [Cu(i)] to yield HO? as a product, resulting in significant degradation of BA. Dehydroascorbic acid, 2,3-diketogulonic acid, and l-xylosone were the predominant detected products of the oxidation of l-AA. However, the generation of H2O2 and degradation of BA were regulated by variations in pH, which results from the contradiction between protonated l-AA that is difficult to chelate with Cu(ii) via electron transfer and hydrogen ions (H+), which are indispensable for the generation of H2O2. Furthermore, the concentration of H2O2 and degradation of BA increased with an increase in the dosage of l-AA. Trace amounts of Cu(ii) are effective for catalyzing the oxidation of l-AA, whereas the generation of H2O2 and degradation of BA increased with an increase in the dosage of Cu(ii). Owing to the formation of Cu(i) chloride complexes or Cu(ii) chloride complexes, the addition of chloride (Cl-) could inhibit the generation of H2O2 and degradation of BA.
- Zhou, Peng,Zhang, Jing,Zhang, Yongli,Liu, Ya,Liang, Juan,Liu, Bei,Zhang, Wei
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p. 38541 - 38547
(2016/06/01)
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