Kinetic Study of Aroxyl-Radical-Scavenging and α‑Tocopherol-Regeneration Rates of Five Catecholamines in Solution: Synergistic Effect of α‑Tocopherol and Catecholamines
Detailed kinetic studies have been performed for reactions of aroxyl (ArO•) and α-tocopheroxyl (α-Toc•) radicals with five catecholamines (CAs) (dopamine (DA), norepinephrine (NE), epinephrine (EN), and 5- and 6-hydroxydopamine (5- and 6-OHDA)) and two catechins (epicatechin (EC) and epigallocatechi...
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Published in | The journal of physical chemistry. B Vol. 120; no. 29; pp. 7088 - 7097 |
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Main Authors | , , , , |
Format | Journal Article |
Language | English |
Published |
United States
American Chemical Society
28.07.2016
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Subjects | |
Online Access | Get full text |
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Summary: | Detailed kinetic studies have been performed for reactions of aroxyl (ArO•) and α-tocopheroxyl (α-Toc•) radicals with five catecholamines (CAs) (dopamine (DA), norepinephrine (NE), epinephrine (EN), and 5- and 6-hydroxydopamine (5- and 6-OHDA)) and two catechins (epicatechin (EC) and epigallocatechin gallate (EGCG)) to clarify the free-radical-scavenging activity of CAs. Second-order rate constants (k s and k r) for reactions of ArO• and α-Toc• radicals with the above antioxidants were measured in 2-propanol/water (5:1, v/v) solution at 25.0 °C, using single- and double-mixing stopped-flow spectrophotometries, respectively. Both the rate constants (k s and k r) increased in the order NE < EN < DA < EC < 5-OHDA < EGCG < 6-OHDA. The k s and k r values of 6-OHDA are large and comparable to the corresponding values of ubiquinol-10 and sodium ascorbate, which show high free-radical-scavenging activity. The ultraviolet–visible absorption of α-Toc• (λmax = 428 nm), which was produced by the reaction of α-tocopherol (α-TocH) with ArO•, disappeared under the coexistence of CAs due to the α-TocH-regeneration reaction. The results suggest that the CAs may contribute to the protection from oxidative damage in nervous systems, by scavenging free radicals (such as lipid peroxyl radical) and regenerating α-TocH from the α-Toc• radical. |
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Bibliography: | ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
ISSN: | 1520-6106 1520-5207 |
DOI: | 10.1021/acs.jpcb.6b04285 |