Characterization of the Radical-Scavenging Reaction of 2-O-Substituted Ascorbic Acid Derivatives, AA-2G, AA-2P, and AA-2S: A Kinetic and Stoichiometric Study

Abstract

The aim of this study was to characterize the antioxidant activity of three ascorbic acid (AA) derivatives Osubstituted at the C-2 position of AA: ascorbic acid 2-glucoside (AA-2G), ascorbic acid 2-phosphate (AA-2P), and ascorbic acid 2-sulfate (AA-2S). The radical-scavenging activities of these AA derivatives and some common low molecular-weight antioxidants such as uric acid or glutathione against 1,1-diphenyl-picrylhydrazyl (DPPH) radical, 2,2-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) radical cation (ABTS˙؉), or galvinoxyl radical were kinetically and stoichiometrically evaluated under pH-controlled conditions. Those AA derivatives slowly and continuously reacted with DPPH radical and ABTS˙؉, but not with galvinoxyl radical. They effectively reacted with DPPH radical under acidic conditions and with ABTS˙؉ under neutral conditions. In contrast, AA immediately quenched all species of radicals tested at all pH values investigated. The reactivity of Trolox, a water-soluble vitamin E analogue, was comparable to that of AA in terms of kinetics and stoichiometrics. Uric acid and glutathione exhibited long-lasting radical-scavenging activity against these radicals under certain pH conditions. The radical-scavenging profiles of AA derivatives were closer to those of uric acid and glutathione rather than to that of AA. The number of radicals scavenged by one molecule of AA derivatives, uric acid, or glutathione was equal to or greater than that by AA or Trolox under the appropriate conditions. These data suggest the potential usage of AA derivatives as radical scavengers.

Antioxidant Properties of Ethyl Vanillinin Vitroandin Vivo

“…This was consistent with our previous studies. 9,20) Vanillin, ethyl vanillin, and apocynin scavenged little or no DPPH radical or galvinoxyl radical, while vanillyl alcohol and vanillic acid continuously quenched both radicals throughout the experimental period ( Fig. 2A, B).…”

“…We found that 2-O--D-glucopyranosyl-L-ascorbic acid (AA-2G), a stable ascorbic acid derivative, exerted radical-scavenging activity toward unnatural model radicals, including DPPH radical [7][8][9][10] and ABTS radical cation (ABTS þ ). 9,11) The chemical properties of AA-2G as a radical scavenger were widely different from those of ascorbic acid, in that the reaction rate with these model radicals of AA-2G was much slower, but the long-term radical scavenging ability per molecule of AA-2G was superior to that of ascorbic acid. Recently, we reassessed the antioxidant activity of arbutin using five in vitro assay systems, though arbutin has been reported to possess weak antioxidant activity as compared to its precursor, hydroquinone.…”

Antioxidant Properties of 2-O-β-D-Glucopyranosyl-L-ascorbic Acid

“…We have found that AA-2G per se, which had been though to no biological activity, exerted radical-scavenging activity toward unnatural model radicals, such as the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical [13][14][15][16] and the 2,2 0 -azinobis(3-ethylbenzothiazoline-6-sulfonic acid) radical cation (ABTS þ ). 15,17) The chemical properties of AA-2G as a radical scavenger were largely different from those of AA, in that the reaction rate with these model radicals of AA-2G was far slower than that of AA, but the long-term radical scavenging ability per molecule of AA-2G was superior to that of AA under optimal conditions.…”

“…15,17) The chemical properties of AA-2G as a radical scavenger were largely different from those of AA, in that the reaction rate with these model radicals of AA-2G was far slower than that of AA, but the long-term radical scavenging ability per molecule of AA-2G was superior to that of AA under optimal conditions. We also found recently that the radical-scavenging activity of AA-2G was biological relevant using a cell-based antioxidant assay system, 2,2 0 -azobis(2-amidinopropane) dihydrochloride (AAPH)-induced erythrocyte hemolysis inhibition assay.…”

Syntheses via phenolic oxidative coupling using crude peroxidase from Brassica juncea (L) Czern leaves and antioxidant evaluation of dimeric thymol

“…The DPPH radical-scavenging activities were assessed as described previously 39 with major modification. Briefly, 1.0 mL DPPH radical (0.5 mM) was mixed with 1.0 mL of thymol or dimeric thymol solution (in methanol).…”