Scavenging rate constants of hydrophilic antioxidants against multiple reactive oxygen species

Abstract

Scavenging rate constants of eight hydrophilic antioxidants, including caffeic acid, chlorogenic acid, genistein, glutathione, N-acetylcysteine, rutin, trolox, and uric acid against multiple ROS, namely superoxide anion, hydroxyl radical, singlet oxygen, and alkoxyl radical were determined with the electron spin resonance method. Direct flash photolysis measurement of the second-order rate constant in the reaction of alkoxyl radical plus the spin trap 5,5-dimethyl-pyrroline N-oxide made it possible to evaluate scavenging rate constants in antioxidants. The magnitudes of scavenging rate constants were notably dependent on the character of each ROS and the overall rate constants were highest in hydroxyl radical scavenging and the lowest in superoxide anion. The highest scavenging rate constant against superoxide anion was obtained by chlorogenic acid (2.9 × 105 M−1 s−1) and the lowest was by N-acetylcysteine (5.0 × 102 M−1 s−1). For singlet oxygen, the highest was by glutathione (9.4 × 108 M−1 s−1) and the lowest was by uric acid (2.3 × 106 M−1 s−1). All other numbers are listed and illustrated. Redox potential measurements of the antioxidants indicated that the antioxidants are likely to react with superoxide anion and singlet oxygen through electron transfer processes.

Uric Acid: A Less‐than‐Perfect Probe for Singlet Oxygen

“… First, with the common approach of monitoring UA disappearance via absorption spectroscopy, the data obtained can be appreciably influenced by absorbance changes due to the time‐dependent composition of UA oxidation products and/or other molecules in the system. As such, one may have to revert to other, more elaborate, quantification techniques. Second, UA is not a probe specific for O 2 (a 1 Δ g ); it reacts with a host of other species, including many common ROS . Thus, the bleaching of UA alone cannot be used to claim the intermediacy of O 2 (a 1 Δ g ) in a given reaction.…”

“…For example, in photosensitized systems, UA could also influence the production of O 2 (a 1 Δ g ) by quenching the sensitizer as well. Although some substantive studies of UA chemistry in photoinitiated oxidizing environments have been published , many of the fundamental concepts reported therein are often overlooked by the community. As such, we feel it is appropriate to better clarify aspects of uric acid behavior under conditions in which O 2 (a 1 Δ g ) is produced.…”

The Chemistry of Neurodegeneration: Kinetic Data and Their Implications

“…[62] b Data for one-electron reduction potentials and second-order rate constants for GSH collected from ref. [63,64] amines occurring in food, such as tyramine. In the brain, MAO B mainly metabolises dopamine, while MAO A predominantly metabolizes serotonin, which is why these two isoforms are key pharmaceutical targets in alleviating the symptoms of Parkinson's disease and depression, respectively [87,88].…”

Myoglobin microplate assay to evaluate prevention of protein peroxidation

“…In fact, the interaction of thiols with reactive radicals can generate thiyl radicals which have a pro-oxidant effect, especially in iron-rich environments, which is the case of iron atoms release during Mb autoxidation [27]. However, reduced glutathione represents a powerful endogenous antioxidant as demonstrated by other antioxidant assays that applied different mechanisms of reaction such as metal reduction [28] and scavenging of multiple reactive oxygen species [29].…”