Abstract
Antioxidants are a class of molecules that provide a protective function against reactive oxygen species (ROS) in biological systems by out competing physiologically important molecules for ROS oxidation. In natural waters, the reactivity of antioxidants gives an estimate of oxidative stress and may determine the reactivity and distribution of reactive oxidants. We present an analytical method to measure antioxidant activity in natural waters through the competition between ascorbic acid, an antioxidant, and MCLA, a chemiluminescent probe for superoxide. A numerical kinetic model of the analytical method has been developed to optimize analytical performance. Measurements of antioxidant concentrations in pure and seawater are possible with detection limits below 0.1 nM. Surface seawater samples collected at solar noon contained over 0.4 nM of antioxidants and exhibited first-order decay with a half-life of 3-7 minutes, consistent with a reactive species capable of scavenging photochemically produced superoxide.
Highlights
Reactive oxygen species (ROS) are short lived, oxygen containing molecules including singlet oxygen (1 carbonateO2), superoxide radical (CO−3 ).(O−2 ), hydrogen peroxide In natural systems, these (H2O2), hydroxyl species are capable radical (OH), of oxidizing a and the range of molecules including metal complexes, dissolved organic matter, and biomolecules
Antioxidants are a class of molecules that provide a protective function against reactive oxygen species (ROS) species in biological systems by out competing physiologically important molecules for ROS oxidation (Schlesier et al, 2002)
In natural waters the reactivity of antioxidants gives an estimate of oxidative stress and will determine the reactivity and distribution of ROS (Goldstone and Voelker, 2000; Heller and Croot, 2010; Roe et al, 2016)
Summary
Reactive oxygen species (ROS) are short lived, oxygen containing molecules including singlet oxygen (1 carbonateO2), superoxide radical (CO−3 ).(O−2 ), hydrogen peroxide In natural systems, these (H2O2), hydroxyl species are capable radical (OH), of oxidizing a and the range of molecules including metal complexes, dissolved organic matter, and biomolecules. Indirect antioxidant analysis relies on competitive kinetic reactions between antioxidants and known probe molecules with ROS—often superoxide or hydroxyl radicals (Hosaka et al, 2005; Besco et al, 2007; Giokas et al, 2007; Yu et al, 2008; Anifowose et al., 2015). Indirect measurements do not necessarily measure specific molecule concentrations, but rather weighted antioxidant reactivity defined as the sum of all antioxidant concentrations scaled by their reaction rate constants with specific ROS. In this indirect, competitive kinetics method, experimentally generated superoxide competes with the antioxidants of interest, and an analytically observable probe molecule (Figure 1)
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