4.7 Review

Ascorbate oxidation by iron, copper and reactive oxygen species: review, model development, and derivation of key rate constants

Journal

SCIENTIFIC REPORTS
Volume 11, Issue 1, Pages -

Publisher

NATURE PORTFOLIO
DOI: 10.1038/s41598-021-86477-8

Keywords

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Funding

  1. U.S. National Science Foundation [2001187]
  2. Swiss National Science Foundation [200021_ 192192/1]
  3. California Air Resources Board [17RD012]
  4. Swiss National Science Foundation (SNF) [200021_192192] Funding Source: Swiss National Science Foundation (SNF)
  5. Directorate For Geosciences [2001187] Funding Source: National Science Foundation
  6. Div Atmospheric & Geospace Sciences [2001187] Funding Source: National Science Foundation

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Ascorbic acid is an abundant antioxidant in the lung, playing a key role in biological responses to particulate air pollution. Iron and copper reactions with ascorbic acid are important sinks for the compound, with catalytic rather than redox reactions at play. Rate constants for these reactions are derived from laboratory measurements.
Ascorbic acid is among the most abundant antioxidants in the lung, where it likely plays a key role in the mechanism by which particulate air pollution initiates a biological response. Because ascorbic acid is a highly redox active species, it engages in a far more complex web of reactions than a typical organic molecule, reacting with oxidants such as the hydroxyl radical as well as redox-active transition metals such as iron and copper. The literature provides a solid outline for this chemistry, but there are large disagreements about mechanisms, stoichiometries and reaction rates, particularly for the transition metal reactions. Here we synthesize the literature, develop a chemical kinetics model, and use seven sets of laboratory measurements to constrain mechanisms for the iron and copper reactions and derive key rate constants. We find that micromolar concentrations of iron(III) and copper(II) are more important sinks for ascorbic acid (both AH(2) and AH(-)) than reactive oxygen species. The iron and copper reactions are catalytic rather than redox reactions, and have unit stoichiometries: Fe(III)/Cu(II)+AH(2)/AH(-) +O-2 -> Fe(III)/Cu(II)+H2O2+products. Rate constants are 5.7x10(4) and 4.7x10(4) M-2 s(-1) for Fe(III)+AH(2)/AH(-) and 7.7x10(4) and 2.8x10(6) M-2 s(-1) for Cu(II)+AH(2)/AH(-), respectively.

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