Abstract
Humic acid (HA) is distributed throughout the environment. Many of its properties are known, but its exact structure and function are still in question. To understand the chemistry and biochemical implications of HA on living systems we have focused on understanding radical chemistries of HA in the presence of molecular oxygen and hydrogen peroxide. The work presented here uses EPR spectroscopy to demonstrate that Fe(III) is reduced to Fe(II) by peat derived HA (PHA), and that Fe(III) is reduced by PHA more efficiently when bound to chelators. However, desferroxamine (DFOM) sequesters Fe(III) from being reduced by PHA and inhibits the Fenton reaction. The reduction of molecular oxygen by Fe(II) gives H 2O 2 as a significant product. The hydroxyl radical is also produced in this reduction process and is trapped by 5-Diethoxyphosphoryl-5-methyl-1-pyrroline-N-oxide (DEPMPO). In addition to the formation of H 2O 2 and OH, another oxidant also appears to be present. Although not isolated, this species displays the characteristics of the ferryl ion.
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