Nature and Abundance of Organic Radicals in Natural Organic Matter: Effect of pH and Irradiation

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• 作者：Andrea Paul ; Reinhard Stö ; sser ; Andrea Zehl ; Elke Zwirnmann ; Rolf D. Vogt ; Christian E. W. Steinberg
• 刊名：Environmental Science & Technology
• 出版年：2006
• 出版时间：October 1, 2006
• 年：2006
• 卷：40
• 期：19
• 页码：5897 - 5903
• 全文大小：141K
• 年卷期：v.40,no.19(October 1, 2006)
• ISSN：1520-5851

文摘

Dissolved natural organic matter (NOM) plays an essentialrole in freshwater geochemical and biochemical processes.A major property, its redox behavior, can be attributed tothe chinone building blocks, which can form stableradicals. However, electron paramagnetic resonance(EPR) data indicating free radicals on solid NOM are sparse.Here we present EPR spectra of 23 NOM from Europeansurface waters isolated by reverse osmosis. The organicradical concentrations of NOM ranged from 5 × 10¹⁵ to 1.84× 10¹⁷ spins g^-1, and g values ranged from 2.0031 to2.0045. Number and type of organic radicals in solid NOMare significantly influenced by the pH of raw water. EPRexperiments indicate the presence of semiquinone-type radicals in coexistence with carbon-centered "aromatic"radicals, with the semiquinone-type radicals dominatingat alkaline pH. Basically these processes are reversible.Organic radical concentrations in NOM adjusted to pH 6.5before freeze-drying correlate with iron and aluminumcontents. UV- and VIS-irradiation of solid NOM can leadto more than a 10-fold increase of the concentration of organicradicals. These radicals were long-lived and had thesame g value as the original radical. Similar effects werenot observed with isolated humic and fulvic acids,demonstrating the limited reflection of environmentalproperties of organic carbon by the classical isolationprocedure.