Abstract
ELECTRON paramagnetic resonance studies1 of wood; lignins; tannins, and humic acids, such as are found in soils and coals, show an electron paramagnetic resonance line of 6 ± 2 gauss width at g = 2.003 ± 0.002, indicating the presence of a free radical. I find that this free radical is stable over a period of years in air and is not present in protolignin in plant materials nor is it necessarily the result of simple ageing or rotting of wood. However, it is formed when protolignin in plants is polymerized into lignin by either acid or fungal attack. I also find that the 6 ± 2 gauss electron paramagnetic resonance line is restricted to the fraction of humic material which is extractable with aqueous bases.
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References
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REX, R. Electron Paramagnetic Resonance Studies of Stable Free Radicals in Lignins and Humic Acids. Nature 188, 1185–1186 (1960). https://doi.org/10.1038/1881185a0
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DOI: https://doi.org/10.1038/1881185a0
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