6533b7d1fe1ef96bd125c05a

RESEARCH PRODUCT

Historical and current progress in understanding the origin and structure of humic substances

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Research into humic substances (HS) has focused selectively on the search for aromatic structures. All aromatic compounds are regarded as eligible HS constituents, whereas aliphatic, polysaccharide structural constituents are considered non-HS. Wet chemical methods for analysing HS produce 2–5% aromatic compounds from the original starting material. Only those compounds in the hydrophobic extraction phases are studied carefully. Compounds in the hydrophilic extraction phases, containing mainly aliphatics, are discarded. Solid-state NMR spectra from HS show 30–40% of carbon–carbon unsaturation, which is selectively interpreted as ‘aromatic’. No recognition is given to the fact that NMR spectroscopy of HS cannot distinguish olefinic unsaturation from aromatic unsaturation in molecules. By considering this unsaturation to be more or less olefinic, solid-state NMR shows the structure of HS to be mainly aliphatic. Polysaccharides are recycled in humification via microbial metabolism. Lignin is not formed again...