Characterization of a nitrogen-rich fulvic acid and its precursor algae from solid state NMR

摘要: Abstract A nitrogen-rich fulvic acid (FA) from Pony Lake, a coastal pond in Antarctica, was investigated using advanced solid state nuclear magnetic resonance (NMR) techniques and compared with the precursor algal material. significant fraction of non-protonated alkyl carbons, some bonded to nitrogen, detected; most must be humification products, since they were undetectable lake algae. The corresponding branched structures account for 25–50% carbon FA. Spectral editing detected methylenes (20% all C) ethyl groups attached branch point. COOH are also enriched (∼10% C); 15N NMR spectral CH CN indicates peptides (∼1/4 C, ∼2/5 N), but spectrum exhibits bands up- downfield peptide signal; these associated 157 ppm sp2-hybridized three heteroatoms, which at least two N, according 13C{14N} SPIDER (saturation pulse induced dipolar exchange recoupling) NMR. This component, possibly degradation product penguin guano, accounts nearly half N. OCH, O–CH–O OCH2 moieties, typically found sugar rings, identified (∼12% C). quantitative 13C shows an aromaticity 8%; many aromatic carbons 1H–13C 1H spin diffusion that components within 1 nm non-polar segments, excludes polysaccharide or domains. Overall, structural differences between FA striking.