化学
烷基
碳-13核磁共振
杂原子
质子化
核磁共振波谱
氮气
二维核磁共振波谱
芳香性
自旋扩散
有机化学
立体化学
分子
扩散
热力学
物理
离子
作者
Jingdong Mao,Rose M. Cory,Diane M. McKnight,Klaus Schmidt‐Rohr
标识
DOI:10.1016/j.orggeochem.2007.04.005
摘要
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. A significant fraction of non-protonated alkyl carbons, some bonded to nitrogen, was detected; most must be humification products, since they were undetectable in the lake algae. The corresponding branched alkyl structures account for 25–50% of carbon in the FA. Spectral editing detected methylenes (20% of all C) and ethyl groups attached to a branch point. COOH groups are also enriched (∼10% of all C); 15N NMR and spectral editing of CH and CN groups indicates peptides (∼1/4 of all C, ∼2/5 of all N), but the 15N NMR spectrum also exhibits bands up- and downfield from the peptide signal; these must be associated with a 157 ppm sp2-hybridized carbon bonded to three heteroatoms, of which at least two are N, according to 13C{14N} SPIDER (saturation pulse induced dipolar exchange with recoupling) NMR. This component, possibly a degradation product of penguin guano, accounts for nearly half the N. OCH, O–CH–O and OCH2 moieties, typically found in sugar rings, were identified using spectral editing (∼12% of all C). The quantitative 13C spectrum shows an aromaticity of 8%; many of the aromatic carbons are bonded to N. 1H–13C NMR with 1H spin diffusion shows that most components are within 1 nm from non-polar alkyl segments, which excludes polysaccharide or aromatic domains. Overall, the structural differences between the algal precursor and the FA are striking.
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