Fate of [15N]glycine in peat as determined by carbon-13 and nitrogen-15 CP-MAS NMR spectroscopy

Abstract

2 mm i.d. glass column packed with 3% OV-101 on 80/ 100-mesh Supelcoport (Supelco Co.). The air, hydrogen, the high-dose treatment. A dose-related difference showed the majority of the urinary metabolites were recovered as conjugated products under the high-dose treatment.A significant sex-related metabolic difference was observed under the low-dose treatment. A majority of the urinary metabolites from the female rats were conjugated products, 30% of the administered dose, compared to the 5% observed in the male rats. A similar sex-related difference was also observed in the whole blood residue/time plot, which showed the contribution of biliary recirculation in the disposition of cinmethylin in the female test animals.

Nitrogen-bonded aromatics in soil organic matter and their implications for a yield decline in intensive rice cropping

“…These results indicate the dominance in this sample of CH-NH-CO structures, characteristic of peptides or N-acetyl groups. Indeed, analysis by 15 N NMR of these and other humic acids found a dominance of amide nitrogen (5). The carbon ratios for NCO͞NC arom ͞NCH n obtained from the SPIDER NMR spectra are 1:0.90:0.67 for the triple-cropped MHA and 1:0.63:0.76 for dryland MHA.…”

“…Anilides, with CO-NH groups bonded to aromatic carbons, could form through reaction of lignin-derived phenolic compounds with ammonia (13) and the COOH or NCO groups of amino acids or peptides (14,15). Amine groups might also be expected to bond to aromatic carbons (CH-NH-C arom ) through condensation of phenolic OH groups with NH 2 moieties of amino acids, but the abundance of this nitrogen form seems negligible based on the low intensity of amine nitrogen in 15 N spectra of these samples (5).…”

“…Note that these unprotonated nitrogens, which have large CSAs, are difficult to detect in CP-MAS 15 N NMR spectra (17). Based on the dipolar dephased SPIDER spectrum of Fig.…”

“…Overall, in the Data were calculated from { 14 NϪ} 13 C SPIDER NMR (Fig. 2), 15 triple-cropped MHA, almost 45% of the nitrogen is bonded to aromatic carbons, whereas this fraction is Ͻ30% of total nitrogen in the dryland MHA.…”

“…Lignin residues accumulate in soils that are intensively cropped to irrigated lowland rice (1) because of their slow decomposition under the characteristically anaerobic conditions and their high input rates through multiple incorporations annually of crop residues. Nitrogen directly bonded to or in aromatic rings has been found to be less bioavailable than nitrogen in peptides, based on its rate of degradation through soil microbial processes under laboratory conditions (2-4), but 15 N NMR spectroscopy has been unable to detect significant fractions of nitrogen bonded to aromatic carbons in the organic matter of these rice soils or any other soils (5), raising doubts as to whether nitrogen can be bonded to aromatic carbons under field conditions. Recent developments in solid-state NMR pulse sequences have greatly advanced the possibilities for structural identification and quantification in natural organic matter (6)(7)(8).…”