Elucidation of the nitrogen forms in melanoidins and humic acid by nitrogen-15 cross polarization-magic angle spinning nuclear magnetic resonance spectroscopy

Abstract

TFA derivatives on separate runs (see Table II).Structural Assignment with Respect to Stereoisomers. Immediately following the main fraction of the wine sample, two smaller fractions were eluted which were also present in synthetic 2 derived from a mixture of the diastereomeric 2,3-butanediols. Mass spectra for the three components differed in their abundances at m/e 55, 73, 126, and 182 (see Table II). GC-MS analysis of 4,5-dimethyl-l,3-dioxolane-2-propanamine TFA, 2a, which was synthesized by using essentially pure D(-)-2,3-butanediol, gave only the first (main) fraction. It can therefore be concluded that the main fraction of 4,5-dimethyl-l,3-dioxolane-2-propanamine in wine is an acetal of threo-2,3butanediol and that the two minor fractions are acetals of erythro-(meso-) 2,3-butanediol. Stevens (1969) reported the presence of both 2,4,5-trimethyldioxolane and 2,4-dimethyl-5-ethyldioxolane in wine. Muller et al. (1979) also identified a number of cyclic acetals in sherry. This and the present work suggest that cyclic acetals of other aldehydes may be present in wine. ACKNOWLEDGMENT Grateful acknowledgment is given to William Haddon and Sandra Tillin of the Western Regional Research Laboratories of the U.S. Department of Agriculture, Albany, CA, for the Cl and exact mass work.

Analyses of the Chemical Structures of Melanoidins by13C NMR,13C and15N CP-MAS NMR Spectrometry

“…5). Benzing-Purdie et al 4 ) reported that the nitrogen in the melanoidins obtained from xylose and glycine was mainly in the secondary amide form. Peaks around 100 ppm coincide closely with the chemical shift of amides.…”

“…A recent study using 13C CP-MAS NMR 3 ) and 15N CP-MAS NMR 4 ) showed that the behavior of carbon and nitrogen in melanoidins was similar to that of humic substances in soils.…”

Selective Dephasing of OH and NH Proton Magnetization Based on 1H Chemical-Shift Anisotropy Recoupling

“…Previously, the typical peak near 173 ppm has often been characterized as carboxylic acid groups (24). On the other hand, the relatively large nitrogen content (typically, C : N = 10 : 1) suggests a significant fraction of CO-NH groups (25,26 ). With the present experiment, we can identify these moieties.…”

A solid-state 15N NMR spectroscopic investigation of the origin of nitrogen structures in coal

“…These reactions presumably would occur during early peat formation and should be recognizable as an enrichment of the heterocyclic products with increasing peat maturation. Benzing -Purdie et al (1983) have shown that such reactions are theoretically possible; however, significant amounts of the nitrogen-containing products expected from these reactions could not be identified in soils and sediments (Schnitzer, 1985).…”