Aromatic carbon humin

A major peak in the humin spectra is that of paraffinic carbons at 30 ppm. This component is present in greater abundance than the aromatic carbons in both humin spectra in contrast to its relatively minor abundance in the humic acids. Also, the intensity of this paraffinic peak, relative to the aromatic... 

Comparison of this region of the spectrum with that of the respective humic acids shows that the humin contains significantly less carboxyl (peak at 175 ppm). The peaks at 250 and 0 ppm are spinning sidebands of the aromatic carbon peak. In summary, the primary difference between the spectra of humic acids and humin is the presence of a paraffinic carbon peak at 30 ppm in the spectrum of humin. There is little indication that lignin-like structures exist in either spectrum due to the lack of significant peaks at 55 and 150 ppm for methoxyl and phenolic carbons, respectively. 

Humin isolates from sediments of the Mew York Bight and Potomac River estuary have spectra that are notably different in that aromatic carbons are the dominant components. The spectra resemble that of humin isolated in the same manner from an aerobic soil from southern Georgia (Figure 5). However, unlike the humin from soil which shows a significant peak for carboxyl carbon (175 ppm), spectra of humin from the New York Bight and the Potomac River do not display a discreet peak at 175 ppm and appear to be depleted of carboxy 1/amide groups. Elemental data for these humins (19) are consistent with the NMR results. Atomic H/C ratios of less than 0.8 are not typical of humic material but more like those of highly aromatic coal or coal-like products. The NMR spectra also resemble... 

NMR spectra of humin from three major types of depositional environments, aerobic soils, peats, and marine sediments, show significant variations that delineate structural compositions. In aerobic soils, the spectra of humin show the presence of polysaccharides and aromatic structures most likely derived from the lignin of vascular plants. However, another major component of humin is one that contains paraffinic carbons and is thought to be derived from algal or microbial sources. Hydrolysis of the humin effectively removes polysaccharides, but the paraffinic structures survive, indicating that they are not proteinaceous in nature. The spectra of humin differ dramatically from that of their respective humic acids, suggesting that humin is not a clay-humic acid complex. 

Many C NMR spectra have been published for humin in peat (Hatcher et al., 1980c, 1983a Preston and Ripmeester, 1982 Dereppeetal., 1983) and all appear to contain peaks for carbohydrates and aromatic, carboxyl, and paraffinic carbons, the proportions of which vary considerably. Hatcher et al. (1983a) pointed out that, while the presence of carbohydrates (polysaccharides) and hgnin was expected, the discovery of significant quantities of paraffinic carbons by C NMR has made a major contribution to our knowledge of the components of peat humin. 

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