Humic amide groups

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... 

In common with the other humic substances, many of the properties of HA are due to the nature of its functional groups. These include carboxyl, aliphatic and aromatic hydroxyl, carbonyl and amide groups which can be readily detected by infrared spectroscopy. The results obtained by chemical methods of functional group analysis are often difficult to interpret and may be contradictory. This in part is due to the presence of similar functional groups in the non-humic components ("impurities ) which are extracted along with the humic substances. 

NMR Spectra of Unreacted Samples. Quantitative liquid phase NMR spectra of the unreacted samples are shown in Figure 2. Peak areas of the spectra are listed in Table I together with elemental analyses. Characteristically, the humic acid has a greater aromatic carbon and lesser carboxylic acid carbon content than the fulvic acid. The naturally occurring nitrogen contents are 2.68% and 4.18% for the fulvic and humic acids, respectively. Overlap of functional groups which may serve as substrate sites for nucleophilic addition by aniline occurs within the major peak areas of the spectra. Quinone carbons (190 to 178 ppm) overlap with ketone carbons from 220 to 189 ppm, amides and esters (174 to 164 ppm) overlap with... 

Humic acids of marine and estuarine sediments are characterized by major amounts of paraffinic structures that previous studies have shown to be highly branched and to contain significant quantities of carboxyl/amide and alcohol/ether carbon. Some humic acids, namely those from well preserved sapropelic marine sediments show significant quantities of carbohydrate-like structures incorporated. This, no doubt, is a reflection of the solubility characteristics of polysaccharides which may have some carboxyl functionalities (uronic acid groups). 

A survey of different containing organic molecules indicate that peaks corresponding to the Is— 7t transitions of ketones and aldehydes are around 531 eV carboxylic acids, esters, and amides are around 532 eV (Table 3—in Appendix). There is some overlap of these bands based on the substituents around the functional group in the molecule. Whereas alcohols and ethers exhibit their Is— a (C-O) transitions around 534 and 535.5 eV respectively. The energies of these different functional groups are different, and their NEXAFS spectra can be used in their identification. The NEXAFS spectra of isolated humic substances from aquatic and soils systems also exhibit distinct peaks that correspond to ketones, carboxylic acids and alcohols (SCB Myneni, unpublished data). 

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