Humin lignin

Many, but not all, macromolecules are created by the mutual chemical chain reactions of small molecules called monomers and the arising species contain repeated small units, mers. In that case they are designated oligomers or polymers depending on their molar mass. This means that all oligomers and polymers can be called macromolecular substances but not all macromolecular substances are of oligomeric or polymeric nature (lignin, humin substances, etc.). Properties of macromolecular systems depend on... 

Bourbonniere and Meyers (unpublished) hydrolyzed humic substances from Lake Huron sediments with 5N NaOH at 170°C for 12 hours under a nitrogen atmosphere and found the following organic acids -Ci6 and n-Cig monocarboxylic acids lactic acid, 2-hydroxybutanoic acid, 3,4-dihydroxy-butanoic acid, oxalic acid, and succinic acid. It was proposed that the smaller organic acids were derived from cellulose-related materials. 2-Hy-droxybenzoic acid, 4-hydroxybenzoic acid, 2,5-dihydroxy-3-pentenoic acid, and vanillic acid were also observed. It was believed that 4-hydroxybenzoic acid and vanillic acid originated from lignin and that the ratio of 3,4-dihy-droxybutanoic acid to vanillic acid indicates the proportion of cellulose to lignin. The proportion was in the order of fulvic acid > humic acid > humin. 

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. 

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. 

Other major peaks in the spectra of humin are those derived from lignin (150, 130, and 55 ppm). In contrast to the humin from soil shown earlier, these peaks are much better resolved, especially the peak at 55 ppm for methoxyl carbon. No doubt, lignin is a major component of humin in peats, and it is likely that it exists in a relatively unaltered state in the peat, even at depth. 

On the basis of these studies on woody tissues, it seems that lignin from vascular plants can be selectively preserved compared to biologically degradable polysaccharides when buried. The same can be expected for the lignin in humin from peat the spectra shown in Figure 2 consistently demonstrate this selective preservation with increasing depth. 

A similar selective preservation was observed in peat as discussed earlier where an additional component, lignin, was also preserved selectively. However, the major component of humin from Everglades peat was the paraffinic component that also appeared to be selectively preserved relative to the polysaccharides. It is interesting to note the similarity between the spectra of delignified humin at the 15-16 cm interval in peat (Fig. 5) and that of the algal sapropel from Mangrove Lake at the 272-290 cm interval. The similarity between these two spectra infers that similar structural entities are present in these two depositional environments, and it is probable that the two similar structural components are from a common source, namely, algal and microbial remains. 

In peat, humin is also composed of the three structural entities mentioned above. The anaerobic nature of peat precludes the extensive decomposition that occurs in aerobic soils, and biomolecules are likely to be better preserved. Carbohydrates are major components of humin in near-surface intervals but are decomposed and lost with depth in the peat. Lignin and the paraffinic structures are selectively preserved with depth. When the humin of peat is delignified, the paraffinic structures remain. These components are likely to be derived from nonvascular plant contributors to the peat, namely, algae. 

Soil organic matter (SOM) is often referred to as humus and is derived primarily from the degradation of plant material lignin, carbohydrates, protein, fats, and waxes. Mineral soils may contain 0.5-3.0% of soil organic matter while muck soils and peat contain 50% and higher. Operationally, the material that cannot be extracted by alkaline agents is called humin. The material that precipitates from the alkaline extract on acidification is called humic acid, and what remains in solution fulvic acid. Felback summarized some of the properties of these complex polymeric materials as follows ... 

Biosynthesis H. are formed together with the neutral or weakly acidic humines from dead plant material (probably from the lignins) in the course of compost formation in the soil by chemical and biological processes (humification). Their composition is not uniform and depends on the type of phenol- and amine-containing precursors. Furthermore, the more strongly acidic fitlvic acids (fulvinic acids) are derived from H. but have markedly lower molecular masses. H. occur in normal field soil to 1 -2%, in chernozem (black soil) to 2-7%, in meadow soil 10%, and in marshy soils to 10-20%. They improve the physical structure of the... 

After drying at room temperature, the raw peat was milled and sieved through an 80-mesh screen, after which the plant constituents (hemicelluloses, cellulose and lignin), peat bitumen, humic substances (humic acid (HA), fulvic acid (FA) and humin (Hm)) and other insoluble contents were fractionated using methods that have been previously described. Briefly, the peat bitumen (benzene/ethanol-soluble) was extracted in a Soxhlet apparatus for... 

The residual peat was then correlated with the humic substances, lignin and other insoluble compounds. To accomplish this, the humic substances were removed by acid and alkali extraction. Briefly, the air-dried peat was washed twice with 0.01 M HCl and then treated with NaOH at pH 13.5 for 48 hours, which gave a supernatant fraction (humic and fulvic acids), and a fraction that contained the humin and other insolubles. All fractions were separated by filtration and centrifugation. 

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