Humic fractions compared

It is suggested here that the greater insolubility of the humic fraction of coal may be the result, in part, of polymerization by complexing with metals, particularly aluminum and silicon. These elements are suggested because of their presumed greater availability. The minor elements also play a part, however, only in relation to their availability compared with major elements such as aluminum and silicon. 

Morphological changes were also observed on callus of Pinus laricio cultured for 4 weeks with HS extracted from forest soil under Abies alba and Fagus sylvatica plantation or the hormones 2,4D, IAA, and 6BAP (Muscolo et al., 2005).The results showed that both high- and low-molecular-weight humic fractions inhibited callus growth compared to the control and affected the enzymes involved in carbohydrate metabolism. 

In summary, the chemical characterization data show that humic substances in foam are an aliphatic, carboxyl-poor fraction, that are enriched in humic acid compared to stream humic substances. The carboxyl moiety appears to be the dominant ionic species affecting the surface activity of the humic substances, and foaming ability and foam stability are strongly dependent on pH as the average pKa of the organic acids is 4.2 (25). 

The comparison between NMR spectra of humin and humic acids in this aerobic soil bears out the fact that some basic structural differences exist between these two soil fractions. The lower polysaccharide content of humic acids compared to humin is expected. The greater relative proportion of carboxyl (or amide) carbons (peak at 175 ppm) in humic acids is another minor difference that was noted. The most important difference is the relative concentration of paraffinic carbons with humin having a much greater concentration than humic acids. Excluding the presence of polysaccharides, it is difficult to imagine that humin, in this instance, is a clay complex of humic acids. If this were the case, the spectra would be nearly identical except for the presence of carbohydrates in humin. It is also difficult to imagine that humin is a condensation product of humic acids. Rather, the comparisons show that either humic acids are decomposition products of the humin (where decomposition selectively alters the structure of individual precursors in humin), or humic acids are genetically unrelated to humin. 

Gillam and Wilson (1983) and Harvey et al. (1984) have performed model studies directed toward the synthesis of marine humic material from its assumed precursor compounds, metabolites from planktonic algae. Gillam and Wilson extracted lipid-soluble materials from a large quantity of the diatom Phaeodactylum tricornutum and compared the humic fraction of the extract to a humic material from coastal... 

Pontanen and Morris [8] compared the structure of humic acids from marine sediments and degraded diatoms by infrared and C13 and proton NMR spectroscopy. Samples of marine sediments taken from the Peru continental shelf were extracted with water, sodium hydroxide (0.05mol 1 J) and sodium pyrophosphate (0.05mol l-1) under an atmosphere of nitrogen and fractionated by ultrafiltration. Humic acids of molecular weight 300000 and above were examined. Diatoms were collected from... 

Elemental Analysis. The elemental analyses are presented in Table IV. The atomic ratios H/C for all drinking water samples (nos. 1-10) were between 1.28 and 1.39. These values were comparable to humic acid derived from lake sediments. However, H/C ratios were much lower when compared to the chlorinated model humic substances (e.g., 1.04-1.08 for CFH-1 and CFH-2). Bromine was present in almost negligible quantities, whereas Cl varied between 0.3 and 2.4, and S varied between 0.9 and 2.7 in the drinking water organic matter. All fractions from drinking water showed similar elemental composition. However, they differed from the elemental composition of the CFH samples in all respects, especially in chlorine content. 

The relatively low yield of phenol generated (compared with acetamide, for instance) indicates that humic substances are not major constituents of this higher MW fraction. 

Senesi, N., Plaza, C., Brunetti, G., and Polo, A. (2007). A comparative survey of recent results on humic-like fractions in organic amendments and effects on native soil humic substances. Soil Biol. Biochem., doi 10.1016/j.soilbio.2006.12. 

More recently, Muscolo et al. (2007b), in order to understand if the biological activity of humic substances may be related to their molecular weight and/or chemical structure, compared the activity of two humic substances derived from an uncultivated couch grass and a forest soil, each separated in fractions with low (<3500 Da)... 

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