Polysaccharides fulvic acids

Humic substances are those organic compounds found in the environment that cannot be classified as any other chemical class of compounds (e.g., polysaccharides, proteins, etc.). They are traditionally defined according to their solubilities. Fulvic acids are those organic materials that are soluble in water at all pH values. Humic acids are those materials that are insoluble at acidic pH values (pH < 2) but are soluble at higher pH values. Humin is the fraction of natural organic materials that is insoluble in water at all pH values. These definitions reflect the traditional methods for separating the different fractions from the original mixture. 

Interpretations of the published spectra suggest that there are considerable differences in the amounts of aromatic structures in humic substances of different origins. To some extent these differences can depend on the methods used for the calculations. As much as 68% of the components of fulvic acid fractions have been estimated to be aromatic (Schnitzer, 1982), although it would appear that aromatic structures generally do not amount to more than 35% of the mass of the structural components of soil humic acids. This is not surprising because up to 40% of the mass may be lost as volatile and as hydrolyzable material (such as oligo- and polysaccharide, and peptide structures) when humic acids are boiled in 6M hydrochloric acid (Atherton... 

Leenheer and Malcolm (1973) separated a soil fulvic acid into four fractions by electrophoresis. They found a dramatic change in elemental composition, which correlated with carbohydrate content. Thus, the high polysaccharide fraction had high H/C and 0/C ratios, while the low carbohydrate fractions had low H/C and 0/C ratios. All fractions, however, fitted into the accepted... 

Saito and Hayano (1981) have also interpreted the presence of a band between 3.3 and 4.6 ppm to indicate that there are polysaccharide ether structures in some of their samples. They found that this band was stronger in fulvic acids from marine sediments than the corresponding humic acids. The marine sediment fulvic acids were higher in oxygen than marine sediment humic acids. Aldrich humic, which is presumably terrestrial in origin, has a still lower oxygen content but does not have a band in this region. These data led Saito and Hayano to conclude that their marine sediment fulvic acids have a polysaccharide character. ... 

Humic and fulvic acids as well as humin were isolated from the samples described in Table 1 by standard methods ( ). In short, humic and fulvic acids are extracted with 0.5 N NaOH under N2. Humic acids are protonated on an ion exchange resin, precipitated by acidifying to pH 2, separated by centrifugation, and lyophilyzed. The soluble fulvic acids are concentrated by ultrafiltration and lyophilyzed. Humin, the residue after treatment with NaOH, is treated with concentrated HC1 HF to remove a large portion of the mineral matter and hydrolyzable substances such as proteins and polysaccharides. 

Fulvic acids. Marine sedimentary humic substances soluble in base and acid (fulvic acids) have previously been examined by and NMR (12). The dominant structural components were postulated to be polysaccharide - like substances, probably polyuronic acids. Solid-state NMR spectra of fulvic acids isolated from a number of marine and estuarine sediments are shown in Figure 1. Major peaks at 72 and 106 ppm betray the overwhelming presence of polysaccharide -like substances, and, as shown by Hatcher and others (12.), the moderate peak for carboxyl or amide carbon at 175 ppm suggests that these polysaccharides are more like polyuronides. Aromatic carbons (110 to 160 ppm) are decidedly minor components. Aliphatic carbons (0-50 ppm) are also minor components. H NMR spectra shown by Hatcher and others (12) indicate that these aliphatic structures are highly branched. 

It is noteworthy that fulvic acids from aerobic and anaerobic sediments and from offshore marine and estuarine sediments all have similar NMR spectra. The abundance of polysaccharides and... 

Polysaccharides are present in fulvic acid, humic acid, and humin fractions of soil organic matter. Extractants remove only a small percentage of the total present and hence determinations must be made by means of hydrolysis followed by analysis of the products. These include hexoses, pentoses and uronic acid. There seems to be no doubt that soil polysaccharides are important constituents of soil organic matter. They have a role in... 

Studies of the adsorption of fulvic acids by clays are very limited but apparently the non-polysaccharide portion behaves much like humic acids. According to Evans and Russell (1959) the order of effectiveness of fulvic acid adsorption on bentonite was acid > Ca > Mg > K and Na systems. Only a small proportion of the fulvic acid carbon, as in the case of humic acid carbon, was adsorbed. Kaolin was also an active adsorbent, the order being acid > Ca > K, as in bentonite systems. 

Partially removes autochthonous NOM and hinders bacterial growth in feedwater or on membrane Viruses, humic/fulvic acids, proteins, polysaccharides with acidic groups, colloids smaller than membrane pores... 

The C - NMR spectrum of this material (Figure 3) shows significant presence of substituted aromatic material (125 ppm) as well as aliphatic carbon content. This spectrum shows a considerably reduced presence of polysaccharide decomposition products compared to fulvic acid extracted from wastewater (11). The % -NMR spectrum (Figure 4) also indicates significant presence of substituted aromatic compounds (ca. 7 ppm). 

YOSHIDA M. and KUMADA K. 1979. Studies on the properties of organic matter in buried humic horizon derived from volcanic ash IV. Characteristics of polysaccharides in hydrolysates of fulvic acid and in ethanol precipitates from fulvic acid in buried humic horizon. Soil Science and Plant Nutrition, 25, 217-224. 

Tan, K. H., and Clark, F. E. (1969). Polysaccharide constituents in fulvic and humic acids extracted from soil. Geoderma 2(3), 245-255. 

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