Humin isolation

Qualitative and quantitative identification of the sugars in the hydrolysates of these humin isolates may give indications about their origins (plant or microbial), and identification of the configurations of the sugar linkages could lead to deductions about the sorption mechanisms. To achieve the latter objective will require isolation of the polysaccharide and/or mucopolysaccharide components. That will not be an easy task, but it is doable. 

TABLE 9. Humic Acids and Humin Isolated from Lake Biwa Sediments"... 

Ishiwatari (1977) isolated humic acids and humin from samples at various depths (11-130 m) of Lake Biwa sediment. As shown in Table 9, a small amount of humic acid was extracted from sediments of 11 m depth, but no humic acid was obtained from sediments in deeper layers (45-130 m) although alkali extracts were yellow-colored. Humin isolated from sediment samples increased with depth from 6.2% of the total organic matter to 64%, and at 130 m in depth accounted for 80% of the nonbiochemicals. Ishiwatari and Kawamura (1981) again measured approximate amounts of alkali-ex-traetable humie substances in the long sediment core sample of Lake Biwa by colorimetry (at 400 nm). The ratios of alkali-extractable humic substances to the total organic matter decreased gradually with depth, as shown in Table 10. 

FIGURE 2. NMR spectra of humin isolated from various depth intervals in cores from two peats. The Everglades peat was collected from a sawgrass area in Conservation District lA west of Fort Lauderdale, Florida. The peat core from Mangrove Lake, Bermuda, was collected and described by Hatcher (1978). 

FIGURE 4. C NMR spectra of humin isolated from section 14 (65-70 cm) of the peat core from Conservation District 1A in the Everglades, Florida, and of the same humin hydrolyzed by refluxing in 6N HCI for 2 hours. 

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... 

Many researchers have attempted to unravel the mystery of the structure of humus. One approach has been to isolate fractions by extracting humus using various extraction procedures. These procedures result in the isolation of three or more fractions humic acid, fulvic acid, and humin. Humic material is isolated from soil by treating it with alkali. The insoluble material remaining after this treatment is called humin. The alkali solution is acidified to a pH of 1.0 and the precipitate is called humic acid, while the soluble... 

Soil microorganisms degrade methoprene rapidly and extensively (27). The hydroxy ester was isolated as a minor metabolite over 50% of the applied dose was evolved as 1 C02. Radioactivity from [5-1 0]methoprene incorporated into the humic acid, fulvic acid, and humin fractions of soil. 

Humic (HA) and fulvic acids (FA) and Humin (HU) were isolated utilizing the standard method recommended by the International Humic Substances Society (IHSS). Their amounts were obtained by quantifying carbon in each fraction and in each step of the fractionation procedure. 

The mechanism of acid-catalyzed decarboxylation of hexuronic acids has been the subject of many investigations.231,232 The formation of carbon dioxide is accompanied by the formation of 2-furaldehyde, C5H402 (82) as the main product, along with considerable amounts of humins however, both 5-formyl-2-furoic acid (83) and reductic acid (84) have been isolated as end products from treatment of hexuronic acids with strong acid. 

Soil polysaccharides can amount to as much as 20% of the humic fractions isolated in aqueous media, and identification of the classes of components in humin materials in associations with the soil clays indicates that carbohydrates contribute significantly to those isolated in the DMS0/H2S04 medium (see Sections 1.4.7 and... 

The humin components isolated in DMS0/H2S04 media contain macromolecular components, such as peptides, peptidoglycans, and possibly mucopolysaccharides (Simpson et al., 2007), and these would appear to be strongly sorbed to the soil inorganic colloids. Such species can therefore be considered to have importance in soil particle interactions. 

Figure 2.15. FTIR spectra of the humic-like substances produced by (1) C. maxima, (2) C. maxima + C. hirsutus, and (3) C. hirsutus. Reprinted from Yavmetidinov, I. S., Stepnova, E. V., Gavrilova, V. R, et al. (2003). Isolation and characterization of humin-like substances produced by wood-degrading white rot fungi. Appl. Biochem. Microbiol. 39, 257-264, with permission from Springer.

Operationally, it is common to define HS in terms of the methods used to extract or isolate them from soils, sediments, and natural waters. The classic soil extraction procedure yields three main fractions humic acid [also defined as high-molecular-weight (HMW) or high-molecular-size (HMS) fraction], fulvic acid (FA) [also defined as low-molecular-weight (LMW) or low-molecular-size (LMS) fraction], and humin. These fractions are defined in terms of their solubility in aqueous media as a function of pH or in terms of their extractability from soils or sediments as a function of the pH of the extracting medium. Humic acid is the fraction of HS that is not soluble in water under acidic conditions, but becomes soluble (or extractable) at higher pH values. Fulvic acid is the fraction that is soluble in aqueous media at all pH values. Humin represents the fraction that is not soluble in an aqueous medium (or is not extractable with an aqueous medium) at any pH value. Actually, humin consists of an aggregate of humic and nonhumic materials (Rice and Mac-... 

Humic substances are a broad class of organic compounds operationaUy defined by their solubility at different pHs and retention on hydrophobic resins (Aiken, 1988 Thurman, 1985). There are three operational sub-categories of humic substances humic acids, which are soluble at a higher pH but become insoluble at a pH < 2 (isolated using XAD-8 resin) fulvic acids, which are hydrophilic acids soluble under aU pH conditions (isolated using XAD-4 resin), and humin, which is insoluble at any pH (Ishiwatari, 1992). For a review of humic substances in aquatic systems, see Hessen and Tranvik (1998), Benner (2002), and Chapter 3 by Aluwihare and Meador, this volume. 

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