Humic materials synthesis

The relatively recalcitrant dissolved poly-phenolic compounds resulting from breakdown of higher plants (fulvic and humic acids) complex with many bacterial and algal enzymes, but particularly phosphatases (Wetzel, 1992). The formation of such complexes inactivates phosphomonoesterase (Boavida and Wetzel, 1998), which is inhibited both competitively and non-competitively (Wetzel, 1992). Phosphorus-limited cells therefore need to expend more energy on phosphatase synthesis, and enhanced phosphomonoesterase activity has been reported for waters with increased humic materials (Stewart and Wetzel, 1992b). Wetzel (1992) pointed out these results with frequent observations (e.g. Jones, 1990) that the primary production in humic-rich waters is consistently lower than in clear waters with comparable loadings and light availability. 

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... 

Humic substances A series of relatively high-molecular-weight, yellow- to black-colored substances formed by secondary synthesis reactions. The term is used as a generic name to describe the colored material or its fractions obtained on the basis of solubility characteristics. These materials are distinctive to the soil (or sediment) environment in that they are dissimilar to the biopolymers of microorganisms and higher plants (including lignin)... 

Concepts of the compositions of coals influenced many in considerations of the structures of soil HS. For example, the proposal of Fuchs (1931) for structures of coal HAs (Figure 1.1) influenced soil humic scientists. The proposed structure is composed of heterocyclic aliphatic functionalities, some phenol-derived units, and considerable amounts of carboxylic and hydroxyl acidic functionalities. It may be possible that such structures could arise under conditions of elevated temperature and pressure, with oxidation taking place subsequently. Whereas such conditions might prevail during the synthesis of coals, they would be most unlikely to take place during the transformations of organic materials in the soil environment. 

Summary The possibility of direct synthesis of silicon oi anic compounds based on hydrolysis-resistant organic derivatives of silicon by using biogenic silica (from siliceous rocks) as a new raw material is discussed. The complex triethylphosphate with silica, the ammonium salts of tricatechol, and humic acids of monosilicic acids were obtained. Products were identified by proton magnetic resonance spectroscopy, IR spectrophotometry, or elemental analysis. 

In a mature soil, the balance of humus is maintained by the continued synthesis of new material as part of the old is mineralized consequently, the chemical nature of the humic substances remains constant over time. The humus of each soil may have its own characteristic equilibrium composition, both with regard to chemical nature and composition. 

When the source of plant raw material for humus synthesis is cut off, such as when eroded soil is transported to sediments, humus is exposed to successive cycles of biological attack, with concomitant changes in chemical composition. Easily decomposable compounds, such as proteins and carbohydrates, are attacked first, with the result that these constituents are eliminated at the expense of resistant molecules such as humic and fulvic acids. 

FIGURE 4. Glycerides used as starling materials for the autoxidative synthesis of marine fulvic and humic acids. Compound (4) was used as a procedural blank. 

Nevertheless, it is surprising how often one refers to elemental analysis to confirm the presence of a humic or fulvic acid. It is useful in determining whether a brown, macromolecular acidic material is from a coal, soil, marine sediment, or kerogen. It is most useful in characterizing structural trends in a specific environment, such as in sediments or soil profiles. Atomic ratios, especially 0/C ratios, are the simplest way to display elemental composition of humates. They also help one devise hypothetical structures for humates. As a guide in the synthesis of artificial humic substances, they are invaluable. In addition, atomic ratios help the investigator identify nonhumate contaminants. 

A study of the bulk properties of seawater humic substances was carried out by Kerr and Quinn (1975), while a detailed structural analysis was undertaken by Stuermer (1975) and Stuermer jmd Harvey (1978). Stuermer discussed the structural features in terms of origin, chemical and physical properties, interaction in the sea and eventual fate. As an example of the formation of a humic substance in seawater, we will discuss Stuermer s proposed structure of seawater fulvic material (Gagosian and Stuermer, 1977), the precursor compounds to its formation, and the condensation and polymerization reactions responsible for its synthesis. Although the material isolated by Stuermer represents only a small portion of the total hiunic material, it serves as an example of a possible condensation product. 

A final example of the influence of microwave treatment on adsorption materials involves the synthesis of mesoporous silica materials known as FUD-1. Preparations of FUD-1 used microwave heating both with and without humic acid treatment. The materials were synthesized with a poly(ethylene oxide)-poly-(butylene oxide)-poly(ethylene oxide) triblock copolymer as a template and tetraethylorthosilicate (TEOS) as the source of silica. In addition to being well characterized, the resultant materials were also tested for their ability to adsorb Cd ions from solution at a fixed pH of 6. The incorporation of humic acid into FUD-1 led to significantly higher adsorption capacity of Cd + ions than materials without humic acid. As a result, these materials seem to be promising adsorbents for removal of cadmium and related heavy metal ions from aqueous waste streams. 

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