Humic substances compounds

As an approach to investigating the complex chemistry of natural foams, humic substances (compounds sufficiently nonpolar at pH 2.0 to be isolated by reverse phase on XAD-8 and recovered in 0.1 N sodium hydroxide) were isolated from aquatic foam and associated stream water for chemical characterization and investigations into surfactant behavior. Humic substances were chosen because they represent natural organic compounds present in natural waters that are sufficiently nonpolar at pH 2.0 to be isolated by XAD-8 adsorption. As surfactants also possess moderately nonpolar characteristics it follows that humic substances may contain a significant surfactant component. We hypothesized that foam would be enriched in humic substances compared to stream samples and would show increased hydrophobicity, aliphaticity, and decreased carboxylation in order to sustain surface-active behavior. 

Biogeochemical compartment. The biogeochemical compartment consists of the O, A, E, and B horizons of soils, in which substantial organic matter can be an integral component of the soil. The load of the water leaving the soil from the biogeochemical compartment consists mainly of soluble compounds because the matrix of the soil acts as a filter that retains particulate matter. In some cases, however, clay and particulate humic substances are also car-... 

Further progress may derive from a more accurate definition of the chemical and physical properties of the humic substances present at the rhizosphere and how they interact with the root-cell apoplast and the plasma membrane. An interaction with the plasma membrane H -ATPase has already been observed however this master enzyme may not be the sole molecular target of humic compounds. Both lipids and proteins (e.g., carriers) could be involved in the regulation of ion uptake. It therefore seems necessary to investigate the action of humic compounds with molecular approaches in order to understand the regulatory aspects of the process and therefore estimate the importance of these molecules as modulators of the root-soil interaction. 

MnP is the most commonly widespread of the class II peroxidases [72, 73], It catalyzes a PLC -dependent oxidation of Mn2+ to Mn3+. The catalytic cycle is initiated by binding of H2O2 or an organic peroxide to the native ferric enzyme and formation of an iron-peroxide complex the Mn3+ ions finally produced after subsequent electron transfers are stabilized via chelation with organic acids like oxalate, malonate, malate, tartrate or lactate [74], The chelates of Mn3+ with carboxylic acids cause one-electron oxidation of various substrates thus, chelates and carboxylic acids can react with each other to form alkyl radicals, which after several reactions result in the production of other radicals. These final radicals are the source of autocataly tic ally produced peroxides and are used by MnP in the absence of H2O2. The versatile oxidative capacity of MnP is apparently due to the chelated Mn3+ ions, which act as diffusible redox-mediator and attacking, non-specifically, phenolic compounds such as biopolymers, milled wood, humic substances and several xenobiotics [72, 75, 76]. 

Humic Substances, Mutagenic Compounds and Plant Species Used... 

Georgi A, Trommler U, Reichl A, Kopinke F-D (2008) Influence of sorption to dissolved humic substances on transformation reactions of hydrophobic organic compounds in water. Part II hydrolysis reactions. Chemosphere 71 1452-1460... 

Looser, P. W., Bertschi, S. and Fent, K. (1998). Bioconcentration and bioavailability of organotin compounds influence of pH and humic substances, Appl. Organomet. Chem., 12, 601-611. 

Partitioning of PCBs into other organic compound mixtures or phases found in the environment alters environmental parameters used to estimate their fate and transport. For example, dissolved phase humic substances (i.e., DPUS) can increase the apparent solubility of organic pollutants [381-390] (see Chap. 2). 

Actinomycetes can metabolize a wide variety of organic substrates, including organic compounds that are generally not metabolized, such as phenols and steroids. They are also important in the metabolism of heterocyclic compounds such as complex nitrogen compounds and pyrimidines [42,49]. The breakdown products of their metabolites are frequently aromatic, and these metabolites are important in the formation of humic substances and soil humus [42,49]. 

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