Functional Groups Of Humic Substances Research Articles

A study of intramolecular energy transfer in Cm(III) complexes with aromatic ligands by time-resolved laser fluorescence spectroscopy

Sensitized fluorescence emission of f-element ions was studied for the humate and fulvate complexes of Cm(III) by time-resolved laser fluorescence spectroscopy. Complexation with chelating aromatic carboxylic acids, which may be regarded as complexing functional groups of humic substances, e.g. phthalic and salicylic acids, was investigated in parallel for comparison. Excitation and emission spectra, together with lifetimes of excited states, were investigated for the Cm(III) complex species as well as for the individual pure ligans. The fluorescence enhancement was found to be weak in the Cm(III)-phthalate and strong in the Cm(III)-salicylate. The latter is comparable with the Cm(III)-fulvate. The efficiency of energy transfer was calculated from the excitation at 308 nm. The results are discussed in terms of energy overlapping between triplet states of ligands and excited levels of Cm(III).

Metabolites of xenobiotica and mineral oil constituents linked to macromolecular organic matter in polluted environments

The type of association between pollutants and humic substances of soils, sediments and river waters has been investigated. Metabolites, which can arise from the microbiological degradation of polyaromatic hydrocarbons (PAH) and polychlorinated biphenyls (PCB), were cleaved from the macromolecular matrix by selective chemical degradation techniques (OH −, BCl 3, Rh/H 2). Hydrolysis reactions performed with Na 18OH proved that some metabolites of pollutants form stable ester bonds by condensation processes with functional groups of humic substances, a phenomenon which has major implications for transport, toxicity and bioavailability of xenobiotica.

Some aspects of chemical topology from the evaluation of properties of humic substances

Since many of the properties, including the characteristic and functional groups of humic substances are well known we have investigated the role of humic substances in their possible interactions with xenobiotics partly through our particular humus quality parameters. According to our results K-values expressing the degree of humification as well as reactive N-forms evaluated through our six-step continuous hydrolysis play an important role in the description of the adsorption of toxic compounds. We have also applied new results on chemical topology for the evaluation of such processes. The graph invariant proposed by Randic seems to be suitable for this application. We found a strict correlation between the Randic indices of s-triazine herbicides and their adsorption onto humic substances based on the particular investigations of Walker and Crawford (1968) and also on the results of Hayes et al. (1968). The adsorption on humic substances of these herbicides was correlated to our particular Randic indices. The combination of Randic indices with our particular humus quality parameters are suitable for the evaluation of the properties of humic substances for binding toxic organic compounds (herbicides and pesticides).

INFLUENCE OF ORGANIC ACIDIC FUNCTIONAL GROUPS OF HUMIC SUBSTANCES IN COMPLEXATION WITH CLAY MINERALS

An attempt has been made to assess the involvement of the acidic functional groups of humic substances in the formation of clay-humus complexes. The humic substances used included four different samples of varying acid-group content as well as a series of methylated derivatives of one humic acid (HA). Amounts of soluble HA/FA (fulvic acid) retained by montmorillonite after repeated washing of the predried complexes with water were estimated. Results reveal a trend of decrease in fixation with increase in acidity of the humic samples. Methylation of the acidic groups has the same effect. It is proposed that a decreasing content of acidic groups in humic substances promotes their fixation by montmorillonite because of a lowering of interparticle repulsive forces as well as a reduction in hydration energies; the net energy available for breaking down the clay-humus bonds is consequently decreased. Nonionic attractive forces are important interactive modes in complexes that have been dried.

Le transport chimique de l'or dans les environnements de surface: formation d'un colloïde et complexation organique

Two different categories of experiments were undertaken to determine the significance of humic substances in the chemical transport of gold. The experiments of the first category were designed to study Au(Cl)4− reduction by humic acid at pH 3.5, which is consistent with the formation of this ion in sulfide oxidation zones. These experiments were repeated with denaturated humic acid (obtained by heating in an acid medium). The results show that Au(Cl)4− is reduced by humic acid to an unstable colloid, but not by denaturated humic acid. The purpose of the second category of experiments was to study gold solubility in various organic materials: humic acid, fulvic acid, and potassium humate. Solutions of these substances and demineralized water (the latter served as the reference point) were placed in contact with metallic gold for 1 month at pH 7, the common pH in surface environments. The data indicate an increase in gold solubility according to the following order: humic acid < fulvic acid < potassium humate. A two-step gold chemical-transport mechanism for surface environments is proposed on the basis of our results. In the first step, unstable colloidal gold is formed from inorganic complexes produced in the sulfide oxidation zones (zones with acidic pH). After full oxidization, the pH moves to the normal value, causing the dissociation of functional groups in humic substances. In the second step, these humic substances, through the dissociated functional groups, could form organo-metallic complexes with gold, ensuring gold dispersion in surface environments. [Journal Translation]

A model of solid‐solution interactions in acid organic soils, based on the complexation properties of humic substances

SUMMARYCHAOS (Complexation by Humic Acids in Organic Soils) is a quantitative chemical model of organic soils that incorporates complexation by the functional groups of humic substances and non‐specific ion‐exchange reactions. The two types of interaction are linked by the net humic charge, Z, which depends on the extents of proton and metal complexation, and which in turn determines ionic concentrations in the diffuse part of the electrical double layer, by a Donnan equilibrium. CHAOS was found to account satisfactorily for the results of acid‐base titration experiments (pH range 3–5) with soil samples, giving reasonable simultaneous predictions of solution pH and concentration of A13+. Predictive calculations with CHAOS suggest that organic soils acidified by acid rain would respond on a time‐scale of years‐to‐decades to reductions in rain acidity. An associated effect might be an increase in the concentration of dissolved organic matter in the soil solution.

Removal of NH 3 by a peat biofilter without and with nitrifier

Ammonia was deodorized using fibrous peat on laboratory-scale. The removal of NH 3 by the peat was principally by physical and chemical adsorption of NH 3 with functional groups of humic substances of the peat. The NH 3 adsorption capacities of the various peats tested ranged from 10 to 20 g-N/kg·dry peat, and were decreased by neutralization with Ca(OH) 2. The removal of NH 3 by nitrification could be achieved by seeding the peat with nitrifying bacteria. The maximum removal rate of NH 3 was about 70 percent of the nitrifying capacity which was, in this study, quantified by 48 h nitrifying capacity.