A chemical structure for humic substances

Schulten, H.‐R.; Plage, Bernd; Schnitzer, M.

doi:10.1007/bf01221416

Cited by 156 publications

(45 citation statements)

References 2 publications

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“…It is currently assumed that humic substances constitute a three-dimensional flexible structure built of benzene, naphthalene, and phenanthrene rings connected with chain structures (SCHULTEN et al 1991). Humic substances can form bonds with e.g.…”

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confidence: 99%

Molecular size distribution and hydrophilic and hydrophobic properties of humic acids isolated from forest soil

Dębska¹,

Drąg²,

Banach-Szott³

2007

Soil & Water Res.

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Abstract:The aim of the present paper was to determine hydrophilic and hydrophobic properties and the degree of polydispersity of humic acids depending on their degree of maturity and the properties of the plant material participating in the process of humification. The study involved humic acids isolated from samples taken from organic and mineral horizons of forest soils. The samples were taken under the tree stands of: pine with an admixture of hardbeam, European beech, elm, fir, spruce, and thuja. It was demonstrated that the properties of humic acids of the organic horizon and mineral horizons are determined by the kind of plant litter, mainly by the tree species. The humification process is connected with an increase of the proportion of humic acids of lower molecular size as compared to the proportion of molecules greater in size, and with an increase of hydrophilic fractions and a decrease of hydrophobic fractions. Based on the correlation relationships, it was shown that the degree of polydispersity of molecules of humic acids is related to their hydrophilic and hydrophobic properties. Humic acids with a larger proportion of high-molecular fractions demonstrate also a higher proportion of hydrophobic fractions.

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confidence: 99%

Molecular size distribution and hydrophilic and hydrophobic properties of humic acids isolated from forest soil

Dębska¹,

Drąg²,

Banach-Szott³

2007

Soil & Water Res.

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“…These components are traditionally defined according to their solubilities. Humins are the fraction which is insoluble at all pHs, humic acids are insoluble at pHs below pH 2.0, and fulvic acids are soluble at all pHs.HS are thought to consist of a skeleton of alkyl or aromatic units cross-linked mainly by oxygen and nitrogen groups, with the major functional groups being carboxylic acid, phenolic and alcoholic hydroxyls, ketone, and quinone groups (27,42). This structure allows HS to bind both hydrophobic and hydrophilic materials, and thus they play an important role in the fate and transport of heavy metals and contaminating hydrocarbons in the environment (9, 24, 35-37, 38, 46, 54).…”

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confidence: 99%

Diversity and Ubiquity of Bacteria Capable of Utilizing Humic Substances as Electron Donors for Anaerobic Respiration

Coates

Cole

Chakraborty

et al. 2002

Appl Environ Microbiol

202

129

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Previous studies have demonstrated that reduced humic substances (HS) can be reoxidized by anaerobic bacteria such as Geobacter, Geothrix, and Wolinella species with a suitable electron acceptor; however, little is known of the importance of this metabolism in the environment. Recently we investigated this metabolism in a diversity of environments including marine and aquatic sediments, forest soils, and drainage ditch soils. Most-probable-number enumeration studies were performed using 2,6-anthrahydroquinone disulfonate (AHDS), an analog for reduced HS, as the electron donor with nitrate as the electron acceptor. Anaerobic organisms capable of utilizing reduced HS as an electron donor were found in all environments tested and ranged from a low of 2.31 ؋ 10 1 in aquifer sediments to a high of 9.33 ؋ 10 6 in lake sediments. As part of this study we isolated six novel organisms capable of anaerobic AHDS oxidation. All of the isolates coupled the oxidation of AHDS to the reduction of nitrate with acetate (0.1 mM) as the carbon source. In the absence of cells, no AHDS oxidation was apparent, and in the absence of AHDS, no cell density increase was observed. Generally, nitrate was reduced to N 2 . Analysis of the AHDS and its oxidized form, 2,6-anthraquinone disulfonate (AQDS), in the medium during growth revealed that the anthraquinone was not being biodegraded as a carbon source and was simply being oxidized as an energy source. Determination of the AHDS oxidized and nitrate reduced accounted for 109% of the theoretical electron transfer. In addition to AHDS, all of these isolates could also couple the oxidation of reduced humic substances to the reduction of nitrate. No HS oxidation occurred in the absence of cells and in the absence of a suitable electron acceptor, demonstrating that these organisms were capable of utilizing natural HS as an energy source and that AHDS serves as a suitable analog for studying this metabolism. Alternative electron donors included simple volatile fatty acids such as propionate, butyrate, and valerate as well as simple organic acids such as lactate and pyruvate. Analysis of the complete sequences of the 16S rRNA genes revealed that the isolates were not closely related to each other and were phylogenetically diverse, with members in the alpha, beta, gamma, and delta subdivisions of the Proteobacteria. Most of the isolates were closely related to known genera not previously recognized for their ability to couple growth to HS oxidation, while one of the isolates represented a new genus in the delta subclass of the Proteobacteria. The results presented here demonstrate that microbial oxidation of HS is a ubiquitous metabolism in the environment. This study represents the first description of HS-oxidizing isolates and demonstrates that microorganisms capable of HS oxidation are phylogenetically diverse.Humic substances (HS) are ubiquitous in the environment and can be readily isolated from nearly all soils, waters, and sediments. The natural organic matter content of many soils and sedi...

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“…2), in both control and amended plots, showing a significant relative decrease in the case of N-fertilised plots. Alkylbenzenes, often considered typical fragments of HAs [31,32] behaved differently from fatty acids. In fact, the total yield of these compounds was also very significantly related to the external N-inputs.…”

Section: Resultsmentioning

confidence: 99%

04/00936 Pyrolytic descriptors responsive to changes in humic acid characteristics after long-term sustainable management of dryland farming systems in Central Spain

2004

Fuel and Energy Abstracts

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Structural changes in humic acids from a semiarid soil of an experimental farm in Central Spain have been studied by Curie-point pyrolysis. Soil has received periodic inputs of farmyard manure or crop wastes for the last 16 years, and mineral nitrogen fertilisation in 50% of the plots. Analytical pyrolysis suggested substantial differences in terms of the effect of soil management on the accumulation mechanisms of the humic acid fraction. When compared with control plots, humic acids from plots amended with crop wastes displayed well-defined methoxyphenol assemblages, indicating that the diagenetic transformation of lignin could be a dominant mechanism of organic matter stabilisation. The greatest yields of methoxyphenols after organic inputs were obtained in plots receiving nitrogen fertilisation, what agrees with the expected higher performance of the lignin biodegradation in nitrogen-limited media. Increased yields of lignin-derived methoxyphenols were also observed in plots treated with manure, which released in addition a conspicuous series of alkyl compounds suggesting recalcitrant wax-derived lipids incorporated to the humic acids. Highest yields of pyrolytic fatty acids were observed in humic acids from manure-amended plots without nitrogen fertilisation. Alkylbenzene proportions were also pyrolytic descriptors responsive to mineral nitrogen inputs, showing very significant differences (P B/0.01) in both control and amended plots.

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A chemical structure for humic substances

Cited by 156 publications

References 2 publications

Molecular size distribution and hydrophilic and hydrophobic properties of humic acids isolated from forest soil

Molecular size distribution and hydrophilic and hydrophobic properties of humic acids isolated from forest soil

Diversity and Ubiquity of Bacteria Capable of Utilizing Humic Substances as Electron Donors for Anaerobic Respiration

04/00936 Pyrolytic descriptors responsive to changes in humic acid characteristics after long-term sustainable management of dryland farming systems in Central Spain

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