Emerging Concepts of the Compositions and Structures of Humic Substances

Hayes, M.H.B.

doi:10.1016/b978-1-85573-805-8.50005-7

Cited by 20 publications

(10 citation statements)

References 29 publications

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“…Our findings on the spin concentration of the HS extracted from peat samples was 2.62×10 28 spin g -1 of carbon, with a higher degree of humification than the values reported by Hayes,27 but comparable to the values reported for more humified samples, 28 indicating a high degree of humification of the humic substances under study and corroborating the data obtained from our elemental analysis. …”

Section: Electron Paramagnetic Resonance (Epr)supporting

confidence: 81%

Interaction between humic substances and metallic ions: a selectivity study of humic substances and their possible therapeutic application

Santos¹,

Botero²,

Bellin³

et al. 2007

J. Braz. Chem. Soc.

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Section: Electron Paramagnetic Resonance (Epr)supporting

confidence: 81%

Interaction between humic substances and metallic ions: a selectivity study of humic substances and their possible therapeutic application

Santos¹,

Botero²,

Bellin³

et al. 2007

J. Braz. Chem. Soc.

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“…Many of the most important functions of HS will remain obscure until the nature of these substances are elucidated. Considering that the genesis of HS involves combinations of several reaction pathways and a wide variety of chemical binding systems, it is very difficult to define a clear concept on their composition (Hayes, 1997). Considerable progress has been made in providing an awareness of some of the gross features of HS (Stevenson, 1994), by employing various spectroscopic procedures and Nuclear Magnetic Resonance spectroscopy.…”

Section: Introductionmentioning

confidence: 99%

Stomatal Responses to Humic Substances and Auxin are Sensitive to Inhibitors of Phospholipase A2

et al. 2006

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Two fractions of earthworm humic substances, differing in nominal molecular weight, containing a very low amount of free IAA, and exhibiting auxin-like properties, were prepared and characterised by infrared and 1 H-NMR spectroscopy. In this study we investigate their effects on stomatal opening, as influenced by phospholipase A 2 , in leaf of the Argenteum mutant of pea (Pisum sativum L.) Both of the humic fractions caused stomatal opening in the epidermal peels. The response showed a broad biphasic dose dependence and the effective concentrations were similar for the two fractions. The maximal stomatal apertures in response to both humic substances were similar to that caused by IAA and somewhat less than the response to white light or fusicoccin. Two inhibitors of phospholipase A 2 selectively blocked the response of stomata to both IAA and humic substances, without affecting the response to light or fusicoccin. We conclude that stomatal opening in response to auxin and humic substances involves activation of a phospholipase A 2 that is not involved in signalling the response to light or fusicoccin.

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“…The variability of sources and the chemical heterogeneity of HS have precluded our attaining definite knowledge of their secondary chemical structure and absolute molecular weight (Hayes, 1997). There are still divergent opinions about whether humic substances are real polymeric macromolecules or molecular associations of relatively small molecules held together by weak interaction forces (Clapp and Hayes, 1999).…”

mentioning

confidence: 99%

Chromatographic and Spectrophotometric Properties of Dissolved Humic Substances Compared With Macromolecular Polymers

Piccolo¹,

Conte²,

Cozzolino³

2001

Soil Science

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The commonly accepted polymeric nature of humic substances is still a matter of debate. In this work, both humic matter of different origin and undisputed neutral (polysaccharides) and negatively charged (polystyrenesulphonates) polymers of known molecular weight were studied by high performance size exclusion chromatography after dissolution in mobile phases of different composition but constant ionic strength. Modification of the control mobile phase with methanol, hydrochloric acid, and acetic acid showed a progressive alteration of the chromatographic behavior of humic materials, but it did not alter that of polymers. Absolute size reduction of bulk humic material revealed by a refractive index detector was accompanied by a substantial decrease in absorbance of peaks indicated by the UV detector. Reduction of molecular absorptivity of humic substances with changes in solution composition was confirmed by UV spectroscopy over a wide range of wavelengths. Differences in chromatographic behavior between undisputed polymers and humic samples suggest that humic matter reflects, rather than a polymeric nature, a supramolecular association of heterogeneous molecules held together mainly by weak hydrophobic forces. The content of hydrophilic and hydrophobic carbons in humic substances appears to control the intermolecular hydrogen and dispersive bondings that ultimately stabilize humic conformations in different mobile phases. (Soil Science 2001;166:174-185)

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Emerging Concepts of the Compositions and Structures of Humic Substances

Cited by 20 publications

References 29 publications

Interaction between humic substances and metallic ions: a selectivity study of humic substances and their possible therapeutic application

Interaction between humic substances and metallic ions: a selectivity study of humic substances and their possible therapeutic application

Stomatal Responses to Humic Substances and Auxin are Sensitive to Inhibitors of Phospholipase A2

Chromatographic and Spectrophotometric Properties of Dissolved Humic Substances Compared With Macromolecular Polymers

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