The Supramolecular Structure of Humic Substances

Piccolo, Alessandro

doi:10.1097/00010694-200111000-00007

Cited by 833 publications

(648 citation statements)

References 72 publications

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“…2,3,[26][27][28] The TNB model fragment used in our simulations contains three carboxylic groups, three carbonyl groups, two phenolic groups, two amine groups, and four other R-OH alcohol groups and has a total molecular weight of 753 Da. [38][39][40] The size, composition, molecular weight, degree of aromaticity, and total charge density of this model are in good agreement with available experimental characterization of NOM 26,27,29 , the results of computer assisted 3-D structure elucidation, 42 and stochastic biogeochemical modeling. 33 The composition of the TNB model is also quite close to the composition of Suwannee River NOM, which is often used experimentally.…”

Section: Computational Methods and Detailsmentioning

confidence: 99%

Metal Cation Complexation with Natural Organic Matter in Aqueous Solutions: Molecular Dynamics Simulations and Potentials of Mean Force

Iskrenova-Tchoukova¹,

Kalinichev²,

2010

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Natural organic matter (NOM, or humic substance) has a known tendency to form colloidal aggregates in aqueous environments, with the composition and concentration of cationic species in solution, pH, temperature, and the composition of the NOM itself playing important roles. Strong interaction of carboxylic groups of NOM with dissolved metal cations is thought to be the leading chemical interaction in NOM supramolecular aggregation.Computational molecular dynamics (MD) study of the interactions of Na + , Mg 2+ , and Ca 2+ with the carboxylic groups of a model NOM fragment and acetate anions in aqueous solutions provides new quantitative insight into the structure, energetics, and dynamics of the interactions of carboxylic groups with metal cations, their association and the effects of cations on the colloidal aggregation of NOM molecules. Potentials of mean force and the equilibrium constants describing overall ion association and the distribution of metal cations between contact ion pairs and solvent separated ions pairs were computed from free MD simulations and restrained umbrella sampling calculations. The results provide insight into the local structural environments of metal-carboxylate association and the dynamics of exchange among these sites. All three cations prefer contact ion pair to solvent separated ion pair coordination, and Na + and Ca 2+ show a strong preference for bidentate contact ion pair formation. The average residence time of a Ca 2+ ion in a contact ion pair with the carboxylic groups is of the order of 0.5 ns, whereas the corresponding residence time of a Na + ion is only between 0.02 and 0.05 ns. The average residence times of a Ca 2+ ion in a bidentate coordinated contact ion pair vs. a monodentate coordinated contact ion pair are about 0.5 ns and about 0.08 ns, respectively. On the 10-ns time scale of our simulations, aggregation of the NOM molecules occurs in the presence of Ca 2+ but not Na + or Mg 2+ . These results agree with previous experimental observations and are explained 3 by both Ca 2+ ion-bridging between NOM molecules and decreased repulsion between the NOM molecules due to the reduced net charge of the NOM-metal complexes. Simulations on a larger scale are needed to further explore the relative importance of the different aggregation mechanisms and the stability of NOM aggregates.4

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Section: Computational Methods and Detailsmentioning

confidence: 99%

Metal Cation Complexation with Natural Organic Matter in Aqueous Solutions: Molecular Dynamics Simulations and Potentials of Mean Force

Iskrenova-Tchoukova¹,

Kalinichev²,

2010

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“…HS can be categorized into three groups: fulvic acids (FAs), which are the major component and the smallest structures of HS, and are soluble at any pH; HA, which represents bigger structures that are insoluble at pH b 2; and humin, which is insoluble at any pH (Jones and Bryan, 1998;Piccolo, 2001). The role of HA in nanoparticle transport is of particular interest.…”

Section: Introductionmentioning

confidence: 99%

The effect of humic acid on the aggregation of titanium dioxide nanoparticles under different pH and ionic strengths

Zhu

Wang

Keller

et al. 2014

Science of The Total Environment

196

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“…The 13 C NMR spectra of HA indicated the increase of hydrophobicity (sum of aromatic and alkyl C) with increasing soil C stability (Piccolo, 2001;Ikeya et al, 2004;Spaccini et al, 2006;Xiaoli et al, 2007;Conte et al, 2007;Canellas et al, 2008). This hydrophobicity in HA as a result of increased stability had previously been shown in association with the quinone moieties Perez et al, 2004;Canellas et al, 2007Canellas et al, , 2008 of HA.…”

Section: Introductionmentioning

confidence: 70%

Redox index of soil carbon stability

Baldotto

Canela²,

Canellas

et al. 2010

Rev. Bras. Ciênc. Solo

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SUMMARYAs an alternative to the relatively complex and expensive spectroscopic methods, the redox properties of humic acids, determined by potentiometric titrations, have been used to evaluate the stability of soil organic C. The objective of the present study was to establish a Redox Index of C Stability (RICS) and to correlate it with some properties of the humic acids extracted from different modal soils in Brazil (distinct weathering stages or management) to facilitate system comparison. The RICS was efficient for soil comparison and variations were comparable to those of the chemical and spectroscopic methods used for humic acid characterization. The values of soil pH, point of zero salt effect, sum of bases, exchangeable Ca content, weathering index, as well as the humic acid O/C ratio, quinone and semiquinone free radical contents, aromatic C and fluorescence intensity were closely related with the RICS. The RICS was higher in less weathered soils, with more active clays and higher fertility. The RICS values of soils under long-term sugarcane management were ranked in decreasing order: unburned, burned with vinasse, burned without vinasse.Index terms: soil chemistry, soil organic matter, humic substances, oxidation capacity.(1) Part of the doctoral and post doctoral works from the first author developed at the State University of the North Fluminense "Darcy Ribeiro" -UENF.

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The Supramolecular Structure of Humic Substances

Cited by 833 publications

References 72 publications

Metal Cation Complexation with Natural Organic Matter in Aqueous Solutions: Molecular Dynamics Simulations and Potentials of Mean Force

Metal Cation Complexation with Natural Organic Matter in Aqueous Solutions: Molecular Dynamics Simulations and Potentials of Mean Force

The effect of humic acid on the aggregation of titanium dioxide nanoparticles under different pH and ionic strengths

Redox index of soil carbon stability

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