Relating Ion Binding by Fulvic and Humic Acids to Chemical Composition and Molecular Size. 2. Metal Binding

Christl, Iso; Milne, Chris; Kinniburgh, D.G.; Kretzschmar, Ruben

doi:10.1021/es011010i

Cited by 43 publications

(86 citation statements)

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“…In freshwater, the pH dependence of f H is similar for all metals, although the magnitude and phasing of f H are different in each case. Thus, f H generally increases with increasing pH to around pH 8, an effect that is consistent with metal occupation of acidic (e.g., phenolic and carboxylic) sites on a heterogeneous series of natural ligands (Christl et al 2001). Thereafter, a small reduction in f H is evident, suggesting that available ligands at higher pH are more hydrophilic, or that complexes with inorganic anions (e.g., OH Ϫ , CO ) assume greater importance.…”

Section: Resultssupporting

confidence: 63%

Hydrophobicity and reactivity of trace metals in the low‐salinity zone of a turbid estuary

Turner

Mawji

2005

Limnology & Oceanography

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We chemically fractionated water samples from the low-salinity zone of a turbid estuary (Tamar, UK) using C18 columns to examine the controls on the complexation, hydrophobicity, and reactivity of dissolved trace metals (Co, Cu, Mn, and Pb). The hydrophobic (C18-retained) fraction of metal was related to the solubility of metal in the amphiphilic solvent, n-octanol, and in acid-base titrations and for all metals this fraction exhibited a peak centered around pH 7-8 in both freshwater and brackish water. In freshwater, hydrophobicity decreased in the order Pb Ͼ Cu Ͼ Mn Ͼ Co, and in brackish water, hydrophobicity was either reduced (Cu and Pb) or enhanced (Co and Mn) compared to freshwater, but in all cases peaks were more distinct. Salinity distributions of dissolved trace metals in the estuary indicated significant removal of Co, Cu, and Mn, and a source of Pb that was coincident with the onset of the turbidity maximum, and all distributions could be accounted for empirically by end-member water mixing and sediment resuspension. Salinity distributions of the hydrophobic fraction of metal were not consistent with any variation in water composition (including pH), but revealed that this fraction was preferentially removed from (Co, Cu, and Mn) or added to (Pb) the aqueous phase in the vicinity of the turbidity maximum. Removal implies that hydrophobic species are more reactive than hydrophilic species, and that either re-equilibration between these fractions is not attained within the hydrodynamic timescales of the upper estuary, or new equilibria are established by the buffering effects of additional anions and ligands in the water column. Addition of hydrophobic species of Pb coincided with minimum total and hydrophobic concentrations of Co, Cu, and Mn, and could, therefore, be explained in terms of reduced competition for nonspecific hydrophobic ligands from these and other (e.g., Al) metals in this region of the estuary.

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Section: Resultssupporting

confidence: 63%

Hydrophobicity and reactivity of trace metals in the low‐salinity zone of a turbid estuary

Turner

Mawji

2005

Limnology & Oceanography

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“…The vast majority of research on metal binding has been performed on isolated humic and fulvic acids (Tipping, 1993b;Pinheiro et al, 1999;Pinheiro et al, 2000;Christl et al, 2001;Milne et al, 2003). In recent years, sophisticated models have been developed that are able to describe the acid-base chemistry and metal complexation properties of isolated humic and fulvic acids in a general way.…”

Section: Metals In Natural Waters Generally Exist In Different Physicmentioning

confidence: 99%

Acid–base and copper-binding properties of three organic matter fractions isolated from a forest floor soil solution

Schaik

Kleja

Gustafsson

2010

Geochimica et Cosmochimica Acta

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ABSTRACT.Vast amounts of knowledge about the proton-and metal-binding properties of dissolved organic matter (DOM) in natural waters have been obtained in studies on isolated humic and fulvic (hydrophobic) acids. Although macromolecular hydrophilic acids normally make up about one-third of DOM, their proton-and metal-binding properties are poorly known. Here we investigated the acid-base and Cu-binding properties of the hydrophobic (fulvic) acid fraction and two hydrophilic fractions isolated from a soil solution. Proton titrations revealed a higher total charge for the hydrophilic acid fractions than for the hydrophobic acid fraction. The most hydrophilic fraction appeared to be dominated by weak acid sites, as evidenced by increased slope of the curve of surface charge versus pH at pH values above 6. The titration curves were poorly predicted by both Stockholm Humic Model (SHM) and NICA-Donnan model calculations using generic parameter values, but could be modelled accurately after optimisation of the proton-binding parameters (pH ≤ 9). Cu-binding isotherms for the three fractions were determined at pH values of 4, 6 and 9. With the optimised proton-binding parameters, the SHM model predictions for Cu binding improved, whereas the NICA-Donnan predictions deteriorated. After optimisation of Cu-binding parameters, both models described the experimental data satisfactorily. Iron(III) and aluminium competed strongly with Cu for binding sites at both pH 4 and pH 6. The SHM model predicted this competition reasonably well, but the NICA-Donnan model underestimated the effects significantly at pH 6. Overall, the Cu-binding behaviour of the two hydrophilic acid fractions was very similar to that of the hydrophobic acid fraction, despite the differences observed in 3 proton-binding characteristics. These results show that for modelling purposes, it is essential to include the hydrophilic acid fraction in the pool of 'active' humic substances.

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“…Their structures are complex [12], but various structural models (or pseudostructures) of fulvic acids (FA) [13], and humic acids (HA) have been proposed [13,14]. The main structural features of FA and HA are the ratio of aliphatic and aromatic carbon atoms, and the occurrence of units like phenol, quinone, amino acid, carbohydrate, and carboxylic acid, which are active in complexing metal cations [15][16][17]. Carboxylic acids, especially polycarboxylic acids, are known to form complexes with metal cations.…”

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confidence: 99%

Interaction of the cesium cation with mono-, di-, and tricarboxylic acids in the gas phase. A Cs⁺ affinity scale for cesium carboxylates ion pairs

Mayeux

Tammiku-Taul

Massi

et al. 2009

J. Am. Soc. Mass Spectrom.

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Humic substances (HS), including humic and fulvic acids, play a significant role in the fate of metals in soils. The interaction of metal cations with HS occurs predominantly through the ionized (anionic) acidic functions. In the context of the effect of HS on transport of radioactive cesium isotopes in soils, a study of the interaction between the cesium cation and model carboxylic acids was undertaken. Structure and energetics of the adducts formed between Cs ϩ and cesium carboxylate salts [Cs ϩ RCOO Ϫ ] were studied by the kinetic method and density functional theory (DFT). Clusters generated by electrospray ionization mass spectrometry from mixtures of a cesium salt (nitrate, iodide, trifluoroacetate) and carboxylic acids were quantitatively studied by CID. By combining the results of the kinetic method and the energetic data from DFT calculations, a scale of cesium cation affinity, CsCA, was built for 33 cesium carboxylates representing the first scale of cation affinity of molecular salts. The structural effects on the CsCA values are discussed. (J Am Soc Mass

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Relating Ion Binding by Fulvic and Humic Acids to Chemical Composition and Molecular Size. 2. Metal Binding

Cited by 43 publications

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Hydrophobicity and reactivity of trace metals in the low‐salinity zone of a turbid estuary

Hydrophobicity and reactivity of trace metals in the low‐salinity zone of a turbid estuary

Acid–base and copper-binding properties of three organic matter fractions isolated from a forest floor soil solution

Interaction of the cesium cation with mono-, di-, and tricarboxylic acids in the gas phase. A Cs⁺ affinity scale for cesium carboxylates ion pairs

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Relating Ion Binding by Fulvic and Humic Acids to Chemical Composition and Molecular Size. 2. Metal Binding

Cited by 43 publications

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Hydrophobicity and reactivity of trace metals in the low‐salinity zone of a turbid estuary

Hydrophobicity and reactivity of trace metals in the low‐salinity zone of a turbid estuary

Acid–base and copper-binding properties of three organic matter fractions isolated from a forest floor soil solution

Interaction of the cesium cation with mono-, di-, and tricarboxylic acids in the gas phase. A Cs+ affinity scale for cesium carboxylates ion pairs

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Interaction of the cesium cation with mono-, di-, and tricarboxylic acids in the gas phase. A Cs⁺ affinity scale for cesium carboxylates ion pairs