Quinone–hydroquinone complexes as model components of humic acids: Theoretical studies of their structure, stability and Visible–UV spectra

Tossell, J. A.

doi:10.1016/j.gca.2008.12.029

Cited by 26 publications

(20 citation statements)

References 56 publications

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“…Earlier studies have proposed that the UV-Vis absorption spectra of CDOM at long wavelengths ([350 nm) originate from a continuum of charge transfer (CT) states between a large number of charge acceptors (e.g., quinonelike moieties) and charge donors (e.g., hydroquinone-like moieties) (Del Vecchio and Blough 2004b;Boyle et al 2009;Tossell 2009). The absorption at short wavelengths in UV range, e.g.…”

Section: Discussionmentioning

confidence: 99%

Correlation between molecular absorption spectral slope ratios and fluorescence humification indices in characterizing CDOM

et al. 2010

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Ultraviolet-visible absorption spectral slope ratios S R (slope in 275-295 nm divided by slope in 350-400 nm) and humification index (HIX, integrated fluorescence emission in 435-480 nm divided by that in 435-480 and 300-345 nm) were compared when characterizing chromophoric dissolved organic matter (CDOM) in three humic acids and 44 whole water samples. HIX increased with increasing pH for humic acids, while their S R showed much more complicated dependencies on pH. There was a negative correlation between S R and HIX. S R increased in the order terrestrial coal/peat \ terrestrial soil/ river \ seawater, while HIX increased in the order seawater \ terrestrial soil/river \ terrestrial coal/peat. The comparative study in this work indicates that terrestrially derived CDOM has higher HIX and lower S R than marine CDOM. Investigators may potentially use these two indices to compare qualitatively the character of CDOM in different sources (e.g., terrestrial vs. marine).

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Section: Discussionmentioning

confidence: 99%

Correlation between molecular absorption spectral slope ratios and fluorescence humification indices in characterizing CDOM

et al. 2010

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“…XH 2 o = 2YH . ) are additional factors to consider (Roginsky et al 1999;Tossell 2009). Equilibrium constants for both reactions strongly favor reactants over products (Uchimiya and Stone 2006).…”

Section: Time Course Behaviormentioning

confidence: 99%

Reduction of Substituted p-Benzoquinones by FeII Near Neutral pH

Uchimiya¹,

Stone

2009

Aquat Geochem

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The oxidation of dihydroxyaromatics to benzoquinones by Fe III (hydr)oxides is important in respiratory electron shuttling by microorganisms and has been extensively studied. Prior publications have noted that the Gibbs Free Energy (DG) for the forward reaction is sensitive to dihydroxyaromatic structure, pH, and concentrations of reactants and products. Here, we address the back reaction, benzoquinone reduction by Fe II . Rates markedly increase with increasing pH, in accord with increases in DG. Ring substituents that raise the potential of the p-benzoquinone/hydroquinone half reaction raise reaction rates: -OCH 3 \ -CH 3 \ -C 6 H 5 \ -H \ -Cl. p-Naphthoquinone, with a reduction potential lower than the five substituted p-benzoquinones just listed, yields the lowest reaction rates. The complexity of the reaction is reflected in lag periods and less-pronounced S-shaped time course curves. Benzoquinone reduction by Fe II may be an important link in networks of electron transport taking place in suboxic and anoxic environments.

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“…Secondly, to investigate the effect of HA macromolecular structure, the semiquinones derived from 3,4-dihydroxy-antracene-1-carboxylic acid (34dha) were taken under study in addition to those derived from 34dhb. It should be mentioned that studies on the HA model compounds have proved to be invaluable source of information about these natural systems (Tossell, 2006(Tossell, , 2009Trout and Kubicki, 2006;Niederer and Goss, 2007;Cornard et al, 2008;Witwicki et al, 2008;Burk et al, 2009;Witwicki et al, 2009a,b;Xu et al, 2010). To the best of our knowledge, this is the first report on theoretical study of HA native radicals (and protonated semiquinones in general) dedicated to the influence of the chemical environment on their g tensors.…”

Section: Introductionmentioning

confidence: 87%

Protonated o-semiquinone radical as a mimetic of the humic acids native radicals: A DFT approach to the molecular structure and EPR properties

Witwicki

Jezierska

2012

Geochimica et Cosmochimica Acta

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Quinone–hydroquinone complexes as model components of humic acids: Theoretical studies of their structure, stability and Visible–UV spectra

Cited by 26 publications

References 56 publications

Correlation between molecular absorption spectral slope ratios and fluorescence humification indices in characterizing CDOM

Correlation between molecular absorption spectral slope ratios and fluorescence humification indices in characterizing CDOM

Reduction of Substituted p-Benzoquinones by FeII Near Neutral pH

Protonated o-semiquinone radical as a mimetic of the humic acids native radicals: A DFT approach to the molecular structure and EPR properties

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