Application of a constrained regularization method to extraction of affinity distributions: Proton and metal binding to humic substances

Orsetti, Silvia; Andrade, Estela Marı́a; Molina, Fernando V.

doi:10.1016/j.jcis.2009.04.049

Cited by 7 publications

(11 citation statements)

References 84 publications

(143 reference statements)

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“…Also, conditional affinity distributions can be obtained using constrained regularization methods. 24 If the proton affinity spectrum g(log K H ) is known, a conditional metal affinity distribution f(log K M ) can be estimated solving numerically the equation (assuming uncorrelated proton and metal affinity spectra): 24 …”

Section: ■ Introductionmentioning

confidence: 99%

Pb(II) Binding to Humic Substances: An Equilibrium and Spectroscopic Study

Orsetti

Marco-Brown²,

Andrade³

et al. 2013

Environ. Sci. Technol.

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The binding of Pb(II) to humic acids is studied through an approach combining equilibrium and spectroscopic measurements. The methods employed are potentiometric and fluorometric titrations, fluorescence excitation-emission matrices (EEM) and IR spectroscopy. Potentiometric titration curves are analyzed using the NICA equations and an electrostatic model treating the humic particles as an elastic polyelectrolyte network. EEMs are analyzed using parallel factor analysis, decomposing the signal in its independent components and finding their dependence on Pb(II) activity. Potentiometric results are consistent with bimodal affinity distributions for Pb(II) binding, whereas fluorometric titrations are explained by monomodal distributions. EEM analysis is consistent with three independent components in the humic fluorescence response, which are assigned to moieties with different degree of aromaticity. All three components show a similar quenching behavior upon Pb(II) binding, saturating at relatively low Pb(II) concentrations. This is attributed to metal ion induced aggregation of humic molecules, resulting in the interaction between the aromatic groups responsible for fluorescence; this is also consistent with IR spectroscopy results. The observed behavior is interpreted considering that initial metal binding (observed as strongly binding sites), correspond to bi- or multidentate complexation to carboxylate groups, including binding between groups of different humic molecules, promoting aggregation; further metal ions (observed as weakly binding sites) bind to single ligand groups.

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Section: ■ Introductionmentioning

confidence: 99%

Pb(II) Binding to Humic Substances: An Equilibrium and Spectroscopic Study

Orsetti

Marco-Brown²,

Andrade³

et al. 2013

Environ. Sci. Technol.

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“…These models generally include a description of the intrinsic binding constants in terms of a distribution, the affinity distribution or affinity spectrum, and an electrostatic contribution to account for the colloidal behavior of HS. The intrinsic affinity distribution has been assumed to be either discrete (effectively similar to a mixture of weak acids) ,, or continuous, with some assumed distribution function, ,,, but in both cases two main types of groups or sites have been included: carboxylic sites, with p K a in the range 3−5, and phenolic ones, with p K a about 8−10. The electrostatic contribution modeling has also followed two basic lines: one treated the humic substances as rigid particles, ,,− applying standard colloid chemistry models, whereas other authors applied, albeit sometimes in a restricted and approximate way, the concept of Donnan equilibrium. ,, In Tipping's WHAM models V and VI , a Donnan phase is assumed, surrounding the humic particles and containing only positively charged counterions, whereas the electrostatic effect on binding is accounted by an empirical Boltzmann factor; here the humic particles are assumed to be of fixed size (one value for fulvic acids, FA, and another one for humic acids, HA).…”

Section: Introductionmentioning

confidence: 99%

“…With the aim of introduce physically more realistic modeling, in this work a new electrostatic model for humic substances, the elastic polyelectrolyte network (EPN) model is proposed. This electrostatic model will be combined with a continuous affinity spectrum, in principle obtained from conditional spectrum calculations, and afterward adjusted as part of the procedure. In the following sections, the electrostatic model is introduced and combined with an intrinsic affinity spectrum, the numerical procedures are presented and fitting to literature data is performed.…”

Section: Introductionmentioning

confidence: 99%

Modeling Ion Binding to Humic Substances: Elastic Polyelectrolyte Network Model

2010

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A new model for the electrostatic contribution to ion binding to humic substances is proposed and applied to published data for proton binding to fulvic and humic acids. The elastic polyelectrolyte network model treats humic substance particles as composed by two parts, an external one directly in contact with the solution, and an internal part or gel fraction which is considered, from a statistical point of view, as a charged polymer network swelled by the electrolyte solution, in the framework of the Flory polymer network theory. The electrostatic effect is given by a Donnan-like potential, which can be regarded as an average value over the gel fraction of the humic particle. The gel fraction expands as the pH and humic charge are increased, determining the Donnan potential and consequently the ion activity inside the gel. The model was fitted to published experimental data with good agreement. The model predictions are discussed, and the behavior suggests, for some cases, the presence of a transition between closed and open structures attributed to the presence, at low pH, of intramolecular hydrogen bonds which are removed as the carboxylic sites become deprotonated.

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“…Esta metodologia permitiu verificar que as constantes de acidez são influenciadas pelos íons metálicos. 58 Em outro trabalho interessante sobre a aplicação da equação NICA, Orsetti et al 59 utilizaram um procedimento padronizado para extrair a distribuição de afinidade condicional a partir das curvas de titulação para o hidrogênio e para Cd(II), Pb(II) e Cu(II). Neste trabalho constataram que para o hidrogênio as distribuições são, na maioria dos casos, bimodais (carboxílicos e fenólicos), como assumido na literatura.…”

Section: O Significado Da Equação Nica E Sua Aplicação Na Complexaçãounclassified

Especiação termodinâmica de metais traço com substâncias húmicas: o modelo Nica-Donnan

Pinheiro¹,

Monteiro²,

Janot³

et al. 2017

Quim. Nova

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TRACE METAL THERMODYNAMIC SPECIATION WITH HUMIC SUBSTANCES: THE NICA-DONNAN MODEL. This work presents a critical overview of the NICA-Donnan model for trace metal thermodynamic speciation with humic substances obtained from natural organic matter in soils, natural waters and anthropogenic sources. A first part covers the theoretical aspects of the model, how to obtain good experimental data and perform the modelling. A second part deals with the developments in the last decade namely the use of the generic parameters, criticism and alternatives to the electrostatic modeling, the understanding of the NICA equation and an analysis of the published data, ending with the needs and opportunities for model development.

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Application of a constrained regularization method to extraction of affinity distributions: Proton and metal binding to humic substances

Cited by 7 publications

References 84 publications

Pb(II) Binding to Humic Substances: An Equilibrium and Spectroscopic Study

Pb(II) Binding to Humic Substances: An Equilibrium and Spectroscopic Study

Modeling Ion Binding to Humic Substances: Elastic Polyelectrolyte Network Model

Especiação termodinâmica de metais traço com substâncias húmicas: o modelo Nica-Donnan

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