Determination of intrinsic complexation parameters for Cu²⁺and a soil fulvic acid by ion selective electrode

Copper(II) and lead(II) complexation by humic acid and humic-like ligands

“…However by using "simpler" and stoichiometrically defined ligands of known chemical structure and with similar binding sites to those of humic in the context of chemical composition, electronic and steric effects, a prediction of humic-metal binding can be performed. 17 Considering the fact that the major binding sites of humic acid are attributed to the oxygen-containing functional groups, i.e., carboxylic and phenolic groups, the employment of benzoic and salicylic acids as humic model ligands is justified. 15 The information obtained using benzoic and salicylic acids can be useful in the difficult task of evaluation of the nature and the contribution of the donor sites of humic acid to complexation.…”

Fractionation and Speciation of Trace Elements in Soil Solution

“…As a result, a series of new interesting perspectives on ISEs application in environmental analysis has been identified [82]. For research concerning trace elements in soils, ion-selective electrodes are currently mainly used to measure free metal ion (mainly Cu 2þ ) activities for the assessment of the complexation of trace elements by organic matter [83][84][85][86], their sorption by clays [87], their mobility, availability and toxicity in soils [88][89][90] and their chemical behaviour in rhizosphere microenvironments [91]. They are also frequently used in procedures for validation of speciation models [92].…”

Advantages and Limitations of the Use of an Extended Polyelectrolyte Model to Describe the Proton-Binding Process in Macromolecular Systems. Application to a Poly(acrylic acid) and a Humic Acid

“…When the chemical structure and the chemical nature of both the molecule and the binding sites are well-known, the application of “complete” models is feasible. However, when the chemical structure and the chemical nature of either the molecule or the binding sites are unknown, the direct application of the models used for well-known macromolecular systems involves the need to assume several approximations, principally regarding the specific molecular geometry and related parameters. ,− This fact has led to the frequent use of semiempirical models that, besides being founded on equations related to the chemical nature of both the macromolecules and the absorption process, permit us to obtain values from the adjusting iterative process for the unknown parameters related to the specific macromolecule structure. ,− Furthermore, in some cases, such as the NICCA-Donnan model 14,15 or the model VI, the need to assume a specific molecular geometry is removed by using the Donnan potential approach. However, the application of this type of model, although it gives us a very good mathematical description of the experimental data, also provides, in certain cases, final values for some adjustable parameters that are not easy to interpret on a physicochemical basis. , …”

“…This information, in turn, may also complete that obtained from semiempirical models. Thus, in the polyelectrolyte model (or the equivalent electrostatic model), as proposed by Tanford 10 and others, ,,− the effect of the variations of the electrostatic potential around the binding sites on the value of the association−dissociation constants that define the proton (ion)-binding process is explicitly considered by introducing an electrostatic factor (e -Ψ( Z , z , D ) for association and e Ψ( Z , z , D ) for dissociation). This factor considers the influence of conformational changes undergone by the macromolecule on the electrostatic charge around the ion-binding sites (the effect of the binding-site charges in the molecule on the chemical potential of the reactive species) by means of the calculation of the electrostatic surface potential (Ψ) as a function of the ion (small molecule) charge ( z ), the net molecule charge ( Z ), and the specific molecular geometry (inter-charge distances ( D )).…”