The use of differential equilibrium functions for interpretation of metal binding in complex ligand systems: Its relation to site occupation and site affinity distributions

Evaluating Scatchard and Differential Equilibrium Functions to study the binding properties of Cu(II) to the surface of mixed species of lyophilized Spirulina (Cyanobacteria)

“…Despite the differences of experimental conditions and measurement techniques, the log K DEF and Γ values obtained for the Spirulina are of the same order of magnitude reported in the literature [8][9][10][11]16 for other materials. This suggests that these values are governed by the nature of the metal cation and by the chemical nature of the binding sites, which have some similarity between algal materials and humic substances.…”

“…This decrease of log K DEF with the increase of the log θ may be explained by the fact that the sites with stronger affinity by Cu(II) are occupied first, resulting higher log K DEF values. Table 2 presents the values of K D 0 EF for the three materials studied, as well as the heterogeneity parameters, which were between 0.4 and 0.5, denoting an elevated degree of heterogeneity [8][9][10][11]16 for both, the cell surfaces and the soluble complexants. As mentioned before, this heterogeneity is due to the presence of amine, phenolic, phosphate and carboxylic groups in the studied materials.…”

“…Usually, these studies report results for natural organic matter in waters (humic substances), and using anodic stripping voltammetry (ASV) for measurement of the labile fraction of the metal cation. [8][9][10]16 Rollemberg et al…”

“…To overcome this limitation, a continuous differential equilibrium function has been proposed to interpret the metal binding properties of metal cations to humic substances. [8][9][10] This method was recently applied to study the thermodynamic of Cd(II) uptake by Chlorella marina. 11 When this approach is applied, no a priori assumptions are made, so that effects of the chemical heterogeneity, electrostatic interactions and conformational changes can be evaluated performing the titrations under different conditions of pH, ionic strength and initial metal loading.…”

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

“…Measurement and interpretation of binding between metal ions and the natural ligands occurring in the FA is severely limited by their chemical and physical heterogeneity and further this has an important influence on their environmental behaviour (Altman and Buffle, 1988). That is why the complexation between metals and FA strongly depends on factors such as: the pH of the media, the concentration of dissolved salts (ionic strength); the temperature and even the origin of these substances (Buffle, 1988;Sposito, 1986).…”