Determination of Conditional Stability Constants of Copper(ii) Complexes With Naturally Occurring Macromolecules
type: CreativeWork
description: A critical evaluation was made of models currently in use for determining stability constants of metal complexes with humic and fulvic acids. Most models are shown to reduce to forms based on Adair's equation, in which the macromolecule is assumed to be the central group and where binding is evaluated graphically as a reciprocal plot, a saturation plot, a Scatchard plot, or a Hill plot. Application of a single set of experimental data (ISE and H('+) release measurements were made) for the reactions of Cu(II) with humic acid showed that values of log K* (apparent K) were lowest when calculated by either the Hill plot method (linear form) or by the Bjerrum plot method (where the metal is assumed to be the central group), as compared to the Scatchard plot method. Values for B(,1) (Bjerrum plot method) were 2 or 3 orders of magnitude lower than reported values for k(,1)* (intrinsic apparent k values obtained with the Scatchard plot method). This difference in B(,1)* and k(,1)* could not be attributed to differences between research groups because similar differences were found when B(,1)* and k(,1)* were calculated from the same experimental data. Apparent intrinsic stability constants obtained by Scatchard plot analysis for binding at the strongest (k(,1)*) and weakest (k(,j)*) sites differed by several orders of magnitude. In addition, the Scatchard plot technique yielded log K(,1)* values larger than overall log K* or B* values of other methods. Average log apparent stability constants for 0.25 mg humic acid/ml in 0.01 KClO(,4) at pH 4 for the same set of ISE data points above 10('-6) Cu('2+) were 6.13 (k(,1)*) and 4.97 (k(,j)*), 4.99 (B(,1)*), 4.99 (B(,1)*) and 9.13 (B(,2)*), and 3.66 (k*) for the Scatchard, Bjerrum, and Hill plot methods, respectively. When data below 10('-6) Cu('2+) were used, log k(,1)* was 7.02. Results are also reported for pH values 4, 5, and 6, ionic strengths of 0.01, 0.05, 0.1, and humic acid concentrations of 0.06, 0.09, 0.12, 0.25 mg/ml. …
abstract: A critical evaluation was made of models currently in use for determining stability constants of metal complexes with humic and fulvic acids. Most models are shown to reduce to forms based on Adair's equation, in which the macromolecule is assumed to be the central group and where binding is evaluated graphically as a reciprocal plot, a saturation plot, a Scatchard plot, or a Hill plot. Application of a single set of experimental data (ISE and H('+) release measurements were made) for the reactions of Cu(II) with humic acid showed that values of log K* (apparent K) were lowest when calculated by either the Hill plot method (linear form) or by the Bjerrum plot method (where the metal is assumed to be the central group), as compared to the Scatchard plot method. Values for B(,1) (Bjerrum plot method) were 2 or 3 orders of magnitude lower than reported values for k(,1)* (intrinsic apparent k values obtained with the Scatchard plot method). This difference in B(,1)* and k(,1)* could not be attributed to differences between research groups because similar differences were found when B(,1)* and k(,1)* were calculated from the same experimental data. Apparent intrinsic stability constants obtained by Scatchard plot analysis for binding at the strongest (k(,1)*) and weakest (k(,j)*) sites differed by several orders of magnitude. In addition, the Scatchard plot technique yielded log K(,1)* values larger than overall log K* or B* values of other methods. Average log apparent stability constants for 0.25 mg humic acid/ml in 0.01 KClO(,4) at pH 4 for the same set of ISE data points above 10('-6) Cu('2+) were 6.13 (k(,1)*) and 4.97 (k(,j)*), 4.99 (B(,1)*), 4.99 (B(,1)*) and 9.13 (B(,2)*), and 3.66 (k*) for the Scatchard, Bjerrum, and Hill plot methods, respectively. When data below 10('-6) Cu('2+) were used, log k(,1)* was 7.02. Results are also reported for pH values 4, 5, and 6, ionic strengths of 0.01, 0.05, 0.1, and humic acid concentrations of 0.06, 0.09, 0.12, 0.25 mg/ml. …
author: Fitch, Alanah
language: eng
keywords: Agriculture, Agronomy
date published: 2014-12-14T14:37:36Z
date modified: 2026-07-22T22:25:59Z
provider: University of Illinois - Urbana-Champaign
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: University of Illinois at Urbana-Champaign

PropertyValue
property ID: Handle
value: http://hdl.handle.net/2142/68475