Binding Affinity Of Cu Research Articles

Copper(II) complexation by humic and fulvic acids from pig slurry and amended and non-amended soils

The effect of the consecutive annual additions of pig slurry at rates of 0 (control), 90 and 150 m 3 ha −1 y −1 over a 4-year period on the binding affinity for Cu(II) of soil humic acids (HAs) and fulvic acids (FAs) was investigated in a field plot experiment under semiarid conditions. A ligand potentiometric titration method and a single site model were used for determining the Cu(II) complexing capacities and the stability constants of Cu(II) complexes of HAs and FAs isolated from pig slurry and control and amended soils. The HAs complexing capacities and stability constants were larger than those of the corresponding FA fractions. With respect to the control soil HA, pig-slurry HA was characterized by a much smaller binding capacity and stability constant. Amendment with pig slurry decreased the binding affinity of soil HAs. Similar to the corresponding HAs, the binding affinity of pig-slurry FA was much smaller while that of amended-soil FAs were slightly smaller when compared to the control soil FA. The latter effect was, however, more evident with increasing the amount of pig slurry applied to soil per year and the number of years of pig slurry application.

Sorption of Copper and Zinc to the Plasma Membrane of Wheat Root

Sorption of Cu(2+) and Zn(2+) to the plasma membrane (PM) of wheat root (Triticum aestivum L cv. Scout 66) vesicles was measured at different pH values and in the presence of organic acids and other metals. The results were analyzed using a Gouy-Chapman-Stem model for competitive sorption (binding and electrostatic attraction) to a negative binding site. The binding constants for the two investigated cations as evaluated from the sorption experiments were 5 M(-1) for Zn(2+) and 400 M(-1) for Cu(2+). Thus, the sorption affinity of Cu(2+) to the PM is considerably larger than that of Ca(2+), Mg(2+) or Zn(2+). The greater binding affinity of Cu(2+) was confirmed by experiments in which competition with La(3+) for sorption sites was followed. The amount of sorbed Cu(2+) decreased with increasing K(+), Ca(2+), or La(3+) concentrations, suggesting that all these cations competed with Cu(2+) for sorption at the PM binding sites, albeit with considerable differences among these cations in effectiveness as competitors with Cu(2+). The sorption of Cu(2+) and Zn(2+) to the PM decreased in the presence of citric acid or malic acid. Citric acid (as well as pH) affected the sorption of Cu(2+) or Zn(2+) to PM more strongly then did malic acid.

Cu + distribution in metallothionein fragments

The differential distribution of Cu + between separate α and β domains of metallothionein (the isolated peptide fragments) and the rate of transfer of Cu + between the two domains using copper–thiolate specific emission spectroscopy are reported. Kinetic data show the rate of transfer of Cu + from the Cu 6α to the Cd 3β domain is 2 × 10 −1 s −1 while the transfer from Cu 6β to the Cd 4α domain is much slower at 8 × 10 −3 s −1, indicating the greater binding affinity of Cu + for the MT β domain. We report that the emission intensity of Cu 6β is 0.45 the emission intensity of Cu 6α–MT. λ max is shown to be a probe of the environment of the Cu +. A series of copper-containing domain intermediates to the formation of the filled Cu 6S 9-β and Cu 6S 11-α-clusters are identified. A mechanism is proposed for the formation of Cu 12(βα)–MT that involves metal exchange reactions of Cu + ions from the α to the β domain with initial formation of a Cu 4β-cluster.

Peptides mimicking the N-terminal Cu(II)-binding site of bovine serum albumin: synthesis, characterization and coordination with Cu(II) ions.

The N-terminal region of bovine serum albumin (Asp-Thr-His-Lys) is known to provide a specific binding site for Cu(II) ions, with the histidine residue thought to be mainly responsible for the specificity. Thiomolybdates have been found to increase the binding affinity of Cu(II) to some serum albumins. As part of a series of studies to study the interactions between Cu(II), thiomolybdates and bovine serum albumin, we have performed the syntheses and characterization of small model peptides such as His-Lys, Thr(Ac)-His-Lys and Thr-His-Lys. Proton NMR spectra have been monitored in H(2)O solution as a function of pH and added Cu(II) concentration. Reliable K(a) values for His-Lys and Thr(Ac)-His-Lys have been established. Probable binding sites of Cu(II) and the relative strengths of binding to these peptides are also discussed.

Binding affinity of Cu(II)–VP-16 (etoposide) complex and its analogues to DNA and hydroxyl radical generation During DNA strand breaks

Conformational effects and affinities of VP-16 (etoposide) and its derivatives to DNA in the presence of Cu(II) ion were examined by circular dichroic (CD) spectra. The Cu(II)/Cu(I) redox kinetics and the hydroxyl radical (·OH) generation from the Cu(II)-complexes were estimated by the stopped-flow kinetics. Based on the results, DNA-cleaving activity of Cu(II)-complexes of VP-16 has been shown to be related with binding affinity of the complex to DNA, Cu(II)/Cu(I) redox and ·OH generation, emphasising the mechanism of generated ·OH attack to DNA.

Metabolism-independent binding of toxic metals by Ulva lactuca: cadmium binds to oxygen-containing groups, as determined by NMR

The metabolism-independent metal binding characteristics of Ulva lactuca were investigated using both freeze-dried thalli and cell walls stripped of intracellular material by incubation in Triton-X followed by methanol. Biosorption of Cd, Zn, Cu and Co by freeze-dried thallus was concentration-dependent and followed Freundlich and Langmuir isotherms. The Freundlich plot suggested that freeze-dried U. lactuca had the greatest binding affinity for Cu compared with Cd, Zn and Co. The BET (Brunauer–Emmett–Teller) plot, which indicates a more complex form of adsorption, and the Scatchard plot were not adequate models for Cu adsorption. The Scatchard plot of Cd suggested that two Cd binding sites were available on the freeze-dried thallus, with the second, lower affinity site only becoming available at Cd loading capacities greater than 4.9mmol g dry wt. Cd nuclear magnetic resonance (NMR) studies confirmed that two binding sites were available for Cd on the freeze-dried algal powder, though only one was available on the cell wall, and that the affinity of the binding sites was greater for Cu than for Cd. The results of the NMR experiments suggested that Cd binds to oxygen-containing functional groups in the algal powder and on the cell wall. It is proposed that sulphate or hydroxyl groups attached to polysaccharide subunits are possible sites.

Trace Metal Redistribution during Extraction of Model Soils by Acetic Acid/Sodium Acetate

A number of model soils synthesized with various known amounts of natural minerals and humic acid were employed to study copper and lead redistribution during extraction by 1 M HOAc/NaOAc. The adsorption intensities of the individual constituent phases were measured from adsorption isotherms, and the redistribution behavior was studied by the standard additions method. Humic acid and pyrolusite are found to exhibit the highest binding affinity for Cu and Pb, respectively, and their relative importance relies upon both their binding ability and their abundance. The extractable concentrations of the metals and the extent of recovery depend largely upon the composition of the model soils, owing to different binding strength presented in the various systems investigated. The presence of dissolved humic acid during extraction has a significant influence on metal redistribution, as evidenced by the increase in the adsorption of Cu and decrease in the adsorption of Pb. In view of the diverse compositions and various competing reactions involved, it is recognized that redistribution behavior will vary widely among both natural soil systems and given metals.