Cadmium ions, interactions with

Polarographic evidence is available on the anodic wave due to oxidation of the iodide ion in various EPD solvents in the presence of an excess of cadmium ions that function as EPA 20). The extent of interaction depends on the EPD properties of the solvent competing with the iodide ions for coordination with the cadmium ions. The EPA properties of the cadmium ion are decreased by an increase in the donicity of the solvent thus it is clear that redox potentials in different solvents are related to its donicity. The stabilization of the iodide ion by cadmium ions increases with decreasing donicity and the redox potential shifts to more positive values 20). 

The cadmium electrodeposition on the cadmium electrode from water-ethanol [222, 223], water-DMSO [224], and water-acetonitrile mixtures [225-229] was studied intensively. It was found that promotion of Cd(II) electrodeposition [222] was caused by the formation of unstable solvates of Cd(II) ions with adsorbed alcohol molecules or by interaction with adsorbed perchlorate anions. In the presence of 1 anions, the formation of activated Cd(II)-I complex in adsorbed layer accelerated the electrode reaction [223]. 

Christoffersen, J., Christoffersen, M. R., Larsen, R., Rostrup, E., Tingsgaard, P., Andersen, O. Grandjean, P. 1988. Interaction of cadmium ions with calcium hydroxyapatite crystals a possible mechanism contributing to the pathogenesis of cadmium-induced bone diseases. Calcified Tissue International, 42, 331 -339. 

Cadmium complexes with glycine, 3,49 histidine,263 alanine,264,266 DL-norleudne,263 valine269 and numerous other amino acids267,268 have been reported. A study of the interaction of dipeptides with cadmium ions has also been described. 69... 

For cadmium, Weigel (1985 a, b) concluded that, in vitro, this metal inhibits photosynthesis mainly by interaction with several sites in the Calvin cycle and not by interaction with photochemical reactions located on the thylakoid membrane. In vitro studies showed a 90% inhibition of phosphoribulokinase (EC 2.7.1.18) by cadmium ions (Hurwitz et al., 1956). This element also inhibited light activation of the Calvin cycle enzymes glyceraldehyde-3-phosphate kinase (EC 1.2.1.13) and ribulose-5-phos-phate kinase (EC 2.7.1.19) in mesophyll protoplasts of Valerianella locusta (Weigel,... 

A plausible rationalization would be that there is a competition for the transport route through the intestinal wall between cadmium and manganese on the one side, and between iron and manganese on the other. The competition, i.e., absorption in the intestinal tract, depends upon the relative concentration of these ions and kinetics of and affinity for their interaction with the binding sites in the intestinal mucosa. 

Figure 35 shows the photolumincsccnce spectrum of CdS supported on PVG with a relatively high loading 196). Peaks are observed near 520, 560, and 680 nm. The 680-nm peak is associated with the sulfur vacancy since the presence of excess sulfide ions quenches the photoluminescence however, the presence of excess cadmium has no effect on the emission. The 520- and 560-nm photoluminescence are associated with the major bulk emission 197-199). The 520-nm emission is attributed to the band-to-band transition, and the 560-nm emission is attributed to a typical radiative clcctron-hole recombination at the particle surface. As shown in Fig. 35 (b), the addition of H2O to the catalyst has a significant effect on the spectrum. The 560-nm photoluminescence is completely quenched, as expected if the radiative recombination of electrons and holes occurs at the surfaces where H2O molecules easily interact with these electrons and holes, thereby reducing the energy and intensity of the photoluminescence. On the other hand, the 520-nm emission from the bulk emitting sites is not affected by the addition of H2O. The photoluminescence... 

The competitive adsorption of metal ions is dependent on both the metal ions and the adsorbent, its magnitude being related to the adsorption mechanism. In the case of competition between metal ions for the same adsorption sites, it has been shown that the favored metal ion is that which presents the faster adsorption kinetics on the same activated carbon in a monocomponent solution. This is the case for the adsorption of Cu(II) and Pb(II) onto activated carbon cloths [17]. When metal ions present in solution do not interact with the same adsorption sites, the removal of both ions is not affected compared with monocomponent adsorption. For example, in a study performed with different activated carbons, nickel removal was not affected by the presence of cadmium, because the sites that interact with nickel do not strongly interact with cadmium [18]. Finally, due to the strong relationship that exists between the metal ion adsorption mechanism and pH (see Section 24.2.1.4), it as been demonstrated that competitive adsorption is also influenced by pH [19],... 

The dimer interaction in Cd(TPP) is quite unusual. The cadmium(II) ion is displaced 0.74 A from the 24-atom plane and 0.58 A from the four nitrogen plane. The core conformation shows the essential saddle conformation (Sad) expected for a dimer although it is somewhat less regular than most of the other species described earlier in this review. A most unexpected feature of the structure is the unusually close approach of the cadmium ion to an a-pyrrole carbon atom of the adjacent molecule with a Cd—C distance of 2.84 A, a distance considerably shorter than the average mean plane separation of 3.64 A. As expected, the dihedral angles between peripheral phenyls (three) and the mean plane of the core are less than 60°. 

However, if the cadmium-nickel interaction is beneficial for cadmium deposition, the cadmium-cadmium interaction has a harmful influence. It was proposed that when a metal ion M is deposited as a submonolayer, the activity of the reductant should be less than 1 and would vary with the surface coverage [238]. 

---