China
Africa
Explore chapters and articles related to this topic
Biochemical and Cytological Assessments of Metal Toxicity in Marine Animals
Published in Robert W. Furness, Philip S. Rainbow, Heavy Metals in the Marine Environment, 1990
Several trace metals (e.g., Cu, Zn) are chemically highly reactive (hence their utilization as catalysts) and while they are essential and show a “beneficial” dose response curve at low concentrations, with increasing concentration, they may become inhibitory and ultimately toxic. There are several reasons for this effect; the catalytic activities of metalloenzymes are a feature of their specific three-dimensional configuration and, therefore, if a different metal is bound, the geometry of the active site and hence enzyme activity, will be altered. Metal ions bind to organic ligands with different affinities, following the Irving-Williams series. For example, the relative stability constants for cysteine -SH co-ordination are Cu+ + Ni+ + = Zn+ + >Co+ + Fe+ + >Mn+ + ; thus Cu will displace Zn, Fe, etc. When free metal ion concentrations rise, these metal substitution reactions will become significant and inhibition of enzyme activity or destabilization of structural components of cellular molecules may occur. Toxicity may also be indirect, the displaced metal itself exerting toxic effects by binding to other cellular components. These substitution and displacement reactions are particularly important for metal ions which show closely related chemical behavior, such as Ag+ + , Cu+ , Hg+ , Cd+ + , and Zn+ + . Thus the toxicity of nonessential “pollutant” metals e.g., Ag, Cd, Hg is due to Cu/Zn competition as well as to “spillover” onto other binding ligands. For other metals, toxic effects are quite specific. For example, in the case of Cr3+ which appears to function only in the glucose tolerance factor, toxicity is due to covalent binding to proteins and nucleic acids.1 Lead on the other hand binds to nucleic acids and is substituted for Ca in bone, and the toxic effects of organometallic compounds, such as methylHg and tributylSn are similarly specific (see Section V).
Phenoxy-imino ligands: coordination chemistry and binding properties with copper(II) cations
Published in Journal of Coordination Chemistry, 2022
Kelvin Wambugu, George S. Nyamato, Joanne Ogunah, Stephen O. Ojwach
We have demonstrated that phenoxy-imino ligands form stable monometallic complexes with copper(II) adopting a tridentate mode. The ligands show good potential as chelating agents for the removal of the heavy metals copper(II), zinc(II), lead(II) and cadmium(II) from water with a high preference for copper(II) cation. The results also demonstrated the potential application of the phenoxy-imino ligands in the extraction of copper(II) and zinc(II) from sewage effluent. The nature of the metal ion, ligand architecture, and Irving-Williams series influenced the extraction ability of the ligands.