Toxic transition metal ions

In biological studies, apart from alkali and alkaline earth cations, zinc sensing is very important, especially in neuroscience. Binding of zinc and other (often toxic) transition metal ions requires receptors of different structure and coordination properties. Polypyridines, dendritic pyridines, and thiacrown ethers are the receptors of choice. 

Unlike Cr(VI), a recognized human carcinogen (Section III. A) (2), Cr(III) is often considered as one of the least toxic transition metal ions on the basis of its poor absorptivity and kinetic inertness, as well as from the lack of acute toxicity of large doses of Cr(III) compounds in rats (3). A concern about the safety of the use of Cr(III) in food supplements firstly arose after the finding of Stearns et al. (607) that Xlla (0.050-1.0 mM Cr) caused chromosome damage in culmred mammalian cells. In addition, mutations in the hprt locus, ultrastmcmral... 

The accumulation of toxic transition metal ions from the plastics in the stems, leaves, fruit and tubers from the growing of soft fruits and vegetables. Table 8 [24] shows that even if the soil is loaded with much higher concentrations of Ni salts than can ever be obtained from degraded plastic films, the plants take up only the amount of... 

Injury to cells and tissues may enhance the toxicity of the active oxygen species by releasing intracellular transition metal ions (such as iron) into the surrounding tissue from storage sites, decompartmentalized haem proteins, or metalloproteins by interaction with delocalized proteases or oxidants. Such delocalized iron and haem proteins have the capacity to decompose peroxide to peroxyl and alkoxyl radicals, exacerbating the initial lesion. 

A review article has appeared (237) which discusses the biological activity of thioethers and their derivatives with particular reference to interactions with transition-metal ions. Accordingly, only some of the more salient points will be discussed here. In any biological studies, the toxicity of Me2SO 482) and of its transition-metal complexes 140) should be borne in mind. 

Besides the applications of the electrophilicity index mentioned in the review article [40], following recent applications and developments have been observed, including relationship between basicity and nucleophilicity [64], 3D-quantitative structure activity analysis [65], Quantitative Structure-Toxicity Relationship (QSTR) [66], redox potential [67,68], Woodward-Hoffmann rules [69], Michael-type reactions [70], Sn2 reactions [71], multiphilic descriptions [72], etc. Molecular systems include silylenes [73], heterocyclohexanones [74], pyrido-di-indoles [65], bipyridine [75], aromatic and heterocyclic sulfonamides [76], substituted nitrenes and phosphi-nidenes [77], first-row transition metal ions [67], triruthenium ring core structures [78], benzhydryl derivatives [79], multivalent superatoms [80], nitrobenzodifuroxan [70], dialkylpyridinium ions [81], dioxins [82], arsenosugars and thioarsenicals [83], dynamic properties of clusters and nanostructures [84], porphyrin compounds [85-87], and so on. 

Metal Complexation. Azo dyes containing hydroxy or carboxylic acid gronp substituents adjacent to the azo gronp react with transition metal ions, e.g. chromium, cobalt and copper to produce complexes, e.g. Cl Acid Violet 78 (2.15)7 These metal complex dyes are more stable to light than their unmetallised precursors and have been widely nsed as dyes for polyamide and wool fibres. However, there is now a move away from chrominm complexes due to toxicity concerns (see section 2.3.2.). 

Researchers at Oregon State University are currently studying apphcations of chitosan beads for the removal of toxic metal ions from wastewater. Chitosan has potential applications to waste removal because it selectively adsorbs toxic Group III transition metal ions in preference to less dangerous alkali or alkaline earth metal ions. The technology has been the focus of bench-scale studies and is not commercially available but it is available for licensing. 

However, the superoxide dismutase may be overwhelmed by the amount of superoxide being produced after a toxic dose of paraquat. The superoxide may then cause lipid peroxidation via the production of hydroxyl radicals. These may be produced from hydrogen peroxide in the presence of transition metal ions (see chap. 6). 

More Metals. The apparent simplicity of the problem is misleading because although the concentration of transition metal ions is small, the ocean assuredly contains trace quantities of all naturally occurring metals. We now recognize two results of coordination the properties of the metal are altered, and, equally important, the properties of the ligand are altered (coordinated ammonia is less basic, cyanide ion is less toxic) (5). Most of the catalytic activity of coordination entities recently summarized involved coordination entities of transition metal ions examples involving magnesium ion constitute the main exceptions (24). 

Polyaza-, polythia-ligands. Recognition of transition metal ions. Replacing the oxygen sites with nitrogen or sulphur yields macrocycles and cryptands that show marked preference for transition metal ions and may also allow highly selective complexation of toxic heavy metals such as cadmium, lead and mercury [2.41-2.44, A.14]. 

Sensitization of anoxic cells is also brought about by non-toxic concentrations of transition metal ions (< some 10-4 mol dm-3) such as Cu(I). A dose-modifying factor of 1.5 (at 6.6 x 10-5 mol dm-3 Cu(I)) has been observed for mammalian cells (Hesslewood et al. 1978), but no sensitizing effects were observed for oxygenated cells. Under anoxic conditions, reduction of Cu(II) to Cu(I) occurs within the cells without an added reductant (see also Cramp 1967). It would be premature to come up with detailled mechanistic concepts, but some aspects of the actions of transition-metal ions have been discussed in Chapter 2.5. 

Besides the above hypothesis, there are only a few documented cases where superoxide toxicity does not involve H2O2 and/or metal ions. Accordingly, for the last decade, it was repeatedly stated that 02" served as a precursor of a much more reactive and oxidizing species such as OH. Because the Haber-Weiss reaction was extremely slow, it was suggested that 02 triggered OH production by recycling the reduced form of transition metal ions involved in Fenton reactions [42] ... 

Chromium Organometallic Chemistry Coordination Organometallic Chemistry Principles Magnetism of Transition Metal Ions Metal Ion Toxicity Nutritional Aspects of Metals Trace Elements Oxidation Catalysis by Transition Metal Complexes. 

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