Metal complexes and chelates

We start with butane-2,3-dione dioxime, more commonly known as dimethylglyoxime (dmg). It is a classic reagent for the analysis of NP, the green aqueous solution of metal ions transforming into a vibrantly red precipitate of Ni(dmg)2 complex it is one of the stars of the show in Ponikvar and Liebman s analytical chemistry chapter in the current volume. Here the stereochemistry is well-established and well-known—both OH groups are found on the same side as their adjacent CH3 group on the butanedione backbone. There have been several measurements of the enthalpy of formation of this species for which we take the one associated with this inorganic analytical chemistry application, i.e. with diverse metal complexes and chelates . 

In addition to metal complexes and chelates, another major type of environmentally important metal species consists of organometallic compounds. These differ from complexes and chelates in that the organic portion is bonded to the metal by a carbon-metal bond and the organic ligand is frequently not capable of existing as a stable separate species. 

These factors may now be considered the basis for the differences in solution stabilities of metal complexes and chelate compounds and account for the chemical phenomena summarized in the term chelate effect. Those factors that emerge as the most important in light of this paper are designated in Table VII as footnote b. 

D-penicillamine is so named because it was first isolated as an amine, from the degradation products of penicillin by Abraham et al [87]. Later studies showed the characteristic chemical behavior of D-penicillamine which involve three types of reactions, formation of disulphide links, formation of thiazolidine rings, and formation of metal complexes and chelates [67]. It was first used in 1956 in the treatment of Wilson s disease [88]. D-penicillamine has since been used in the treatment of many diseases, such as cystinuria [89], rheumatoid arthritis [90-92], systemic sclerosis [93], primary bdiary cirrhosis [94], heavy metal poisoning due to lead [95], cadmium [%], and mercury [97], and hyperviscosity syndrome [99]. In rheumatoid arthritis, D-peni-cdlamine has been widely accepted as an effective second line treatment. Despite of its effectiveness, it causes many adverse effects, such as skin rashes [99,100], taste abnormalities [100,101], hepatic dysfunction [102-104], gastrointestinal toxiciiy [99,105], proteinuria [100,106], hematuria [107, 108], thrombocytopenia [92, 109], aplastic anemia [110], lupus-like syndrome [111, 112], Goodpasture s-tike pulmonary renal syndrome [113-115], vasculitis [116,117], myasthenia gravis [118-122], polymyositis [123, 124], and dermatomyositis [125]. 

This type of bond is found in metal complexes and chelates. A metal chelate (Greek chela, a... 

There is a growing interest in metal-based chemotherapeutic drugs and radiopharmaceuticals, as well as in metol-chelators that nmy control metal-ion trafficking or inhibit specific metalloenzymes.(40-44) A number of metal-con5>lexes have been reported to have activity against melanoma,(4J-iO) thus the proven metal-sensitivity of melanoma suggests it may be a likely target of other lipophilic metal complexes and chelators. 

Metal complexes of chelating olefin-group V ligands. D. I. Hall, J. H. Ling and R. S. Nyholm, Struct. Bonding (Berlin), 1973,15,1-51 (66). 

J. Lewis and R. S. Nyholm Structure and reactions of metal complexes of chelate olefin ligands, pp. 61-99 (37). 

Redox Properties Changes Effected by Coordination. Vol. 15, pp. 141—166. Hall, D. I., Ling, J. H., and Nyholm, R. S. Metal Complexes of Chelating Olefin-... 

The use of ligands which chelate extensively and therefore give rise to highly stable metal complexes, and possess additional functionality allowing targeting is illustrated for radiopharmaceuticals in this section, and in Section V. 

A route for designing Gd(HI) complexes whose relaxivity depends on the presence of lactate, is provided by the ability shown by some hexa- or hepta-coordinate chelates to form ternary complexes with a wide array of anionic species (154-161). The interaction between the coordinatively unsatured metal complex and lactate involves the displacement of two water molecules coordinated to Gd(III) ion with the two donor atoms of the substrate, thus leading to a marked decrease in the relaxivity. Lactate is a good ligand for Gd(IH) ion because it can form a stable 5-membered ring by using the hydroxo and carboxylic oxygen donor atoms (Fig. 19). 

The catalytic effect is achieved through the weak Lewis acid properties of the metal ion as the active site in the metal chelate compound. The residual Lewis acid activity of aquo metal ions and incompletely coordinated metal ions in complexes and chelates in aqueous solution is actually very weak compared to that of the hydrogen ion on the other hand, metal ions and complexes are available in solution at high pH values, where the concentration of hydrogen ions is so low that their catalytic effect cannot be significant. 

It is important to segregate waste streams containing chelating agents from those that do not, for otherwise the chelators will inhibit metals precipitation. Waste stream segregation can reduce the amount of ferric chloride and other chemicals needs to break down metal complexes, and can minimize sludge formation. 

The ability of a metal ion to increase the rate of hydrolysis of a peptide has enormous implications in biology, and many studies have centred upon the interactions and reactions of metal complexes with proteins. However, hydrolysis is not the only reaction of this type which may be activated by chelation to a metal ion, and chelated esters are prone to attack by any reasonably strong nucleophile. For example, amides are readily prepared upon reaction of a co-ordinated amino acid ester with a nucleophilic amine (Fig. 3-11). In this case, the product is usually, but not always, the neutral chelated amide rather than a depro-tonated species. 

It should now be possible to determine whether the macrocyclic effect is entropic or enthalpic in origin. Initial investigations were made on transition metal complexes and most workers had a prejudice towards an entropic origin, similar to that of the chelate effect. More recently, it has become apparent that there is no single cause to which the... 

Once mineral-bound aluminum is recovered from ores, it forms metal complexes or chelates. Examples of the different forms of aluminum include aluminum oxide, aluminum chlorhydrate, aluminum hydroxide, aluminum chloride, aluminum lactate, aluminum phosphate, and aluminum nitrate. The metal itself is also used. With the exception of aluminum phosphide, the anionic component does not appear to influence toxicity, although it does appear to influence bioavailability. Aluminum phosphide, which is used as a pesticide, is more dangerous than the other forms however, this is because of the evolution of phosphine gas (a potent respiratory tract and systemic toxin) rather than to the exposure to aluminum. 

The idea of this method is an exchange of mainly akali metals (M) to transition ones (M ) in complexes of different types (molecular complexes and chelates) ... 

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