Chelates, with metal ions

The sulfur atom of the thiocarbonyl group is a good nucleophile, and reaction between benzyl bromide and l-(2-thiazolyl)thiourea yields the isothiouronium salt (496). The sulfur atom may also be engaged in a chelate, as exemplified by the Cu chelate of 2-thioureido-4-methylthiazole (491). These chelates with metal ions were thoroughly studied in acidic, neutral, and alkaline media for 66 metal ions in order to define their analytical use. They are formed in the molar ratio of 1 2 for metal II compounds (498). 

These iniferter sites containing an N-H group can be easily transformed into the corresponding thiol which leads to disulfide by oxidative coupling and can form chelation with metal ions (Eq. 47) [171,172]. Poly(St) prepared for polymerization with 44 and 45 was applied to the chain-extension reaction by the S-S bond or chelation bond formations. 

Eorms stable chelates with metal ions without causing irreversible damage... 

Chelation with metal ions dramatically affects the reactivity of the porphyrin macrocycle, and this can be used to advantage in many cases. For example, for efficient electrophilic substitution of the ring, metals can be chosen (vide infra) which effectively release electron density to the organic porphyrin ligand, while reductions are best carried out on metallo-porphyrins in which the metal tends to deplete the porphyrin ligand of its electron density by way of back-bonding. 

A method based on a metal chelate affinity chromatography (MCAC) was described by Carson (24). Generally, it consists of extraction/precipitation with succinate buffer followed by cleanup on a Chelating Sepharose column preloaded with copper(II) sulphate when TCs are specifically adsorbed by chelatation with metal ions bound. Elution of TCs was achieved using EDTA-containing buffer. 

Since TCs form highly fluorescent chelates with metal ions at the appropriate pH value, their complexation with 5% zirconium chloride solution added postcolumn to the eluate from HPLC was used for fluorescence detection. The highest yield of fluorescence was observed at pH 2.0 therefore a pH adjustment of the mobile phases was necessary (25-27). Moreover, using a mobile phase of pH 2.0, the formation of both the C4 epimers and anhydroTCs are minimized. 

The complexation chemistry of the low-molecular analogs shows that the stability of the chelates with metal ions is strongly dependent on the structure of the amine moiety. As poly(ethyleneimine) contains three different types of amino groups the complexation properties are correspondingly versatile and interesting. 

Bisphosphonates - must be taken on an empty stomach as they chelate with metal ions in food. Available as daily, weekly or monthly formulations to improve compliance. Increases bone mass by 3% per year when given in conjunction with calcium and vitamin D. 

Strontium ranelate - must be taken on an empty stomach as it chelates with metal ions in food. 

The carbonyl functionality is one of the most abundant functional groups in biomolecules and pharmaceuticals, including many a- and /3-carbonyl derivatives of ketones and aldehydes and their enol tautomers, which upon deprotonation can form entropy-favored 5-membered (37) and 6-membered (38) chelates with metal ions. In this section, the role of metal ions in the action of some enol-containing biochemicals and pharmaceuticals and the structures of their metal complexes are discussed. 

Trisodium salt (Na3) of HEEDTA. Used to form chelates with metal ions including ferric ion from pH 1 to 13. Particularly effective in presence of strong oxidizing agents. 

P-Diketonates. /3-Diketones chelate with metal ions, including actinides, to form neutral species via the deprotonated enolate anions as illustrated in Figure 24. " A very wide array of homoleptic complexes of the general formula Au(R COCR COR )4 have been reported for... 

The elements which can be separated from each other and from the matrix in small and trace amounts by extraction are shown in Table 1.2. The symbols of elements are accompanied by the typical compounds used in the extractions. The extraction methods provide large possibilities in separation of traces. An important role in concentrating traces by extraction is played by organic reagents which form chelates with metal ions. 

Mercaptoquinoline (thio-oxine, formula 4.44), the sulphur analogue of 8-hydroxyquinoline, forms sparingly soluble chelates with metal ions (Fe, Cu, Mn, Cd, Co,... 

A number of amino acids esters that can form chelates with metal ions have been found to be readily hydrolyzed, whereas the hydrolysis of esters having only one oxygen donor atom per molecule was found to be comparatively unaffected by metal ions. In the examples of ester hydrolysis described below, it is postulated that a metal chelate ring system is formed and undergoes hydrolysis via a nucleophilic process. 

Metal complexing assays (i.e. Jerumanis method) are generally more specific than redox-based assays, because the color of the complexes depends on a specific pattern of substitution on the phenolic rings [108]. Procyanidins form chelates with metal ions via their ortho-diphenolic groups on the B-rings [112],... 

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