Metal complexes properties

Phase-transfer catalysis succeeds for two reasons. First, it provides a mechanism for introducing an anion into the medium that contains the reactive substrate. More important, the anion is introduced in a weakly solvated, highly reactive state. You ve already seen phase-transfer catalysis in another fonn in Section 16.4, where the metal-complexing properties of crown ethers were described. Crown ethers pennit metal salts to dissolve in nonpolai solvents by sunounding the cation with a lipophilic cloak, leaving the anion free to react without the encumbrance of strong solvation forces. 

The physical and chemical properties of formazans have been reviewed in detail.1,2 In this discussion only those properties that directly or indirectly affect the choice of a tetrazolium salt as a leuco dye will be discussed. Spectral, acid—baseyedox, and metal complexing properties will be stressed. 

The material included in this chapter has been organized by oxidation state, with further subdivision into ligand donor type, and was obtained from reports published in primary research journals. The article will cover coordination complexes of copper in three oxidation states Cum, Cu11, and Cu1. The sections dealing with specific ligand donor types cut across several structural types. In view of the all-inclusive nature of the previous review of CCC(1987), no effort will be made here to present a comprehensive account. Instead, specific cases will be chosen for discussion because they exemplify important concepts concerning the relationship of ligand structure to metal complex properties. 

Haymore (4) has pointed out that the noncyclic ligand has many degrees of freedom with respect to rotations about single bonds, whereas the cyclic analog has fewer since the ends are connected. Thus, the cyclic chelate should be greatly favored from an entropy consideration. If correct, this explanation allows one to postulate that the poor metal complexing properties observed for non-cyclic ethers is a result of small... 

The metal complexing properties of macrocyclic compounds, coupled with the solubilities of their metal complexes in a variety of organic solvents, make them especially useful as reagents in organic syntheses. They provide a unique method for solubilizing inorganic salts such as KC1 in organic solvents. Despite their promise and the favorable results obtained thus far, it has been observed that few synthetic applications of these compounds have been reported (53). 

Great attention has been paid to the excellent metal-complexation properties of cyclic peptides. 1 615 631 Naturally occurring examples include enniatin, valinomycin, 616 or antama-nide, 316 and cyclosporin A. 632 Several libraries of cyclic peptides have been synthesized to address these properties, 402 but also bicyclic peptides have been synthesized in this context. t617-620 ... 

The biological functions of vitamin C appear to be related principally to its well-established reducing properties and easy one-electron oxidation to a free radical or two-electron reduction to dehydroascorbic acid. The latter is in equilibrium with the hydrated hemiacetal shown at the beginning of this box as well as with other chemical species.1 Vitamin C is a weak acid which also has metal complexing properties. 

The conformational properties of aromatic heterocycles are related to those of phenyl rings but with the added perturbations due to heteroatoms. We have carried out a systematic study of what we called aromatic propellenes, the heterocyclic analogs of hexaphenylbenzene (13) [27, 28], which possess interesting conformational [29] and metal complexing properties (14) [30],... 

Metal complex properties Developed functions Refs. 

Tuning of metal complex properties with photoisomerization ... 

Inulin can be modified to compounds that display good heavy metal complexing properties similar to ethylene diamine tetra-acetic acid (EDTA) but with better biodegradation properties (Bogaert et al., 1998). Inulin is first oxidized using sodium periodate to the dialdehyde, and then reduced to a polyol using Pt/C and hydrogen. The polyol can then be modified with carbon disulfide to form xanthate or with S03-pyridine to obtain an inulin sulfate. Alternatively, the dialdehyde can be animated with diaminoethane and sodium cyanoborohydride and the product reacted with monochloroacetic acid sodium salt to form carboxymethylamino inulin. Each of these compounds can be used to precipitate heavy metals. 

Feeney, R. E., and St. K. Komatsu Role of Tyrosines in Metal-Complexing Properties of Transferrins. (To be presented at the 152nd meeting of the American Chemical Society, September 12-18, 1966, New York, N. Y.) The role of hydroxyls (tyrosyls) in the binding of metals by human serum transferrin and chicken ovotransferrin has been shown by chemical means. Acetylation of the transferrins with N-acetyl imidazole inactivated the metal-binding activity. Deacetylation of the acetylated transferrins with hydroxylamine reactivated the transferrins. 

Due to their metal complexation properties, Buono et al. have envisioned the use of titanium alkoxide-chiral o-hydroxyarylphosphine oxides complexes in a catalytic enantioselective trimethylsilylcyanation reaction of various aromatic aldehydes [56] (Table 6). 

In an earlier paper, we compared the metal complexation properties of polymeric phenolic oximes of type lA to the analogou.s monomeric compounds of type IB, and found striking differences between the two. Phase transfer of cupric ions from an aqueous phase by complexation with soluble hydrophobic compounds of type IB, in an organic phase (toluene, chloroform) proceeds very well. By contrast, ion complexation by the insoluble... 

Because ground waters, like other natural waters, are dilute solutions of many compounds, metal speciation measurements are difficult. Therefore, the metal-complexing properties of natural waters are operationally defined by many factors, including the analytic method used for speciation, the conceptual and mathematical models used to analyze the data, the range of titrant metal concentrations used, and conditions such as pH, ionic strength, and temperature. The analytical methods used to determine metal speciation all have inherent assumptions and limitations. Most published studies of metal complexation in natural waters have used one analytical method. However, confirmation of results (e.g. stability constants, ligand concentrations) by independent methods would add confidence to such results. In the present work, three independent methods were used. 

Chemical Properties of Thiazolidines. - The metal-complexing properties of L-thiazolidine 4-carboxylic acid and of 2-amino-A -thiazoline hydrochloride with Ca Ni ", Mn ", Cu, and Zn have been investigated. ... 

A comparative summary of the apparent metal-complexing properties of natural waters and waters reconstituted with natural and synthetic organic ligands... 

Orita Y, Ando A, Urakabe S and Abe H, A metal complexing property of furosemide and bumetanide Determination of pK and stability constant, Arzneim.-Forsch., 26(1), 11-13 (1976). Cited in Tata PNV, Venkataramanan R and Sahota SK, Bumetanide, APDS, 22, 107-144, 1993. 

Bis(2,4,4-trimethylpentyl)phosphinic add (CYAN EX 272) is extremely selective toward extracting cobalt from aqueous cobalt/nickel solutions [56, 57], and consequently, the corresponding bis(2,4,4-trimethylpentyl)phosphinate salt prepared form entry 6 [58] may have some unique selective metal complexing properties. 

Metal-complexing properties. The stability constants Kgtab of AA complexes with different metals strongly depend on the nature of the solvent. They are greater in lipophilic non-polar solvents than in more hydrophilic ones and are practically zero in the presence of water. It may be sufficient to show the values for AA in acetonitrile with Na 3 x 10", 1.9 x 10, Li 1 x 10 and in... 

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