Chelating metal ions

Metal Deactivators. The abiUty of metal ions to catalyse oxidation can be inhibited by metal deactivators (19). These additives chelate metal ions and increase the potential difference between the oxidised and reduced states of the metal ions. This decreases the abiUty of the metal to produce radicals from hydroperoxides by oxidation and reduction (eqs. 15 and 16). Complexation of the metal by the metal deactivator also blocks its abiUty to associate with a hydroperoxide, a requirement for catalysis (20). 

Chromium is the principal metal used with mordant dyes for wool, whereas both chromium and cobalt are used extensively ia premetallized types for wool and nylon. Copper(II) is employed almost exclusively as the chelating metal ion ia both metaUizable and premetallized direct dyes for cotton. 

Chelation is an equiUbrium reaction. There are always some free-metal ions present as well as chelated metal ions. In a system where a metal salt is being reduced, such as in metal plating, the rate of the reaction forming the metal can be controlled by using the metal citrate chelate. 

The log function of the ratio of chelated metal ions to free-metal ions is expressed as the stabiUty constant or formation constant as shown in Table 6. The higher the stabiUty constant the greater the percentage of metal ions that are chelated (11). 

Cosmetics and Toiletries. Citric acid and bicarbonate are used in effervescent type denture cleansers to provide agitation by reacting to form carbon dioxide gas. Citric acid is added to cosmetic formulations to adjust the pH, act as a buffer, and chelate metal ions preventing formulation discoloration and decomposition (213—218). 

Phytate (myo-inositol hexaphosphate Fig. 15.3, structure 33) is found in many food species and can be considered as a phytochemical. Its role in the plant is primarily as a phosphate store in seeds, but it is found in other tissues as well, for example, tubers (Harland et al., 2004). Phytate and its hydrolysis products are anti-nutrients that chelate metal ions and thus reduce their bioavailability (Persson et al., 1998 House, 1999). This is particularly a problem with cereal grains, but pre-processing can improve mineral absorption from these foods (Agte and Joshi, 1997). There is some concern that high phytate foods could also contain higher levels of toxic heavy metals caused by natural accumulation. Plants also contain phytate-degrading enzymes that can also influence metal ion bioavailability (Viveros et al., 2000). 

Chemicals that chelate metal ions in food may form insoluble complexes and will not he adequately absorbed. 

Note that it is important to avoid carboxy cation exchangers. A proportion of the charged groups on a carboxy cation exchanger exist in a relative proximity that endows them with the ability to chelate metal ions. These chelating sites may competitively displace metals from proteins in the sample, creating a source of assay variability. Use a noncarboxy cation exchanger such as sulfomethyl, ethyl, or propyl. 

Separation is based on the reversible chelate-complex formation between the chiral selector covalently bonded to the chromatographic support, and the chiral solute with transition metal cations. Chelation properties of both the chiral selector and the chiral solute are required. Compounds therefore need to have two polar functional groups in a favorable arrangement to each other, like a )3-amino acids, amino alcohols and a-hydroxy acids, which can form rings membered with central chelating metal ions, like Cu(II), Zn(II), Cyclic... 

The /s.min of 12.9 eV of neutral acetoxime implies that it should also act as a base, somewhat weaker than pyridine. Indeed an important application, especially of the double oxime dimethylglyoxime (12), is in chelating metal ions. ... 

Metal Deactivator - chelates metal ions, primarily copper. Copper catalyzes the oxidation and degradation of jet fuel. Use is not permitted in aviation gasoline. A metal deactivator is permitted in civil and military jet fuels. 

Important characteristics of chitosan are its MW, viscosity, DD (Bodek, 1994 Ferreira et al., 1994a,b), crystallinity index, number of monomeric units, water retention value, pKa, and energy of hydration (Kas, 1997). Chitosan has a high charge density, adheres to negatively charged surfaces, and chelates metal ions. 

The tetracyclines Form an important group of antibiotics. The activity appears to result from their ability to chelate metal ions since the extent of antibacterial activity parallels the ability to form stable chelates. The metal in question appears to be magnesium or calcium since the addition of large amounts of magnesium can inhibit the antibiotic effects. In addition, it is known that in blood plasma the tetracyclines exist as calcium and magnesium complexes.,JS... 

Thiosemicarbazones have been known for some time to exhibit a range of biological activity, including action against smallpox and certain kinds of tumour. This activity has frequently been thought to be due to their ability to chelate metal ions,436 It is perhaps surprisingly therefore that virtually no thermodynamic data are available for thiosemicarbazones. 

Studies of chelated poly(vinyl alcohol) (107) also show that conductivity is not increased by the presence of chelated metal ions. However, in some cases chelation may enhance conductivity but regular... 

The phosphates appear to prevent autoxidation by chelating metal ions, although the exact mechanism is not known. Other work, however, has shown that metal chelators do protect meat against autoxidation (1, 22). EDTA has been shown to inhibit development of WOF by cheTating the non-heme iron in cooked meat (lj)). Thus, evidence suggests that the phosphates probably chelate Fe + and thus inhibit WOF. 

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