Sequestering metal ions

Paper. Citric acid is added to the pulp slurry prior to bleaching to sequester metal ions and prevent discoloration (208—211). Citrates are used in cigarette paper to control the burning rate to match that for tobacco. 

EDTA sequesters calcium and magnesium from hard water, preventing them from forming insoluble soap films (scum) with soaps and detergents. Chelators are sometimes used to sequester metal ions that interfere with dyes and perfumes. 

Diethylene triamine pentaacetic acid is a chelating agent that sequesters metal ions so they cannot combine with other ingredients in a product. 

Concerns about the effect of TPP on eutrophication have led many states, cities, and regional governments to ban the use of the compound in syndets. Such bans have caused serious problems for detergent manufacturers, however, because no entirely satisfactory substitute for TPP has yet been found. Two promising candidates are the sodium salt of nitrilotriacetic acid, 3Na, N(CH2C02)3 , or NTA and ethylenediaminetetraacetic acid (EDTA). Both of these compounds act in much the same way as TPP, that is, by sequestering metal ions. Other builders that have been incorporated into syndet formulations include sodium carbonate, synthetic zeolites, borates, and organic polymers known as polycarboxylates. 

As a consequence, metal chelation is an alternative antioxidant strategy based on sequestering metal ions to prevent metal-catalyzed free radical formation [Brown et al., 1998 Guo et al., 1996 Morel et al., 1998]. To have an antioxidant action by metal chelation, a compound should be (i) able to complex the metal and yield a stable product, and (ii) the resultant complex should be a poor catalyst for the free radical generating reactions where the metal is involved. 

The principal use of the condensed phosphates is to sequester metallic ions in water. They form water-soluble complexes with the metals and prevent metallic compounds from precipitating to cause discoloration, scale, and sludges. 

Wang, J., V. P. Evangelou, M. T. Nielsen, and G. J. Wagner. 1992. Computer-simulated evaluation of possible mechanisms for sequestering metal ion activity in plant vacuoles. II. Zinc. Plant Phys. 99 621-626. 

Vfhite crystalline powder, 99 to 100% active. Sequesters metal ions in aqueous solutions over a fairly wide pH range rendering them soluble in conditions which would normally lead to precipitation of their metallic salts. The adverse effects of small concentrations of metal ions such as calcium, magnesium, iron and copper are thus successfully eliminated. Tetralon acid neutralised with a suitable base is used where maximum purity or freedom from sodium ions is desired. 

Tetra sodium salt of ethylene diamine tetracetic acid. 40% aqueous solution. Sequesters metal ions as described for TETRALON ACID above and would be chosen for economy and where liquids are suitable. 

Highly concentrated agent to sequester metal ions. Effective over wide pH range. 

The addition of phosphate — pyro-, tripoly-, and hexametaphosphate — also protects cooked meat from auto-oxidation. Ortophosphate gives no protection. The mechanism by which phosphates prevent autooxidation appears to be related to their ability to sequester metal ions, particularly ferrous iron, which is the major prooxidant (Pearson et al., 1977). The addition of NaCl increases retention of moisture in meat and meat products. 

If polyphosphates of chain lengths greater than about 350 are to be obtained a crystallization process is required in which a seed crystal is behaving as a templet for chain growth. The templet aids the crystallization to proceed without the chains of molten polyphosphate "sequestering" metal ions to terminate their growth or thermal activity rupturing the molecules. 

EDTA sequesters metal ions (like Ca and Mg ) which are essential for growth and function, thereby depriving the bacteria to grow and multiply. 

In this specific case, the colloid stabilizers are dendrimers, for instance, polyamidoamine (PAMAM), which are hyperbranched polymers that ramify from a single core and form a porous sphere [103, 104] (Scheme 17.1). Dendrimer-encapsulated nanoparticles (DENs) are synthesized by sequestering metal ions within appropriate dendrimers, and then by chemically reducing the resulting composite. They can be synthesized in various media, such as water or ethanol. The size of the nanoparticles is usually nearly monodisperse, and can be tuned by varying the metal-to-dendrimer ratio prior to reduction. Supported catalysts can then he prepared by immobilizing DENs onto a sohd support. As in the case of colloids, the last step, which consists in the removal of dendrimers hy thermal treatment, may lead to an increase in both the metal-particle size and particle-size distribution. 

Phosphates such as sodium tripolyphosphate, shown here, are used to complex or sequester metal ions in hard water so these ions cannot interfere with the action of soap or detergents (Section 18.6)... 

The best known chelating agent, with wide applications in several fields is edta, or the tetraanion of ethylenedi-aminetetraacetic acid (Scheme 19a). Its high efficiency in sequestering metal ions has led to a number of applications. On the other hand, the conformational flexibility of its aliphatic skeleton makes it a less than ideal building block for supramolecniar architectures. Edta can arrange... 

In addition to its use in medicine and chemical analysis, EDTA is used as a food additive to sequester metal ions. EDTA sequesters copper, iron, and nickel ions that would otherwise catalyze the oxidation reactions that cause food to spoil. EDTA is a common preservative in a wide variety of consumer products. 

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