Sequester

H02CCH2)2N-CH2 CH2-N(CH2C02H)2-An important compound, which owes its use to its sequestering properties. A multidentate chelating agent. Forms complexes with most elements. 

Gluconic acid and other hydroxy acids act similarly. Sequestering agents are used extensively, e.g. for preventing deleterious catalytic effects of traces of Fe or Cu and in analysis. 

Turro N J and Cherry W R 1978 Photoreaction in detergent soiutions. Enhancement of regioseiectivity resuiting from the reduced dimensionaiity of substrates sequestered in a miceiie J. Am. Chem. Soc. 100 7431-2... 

A salt originally called sodium hexametaphosphate, with n believed to be 6, is now thought to contain many much larger anion aggregates. It has the important property that it sequesters , i.e. removes, calcium ions from solution. Hence it is much used as a water-softener. 

Orthophosphate Hquid mixtures are ineffective as micronuttient carriers because of the formation of metal ammonium phosphates such as ZnNH PO. However, micronutrients are much more soluble in ammonium phosphate solutions in which a substantial proportion of the phosphoms is polyphosphate. The greater solubiHty results from the sequestering action of the polyphosphate. The amounts of Zn, Mn, Cu, and Fe soluble in base solution with 70% of its P as polyphosphate are 10 to 60 times their solubiHties in ammonium orthophosphate solution. When a mixture of several micronutrients is added to the same solution, the solubiHty of the individual metals is lowered significantly. In such mixtures the total micronuttient content should not exceed 3% and the storage time before precipitates appear may be much shorter than when only one micronuttient is present. 

Other Additives. To provide and maintain the clarity of clear shampoos, the use of either ethyl or isopropyl alcohol maybe employed. Perfumes are added to make shampoos more pleasing in terms of odor, while dyes are incorporated to give visual aesthetics to the products. Salts of ethylenediaminetetraacetic acid are found to sequester and prevent formation of insoluble alkaline-earth metal salts. 

Many stabilizer systems have been tailored to a particular industry need or for particular areas where dilution water quaUty is poor. These grades are heavily stabilized and may contain organic sequestering agents, ie, staimate, phosphates, and nitrate ions, so that the weak solutions produced by dilution from hard water retain acceptable stabihty. The nitrate is not a stabilizer, but it inhibits corrosion of aluminum storage tanks by chloride ion. 

Alcohol autoxidation is carried out in the range of 70—160°C and 1000—2000 kPa (10—20 atm). These conditions maintain the product and reactants as Hquids and are near optimum for practical hydrogen peroxide production rates. Several additives including acids, nitriles, stabHizers, and sequestered transition-metal oxides reportedly improve process economics. The product mixture, containing hydrogen peroxide, water, acetone, and residual isopropyl alcohol, is separated in a wiped film evaporator. The organics and water are taken overhead and further refined to recover by-product acetone and the... 

T-Lymphocytes (4,5) and other cellular components of the immune system also have equally wide implications in regulation of the normal immune system. The T-lymphocytes play a central role in the body s response to harmful antigens and tumor—host interaction (4). Responses involve antigens derived from vimses, bacteria, parasites, and tumors. T-ceUs also participate in the immune surveillance response, where self-antigens are recognized, but usually sequestered within the cell and, when exposed, become markers of cellular damage. 

DDT is slowly converted in vivo by reductive dechlorination to DDD and by further dechlorinations to 4,4 -dichlorodiphenylacetic acid [83-05-6] (DDA), the predominant excretory metaboUte. Anaerobically, it may form 4,4 -dichlorodiphenyiacetonitrile [20968-04-1] (DDCN). However, most DDT that enters the environment is sequestered as DDE, which is ubiquitously present in the body Hpids of invertebrate and vertebrate animals. In humans. 

Water Treatment Industrial CleaningPipplications. Boiler and cooling tower waters are treated with lignosulfonates to prevent scale deposition (78). In such systems, lignosulfonates sequester hard water salts and thus prevent their deposition on metal surfaces. They can also prevent the precipitation of certain iasoluble heat-coagulable particles (79). Typical use levels for such appHcatioas range from 1—1000 ppm. 

Complex Ion Formation. Phosphates form water-soluble complex ions with metallic cations, a phenomenon commonly called sequestration. In contrast to many complexing agents, polyphosphates are nonspecific and form soluble, charged complexes with virtually all metallic cations. Alkali metals are weakly complexed, but alkaline-earth and transition metals form more strongly associated complexes (eg, eq. 16). Quaternary ammonium ions are complexed Htde if at all because of their low charge density. The amount of metal ion that can be sequestered by polyphosphates generally increases... 

Textiles. Sorbitol sequesters iron and copper ions in strongly alkaline textile bleaching or scouring solutions (see Textiles). In compositions for conferring permanent wash-and-wear properties on cotton fabrics, sorbitol is a scavenger for unreacted formaldehyde (252) and a plasticizer in sod-resistant and sod-release finishes (253). 

Additionally, organotin mercaptides can act as antioxidants, as they can sequester free-radical degradation mechanisms (48). The one drawback of mercaptide-based tin stabilizers is the discoloration of the sulfur after exposure to uv-radiation. Special precautions or formulations need to be developed for outdoor apphcations. 

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