Sodium ions Sequestration

A common form of EDTA used as a preservative is calcium disodium EDTA (CaNa2EDTA). What metals will this form of the sequestrant scavenge effectively The dissolution of the solid will yield calcium ions, sodium ions, and the EDTA anion. Any metal more effectively complexed than calcium will be readily scavenged, including all ions listed in Table 9.1 except silver (Ag+) and magnesium (Mg2+). (In the absence of the calcium counterion, as in the case of the acid form of EDTA, chelation of calcium in the body can occur. In fact, EDTA administered orally is an FDA-approved treatment for calcium deposits in the bloodstream that lead to cardiovascular disease.) Citric acid (Fig. 9.3.3) is another sequestrant of metal ions in foodstuffs. 

NaCIO is an acknowledged novel absorption enhancer for ampicillin sodium [99], glycyr-rhizin [100,101], gentamicin [102], phenoxymethyl penicillin [103], cefoxitin sodium [104,105], and acyclovir [106], Takahashi et al. [107] reported that the enhanced membrane permeability of phenolsulfonphthalein depends on the disappearance kinetics of CIO from the loop and its calcium ion sequestration capacity. The enhancing mechanisms of NaCIO are proposed to be involved in (1) Ca2+ sequestration, (2) increase in pore size and solvent drag, (3) interaction with membrane proteins and lipids, and (4) increase in the intracellular calcium level [104,105,108-111],... 

Rivera TM, Leone-Bay A, Paton DR, Leipold H, Baughman RA (1997) Oral delivery of heparin in combination with sodium N-[8-(2-hydroxybenzoyl) aminojcaprylate pharmacological considerations. Pharm Res 14 1830-1834 Sakai K, Kutsuna TM, Nishino T, Fujihara Y, Yata N (1986) Contribution of calcium ion sequestration by polyoxyethylated nonionic surfactants to the enhanced colonic absorption of p-aminobenzoic acid. J Pharm Sci 75 387-390 Sakai M, Imai T, Ohtake H, Azuma H, Otagiri M (1997) Effects of absorption enhancers on the transport of model compounds in Caco-2 cell monolayers assessment by confocal laser scanning microscopy. J Pharm Sci 86 779-785... 

The primary functions of builders in laundry detergent formulations is to remove hardness ions to protect the surfactant. Calcium and magnesium ions in wash water can react with surfactants to form insoluble or nonfunctional complexes. Builders reduce water hardness by three main mechanisms. Sequestration forms a soluble complex between builder and hardness ions. Precipitation forms an insoluble complex with hardness ions. Ion exchange removes calcium and magnesium ions by replacing them with soluble sodium ions. 

Sequestration forms the basis for detergent and water-treatment appHcations of polyphosphates. Sequestration of hardness ions by sodium tripolyphosphate used in detergent formulations prevents the precipitation of surfactants by the hardness ions. Sodium polyphosphate glass (SHMP) may be added to water system to prevent the formation of calcium or magnesium scales by reducing the activity of the hardness ions. However, if the ratio of cation to polyphosphate is too high at a given pH, insoluble precipitates such as may result instead of the soluble polyphosphate complexes. The... 

The sodium and calcium salts of EDTA (ethylenediaminetetraacetic acid, Fig. 9.3.1.) are common sequestrants in food products. A three-dimensional representation of EDTA is shown in color Fig. 9.3.2. The EDTA ion is an especially effective sequestrant, forming up to six coordinate covalent bonds with a metal ion. These bonds are so named because a lone pair of electrons on a single atom serves as the source of the shared electrons in the bond between the metal ion and EDTA. The two nitrogen atoms in the amino groups and the oxygen... 

The colloidal dispersion resulting from thermal/chemical oxidative conversion can rapidly retrograde, which makes immediate neutralization of the acid product to a pH 8.0 to 8.5 mandatory. Discoloration of the paste is lessened when sodium bisulfite is added to the starch slurry and/or sodium sulfite added to the paste. Multivalent ions in the paste can induce colloidal destabilization, and may require the addition of a sequestrant."... 

Sodium tripolyphosphate (STP) was commercially available in the mid-1940s and had replaced TSPP because of its superior detergent processing, solubility, and hardness ion-sequestering characteristics. Sequestration is defined as the reaction of a cation with an anion to form a soluble complex. The sequestration of Ca and Mg " ions leads to softened water and is the most important function of any detergent builder [3, 4]. 

Sequestration of lead ions. Goto and Kishi found that sodium borohydride reduction of the 7a-bromo-3/3,5a-diol-6-one diacetate (1) in fully purified methanol-dioxane atBTords the bromohydrin (2) in excellent yield but that on addition of no more than 4y of lead acetate/200 mg. of (I) the reaction product is the debrominated... 

Generally, sodium and potassium react only to a limited extent with proteins, whereas calcium and magnesium are somewhat more reactive. Transition metals, e.g., ions of Cu, Fe, Hg, and Ag, react readily with proteins, many forming stable complexes with thiol groups. Calcium cations and ferrous, cupric, and magnesium cations may be integral parts of certain protein molecules or molecular associations. Their removal by dialysis or sequestration appreciably lowers the stability of the protein structure toward heat and proteases. 

In sequestration (chelation) the hardness ions are bound to the builder in the form of soluble complexes. Phosphates, citrates, and nitrilotriacetic acid (NTA) are examples of this class of builder compound. Table 8.3 lists the calcium binding capacities of various builders. Other strongly chelating compounds exist, such as phosphonates and EDTA, but they are generally not extensively used in HDLDs. The most efficient builder is sodium tripolyphosphate (STPP). Unfortunately, tripolyphosphate has been identified as a possible cause of eutrophication in lakes and rivers. It is severely controlled and even banned in several countries. As a result, most countries in North America and Europe have converted to nonphosphate formulations. Other regions are also gradually imposing restrictions on the use of phosphates. 

FIG. 8.13 Sequestration of water hardness ions by detergent builders. Sodium polyacrylate Mw = 170,000, STPP (sodium tripolyphosphate), NTA (nitrilotriacetic acid), EDTA (ethylenediamine tetraacetic acid), sodium citrate, CMOS (sodium carboxymethoxysucci-nate), sodium carbonate, zeolite A. (Reproduced from Nagarajan, M.K., J. Am. Oil Chem. Soc., 62, 949, 1985. With permission.)... 

These builders are generally available as sodium, potassium, or mixed-metal salts, the latter being more soluble in water but also more costly. The widespread use of sodium TPP (STPP) in LADD formulations can be attributed to the many functions it performs during the wash cycle. Besides its efficient sequestration of hardness ions, STPP works to disperse and suspend soils, enhance the surface action of anionic surfactants, solubilize proteinaceous soils, and provide alkalinity and buffering action. Pyrophospates have been included in some LADD formulations because of its better solubility properties relative to tripolyphosphate [20],... 

A builder that has been studied as a possible phosphate replacement is sodium citrate. The structure of the citrate trianion is shown in Figure 9.4. Several properties of sodium citrate restrict its use in LADD formulations. First, it is incompatible with hypochlorite, precluding its use in most LADD compositions. It is also inferior to STPP in its sequestration efficiency for calcium ions. Finally, it is almost three times more expensive than STPP. This combination renders citrate unsuitable as a replacement for STPP. In Europe, where the different wash conditions allow for the use of milder peroxygen bleaches or enzymes and the water is presoftened, citrate-built products are possible. 

Another use for sequestrants such as EDTA and sodium gluconate is in the alkaline rinse used after a conventional acid stage. The sequestrants prevent the precipitation of dissolved metal ions by the alkali. Less rinsing saves time and rinse water. 

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