Polysaccharide-Metal

Many naturally occurring ionic polysaccharides are mixed salts of alkali, alkali-earth, and transition metals with different insolubilities. Salts of alkali metals are invariably soluble. Sodium, the most ubiquitous alkali, possesses a single valence electron, large atomic and ionic radii, and very low ionization potential. Na+ hydrates in aqueous solution and retains its coordination water in the solid state. Prior to use, native polysaccharide salts are usually converted to the sodium form whence they acquire functionality. 

Alkali-earth metals (calcium, barium, and magnesium) complex with polysaccharides extensively (Reisenhofer et al., 1984). Calcium has a smaller atomic and ionic radius than does sodium and, because it has two valence electrons, it is endowed with greater polarizing and bonding ability than Na+. Ca and Ca2+ easily form insoluble complexes with oxygenated compounds. Polysaccharide salts of alkali-earth metals are generally insoluble. 

Aluminum is an amphoteric element that acts as a nonmetal in alkali and develops a hydrated gelatinous aluminate of a species [Al(OH)4]. As a result of this reaction, certain suspended matter including polysaccharide polyanions coprecipitates by entrainment. This element, applied in atomic or ionic form, is a common technique for commercial isolation of pectin. In acid, Al3+ supposedly neutralizes polyanions to yield the aluminum salt. After precipitation of the pectin-aluminum complex, the metal ligand is removed by acidification and washing. 

Boron is devoid of metallic character in water, it generates weakly acidic boric acid [B(OH)3]. This hydroxide bonds covalently with vicinal (neighboring) hydroxyl groups to form negatively charged, acidic complexes. 

Iron is a nonamphoteric, transition element with the ability to exist in two oxidation states—Fe2+ (ferrous) and Fe3+ (ferric). A positive reaction to alkaline ferric chloride is an indication of the presence of hydroxyl groups with which Fe2+ forms colored complexes. Stable copper and iron chelates 

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Poly(8-quinolinol) electrode coatings, 19 Polysaccharides metal complexes geochemistry, 868 Polyselenides metal complexes geochemistry, 854 Polytyramines electrode modification, 23 Polyvinylferrocene electrode coatings, 19 attachment, 19 Poly(N-vinylimidazole) metal complexes color photography, 109 Poly(4-vinylpyridine) electrode coatings, 17 redox centres, 17 electrodes, 16 Porins... 

Catalytic oxidation ia the presence of metals is claimed as both nonspecific and specific for the 6-hydoxyl depending on the metals used and the conditions employed for the oxidation. Nonspecific oxidation is achieved with silver or copper and oxygen (243), and noble metals with bismuth and oxygen (244). Specific oxidation is claimed with platinum at pH 6—10 ia water ia the presence of oxygen (245). Related patents to water-soluble carboxylated derivatives of starch are Hoechst s on the oxidation of ethoxylated starch and another on the oxidation of sucrose to a tricarboxyhc acid. AH the oxidations are specific to primary hydroxyls and are with a platinum catalyst at pH near neutraUty ia the presence of oxygen (246,247). Polysaccharides as raw materials ia the detergent iadustry have been reviewed (248). 

Ion Exchange. Acidic polysaccharides containing uronic acids, sulfate, or phosphate groups are cation exchangers, binding metal ions. The... 

Wood preservatives appear not to affect emission of corrosive vapours from wood, suggesting that the hydrolysis of acetyl polysaccharides is chemical, not biochemical. Some copper-base preservatives can give enough leachable copper ions to cause galvanic corrosion of other metals, notably aluminium and steel. 

This chapter describes two important and diverse roles played by polysaccharides in development of biocomposites viz. as reinforcing agents in polymers matrix and second as matrix for synthesis of green metal nanocomposites... 

Compositions containing mixtures of metal hydroxides a polysaccharide, partially etherified with hydroxyethyl and hydroxypropyl groups, are used as fluid loss additives for aqueous, clay-mineral-based drilling muds [1437]. 

A process that successfully removes filter-cake contains polysaccharide polymers and certain bridging particles and uses alkaline earth metal peroxides and zinc peroxide in an acidic aqueous solution [499,1239]. On soaking the filter-cake, a loosely adherent mass is left behind on the walls of the borehole. Thereafter, a wash solution in which the bridging particles are soluble is used to remove the remaining filter-cake solids from the sides of the borehole. 

Some microbes are able to decrease the permeability of their membranes to prevent toxic metals from entering. If the toxic metals are not able to physically enter the cell, they will not be able to affect vital metal-sensitive structures, such as proteins. One way to prevent heavy metals from entering is by decreasing the production of membrane channel proteins.18 It is also possible for the metal-binding sites in the membrane and periplasm to be saturated with nontoxic metals.37 A third possibility is the formation of an extracellular polysaccharide coat, which binds and prevents metals from reaching the surface of the cell.24,38... 

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