Amylose salt complexes

A similar series of salt complexes of amylose were also described earlier by Senti and Witnauer (3b). A salt complex, such as KBr-amylose, is obtained from KOH-amylose by neutralization of the alkali. Although KBr-amylose has been studied since the initial description of the series, a definitive crystal structure determination by Miller and Brannon appears in this volume (12). 

Fig. 4.—Effects of various salts on the formation of the amylose-iodine complex. The effect is expressed as the shift of the 605-nm band (above) and the variation of the extinction of that band (below). 1, KC1 2, NaN03 3, (NH4)2S04 4. CaCl2 5, ZnS04 6, KBr 7, KI. (From Kuge and Ono.91)...

Fig. 5.—Changes of absorbance of the amylose-iodine complex (at 610 nm with increasing concentrations of various salts) 1, A12(S04)3 2, Pb(N03)2 3, Na2S04 4, NH4C1 5, CH3C02Na 6, Sr(N03)2 7, KI 8, KN03. (From Kuge and Ono.91)...

Formation of crystalline cyclohepta-amylose inclusion complexes has been followed by recording continuously the turbidity of the aqueous solution of cyclohepta-amylose and the guest molecule (solvent, drug, or aromatic compound) from 60 C downwards. The concentrations of the guest molecules were such that they could not form crystals above the crystallization temperature of pure cyclohepta-amylose. The appearance of turbidity caused by crystal formation before the characteristic temperature of cyclohepta-amylose crystallization is therefore considered to be evidence for inclusion complex formation. The influence of parameters such as concentration, pH, cooling speed, presence of inorganic salts, and inoculating crystals was studied. 

Molecular Interactions. Various polysaccharides readily associate with other substances, including bile acids and cholesterol, proteins, small organic molecules, inorganic salts, and ions. Anionic polysaccharides form salts and chelate complexes with cations some neutral polysaccharides form complexes with inorganic salts and some interactions are stmcture specific. Starch amylose and the linear branches of amylopectin form inclusion complexes with several classes of polar molecules, including fatty acids, glycerides, alcohols, esters, ketones, and iodine/iodide. The absorbed molecule occupies the cavity of the amylose helix, which has the capacity to expand somewhat to accommodate larger molecules. The starch—Hpid complex is important in food systems. Whether similar inclusion complexes can form with any of the dietary fiber components is not known. 

Polycrystalline and well-oriented specimens of pure amylose have been trapped both in the A- and B-forms of starch, and their diffraction patterns84-85 are suitable for detailed structure analysis. Further, amylose can be regenerated in the presence of solvents or complexed with such molecules as alcohols, fatty acids, and iodine the molecular structures and crystalline arrangements in these materials are classified under V-amylose. When amylose complexes with alkali or such salts as KBr, the resulting structures86 are surprisingly far from those of V-amyloses. 

Another group of crystalline amyloses consists of complexes with ionic substances, for example, alkali or salts such as KBr. 

Inclusion complexes of amylose are rather well defined, and a consistent theory of such complexes is available that explains amylose complexes with iodine, fatty acids, alcohols, and other guest molecules.4,5 This subject is surveyed in this article because of the growing interest and importance of such complexes in pharmacology and in the food industry. It is probable that starch in its biological sources (tubers, granules) exists in the form of native complexes with proteins, lipids, mineral salts, and water. 

Although the precipitation of amylose by salts does not depend on the complex-forming properties of amylose, it is to be noted that the addition of complexing agents to the salt stem changes the process totally. Addition of 1.0% of 2-methyl-l-butanol to the system (containing, for example. 

It will be noted that this type of complex-formation is entirely different from that in which complexes are formed between amylose and certain polar, organic compounds. In contrast to the precipitates of the latter complexes (which are of a distinct, crystalline appearance), the starch-alkaline-earth hydroxide complexes are amorphous, curdlike flocculates. These complexes di,s.sociate on diluting them with water, and the starch redissolves. According to the patent description, the amylose complexes dissolve much more easily than the amylopectin complexes hence, fractionation must occur if water is added stepwise. Likewise, fractionation will take place if the starch complexes are partially neutralized, by the gradual addition of an acid. For obvious reasons, such acids as carbonic acid and sulfuric acid (which give insoluble calcium salts) are preferred. Furthermore, it is claimed that gradual addition of caustic alkali to a starch solu-... 

Most starches contain 20-30% amylose (Table 4.24). New corn cultivars (amylomaize) have been developed which contain 50-80% amylose. The amylose can be isolated from starch, e. g., by crystallization of a starch dispersion, usually in the presence of salts (MgS04) or by precipitation with a polar organic compound (alcohols, such as n-butanol, or lower fatty acids, such as caprylic or capric), which forms a complex with amylose and thus enhance its precipitation. 

Beginning with polyvinyl alcohols and PVP we found that more than 20 hydrophilic polymers formed colored inclusion or clavic compounds with I3 in aqueous solution " . Rates of formation were studied and promotion by salts and lower temperatures was discovered. Doubt was cast upon the old theory that amylose, cellulose, and polyvinyl alcohols (PVA) require helical conformations for the insertion of iodine. While studying PVA-iodine complexes a novel method of making PVA fibers from foams was discovered . 

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