Amylose Group

Amylose, amylopectin, glycogen, and dextrin belong to the amylose group. Amylose ( -20%) and amylopectin ( 80%) are the components of starch. 

Amylose itself is poly[a-(l- 4)-D-glucose]. Thus, acid hydrolysis yields exclusively D-glucose. On the other hand, maltose is the predominant prod- 

Since branch points are randomly distributed in amylopectin, and since starch consists of amylopectin and amylose, starch is likewise not a single substance, but a mixture of compounds. The amylose content of various starches is generally about 15-25%, but can approach 34% (lily bulbs), or even 67% (steadfast pea). Amylose can be separated from amylopectin by precipitation from an aqueous solution with butanol or by dissolution in liquid ammonia. 

Natural amyloses possess a degree of polymerization of 6000. Amylose can also be synthesized in vitro from glucose-1-phosphate, an enzyme from the liquid of crushed potatoes and a primer or with muscle phosphorylase plus a primer. Higher sugars are effective as primers and actual starters maltotriose is also effective as a primer with potato juice. 

With a conventionally prepared phosphorylase, only a relatively low degree of polymerization of 30-250 is obtained. However, if the enzymic solution is heated, then the degree of polymerization increases up to that of natural amylose. Therefore phosphorylase must contain a thermolabile, hydrolyzing enzyme. The higher the primer concentration, the higher will be the degree of polymerization. Since there are many more starter molecules than enzyme molecules in the system, the enzyme must move from chain to chain. Synthetic amylose possesses a very narrow molecular-weight distribution. 

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The amylose group molecules consist of D-glucose residues bonded together in the a-( 1 4) position ... 

Amylose, amylopectin, glycogen, and dextrin belong to the amylose group. Amylose and amylopectin are components of starch, the reserve polysaccharide of plants. Glycogen is the animal reserve polysaccharide, found, for example, in the liver and in the brain. Dextrins are cyclic decomposition products of amylose, amylopectin, or glycogen. 

FIGURE 7.21 Amylose and amylopectin are the two forms of starch. Note that the linear linkages are o (1 4), but the branches in amylopectin are o (1 6). Branches in polysaccharides can involve any of the hydroxyl groups on the monosaccharide components. Amylopectin is a highly branched structure, with branches occurring every 12 to 30 residues. 

Fig. 13.—Packing arrangement of extended, 6-fold, KOH-amylose (11) helices, (a) Stereo view of two unit cells approximately normal to the ftc-plane. The helix (filled bonds) at the center is antiparallel to the two helices (open bonds) at the comers in the back. Potassium ions (crossed circles) have water molecules (open circles) and hydroxyl groups from amylose helices as ligands.

This helical arrangement of amylose, known as the V-form, may be precipitated from certain solutions (e.g. in butanol or DMSO) of amylose. Either hydrated (Vh-) or anhydrous (Va-) amylose absorbs I2 vapour to produce the blue compound with the necessary I" being produced in situ. Alternatively the compound may be formed from iodine-iodide mixtures in solution which allows the V-form to be produced and stabilised as the polyiodide compound 141 The compound was reported 142) to have the orthorhombic space group 7>212121. 

Fig. 13. Projection view of Vh-amylose on the a, b plane. The amylose chains are packed in an antiparallel manner in space group />212121. Guest water molecules are represented as filled circles in the helical canals and in interstitial sites between the helices...

It is now realised that amylose-polyiodide compounds can also involved Va- and Vh-forms 155 . Recent studies on the Vh-compound 154) have shown that the early structural ideas described above are essentially correct but that rather than P2l2i2i the monoclinic space group P2X is applicable. An almost linear arrangement of iodine atoms was present in the helical canals but the length of the iodide chain could not be determined. In addition to this guest, eight water molecules were present in the unit cell and once again these were present in the interstitial sites (see Fig. 14). 

The pH dependence of the reaction of m-tolyl acetate with cyclohexa-amylose implies a pAa of 12.1 for the catalytically active secondary hydroxyl group (Van Etten et al., 1967b). Although this pK at first appears low for the ionization of an aliphatic alcohol, it is consistent with the value of 12.35 determined thermodynamically for the ionization of the secondary hydroxyl groups of the ribose moiety of adenosine (Izatt et al., 1966 Christensen et al., 1966), and with the value of 12.2 reported by Lach for the... 

An interesting procedure has been proposed for the synthesis of amylose-b-PS block copolymers through the combination of anionic and enzymatic polymerization [131]. PS end-functionalized with primary amine or dimethylsilyl, -SiMe2H groups were prepared by anionic polymerization techniques, as shown in Scheme 56. The PS chains represented by the curved lines in Scheme 56 were further functionalized with maltoheptaose oligomer either through reductive amination (Scheme 57) or hydrosilyla-tion reactions (Scheme 58). In the first case sodium cyanoborohydride was used to couple the saccharide moiety with the PS primary amine group. 

Okamoto et al [85] performed the optical resolution of primaquine and other racemic drugs by high performance liquid chromatography using cellulose and amylose tris-(phenylcarbamate) derivatives as chiral stationary phases. Primaquine and other compounds were effectively resolved by cellulose and/or amylose derivatives having substituents such as methyl, tertiary butyl, or halogen, on the phenyl groups. 

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