Amylopectins

Amylopectins. — The effects of acrylamide graft copolymerization on the solution properties of amylopectin have been discussed. Amylopectin has been dyed with DyAmyl-L and used in this form as a substrate for the assay of a-amylase. Amylopectin has been treated with isocyanate derivatives of 4-amino-( 1,1-dimethyl ethyl)-3-(methylthio)-l,2,4-triazin-5(4/f)-one ( metribuzin ) or acid chloride derivatives of 2,4-dichlorophenoxyacetic acid ( 2,4-D ) and 2,2-dichloropropionic acid ( dalapon ), to produce controlled-release polymeric pesticide systems. The solvent system utilized for these reactions, a lithium chloride or bromide salt in AW-dimethylacetamide, allows dissolution of the reactant salt and facilitates analysis of the polymer product by such techniques as i.r., U.V., and n.m.r. spectroscopies and gel permeation chromatography. Derivatives of other naturally occurring polysaccharides, including amylopectin, cellulose, chitin, and dextran, were also prepared. 

Amylose. — The effects of acrylamide graft copolymerization on the solution properties of amyloses have been discussed. As part of a study of the blue 

Reagents i, carbodi-imide, NaBH4 Br -HjO, pH 7.0 iii, NH,Ac, NaCNBH. iv, glacial AcOH dmf, SOj-pyr 

spectra have been recorded for previously reported comb-like derivatives of amylose produced by orthoester and Helferich condensations of D-glucose and amylose. It was anticipated that, for these polymer condensations, the Helferich and orthoester condensations would favour a- or 3-D-glyco-sylation, respectively, as for monomeric systems. However, the spectra indicate extensive, if not exclusive, j3-D-glycosylation for both the Helferich and the orthoester conditions. 

The crystal and molecular structure of a tri-O-ethylamylose polymorph, TEA-3, has been solved by stereochemical conformation and packing analysis, combined with X-ray fibre diffraction analysis. The unit cell is orthorhombic, space group jP2i2i2i, with a = 15.36 ( 0.03)A, Z = 12.18 ( 0.05)A, and c (fibre repeat) = 15.48 ( 0.01) A. The actual chain conformation is a 43 helix with the 6-ethoxy-group in the tg position, as was previously found for the polymorph TEA-1. 

Amylopectins.— A TMS derivative of amylopectin has been prepared using hexamethyldisilazane in DMF as the silylating reagent. The extent of tri-methylsilylation, which ranged from d.s. 0.9 to 2.2, depends on the structure and solubility of the polysaccharide. Trimethylsilylated amylopectin was found to be completely soluble in such organic solvents as toluene, benzene, and chloroform. 

Amyloses.—Amylose has been labelled at the reducing end by treatment with D-[ C]glucose 1-phosphate and phosphorylase the labelled polysaccharide was used as a substrate in a study of the kinetics of amylolysis. Malto-oligosac- 

The effects of y-radiation on the depolymerization and selected physical properties of amylose in the solid state and in solution have been investigated under conditions of graft copolymerization. Irradiation furnished an alkali-sensitive material (G-value for scission 2.8), most likely owing to the presence of a j8-alkoxycarbonyl structure. The G-value (1.3) obtained on irradiation of solid amylose at 0 °C under nitrogen is lower than values previously reported for amylose and other polysaccharides. A solution of amylose in water was protected against y-radiation by the addition of DMSO (G-value of 2.3 vs. 30). A solvent system of DMSO-acetic acid-water degraded y-irradiated amylose less than did aqueous DMSO. 

The susceptibility of 6-amino-6-deoxyamyloses to a-amylases has been investigated. Replacement of the primary hydroxy-groups of the D-glucopyranosyl residues evidently caused changes in the nature of the enzyme-substrate interaction, but such substitution did not prevent the hydrolysis of unsubstituted regions of the polysaccharide by the enzyme, provided the degree of substitution overall is low. 

Chlorite-oxidized amylose (oxyamylose) has been found to possess a leukaemo-suppressive activity against established Friend virus leukaemia.  

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Starch can be split into amylose and amylopectin by a commercial process based on selective solubilities. Amylose is used for making edible films, and amylopectin for textile sizing and finishing, and as a thickener in foods. 

Amylopectin and glycogen are saccharides similar to amylose, except with branched chains. 

Similar materials are available based on potato starch, eg, PaseUi SA2 which claims DE below 3 and has unique properties based on its amylose—amylopectin ratio pecuhar to potato starch. The product contains only 0.1% proteia and 0.06% fat which helps stabilize dried food mixes compounded with it. Another carbohydrate raw material is waxy-maize starch. Maltodextrias of differeat DE values of 6, 10, and 15, usiag waxy-maize starch, are available (Staley Co.). This product, called Stellar, is offered ia several physical forms such as agglomerates and hoUow spheres, and is prepared by acid modification (49). Maltodextrias based oa com starch are offered with DEs of 5, 10, 15, and 18 as powders or agglomerates (Grain Processing Corp.). 

Specific optical rotation values, [a], for starch pastes range from 180 to 220° (5), but for pure amylose and amylopectin fractions [a] is 200°. The stmcture of amylose has been estabUshed by use of x-ray diffraction and infrared spectroscopy (23). The latter analysis shows that the proposed stmcture (23) is consistent with the proposed ground-state conformation of the monomer D-glucopyranosyl units. Intramolecular bonding in amylose has also been investigated with nuclear magnetic resonance (nmr) spectroscopy (24). 

Amylase occurs in many plants, such as barley, wheat, rye, soy beans, and potatoes, where it is generally accompanied by some a-amylase. [ -Amylase initiates hydrolysis at the nonreducing end of an amylose or amylopectin chain, and removes maltose units successively until the reducing end of the molecule is encountered in amylose or a branch is met in amylopectin. ( -Amylase is used commercially in the preparation of maltose symps. After P-amylase hydrolysis of amylopectin there remains a P-amylase limit dextrin. ( -Amylase has been used as a probe of the fine stmcture of amylopectin (43-46). 

Com and rice starches have been oxidized and subsequently cyanoethylated (97). As molecular size decreases due to degradation during oxidation, the degree of cyanoethylation increases. The derivatized starch shows pseudoplastic flow in water dispersion at higher levels of cyanoethylation the flow is thixotropic. Com and rice starches have been oxidized and subsequently carboxymethylated (98). Such derivatives are superior in the production of textile sizes. Potato starch has been oxidized with neutral aqueous bromine and fully chemically (99) and physically (100) characterized. Amylose is more sensitive to bromine oxidation than amylopectin and oxidation causes a decrease in both gelatinization temperature range and gelatinization enthalpy. 

Starch acetates may have low or high DS. The industrial importance of low DS acetates results from their abiUty to stabilize aqueous polymer sols. Low DS acetates inhibit association of amylose polymers and reduce the association of the longer outer chains of amylopectin. These properties are important in food appHcations. Highly derivatized starches (DS 2—3) are useful because of their solubiHty in organic solvents and abiHty to form films and fibers. 

The distinctions between these homopolymers arise from the different ways in which the monomer units are hooked together in polyacetal chains. Starch (qv), plant nutrient material, is composed of two polysaccharides a-amylose and amylopectin. cx-Amylose is linear because of exclusive a (1 — 4) linkages, whereas amylopectin is branched because of the presence of a (1 — 6) as well as a (1 — 4) links. The terms linear and branched refer only to primary stmcture. 

Fig. 1. Primary stmctures of some common polysaccharides, (a) Alpha-glycoside linkages characterize amylose, amylopectin, and glycogen (b) cellulose has...

Normal com starch is composed of 20—30% of the linear polysaccharide amylose and 70—80% of the branched polysaccharide amylopectin. 

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. 

Amylases are exoen2ymes that attack amylose chains and result in the successive removal of maltose units from the nonreducing end. In the case of amylopectin, the cleaving stops two to three glucose units from the a-1,6-branching points. ( -Amylase [9000-91-3] is used for the production of maltose symps and for adjunct processing in breweries. The most important commercial products are made from barley or soybeans. 

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