Amylose-1-butanol complex

Lewis and Johnson compared the c.d. spectra of amylose and cyclomaltohexaose, and showed that amylose is helical in aqueous solution. Cyclomaltohexaose is chromophorically equivalent to amylose, and it is known to assume a pseudohelix having zero pitch, and thus, no helical chirality. The conformation of amylose is clearly different from that of cyclomaltohexaose, as their c.d. spectra are very different (see Fig. 9). The difference in conformation was considered to be a matter of helical chirality. To confirm this, these workers measured the c.d. spectrum of an amylose-1-butanol complex presumed to have the V-form of helical conformation with the 1-butanol complexed in the channel of the helix. The c.d. spectrum of the complex is identical to that of amylose in aqueous solution. 

The discovery of the V-type, helical amylose (see p. 265) that forms when amylose interacts with 1-butanol was crucial for the development of the chemistry of starch inclusion complexes. It soon appeared that 1-butanol complexes solely with the amylose component. This selectivity became the first convenient method of fractionating starch. This method was first described by Schoch699 and later developed by Kerr et al.700-702 and oth-ers 680,703 An impr0ved procedure was subsequently patented.704 The amount of 1-butanol adsorbed in amylose is increased by the presence of moisture and is also dependent on two key factors the time of contact with that alcohol and the origin of the amylose, as shown in Table XXIX. 

X-ray diffraction analysis754 of a series of amylose complexes with lower and higher fatty acids revealed that the crystal structures depend on whether amylose was complexed in the dry or wet state. Both the 6, and 7i helical conformations of amylose were found in these complexes. The conformation appears to depend on the length of the hydrophobic moiety. Dry amylose forms crystalline complexes with a unit cell identical to that of the anhydrous 1-butanol-starch complex (lattice parameters a = b = 25.6 A). An orthorhombic unit cell was proposed for the 7i -helical structure of the wet complexes of monobasic acids (acetic, butanoic, pentanoic, hexanoic,... 

Fourier transform infrared (FTIR) second-derivative spectra of thermoplastic starch and vinyl alcohol copolymer systems with droplet-like structure, in the range of starch ring vibrations between 960 and 920 cm , provide for an absorption peak at about 947 cm (Figure 2.7), as observed for amylose when complexed (V-type complex) by low-molecular-weight molecules such as butanol and fatty acids. 

The effect of chain length on the ability of degraded amylose to form complexes was studied by Whistler and associates.63 When amylose is hydrolyzed to a degree of polymerization of 20 to 40, it no longer forms insoluble complexes with nitrobenzene, n-pentyl acetate and 2-heptanone, although it still does with 1-butanol and 2-nitropropane. 

Electron diffraction by lamellar, single crystals leads to a two-dimensional, tetragonal unit-cell with a = b = 22.9 A (2.29 nm). From X-ray diffraction data obtained from a film of sedimented, lamellar crystals, it was found that the c axis spacing (7.8 A 780 pm) is equivalent to that in 6-fold and 7-fold amylose helices. The true helical diameters of the 1-butanol, isopropyl alcohol, and 1-naphthol complexes were calculated from experimental data. The ratios of 6 7 8 indicated that the 1-naphthol complex has eight D-glucose residues per turn. The diversity of helical orientations in V-amylose crystals was discussed. 

Partial hydrolysis with alpha amylase (EC 3.2.1.1), followed by gel chromatography, has been used to study aspects of the physical structures of the amylose complexes formed with such organic compounds as 1-butanol, and of retrograded amylose. Differences were detected.387b... 

The unit cell dimensions of all crystalline amyloses that have been determined in some detail, are listed in Table I. Also included are some intermediate forms between the va and Vjj amyloses (Ji.) and some V-amylose complexes with n-butanol, which, although not yet completely determined, have been added to illustrate the range of variability in unit cell dimensions. In the case of the Va-BuOH complex, a doubling of one unit cell axis was detected after a careful study of electron diffraction diagrams of single crystals ClO). A consequence of the doubling is that the unit cell now contains four chains, instead of the two normally found in amylose structures. Cln a strict sense, the A- and B-amyloses should also be considered as four-chain unit cells, but their double-helical structure still results in only two helices per cell) (13,1 ). 

Using results of these kinds of studies, the characteristic structure of amylose can be differentiated from that of amylopectin. Amylose has a small number of branches and crystallizes and precipitates when complexed with 1 -butanol. The iodine affinity of amylose is much greater (i.a. 18.5 to 21.1) than that of amylopectin (i.a. 0.0 to 6.6),79,152-158,163,169-174 and the iodine affinity of amylose (3-limit dextrin is similar to that of the parent amylose. The average chain length of amylose (3-limit dextrins is much larger than that of the amylopectin (3-limit dextrin.160... 

Microbiological action in starch dispersions results in a drop in pH, loss of viscosity and the development of odor. Retrogradation may be accelerated by the drop in pH or especially if butanol, which complexes with amylose, is generated via starch fermentation. Sulfate-reducing bacteria will cause black deposits due to reaction with iron in the process water. For quality control, preservatives are added to starch slurry, cooked starch, surface size and coating color. 

Broad categories of starch granule sizes are possible by fractionation with butanol (Schoch, 1942). This solvent enters the interior of the amylose helix and forms an insoluble inclusion complex. 

It should be noted that the different structures of amylose and amylopectin confer distinctive properties to these polysaccharides (Table II). The linear nature of amylose is responsible for its ability to form complexes with fatty acids, low-molecular-weight alcohols, and iodine these complexes are called clathrates or helical inclusion compounds. This property is the basis for the separation of amylose from amylopectin when starch is solubilized with alkali or with dimethylsulfoxide, amylose can be precipitated by adding 1-butanol and amylopectin remains in solution. 

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