Conformation amylopectin

Vinyl alcohol copolymers, as well as butanol, leave the amylopectin conformation unchanged. A model has been proposed considering large individual amylopectin molecules interconnected at several points per molecule as a result of hydrogen bonds and entanglements by chains of amylose/vinyl alcohol copolymer V complexes. This structure has been defined in the literature as interpenetrated [92]. 

Therefore, the absorption at 947 cm" does not correspond to crystalline or gelatinised amylose, bnt to a complexed one (V-type complex), as in the presence of low molecular weight molecules such as butanol and fatty acids [4, 134]. Starch-based materials with an amylose content close to zero, even in the presence of vinyl alcohol copolymers, do not show any peak at 947 cm demonstrating that vinyl alcohol copolymers, as well as butanol, leave the amylopectin conformation unchanged. 

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). 

Chemically, both varieties of starch are polymers of glucose with the a-D-glucose units in the 4Ci conformation. The glucose units are linked -(1 ->4)- in both amylose and amylopectin but in amylopectin roughly one residue in twenty is linked -(1 ->6)-, which forms branch points. The proportion of branch points varies, depending on the source of the amylopectin. 

Aberle, T., Burchard, W., Vorwerg, W., Radosta, S. (1994). Conformational contributions of amylose and amylopectin to the structural properties of starches from various sources. Starch/Stdrke, 46, 329-335. 

Diffusion measurements " have been made on starch acetates dissolved in such solvents as acetic acid and acetic anhydride, and molecular weight values up to 224,700 have been indicated. Unfortunately, diffusion constants of starch fractions have been investigated only to a very limited extent. Diffusion measurements probably would provide evidence of value in the determination of the physical shape of the molecules of the two starch fractions the rate of diffusion of the amylopectin acetate should conform most nearly to the normal hydrodynamic predictions for spherical macromolecules. 

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