Amylose deacetylation

Senti and Witnauer206 have reported studies on the fiber diagrams from various alkali-amyloses. Specimens were obtained by deacetylating clamped specimens of amylose acetate with the appropriate alkali. The positions of the alkali ions and the lateral packing of the amylose chains were determined with the aid of Patterson projections. In the A - and B -modifica-tions, the fiber period was 22.6 A. (extension of 6 D-glucose units), whilst in the V -modification it was 8.0 A. These authors have also studied in detail the addition compounds of amylose and inorganic salts with special reference to the structure of the potassium bromide-amylose compound.206 Oriented alkali fibers were treated with the appropriate salt solution. Stoichiometric compounds were formed. The x-ray patterns from these showed that the addition compounds with potassium salts crystallized in... 

Acetates can be used instead of the free polysaccharide for preparing polysaccharide adducts. For example,17 at concentrations of 0.1 M alkali metal (lithium, sodium, and potassium) hydroxide in 25% aqueous ethanol, amylose triacetate is deacetylated to form adducts containing approximately one molecule of alkali metal hydroxide per three D-glucose residues. Partially crystalline amylose adducts can be obtained by immersing stretched filaments of amylose triacetate in the deacetylating solution. 

A series of alkali-amylose complexes can be obtained during the solid-state deacetylation of amylose triacetate, as first described by Senti and Witnauer (32). The unit cells of the individual members of the series of LiOH-, K0H-, NH3OH-, CsOH and guanidinium hydroxide-adducts of amylose appeared to fit an iso-morphous series based on the space group P212 2i> and a tentative crystal structure was proposed (32). The detailed structure of the KOH-amylose complex has now been determined (ll) and the overall structure is similar to that proposed earlier. It is, therefore, likely that all members of the series are isomorphous. 

Physicochemical studies of the solution properties of amylose benzoate by light-scattering, osmometric, and viscosimetric techniques showed that the molecules behave as coils. Factors affecting the rate of dissolution of cellulose acetate phthalate in aqueous solution are important from the point of view of use as an enteric-coating material. The removal of the benzoyl group during methanolysis is slow and concurrent with the methanolysis, " whereas deacetylation precedes methanolysis. 

Aqueous amylose solution (1%) was prepared by dissolving amylose powder in hot water (80°C). A 1% salt free aqueous water-soluble chitosan (WSC) was obtained by the dialysis of a WSC solution that included NaCl produced by the neutralization of a dilute hydrochloric acid solution of WSC with NaOH. Each film having a thickness of 40-50 om was prepared by casting the amylose, WSC, or their mixed solutions at 60°C. A film of fully deacetylated chitosan was obtained by casting a 0.1 M aqueous AcOH solution of fully deacetylated chitosan (1%) on a Kapton (polyimide) film. The resulting acidic chitosan film was neutralized with 1M aqueous NaOH followed by washing with water and then dried. 

A combination of stereochemical structural refinement and. T-ray diffraction analysis has been used to determine the crystal stracture of potassium hydroxide-complexed amylose, obtained by heterogeneous deacetylation of amylose acetate. The complex crystallizes as an orthorhombic unit cell with p2,2,2 symmetry and dimensions a = 8.84,6 = 12.31, and c = 22.41 A. The conformation of the amylose chain is a distorted left-hand helix with six o-glucose residues per turn. Each three-residue asymmetric unit is complexed with one molecule of potassium hydroxide and three molecules of water. Extension of the amylose chain probably arises because of the co-ordination of the K ion. 

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