Single crystals of V amylose complexed with n-butanol or n-pentanol: structural features and properties

Rectangular single crystals of amylose complexed with n-butanol or n-pentanol were prepared by adding these precipitants to metastable aqueous solutions of amylose. The crystals were analysed by electron and X-ray diffraction. It was confirmed that the crystals have an orthorhombic P212121 symmetry with cell parameters: a=2.74 nm, b=2.65 nm and c (chain axis)=0.8 nm. Within the unit cell, the amylose chains were organized in antiparallel pairs of parallel 65 amylose helices with four molecules of precipitant located between the helices and occupying about 10% of the cell volume. Upon desolvation, the crystals were invariably converted to the hexagonal close-packed VH amylose. The crystals could also be swollen in a series of solvents or solvent mixtures without losing their single crystal characteristics. Such treatments retained the orthorhombic symmetry but resulted in an expansion of their a and b cell parameters while c remained constant at 0.8 nm.