Configurational statistics of polysaccharide chains. Part I. Amylose

Abstract

The conformational energy of amylose molecule was computed as a function of rotations φ and Ψ about interunit glycosidic bonds. The characteristic ratio 〈r²〉₀/Nl^V₂ of the mean-square end-to-end distance of the unperturbed chain to the product of n, the number of glucose residues in the chain and the square of the virtual bond length l_V = 4.2 Å calculated for amylose chain is about 6.9, which is in good agreement with the experimental value (6.6 ± 0.2). The value of this ratio calculated for free rotation about the inter unit glycosidic bond is 1.1. The conformational map reveals that the rotations of pyranose units about the interunit glycosidic bonds are highly restricted; this tends to lock these units in a preferred orientation. From the probability of occurrence of the glucose residue conformations it is concluded that amylose exists as a random coil with short helical sequences in neutral aqueous solutions.