Conformation of cyclomaltooligosaccharide (“cycloamylose”) of dp21 in aqueous solution

The conformation of a cyclomaltooligosaccharide [“cycloamylose”, cyclic (1 → 4)-α-d-glucan] having degree of polymerization 21 was characterized by means of small-angle X-ray scattering (SAXS) with the aid of simulations of scattering profile based on molecular models. The results indicate that the cycloamylose chains adopt a circularized three-turn single helical structure with a radius of gyration of 11.5 Å. The scattering profiles calculated for double helical structures with foldbacks at each end are not in good agreement with experimental profiles. Molecular dynamics simulations in water show that overall the conformation of the three-turn single-helical form is maintained at 300 K, although replacements of glucose units are observed. In one model, ninety-six water molecules are interacting with a cycloamylose molecule judging from hydrogen-bonding distances and angles. The conformation of cyclic (1 → 4)-α-d-glucan (cycloamylose) was determined via small-angle X-ray scattering (SAXS).