Structural study of amylose polymorphs by cross-polarization-magic-angle spinning, 13C-N.M.R. spectroscopy

C.p.-m.a.s. 13C-n.m.r. spectra and 13C spin-lattice relaxation times (T1) at room temperature have been measured for recrystallized samples of different polymorphs of amylose. Although the spectra of A- and B-amyloses in the dry state are very broad and almost structureless, the respective resonance lines of the samples soaked in H2O narrow markedly, and fine splittings can be observed in the C-1 lines, namely, a triplet for the A-type crystal form and a doublet for the B-type crystal form. These multiplicities had already been reported for native A- and B-starches, but the resolution is much higher for the recrystallized samples. In contrast, all resonance lines are composed of single signals for the hydrated and anhydrous V-amyloses, without any significant effect of hydration. It is also found that 13C t1 values of the crystalline components of amyloses are much shorter than those of celluloses. This suggests that the enhanced torsional motion about the α-D-(1→ 4)-glycosyl linkages is allowable for amyloses, even in the crystalline region, because of the flexible, helical structure.