The conformation of amylose in dimethyl sulfoxide (DMSO) at 25-degrees-C is studied by light scattering, sedimentation equilibrium, and viscosity measurements on narrow-distribution samples of amylose and its oligomers covering a broad range of weight-average molecular weight M(w) from 342 (the dimer) to 1.7 x 10(6). For M(w) above 10(5), the z-average mean-square radius of gyration [S2]z and the intrinsic viscosity [eta] vary as M(w)1.2 and M(w)0.7, respectively, indicating that in this molecular weight region, the amylose chain behaves as a random coil expanded by excluded-volume effect. Below M(w) approximately 10(4), [eta] exhibits an unusually weak dependence on M(w) and finally becomes almost independent of molecular weight. This behavior of [eta] is explained by solvation of DMSO molecules and some helical nature of the amylose chain on the basis of the theory of Yoshizaki et al. for unperturbed helical wormlike chains. The estimated stiffness parameter is comparable to that for atactic poly(methyl methacrylate), a flexible chain, being consistent with the above conclusion from the [S2]z and [eta] data for M(w) above 10(5). The characteristic ratio at infinite molecular weight is found to be about 5, a value close to the reported values for aqueous amylose. Thus it is further concluded that without excluded-volume effect, the conformations of high molecular weight amylose in water and DMSO are similar.
