CONFORMATION OF AMYLOSE IN DIMETHYL-SULFOXIDE

The conformation of amylose in dimethyl sulfoxide (DMSO) at 25-degrees -C is studied by light scattering, sedimentation equilibrium, and visc osity measurements on narrow-distribution samples of amylose and its o ligomers 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-ave rage 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 th is 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 exp lained by solvation of DMSO molecules and some helical nature of the a mylose chain on the basis of the theory of Yoshizaki et al. for unpert urbed helical wormlike chains. The estimated stiffness parameter is co mparable to that for atactic poly(methyl methacrylate), a flexible cha in, being consistent with the above conclusion from the [S2]z and [eta ] data for M(w) above 10(5). The characteristic ratio at infinite mole cular weight is found to be about 5, a value close to the reported val ues for aqueous amylose. Thus it is further concluded that without exc luded-volume effect, the conformations of high molecular weight amylos e in water and DMSO are similar.