Amylose conformational transitions in binary DMSO/water mixtures

The effects of percentage water content in DMSO/water mixtures on amylose conformation were measured by following changes in specific optical rotation,limiting viscosity number, and C-13-NMR chemical shifts. The temperature dependence of specific optical rotation showed differences in amylose conformation for four ratios of dimethyl suphoxide/water. The changes in limiting viscosity of amylose in different proportions of DMSO/water with increasing temperature, and the effect of tetramethylurea on the specific rotation of amylose, indicate that the number of intramolecular hydrogen bonds decreases with increased water content. An amylose conformational change was also deduced from C-13-NMR chemical shift changes. Thirty-three percent water appears to be a crossover concentration, above which the helical conformation is progressively lost with increased temperature. With further increase in water content to 66.6%, transition to a random coil conformation is complete, and iodine complexation may take place. The transition of amylose conformation from helix to loose helix to random coil with increasing water content was deduced from the experimental results.