AMYLOSE CONFORMATIONAL TRANSITIONS IN BINARY DMSO WATER MIXTURES/

The effects on amylose conformation of percentage water in dimethyl su lfoxide (DMSO)/water mixtures were measured by following changes in sp ecific optical rotation, limiting viscosity number, and C-13-NMR chemi cal shifts. The temperature dependence of specific optical rotation sh owed differences in amylose conformation at four chosen ratios of dime thyl sulfoxide/water. An amylose conformational change was also deduce d from C-13-NMR chemical shift data. Changes in limiting viscosity of amylose in different proportions of DMSO/water, and the effect of tetr amethylurea on the specific rotation of amylose, indicate that intramo lecular hydrogen bonding decreases with increased water content. 66.6% DMSO appears to be a crossover concentration, below which the helical conformation is progressively lost as water is added. When water cont ent is over 60%, transition to a conformation which allows iodine comp lexation to take place is complete. A transition of amylose conformati on from helix to loose helix to random coil with increasing water cont ent was deduced from the experimental results. (C) 1998 Elsevier Scien ce Ltd. All rights reserved.