Structured water mobile below the freezing point in aqueous solutions of a triple-helical polysaccharide schizophyllan

Abstract

Aqueous solutions of schizophyllan are known to undergo a sharp order-disorder structure transition, where the ordered structure is formed of the side chains of the polysaccharide along with nearby water molecules around its helix core. The structured water in the ordered state is positionally fixed but rotates reacting with an electric field of about 100 MHz as detected by time-domain reflectometry. The same method was extended to a wide temperature range between -20 and 30°C encompassing the freezing point of about -6°C. A 17.8 wt% D2O solution showed both free and structured water dispersions at 0°C, but only the latter one below the freezing point. Thus we concluded that the structured water around the helix core remains unfrozen and mobile even when the system is frozen and no free water exists.