Effect of OH groups on the polyamorphic transition of polyol aqueous solutions

Polyamorphic transition in water is expected to occur at low temperatures and high pressures. Recently, the polyamorphic transitions of polyol aqueous solutions were examined under pressure at low temperatures, and the location of their liquid-liquid critical points was estimated experimentally. The addition of polyol solute in water induces the shift of polyamorphic transition pressure toward the lower pressure side. Here, by comparing the polyamorphic transition of various polyol aqueous solutions, especially by comparing those of dilute 1,2-propanediol and dilute 1,3-propanediol aqueous solutions, it is clarified that the OH-groups in the polyol molecule efficiently affect the polyamorphic behavior of solvent water. This suggests that the hydrogen bonding interaction between solvent water and polyol solute relates closely to the polyamorphic behavior of solvent water such as the stabilization of high-density-amorph-like solvent water induced by the presence of polyol solute. In addition, the effect of CH₃ groups in the 1,2-propanediol molecule seems to be opposite to the effect of OH groups. These results have important implications for the understandings of low-temperature phenomena of aqueous solutions, for example, hydration, segregation, phase separation, folding/unfolding of macromolecules, glass forming, and nucleation of crystalline ice Ih.