Cluster Structure in Helix-promoting Hexafluoro-iso-propanol–Water Mixtures

Abstract

Neutron diffraction measurements with H/D isotopic substitution have been performed for hexafluoro-iso-propanol (HFIP; 1, 1, 1, 3, 3, 3-hexafluoro -2-propanol)–water mixtures at 0.1, 0.2 and 0.4 of HFIP mole fractions (x_HFIP). The nine partial structure factors obtained were subjected to an empirical potential structure refinement (EPSR) method to derive all site–site pair correlation functions. It has been found that with increasing HFIP concentration the degree of hydrogen bonding between water–water, HFIP–water, HFIP–HFIP increases as have previously been found for aliphatic alcohols–water mixtures. There was no evidence that water structure is well defined around the hydrophobic groups of HFIP. At x_HFIP = 0.1, the hydrophobic groups of HFIP contact with each other, whereas a zigzag chain structure due to hydrogen bonds via the hydroxyl groups grows in the more concentrated HFIP mixtures.