Water's response to the fear of water

Abstract

Spectroscopic analysis reveals that, at low temperatures, hydrophobic molecules dissolved in water strengthen the hydrogen bonding between nearby water molecules. But at high temperatures, the reverse can be true. See Letter p.582 The hydrophobic interactions that prevent oil and water from mixing also play a central part in biological processes ranging from cell-membrane formation to protein folding and drug binding. Yet little is known about how an oil molecule changes the structure of water, and thus facilitates such processes. Joel Davis et al. report spectroscopic measurements revealing that at low temperatures, the water in hydrophobic hydration shells has greater tetrahedral order and fewer weak hydrogen bonds than the surrounding bulk water. As the temperature increases, this structure disappears and another appears that is more disordered and has weaker hydrogen bonds than the bulk — but only around nonpolar chains longer than ∼1 nanometre.