Both water and chirality is essential to life on earth as we know it. Whereas individual water molecules are not chiral, water molecules hydrogen-bonded together could form chiral superstructures. Such chiral water structures can be templated by biomolecules through the specific interaction of water with the biomolecules. Here we present chiral sum-frequency generation (SFG) spectroscopy showing the existence of a chiral water structure surrounding DNA. X-ray experiments at cryogenic temperatures have shown the existence of structural water molecules in the minor groove of DNA near AT base pairs giving rise to the notion of a spine of hydration of DNA. MD simulations have shown that water molecules in the minor groove are greatly slowed down compared to bulk and major groove waters. Our experiments confirm the existence of a spine of hydration at room temperatures and show that this spine of hydration for a chiral water structure. Furthermore, the chiral SFG experiments provide insight into the hydrogen-bonding strength of the solvation shell of DNA. We observe that the chiral water structure is generally more strongly hydrogen-bonded compared to the achiral solvation shell but that there exist non-hydrogen-bonded OH bonds in the narrow minor groove for a DNA duplex consisting of alternating A-T base pairs. Due to the ubiquity of chirality in biological systems, chiral SFG could prove to be a general method for studying biological water.

Chiral water structures in biological systems

253rd National Meeting (2017)

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