Hydration modulates structures and dynamics of biomacromolecules. Understanding hydration is therefore crucial in unraveling mechanisms of biomacromolecular functions. Although various methods exist for probing biomacromolecular hydration, detecting dynamical interactions between water and biomacromolecules in situ and in real time is still challenging. We combine experimental and computational methods of chiral sum frequency generation spectroscopy (chiral SFG) to study two model systems, a β-sheet protein (LK7β) and a double-helix DNA (dA12●dT12). We show that chiral SFG vibrational signals of water O-H stretches are predominately generated from the first hydration shells. We examine the O-H stretching frequency to probe local H-bonding interactions of water. Using the chiral water signals, we investigate site-specific binding of a drug to the double-helix DNA and the molecular mechanism of denaturation and stabilization of the β-sheet protein. We ask a paradoxical question of how achiral water molecules can generate the chiral optical SFG signals. In addressing this question, we find that mirror-image secondary structures formed by the (L-) and (D-) forms of the protein, and also the DNA, generate the chiral water signals with opposite signs. This result suggests that the biomacromolecules can transfer their chirality to surrounding water, offering a mechanistic explanation for the remarkable selectivity of chiral SFG to water vibrational structures in the first hydration shell. The result also implies that a description of biomacromolecular chirality is incomplete without hydration, leading to a new line of inquiries about the role of water in chiral selectivity of biomolecular interactions and the origin of homochirality of life.

Probing water structures in the first hydration shell of biomacromolecules using chiral sum frequency generation vibrational spectroscopy

Fall 2022 abstracts, posters, and presentations will launch in mid-September.

ACS Fall 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.