Professor Ward Thompson named April 2024 Sutton Family Research Impact Award recipient

The Department of Chemistry congratulates Professor Ward Thompson on receiving the April 2024 Sutton Family Research Impact Award!

The Sutton Award is a monthly competition among chemistry faculty. Every month, the Chemistry Department Chair and Associate Chairs review the peer-reviewed papers published by chemistry faculty from the three previous months to select a winner. The recipient receives a $500 cash prize and is featured on the departmental website.

For a full list of winners, visit our Sutton Family Research Impact Award webpage.

A structure–dynamics relationship enables prediction of the water hydrogen bond exchange activation energy from experimental data

By Zeke A. Piskulich,* Damien Laage,* and Ward H. Thompson,*

Chemical Science, 2024, 15, 2197-2204

https://doi.org/10.1039/D3SC04495E

Most of the special properties of water originate from its ability to engage in hydrogen bonding. This is particularly true of the dynamics of liquid water, e.g., diffusion, reorientation, solvation, where the key underlying event of almost all processes is the exchange of one hydrogen-bond acceptor for another. However, these exchanges in neat liquid water have so far escaped experimental measurements. This has left a significant gap in our understanding of water dynamics. In this Chemical Science paper, the Thompson group led by recent graduate Dr. Zeke A. Piskulich (shown in the photo below) and in collaboration with Prof. Damien Laage at École Normale Supérieure in Paris, demonstrated how the structural properties of the hydrogen-bonding network can be used to infer the dynamical properties of liquid water.

The essential idea is to recognize how the barriers for the hydrogen-bond exchange are encoded in the water structure. This structure is typically quantified using a “radial distribution function” that gives the relative probability of finding a water molecule a given distance away from another water molecule. Importantly the radial distribution function can be measured by X-ray or neutron diffraction and this has been done (many times) for water, including at different temperatures. Dr. Piskulich, following earlier work from Prof. Laage, showed how the radial distribution function can be used to estimate the free energy barriers for water molecules to move into and out of a central molecule’s first solvation shell. Moreover, he showed how the temperature dependence of the radial distribution function gives the enthalpic barriers for these processes. Then, the barrier for an exchange of hydrogen-bond partners is the sum of that for the original acceptor to leave the first solvation shell plus that for the new acceptor to enter the solvation shell (plus a small component for the OH group to rotate from the first to the second acceptor). Using several water models in simulations, he showed that this gives an excellent correlation between the barrier calculated from this structural data and the actual activation energy for hydrogen-bond exchange. Then, using the structural barriers extracted from the temperature-dependent X-ray diffraction measurements, Dr. Piskulich was able to estimate the experimental activation energy for hydrogen-bond exchange as 3.43 kcal/mol (which, again, cannot currently be measured) from this correlation.

Knowledge of this activation energy for hydrogen-bond exchange is critical for developing a complete theory of water dynamics that is centered on this key elementary event. It will also be useful for understanding water dynamics in more complex environments, e.g., in electrolytes, at interfaces, solvating biomolecules, and in confinement.

Dr. Zeke A. Piskulich