Chemical Continuum: Overcoming Discrete Notions Underlying Fluctuations in Water

DIPC Seminars

Ali Hassanali
The Abdus Salam International Center for Theoretical Physics (ICTP), Trieste, Italy
Hybrid Seminar: Donostia International Physics Center
Ricardo Diez Muino
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Chemical Continuum: Overcoming Discrete Notions Underlying Fluctuations in Water

Is Liquid Water really a tale of two liquids? Is the structure of the excess proton in water an Eigen or Zundel species? Can molecules dissolved in water be rigidly classified into hydrophobic or hydrophilic? Discrete or binary classifications are at the heart of the interpretation of phenomena associated with understanding the properties of aqueous solutions. In this discussion, I will share three stories that have recently emerged from our group that will attempt to challenge some of these ideas.

One of the most well studied and common interpretations of water's anomalous properties is the existence of two liquids namely the low-density liquid (LDL) and high-density liquid (HDL). Similarly, two-state models (Eigen or Zundel) are central to acid-base chemistry which is at the heart of characterizations of proton transfer in liquid water. Here, I will illustrate some recent work leveraging unsupervised learning techniques to highlight how chemical discreteness limits our interpretations of fluctuations of the hydrogen- bond network in these contexts.

A critical first step in solvation theory is the creation of a cavity. The thermodynamics associated with this process is at the heart of hydrophobicity and its two-length scale cross over. I will share some recent data-driven approaches that will illustrate how shape and geometry affects the crossover in hydrophobicity.
In the final part of my talk, I will discuss some recent findings on how oily (non-polar) molecules can pick up polar traits due to subtle quantum mechanical effects. We believe that this feature is central to an ongoing raging debate in the field on the origin of the negative charge at hydrophobic surfaces which we attribute to the coupling between the hydrogen-bond network topology and charge transfer.