Pressure Dependence of the Dynamic Crossover Temperatures in Protein and its Hydration Water

TL;DR

This study demonstrates that the fragile-to-strong dynamic crossover temperature in hydration water around a protein shifts with pressure, aligning with the Widom line from a liquid-liquid critical point, indicating pressure influences protein hydration dynamics.

Contribution

It reveals the pressure dependence of the protein hydration water's dynamic crossover, linking it to the liquid-liquid critical point and Widom line in confined water systems.

Findings

FSC crossover temperature decreases with pressure.

Hydration water's MSD slope change aligns with protein dynamics.

Crossover follows the Widom line from the liquid-liquid critical point.

Abstract

Recently we have shown experimental evidence for a fragile-to-strong dynamic crossover (FSC) phenomenon in hydration water around a globular protein (lysozyme) at ambient pressure. In this letter we show that when applying pressure to the protein-water system, the FSC crossover temperatures in hydration water of lysozyme tracks the similar Widom line emanating from the existence of a liquid-liquid critical point in a 1-D confined water (in MCM-41-S). The mean squared displacements (MSD) of hydrogen atoms in lysozyme and in its hydration water show a sudden change of slopes at the same characteristic temperature, which decreases with an increasing pressure. These results taken together give support of the idea that the dynamic crossover (or so-called glass transition) of the protein is a function of both temperature and pressure, following the FSC of its hydration water.