Glass transition in biomolecules and the liquid-liquid critical point of water

TL;DR

This study uses molecular dynamics simulations to explore how the dynamic transitions of biomolecules relate to the properties of hydration water, supporting the hypothesis of a liquid-liquid critical point in water.

Contribution

It links the protein glass transition to the Widom line associated with the hypothesized second critical point of water, providing new insights into biomolecular dynamics.

Findings

Protein glass transition coincides with the dynamic crossover in hydration water.

Maxima in specific heat and orientational order derivative align with the transition.

Results support the liquid-liquid critical point hypothesis in water.

Abstract

Using molecular dynamics simulations, we investigate the relation between the dynamic transitions of biomolecules (lysozyme and DNA) and the dynamic and thermodynamic properties of hydration water. We find that the dynamic transition of the macromolecules, sometimes called a ``protein glass transition'', occurs at the temperature of dynamic crossover in the diffusivity of hydration water, and also coincides with the maxima of the isobaric specific heat $C_P$ and the temperature derivative of the orientational order parameter. We relate these findings to the hypothesis of a liquid-liquid critical point in water. Our simulations are consistent with the possibility that the protein glass transition results from crossing the Widom line, which is defined as the locus of correlation length maxima emanating from the hypothesized second critical point of water.