Re-defining the concept of hydration water in water under soft confinement

TL;DR

This paper reviews recent findings showing that biological membranes influence water properties beyond the traditional hydration layer, suggesting the need to redefine the concept of hydration water in biological contexts.

Contribution

It demonstrates that membrane effects on water extend beyond 1 nm, challenging the conventional hydration water definition and proposing an extended understanding of water-biomembrane interactions.

Findings

Membranes influence water structure at distances greater than 1 nm.

The hydrogen bond network of water is altered by membrane proximity.

The concept of hydration water should be extended beyond the traditional 1 nm boundary.

Abstract

Water shapes and defines the properties of biological systems. Therefore, understanding the nature of the mutual interaction between water and biological systems is of primary importance for a proper assessment of biological activity and the development of new drugs and vaccines. A handy way to characterize the interactions between biological systems and water is to analyze their impact on water density and dynamics in the proximity of the interfaces. It is well established that water bulk density and dynamical properties are recovered at distances in the order of $\sim1$~nm from the surface of biological systems. Such evidence led to the definition of \emph{hydration} water as the thin layer of water covering the surface of biological systems and affecting-defining their properties and functionality. Here, we review some of our latest contributions showing that phospholipid membranes affect the structural properties and the hydrogen bond network of water at greater distances than the commonly evoked $\sim1$~nm from the membrane surface. Our results imply that the concept of hydration water should be revised or extended, and pave the way to a deeper understanding of the mutual interactions between water and biological systems.