Crossovers in supercooled solvation water: Effects of hydrophilic & hydrophobic interactions

TL;DR

This study uses ab initio molecular dynamics to explore how water's structure and dynamics change near hydrophobic and hydrophilic groups, revealing temperature-dependent crossovers relevant to protein behavior.

Contribution

It provides detailed insights into the temperature-dependent crossover behaviors of water near different groups, linking microscopic interactions to protein denaturation mechanisms.

Findings

Crossovers in water dynamics at 256K and 265K near hydrophobic and hydrophilic groups.

Bulk water shows an apparent divergence at 210K.

Structural and thermodynamic transitions relate to protein cold denaturation.

Abstract

We use systematic 8 ns ab initio molecular dynamics (AIMD) to study the structure and dynamics of water in bulk, and close to both hydrophobic and hydrophilic (carbonyl) groups of tetramethylurea (TMU). We observe crossovers in the dynamical behavior around the hydrophobic group at $T_X = 256 \pm 4$K and another one at $265 \pm 5$K related to the relative strength of water-water and water-carbonyl hydrogen bonds (HBs). For bulk water, the temperature of the apparent divergence in relaxation times is located at $T_c = 210 \pm 10$K. To better identify the effects arising from the hydrophilic carbonyl group, systems of water with a methane molecule were used as references. These findings are related to the structural and thermodynamic transitions reported for proteins in solution and may also play a role in the mechanism of cold denaturation of proteins.