Hydrophobic pattern of alkylated ureas markedly affects water rotation and hydrogen bond dynamics in aqueous solution.

Bogdan A Marekha,Johannes Hunger

doi:10.1039/c9cp04108g

Abstract

Alkylated ureas are frequently used amphiphiles to mediate biomolecule water interactions, yet their hydrophobic substitution pattern critically affects their function. These differences can be traced back to their hydration, which is poorly understood. Here, we investigate subtle effects of the hydrophobic pattern of ureas on hydration dynamics using a combination of linear and non-linear infrared spectroscopies on the OD stretching vibration of HDO. Isomeric 1,3-dimethylurea (1,3-DMU), 1,1-dimethylurea (1,1-DMU) and 1-ethylurea (1-EU) exhibit very similar and rather weak modulation of the water hydrogen-bond strength distribution. Yet, only 1,3-DMU and 1,1-DMU enhance the hydrogen-bond heterogeneity and slow-down its fluctuation dynamics. In turn, rotational dynamics of water molecules, which is dominated by hydrogen bond switches, is significantly impeded in the presence of 1,3-DMU and only weakly by 1,1-DMU and 1-EU. These marked differences can be explained by both excluded volume effects in hydration and self-aggregation, which may be the key to their biotechnological function.

Highlights

The interaction of hydrophobic moieties is largely mediated by the solvent water[1] and is arguably the most abundant origin for assembly of molecules in both biology and technology
Force-field molecular dynamics (MD) simulations have suggested that shorter residence times of the water molecules in the vicinity of the methyl groups of 1,1-DMU and their lower hydration number are responsible for the very limited retardation of water dynamics, as measured with dielectric relaxation (DR) spectroscopy.[23]
Our results demonstrate that the substitution pattern of hydrophobic fragments in RUs is decisive for solute hydration

Summary

Introduction

The interaction of hydrophobic moieties is largely mediated by the solvent water[1] and is arguably the most abundant origin for assembly of molecules in both biology and technology.

Results

Conclusion