Liquid structure and dynamics in the choline acetate:urea 1:2 deep eutectic solvent.

Alessandro Triolo,Martin Brehm,Fabrizio Lo Celso,Olga Russina,Valerio Di Lisio,Andrea Martinelli,Philip Chater,Andrea Mele,Maria Enrica Di Pietro

doi:10.1063/5.0054048

Abstract

We report on the thermodynamic, structural, and dynamic properties of a recently proposed deep eutectic solvent, formed by choline acetate (ChAc) and urea (U) at the stoichiometric ratio 1:2, hereinafter indicated as ChAc:U. Although the crystalline phase melts at 36-38°C depending on the heating rate, ChAc:U can be easily supercooled at sub-ambient conditions, thus maintaining at the liquid state, with a glass-liquid transition at about -50°C. Synchrotron high energy x-ray scattering experiments provide the experimental data for supporting a reverse Monte Carlo analysis to extract structural information at the atomistic level. This exploration of the liquid structure of ChAc:U reveals the major role played by hydrogen bonding in determining interspecies correlations: both acetate and urea are strong hydrogen bond acceptor sites, while both choline hydroxyl and urea act as HB donors. All ChAc:U moieties are involved in mutual interactions, with acetate and urea strongly interacting through hydrogen bonding, while choline being mostly involved in van der Waals mediated interactions. Such a structural situation is mirrored by the dynamic evidences obtained by means of 1H nuclear magnetic resonance techniques, which show how urea and acetate species experience higher translational activation energy than choline, fingerprinting their stronger commitments into the extended hydrogen bonding network established in ChAc:U.

Highlights

In the last decade large interest has been growing around deep eutectic solvents (DES)[1,2] and their applications in several fields[3,4,5,6,7,8]
We determined the liquid structure of acetaline at ambient temperature, without incurring into sample crystallization during the experiment time duration
Hydrogen bonding plays a major role in determining structure in liquid acetaline

Summary

Introduction

In the last decade large interest has been growing around deep eutectic solvents (DES)[1,2] and their applications in several fields[3,4,5,6,7,8]. We present a detailed experimental and computational study of structural and dynamic properties of liquid acetaline, a DES composed by CAc and urea at 1:2 molar ratio.

Results

Conclusion