The influence of chirality on the structure of a tartaric acid-choline chloride deep eutectic solvent

Abstract

The wide range of properties, relative ease and low cost of using Deep Eutectic Solvents garners them interest in an ever expanding range of applications. Among common DES components many are naturally occurring chiral molecules. Here we present the liquid structure of either single enantiomeric or racemic tartaric acid with choline chloride at a molar ratio of 2 choline chloride to 1 tartaric acid, as well as the influence of low amounts of added water (2:1:2) from neutron scattering data with H/D isotropic substitution, refined using empirical potential structure refinement. We show that the overall structure remains the same between the different enatiomeric compositions, with small differences in interactions only occurring between the tartaric acid molecules. The overall structure is also robust towards hydration, similar to what has been found in other DES. We also compare our structures to the structures of DES comprising of similar carboxylic acids (1:1 choline chloride - malic acid, 1:1 choline chloride - oxalic acid), finding overall similar dominant interactions, with differences that may be attributable to the number of available hydrogen bonding sites and steric effects.