# Designing Ternary Chiral DES to Enhance Enantioselectivity

## TL;DR

This paper explores how adding a third component to chiral solvents can improve their ability to distinguish between mirror-image molecules.

## Contribution

The study introduces ternary chiral deep eutectic solvents with enhanced enantioselectivity compared to binary versions.

## Key findings

- Ternary DES with (R)-MHPP showed higher enantioselectivity than binary DES.
- TOABr:TBABr:(R)-EM mixtures remained liquid over a wider mole fraction range.
- Circularly polarized luminescence confirmed improved enantioselectivity in ternary DES.

## Abstract

Deep eutectic solvents (DES) are mixtures of two or three
components
that have a freezing point lower than that of the components. The
properties of DES are tunable through the choice and ratio of the
components. Three-component or ternary DES increase the flexibility
to control the properties compared to binary DES. Two chiral ternary
DES composed of tetraoctylammonium bromide (TOABr), tetrabutylammonium
bromide (TBABr), (R)-ethyl mandelate ((R)-EM) or methyl-(2R)-2-hydroxy-3-phenylpropanoate
((R)-MHPP) were studied. Solid–liquid equilibrium
measurements showed that only TOABr:TBABr:(R)-MHPP
with 0.66 mole fraction of (R)-MHPP were liquid at
room temperature, but TOABr:TBABr:(R)-EM mixtures
were liquid over a wider range, 0.6–0.8, mole fraction of (R)-EM. The density, viscosity, conductivity, and polarity
were measured for three TOABr:TBABr:(R)-MHPP and
six TOABr:TBABr:(R)-EM mixtures and compared to the
TBABr:(R)-MHPP and TBABr:(R)-EM.
The enantioselectivity of the ternary DES was measured using circularly
polarized luminescence (CPL) spectroscopic measurements of a luminescent
lanthanide complex dissolved in the solvents. The ternary DES, TOABr:TBABr:(R)-MHPP and TOABr:TBABr:(R)-EM, exhibit
higher enantioselectivity than the corresponding binary DES, TBABr:(R)-MHPP, TBABr:(R)-EM, and TOABr:(R)-EM.