Chiral Deep Eutectic Solvents: Hydrogen-Bond Characterization, Physical Properties, and Biomass Dissolution Performance

This study examines the effect of chiral centers on the physicochemical properties and solvation behavior of deep eutectic solvents (DESs) prepared from chiral or racemic acids and standard hydrogen-bond acceptors (HBAs). Circular dichroism spectroscopy, nuclear magnetic resonance spectroscopy, and Fourier transform infrared spectroscopy analyses confirmed retention of hydrogen-bond donors (HBDs) chirality and revealed chirality-dependent hydrogen-bonding networks. DESs showed acidic pH (1.81–2.68), high densities (1.13392–1.35126 g·cm –3 ) and viscosities (16.940–1340.900 mPa·s) dependent on HBA/HBD type, ratio and chirality, with D-type DESs generally exhibiting higher density and viscosity. Microcrystalline cellulose (MCC) solubility (1.8–59.5 wt %) generally increases with solvent H-bond donor ability and polarity. d -glucose in aqueous DES solutions exhibited pronounced chirality-dependent solvation with ethylene glycol: l -malic acid ( n: n = 4:1) displayed higher limiting apparent molar volumes ( V ϕ 0 = 115.39 to 118.38 × 10 –6 m 3 ·mol –1 ) and negative concentration coefficients ( S v = −10.34 to −13.76 × 10 –6 m 3 ·mol –2 ·kg), whereas ethylene glycol: d -malic acid ( n: n = 4:1) had lower V ϕ 0 (90.58–103.39 × 10 –6 m 3 ·mol –1 ) and positive S v (15.58–49.45 × 10 –6 m 3 ·mol –2 ·kg) reflecting weaker, less ordered solvation. This correlates with their MCC solubilities, with 4EG:L-Mac and 4EG:D-Mac achieving 59.5 and 44.7 wt %, respectively. Overall, DES properties and solute–solvent interactions are governed by hydrogen bonding and stereochemistry, informing chiral solvent design for biomass processing.