Rational Design of Hydrophilic Deep Eutectic Solvents to Outperform Oxidoreductase Activity in Aqueous Media

Outperforming biocatalysis through nonconventional media opens new avenues in synthesis, from process intensification to industrial integration. While hydrophobic deep eutectic solvents (DESs) based on fatty acids have emerged as a promising landscape for oxidoreductases, the potential of hydrophilic DESs to rival or surpass aqueous systems remains largely underexplored. Building on findings that glycerol aids alcohol dehydrogenase (ADH) catalysis and choline chloride hinders it, this study designs enzyme-friendly glycerol-based DESs using betaine and sarcosine at varied ratios and water contents. Consistently, a higher glycerol fraction (mol:mol, 1:8) contributed to a stronger stabilizing effect on ADHs, and betaine emerged as the most favorable component, followed by sarcosine and choline chloride. Enzyme thermostability improved in Bet-Gly and Sar-Gly, though activity was lower in all hydrophilic DESs; Bet-Gly (1:8) with 80% buffer showed the best performance. Encouragingly, the enzyme's specific activity for the cyclohexanone reduction outperformed that observed in the pure buffer, and the optimal eutectic conditions of Bet-Gly (1:8) and Sar-Gly (1:8) with 60 vol.% buffer outperformed the pure buffer system in cinnamaldehyde reduction (a more industrially-sound reaction). This study advances DES research and aids in the design of DESs for redox biocatalysis in hydrophilic media.