Chemical stability and catalytic activity of redox enzymes in NADES

Natural Deep Eutectic Solvents (NADESs) represent a new generation of biocompatible solvents, formed by eutectic mixtures of two or more hydrogen bond donor (HBD) and hydrogen bond acceptor (HBA) compounds of natural origin, with a lower melting point compared to that of pure components.¹ This feature is due to the strong ability of association between the components of the mixture through hydrogen bonds, that leads to a supramolecular assembly, configured as a new entity with peculiar properties. The ease of preparation, sustainability, low cost and nontoxicity of NADESs have allowed these solvents to be investigated in many applications. Recently, good results have been obtained with NADES as solvents in biocatalytic reactions, where they can improve substrate supply, conversion, and enzymatic stability.²

In this communication we describe the enzymatic activity of two oxidoreductases, the Horse Liver Alcohol Dehydrogenase (HLADH) and the Enoate Reductase from Thermus scotoductus (TsER) in buffer solution and in mixtures choline-based NADES/buffer. In particular, we have studied the lactonization of 3-methyl-1,5-pentanediol into 4-methyl-δ-valerolactone and the ketoisophorone bioreduction into levodione, evaluating the reaction rate, enantioselectivity and stability of the two enzymes. The stability of the nicotinamide cofactors NADH and NADPH was also evaluated.

1. Liu, Y.; Friesen, J. B.; McAlpine, J. B.; Lankin, D. C.; Chen, S.-N.; Pauli, G. F. Natural Deep Eutectic Solvents: Properties, applications, and perspectives. Nat. Prod. 2018, 81, 679-690.
2. Pätzold, M.; Siebenhaller, S.; Kara, S.; Liese, A.; Syldatk, C.; Holtmann, D. Deep Eutectic Solvents as efficient solvents in biocatalysis. Trends Biotechnol. 2019, 37, 943-959.