Modeling Alcohol Dehydrogenase Catalysis in Deep Eutectic Solvent/Water Mixtures

Abstract

The use of oxidoreductases (EC1) in non‐conventional reaction media has been increasingly explored. In particular, deep eutectic solvents (DESs) have emerged as a novel class of solvents. Herein, an in‐depth study of bioreduction with an alcohol dehydrogenase (ADH) in the DES glyceline is presented. The activity and stability of ADH in mixtures of glyceline/water with varying water contents were measured. Furthermore, the thermodynamic water activity and viscosity of mixtures of glyceline/water have been determined. For a better understanding of the observations, molecular dynamics simulations were performed to quantify the molecular flexibility, hydration layer, and intraprotein hydrogen bonds of ADH. The behavior of the enzyme in DESs follows the classic dependence of water activity (aW) in non‐conventional media. At low aW values (<0.2), ADH does not show any activity; at higher aW values, the activity was still lower than that in pure water due to the high viscosities of the DES. These findings could be further explained by increased enzyme flexibility with increasing water content.

Convergent Cascade Catalyzed by Monooxygenase–Alcohol Dehydrogenase Fusion Applied in Organic Media

“…To use nonaqueous media, that is, solvent‐free systems or organic solvents for redox catalysis, cofactor regeneration is still a challenge to be solved. During the 1980s and 1990s, extensive studies on the use of oxidoreductases under water‐deficient conditions were reported by the research groups of Klibanov and Adlercreutz, It has been shown that substrate‐coupled cofactor regeneration is possible in low‐water media, whereas enzyme‐coupled cofactor regeneration is still not trivial because the nicotinamide cofactor (oxidized and reduced forms) needs to diffuse from one active site to the second one during the course of the reaction.…”

The rise of continuous flow biocatalysis – fundamentals, very recent developments and future perspectives

“…To overcome these issues, the subfield of enzyme catalysis in organic solvents was constituted early and eventually. [238][239][240][241][242] It was 1980s-90s when the use of enzymes in non-aqueous media was documented by pioneers of the field: Klibanov, 243 Halling, 244 Mattiasson and Adlercreutz. 245 Furthermore, it was at the beginning of the 2000s, when the first papers were published on biocatalytic reactions in ionic liquids (ILs) (see also above, chapter 4.2.2).…”

“…248 The topic of 'biocatalysis in non-conventional media' (BNCM) was recently augmented by the field of using deep eutectic solvents (DES) as efficient solvents and reaction (co) media in biocatalysis. 240,[249][250][251][252][253][254] DESs gained much attention in the last years being neoteric solvents which special benefits, such as an easy and fast preparation procedure and several tunable properties. Eutectic mixtures are obtained mixing Lewis or Brønsted acids and bases containing a variety of anionic and/or cationic species.…”

“…Eutectic mixtures are obtained mixing Lewis or Brønsted acids and bases containing a variety of anionic and/or cationic species. [255][256][257] However, the final solvent has a lower intrinsic toxicity compared to ionic liquids, making them to promising substitutes. 258 Its main disadvantage is the high viscosity (which depends on the starting materials) being a problem for the scale-up of the process, but it can be easily overcome by mixing them with other (co)solvents.…”

“…up to 20% v/v) has shown a significant decrease in viscosity. 256,[259][260][261] All these properties make DESs particularly suitable for use in continuous flow chemistry, and their tailor-made properties make multi-stage continuous flow processes and cascade reactions with them ideal.…”