Can Deep Eutectic Solvents Sustain Oxygen-Dependent Bioprocesses?-Measurements of Oxygen Transfer Rates

The oxygen transfer rate (OTR) of dioxygen to solutions describing the transport of oxygen gas from the gaseous phase into the liquid phase of a reaction system over a given period is an important measure for biotechnological applications. The OTRs have already been described for aqueous systems and also recently for organic and nonconventional media, whereas the OTRs of a novel class of solvents, deep eutectic solvents (DESs), have not been determined yet. In this letter, we report for the first time on the OTRs of diverse DESs such as choline chloride:ethylene glycol (DES1, ChCl:EG), ethylammonium chloride:ethylene glycol (DES2, EAC:EG), choline chloride:glycerol (DES3, ChCl:GIy), lidocaine:oleic acid (DES4, LID:OA), and choline chloride:levulinic acid (DES5, ChCl:LA) while using water as a reference. In addition, we evaluated the effects of different molar ratios of ChCl to Gly (1:2, 1:4, and 1:9) for DES3 and addition of external water (up to 30% (v/v)) to DES1 (ChCl:EG (1:2)) on dynamic viscosity (eta), dynamic water activity (a(w)), and volumetric mass transfer coefficient (k(L)(a)). We applied the dynamic method for OTR measurements and found up to 11-fold lower k(L)a values for DES1 (Cha:EG (1:2)) and 6-fold lower k(L)a values for DES2 (EAC:EG (1:1.5)) than in water at 25 degrees C. With the addition of water at 30% (v/v) to DES1 (ChCl:EG (1:2)), the k(L)a value increased 3 times at 25 degrees C. While changing the molar ratio of Gly for DES3 from 1:2 to 1:9, the increase in viscosity was found to be 64%. Furthermore, we investigated the effect temperature (3.0 and 45 degrees C) has on the k(L)(a) values for those DESs and DES-water mixtures.

Automated summary

This study reported the oxygen transfer rates (OTR) of various deep eutectic solvents (DESs) and evaluated their effects on viscosity, water activity, and volumetric mass transfer coefficient. Results showed that the k(L)a values of different DESs were lower compared to water. Additionally, the addition of external water and adjustment of DES composition can impact the k(L)a values.