Stability of cellulase in ionic liquids: correlations between enzyme activity and COSMO-RS descriptors

Jacob Nedergaard Pedersen,Zheng Guo,Bianca Pérez

doi:10.1038/s41598-019-53523-5

Jacob Nedergaard Pedersen, Zheng Guo + Show 1 more

Open Access

https://doi.org/10.1038/s41598-019-53523-5

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Abstract

Ionic liquids (ILs) are effective in pretreating cellulose for enhanced enzymatic saccharification, however ILs can inactivate cellulases. To guide the selection of ILs, the activity of cellulase was correlated with COSMO-RS calculations and descriptors of ILs including hydrogen bond (H-bond) basicity/acidity, polarity and ion size. Trends were deduced using an anion-series and a cation-series of ionic liquids in aqueous solutions. The activity in the cation-series was best correlated with the size of varied cations, whereas the activity in the anion-series showed a pronounced correlation to H-bond basicity and polarity of different anions. COSMO-RS was further used to predict the solubility of cellulose in ILs, which was correlated with cellulase activity on IL-pretreated cellulose. The best correlations were found between the enzyme activity in the anion-series ILs and the logarithmic activity coefficients, the H-bond energy, H-bond basicity and polarizability, underlining that the anion plays a crucial role in cellulose dissolution.

Highlights

Ionic liquids (ILs) are effective in pretreating cellulose for enhanced enzymatic saccharification, ILs can inactivate cellulases
COSMO-RS was used to predict the logarithmic activity coefficients, ln(γ) (Fig. 1), of the midmonomer part of cellotriose (Supplementary Fig. S1) at infinite dilution using a combination of 23 anions and 21 cations (Supplementary Tables S1 and S2) totaling 483 ILs
Anions based on carboxylates, [Cl] and dialkyl phosphates combined with cations such as [HMGua], pyrrolidium-based and [TBA] were predicted to be good ILs for cellulose dissolution due to their highly negative predicted logarithmic activity coefficients

Summary

Introduction

Ionic liquids (ILs) are effective in pretreating cellulose for enhanced enzymatic saccharification, ILs can inactivate cellulases. A pretreatment of the biomass is needed to increase the saccharification yields during enzymatic hydrolysis One such pretreatment method is the use of ionic liquids (ILs), which have attracted a great deal of interest, due to their ability to solubilize cellulose and their perception as green designer solvents[3,4,5,6,7]. As the combinations of possible ILs with different cations and anions are numerous, a rapid and effective screening method is needed to find those ILs that have good cellulose dissolving capabilities but only to a lesser extent inactivate the cellulases. Liu et al.[19] used COSMO-RS to screen the combination of 17 cations and 21 anions for their ability to dissolve cellulose using the logarithmic activity coefficients as an indirect measure of cellulose solubility. No reports exist with respect to the correlation of cellulase activity to the solvent property/descriptors of IL-mediated systems

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