Enzyme kinetics approach to assess biocatalyst inhibition and deactivation caused by [bmim][Cl] ionic liquid during cellulose hydrolysis

Can deep eutectic solvents be the best alternatives to ionic liquids and organic solvents: A perspective in enzyme catalytic reactions

As a new generation of green solvents, deep eutectic solvents (DESs) have been considered as a promising alternative to classical organic solvents and ionic liquids (ILs). DESs are normally formed by two or more components via various h-bonds interactions. Up to date, four types of DESs are found, namely, type I DESs (formed by MClx, namely FeCl₂, AlCl₃, ZnCl₂, CuCl₂ and AgCl et al., and quaternary ammonium salts); type II DESs (formed by metal chloride hydrates and quaternary ammonium salts); type III DESs (formed by choline chlorides and different kinds of HBDs) and type IV DESs (formed by salts of transition metals and urea). DESs share many advantages, such as low vapor pressure, good substrate solubility and thermal stability, with ILs, and offering a high potential to be the medium of biocatalysis reactions. In this case, this paper reviews the applications of DESs in enzymatic reactions. Lipases are the most widely used enzyme in DESs systems as their versatile applications in various reactions and robustness. Interestingly, DESs can improve the efficiency of these reactions via enhancing the substrates solubility and the activity and stability of enzymes. Therefore, the directed engineering of DESs for special reactions such as degradation of polymers in high temperature or strong acid-base conditions will be one of the future perspectives of the investigation DESs.

Enhanced activity of hyperthermostable Pyrococcus horikoshii endoglucanase in superbase ionic liquids

Objectives

Ionic liquids (ILs) that dissolve biomass are harmful to the enzymes that degrade lignocellulose. Enzyme hyperthermostability promotes a tolerance to ILs. Therefore, the limits of hyperthemophilic Pyrococcus horikoschii endoglucanase (PhEG) to tolerate 11 superbase ILs were explored.

Results

PhEG was found to be most tolerant to 1-ethyl-3-methylimidazolium acetate ([EMIM]OAc) in soluble 1% carboxymethylcellulose (CMC) and insoluble 1% Avicel substrates. At 35% concentration, this IL caused an increase in enzyme activity (up to 1.5-fold) with CMC. Several ILs were more enzyme inhibiting with insoluble Avicel than with soluble CMC. K_m increased greatly in the presence ILs, indicating significant competitive inhibition. Increased hydrophobicity of the IL cation or anion was associated with the strongest enzyme inhibition and activation. Surprisingly, PhEG activity was increased 2.0–2.5-fold by several ILs in 4% substrate. Cations exerted the main role in competitive inhibition of the enzyme as revealed by their greater binding energy to the active site.

Conclusions

These results reveal new ways to design a beneficial combination of ILs and enzymes for the hydrolysis of lignocellulose, and the strong potential of PhEG in industrial, high substrate concentrations in aqueous IL solutions.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10529-022-03268-5.

Uses of ionic liquids to obtain bioactive compounds: insights from the main international regulations for technological applications

Ionic liquids (IL) are innovative alternative solvents to recover bioactive compounds from plant-based sources to replace toxic volatile organic solvents (VOS). ILs are tailored-made solvents with chemical and thermal stabilities, nonvolatile and noninflammable. Although ILs are versatile, cost-effective, and sustainable solutions, the European Commission (EC) has no current regulation to approve extracts obtained with ILs to be applied in foods. Herein, this paper aims to assess the overview of ILs, regulamentation, applications, and its toxic effects, to be used as solvents for extract different bioactive compounds. Studies have suggested novel applications for ILs, such as 1-butyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium tetrafluoroborate and others, to obtain bioactive compounds, for instance phenolic compounds, lignans, alkaloids, carotenoids, polysaccharides, using modern approaches as ultrasound and microwave-assisted extraction. New IL methods increase the efficiency of recovering target compounds and decrease the extraction time and VOS consumption regarding the traditional techniques. Furthermore, to promote the large-scale use of IL in foods, it is essential to investigate individually the toxicity of each IL used in the extraction processes, aiming to obtain a GRAS stamp, due to the currently lack of regulamentation.

The application of green solvent in a biorefinery using lignocellulosic biomass as a feedstock

The high dependence on crude oil for energy utilization leads to a necessity of finding alternative sustainable resources. Solvents are often employed in valorizing the biomass into bioproducts and other value-added chemicals during treatment stages. Unfortunately, despite the effectiveness of conventional solvents, hindrances such as expensive solvents, unfavourable environmental ramifications, and complicated downstream separation systems often occur. Therefore, the scientific community has been actively investigating more cost-effective, environmentally friendly alternatives and possess the excellent dissolving capability for biomass processing. Generally, 'green' solvents are attractive due to their low toxicity, economic value, and biodegradability. Nonetheless, green solvents are not without disadvantages due to their complicated product recovery, recyclability, and high operational cost. This review summarizes and evaluates the recent contributions, including potential advantages, challenges, and drawbacks of green solvents, namely ionic liquids, deep eutectic solvents, water, biomass-derived solvents and carbon dioxide in transforming the lignocellulosic biomass into high-value products. Moreover, research opportunities for future developments and potential upscale implementation of green solvents are also critically discussed.

Growth Performance and Antioxidative Response of Chlorella pyrenoidesa, Dunaliella salina, and Anabaena cylindrica to Four Kinds of Ionic Liquids

Ionic liquids are widely used for lipid and pigment extractions from microalgae. It is possible that ionic liquids are discharged into environments. The evaluation of growth performance and antioxidative response of ionic liquids to microalgae is helpful to explore the stress regulation mechanism and investigate possible environmental risk. Ionic liquids induce production of reactive oxygen species (ROS) to microalgae. These oxidative stresses are possible from cations, anions, and salinity. In this study, the growth inhibitions of [BMIM]Br, [BMIM]Cl, [EMIM]Cl, and [EMIM]EtOSO₃ to Anabaena cylindrica, Chlorella pyrenoidesa, and Dunaliella salina were evaluated. It was interesting that Br^- and two kinds of cations, [BMIM] and [EMIM], had significant effects on growth inhibitions of these microalgae. IC50 values of these ionic liquids for A. cylindrica, C. pyrenoidesa, and D. salina were also estimated based on the results of growth inhibitions. It was proved that [EMIM]Cl is relatively harmless to C. pyrenoidesa and D. salina, and [EMIM]EtOSO₃ is relatively or practically harmless to C. pyrenoidesa. [BMIM]Br and [BMIM]Cl are practically harmless to A. cylindrica and C. pyrenoidesa, and relatively harmless to D. salina. More than 0.8 g/L [EMIM]EtOSO₃ led to bleaching of both A. cylindrica and D. salina at 48 h which was shown that the anion, EtOSO₃^-, had higher inhibition to A. cylindrica and D. salina than Cl^-. In addition, high concentration of ionic liquids led to reductions of chlorophyll content in these three kinds of microalgae, increase of ROS levels and malondialdehyde contents for most of the cases. High concentration of ionic liquids also increased the activities of superoxide dismutase in three kinds of microalgae. There were positive correlations between ROS levels or MDA content, and inhibitions ratios of these ionic liquids to microalgae except [EMIM]Cl to A. cylindrica. These antioxidant enzymes were beneficial for reducing the ROS induced by ionic liquids.

The effects of solid lignin on the anaerobic digestion of microcrystalline cellulose and application of smoothing splines for extended data analysis of its inhibitory effects

Lignocellulose is an abundant substrate for biogas production; however, for efficient utilization, proper pre-treatment is required to enhance the biomethane yield and hydrolysis rate significantly. Phenolic compounds from dissolved lignin, produced during alkali pre-treatment, have inhibitory effects on the anaerobic digestion; however, the possible inhibitory effects of solid lignin have not gathered enough interest. Especially, the effect of solid lignin on methanogenesis remains a knowledge gap. In this study, kraft lignin was used as a model solid lignin substrate for its co-digestion with microcrystalline cellulose. A new approach of modelling biomethane production curves using smoothing splines was developed to describe the long-term inhibitory effects of solid lignin on hydrolysis and methanogenesis. The method gives possibility to describe long-term inhibitory effects by using batch instead of continuous test data. Results revealed that kraft lignin showed mild inhibitory effects on methanogens. However lignin impact combined with volatile fatty accumulation can prolong hydrolysis and reactor recovery start-up by 47.3% and 75.3%, respectively. For small dosages of solid lignin adaptation of methanogens is possible.

Proteins in Ionic Liquids: Reactions, Applications, and Futures

Biopolymer processing and handling is greatly facilitated by the use of ionic liquids, given the increased solubility, and in some cases, structural stability imparted to these molecules. Focussing on proteins, we highlight here not just the key drivers behind protein-ionic liquid interactions that facilitate these functionalities, but address relevant current and potential applications of protein-ionic liquid interactions, including areas of future interest.

A perspective on galactose-based fermentative hydrogen production from macroalgal biomass: Trends and opportunities

This review analyses the relevant studies which focused on hydrogen synthesis by dark fermentation of galactose from macroalgal biomass by discussing the inoculum-related pretreatments, batch fermentation and inhibition, continuous fermentation systems, bioreactor designs for continuous operation and ionic liquid-assisted catalysis. The potential for process development is also revisited and the challenges towards suppressing glucose dominance over a galactose-based hydrogen production system are presented. The key challenges in the pretreatment process aiming to achieve a maximum recovery of upgradable (fermentable) sugars from the hydrolysates and promoting the concomitant detoxification of the hydrolysates have also been highlighted. The research avenues for bioprocess intensification connected to enhance selective sugar recovery and effective detoxification constitute the critical steps to develop future red macroalgae-derived galactose-based robust biohydrogen production system.

The removal of mercury ion pollution by using Fe3O4-nanocellulose: Synthesis, characterizations and DFT studies

In this study, we have attempted to extract cellulose from Cystoseria myricaas algae. Nanocellulose, Fe₃O₄ and Fe3O4-nanocellulose compounds are synthesized by acid hydrolysis and co-precipitation as well as sol-gel methods The synthesized compounds are characterized by x-ray diffraction, transmission electron microscopy, particle size distribution (PSD), scanning electron microscopy (SEM),energy dispersive x-ray spectroscopy, vibrating sample magnetometer and Fourier transform infrared spectroscopy. The Hg (II) uptake on Fe3O4-nanocellulose is investigated by 14 isotherm models, 12 kinetic models, adsorption activation energy as well as thermodynamic of adsorption. The polymers of algae and the interactions between Hg (II) and cellulose are investigated by density functional theory (DFT) in various conditions. The results of both simulations show a good agreement with experimental data.