Insights on the laccase extraction and activity in ionic-liquid-based aqueous biphasic systems

Condensable Gases Capture with Ionic Liquids

Condensable gases are the sum of condensable and volatile steam or organic compounds, including water vapor, which are discharged into the atmosphere in gaseous form at atmospheric pressure and room temperature. Condensable toxic and harmful gases emitted from petrochemical, chemical, packaging and printing, industrial coatings, and mineral mining activities seriously pollute the atmospheric environment and endanger human health. Meanwhile, these gases are necessary chemical raw materials; therefore, developing green and efficient capture technology is significant for efficiently utilizing condensed gas resources. To overcome the problems of pollution and corrosion existing in traditional organic solvent and alkali absorption methods, ionic liquids (ILs), known as "liquid molecular sieves", have received unprecedented attention thanks to their excellent separation and regeneration performance and have gradually become green solvents used by scholars to replace traditional absorbents. This work reviews the research progress of ILs in separating condensate gas. As the basis of chemical engineering, this review first provides a detailed discussion of the origin of predictive molecular thermodynamics and its broad application in theory and industry. Afterward, this review focuses on the latest research results of ILs in the capture of several important typical condensable gases, including water vapor, aromatic VOCs (i.e., BTEX), chlorinated VOC, fluorinated refrigerant gas, low-carbon alcohols, ketones, ethers, ester vapors, etc. Using pure IL, mixed ILs, and IL + organic solvent mixtures as absorbents also briefly expanded the related reports of porous materials loaded with an IL as adsorbents. Finally, future development and research directions in this exciting field are remarked.

New liquid supports in the development of integrated platforms for the reuse of oxidative enzymes and polydopamine production

Polydopamine (PDA), a bioinspired polymer from mussel adhesive proteins, has attracted impressive attention as a novel coating for (nano) materials with an adequate conformal layer and adjustable thickness. Currently, PDA is obtained from dopamine chemical oxidation under alkaline conditions, limiting its use in materials sensible to alkaline environments. Envisaging a widespread use of PDA, the polymerization of dopamine by enzymatic catalysis allows the dopamine polymerization in a large range of pHs, overcoming thus the limitations of conventional chemical oxidation. Moreover, the conventional method of polymerization is a time-consuming process and produces PDA films with poor stability, which restricts its applications. On the other hand, the main bottleneck of enzyme-based biocatalytic processes is the high cost of the single use of the enzyme. In this work, laccase was used to catalyse dopamine polymerization. To improve its performance, a liquid support for integrating the laccase and its reuse together with the PDA production and recovery was developed using aqueous biphasic systems (ABS). Firstly, dopamine polymerization by laccase was optimized in terms of pH, temperature and initial dopamine concentration. It was demonstrated that the highest enzymatic polymerization of dopamine was achieved at pH 5.5, 30°C and 2 mg ml−1 of dopamine. Then, ABS composed of polymers, salts and ionic liquids were evaluated to optimize the laccase confinement in one phase while PDA is recovered in the opposite phase. The most promising ABS allowing the separation of laccase from the reaction product is composed of polypropylene glycol (400 g mol−1) and K2HPO4. The polymerization of dopamine in ABS leads to a remarkable improvement of polymerization of 3.9-fold in comparison to the conventional chemical PDA polymerization. The phase containing the confined laccase was reused for four consecutive reaction cycles, with a relative polymerization of 68.9% in the last cycle. The results of this work proved that ABS are a promising approach to create a liquid support for enzyme reuse allowing the process intensification efforts. The use of biocatalysts in ABS emerges as sustainable and alternative platforms from environmental and techno-economic points of view.

An Overview on the Recent Advances in Alternative Solvents as Stabilizers of Proteins and Enzymes

Currently, the use of alternative solvents is increasing, namely ionic liquids (ILs) and deep eutectic solvents (DESs) in diverse fields of knowledge, such as biochemistry, chemistry, chemical engineering, biotechnology and biomedicine. Particularly, when compared to traditional solvents, these alternative solvents have great importance for biomolecules due to the enhanced solubility, structure stability and the biological activity of biomolecules, such as protein and enzymes. Thus, in this review article, the recent developments and efforts on the technological developments carried out with ILs and DESs for the stabilization and activation of proteins and enzymes are provided. The most studied IL- and DES-based formulations for proteins and enzymes are discussed and the molecular mechanisms and interactions related to the increased stability promoted by these alternative solvents are disclosed, while emphasizing their main advantages.

Current Strategies for Real-Time Enzyme Activation

Enzyme activation is a powerful means of achieving biotransformation function, aiming to intensify the reaction processes with a higher yield of product in a short time, and can be exploited for diverse applications. However, conventional activation strategies such as genetic engineering and chemical modification are generally irreversible for enzyme activity, and they also have many limitations, including complex processes and unpredictable results. Recently, near-infrared (NIR), alternating magnetic field (AMF), microwave and ultrasound irradiation, as real-time and precise activation strategies for enzyme analysis, can address many limitations due to their deep penetrability, sustainability, low invasiveness, and sustainability and have been applied in many fields, such as biomedical and industrial applications and chemical synthesis. These spatiotemporal and controllable activation strategies can transfer light, electromagnetic, or ultrasound energy to enzymes, leading to favorable conformational changes and improving the thermal stability, stereoselectivity, and kinetics of enzymes. Furthermore, the different mechanisms of activation strategies have determined the type of applicable enzymes and manipulated protocol designs that either immobilize enzymes on nanomaterials responsive to light or magnetic fields or directly influence enzymatic properties. To employ these effects to finely and efficiently activate enzyme activity, the physicochemical features of nanomaterials and parameters, including the frequency and intensity of activation methods, must be optimized. Therefore, this review offers a comprehensive overview related to emerging technologies for achieving real-time enzyme activation and summarizes their characteristics and advanced applications.

Enhanced Enzyme Reuse through the Bioconjugation of L-Asparaginase and Silica-Based Supported Ionic Liquid-like Phase Materials

L-asparaginase (ASNase) is an amidohydrolase that can be used as a biopharmaceutical, as an agent for acrylamide reduction, and as an active molecule for L-asparagine detection. However, its free form displays some limitations, such as the enzyme’s single use and low stability. Hence, immobilization is one of the most effective tools for enzyme recovery and reuse. Silica is a promising material due to its low-cost, biological compatibility, and tunable physicochemical characteristics if properly functionalized. Ionic liquids (ILs) are designer compounds that allow the tailoring of their physicochemical properties for a given task. If properly designed, bioconjugates combine the features of the selected ILs with those of the support used, enabling the simple recovery and reuse of the enzyme. In this work, silica-based supported ionic liquid-like phase (SSILLP) materials with quaternary ammoniums and chloride as the counterion were studied as novel supports for ASNase immobilization since it has been reported that ammonium ILs have beneficial effects on enzyme stability. SSILLP materials were characterized by elemental analysis and zeta potential. The immobilization process was studied and the pH effect, enzyme/support ratio, and contact time were optimized regarding the ASNase enzymatic activity. ASNase–SSILLP bioconjugates were characterized by ATR-FTIR. The bioconjugates displayed promising potential since [Si][N3444]Cl, [Si][N3666]Cl, and [Si][N3888]Cl recovered more than 92% of the initial ASNase activity under the optimized immobilization conditions (pH 8, 6 × 10−3 mg of ASNase per mg of SSILLP material, and 60 min). The ASNase–SSILLP bioconjugates showed more enhanced enzyme reuse than reported for other materials and immobilization methods, allowing five cycles of reaction while keeping more than 75% of the initial immobilized ASNase activity. According to molecular docking studies, the main interactions established between ASNase and SSILLP materials correspond to hydrophobic interactions. Overall, it is here demonstrated that SSILLP materials are efficient supports for ASNase, paving the way for their use in the pharmaceutical and food industries.

Evaluation of Aqueous Biphasic Electrophoresis System Based on Halide-Free Ionic Liquids for Direct Recovery of Keratinase

Aqueous biphasic electrophoresis system (ABES) incorporates electric fields into the biphasic system to separate the target biomolecules from crude feedstock. Ionic liquid (IL) is regarded as an excellent candidate as the phase-forming components for ABES because of the great electrical conductivity, which can promote the electromigration of biomolecules in ABES, and thereby enhances the separation efficiency of the target biomolecules from crude feedstock. The application of electric fields to the conventional biphasic system expedites the phase settling time of the biphasic system, which eases the subsequent scaling-up steps and reduces the overall processing time of the recovery process. Alkyl sulphate-based IL is a green and economical halide-free surfactant when compared to the other halide-containing IL. The feasibility of halide-free IL-based ABES to recover Kytococcus sedentarius TWHK01 keratinase was studied. Optimum partition coefficient (Ke = 7.53 ± 0.35) and yield (YT = 80.36% ± 0.71) were recorded with IL-ABES comprised of 15.0% (w/w) [EMIM][ESO4], 20.0% (w/w) sodium carbonate and 15% (w/w) crude feedstock. Selectivity (S) of 5.75 ± 0.27 was obtained with the IL-ABES operated at operation time of 5 min with 10 V voltage supplied. Halide-free IL is proven to be a potential phase-forming component of IL-ABES for large-scale recovery of keratinase.

Sustainable liquid supports for laccase immobilization and reuse: Degradation of dyes in aqueous biphasic systems

Novel liquid supports for enzyme immobilization and reuse based on aqueous biphasic systems (ABS) constituted by cholinium-based ionic liquids (ILs) and polymers for the degradation of dyes are here proposed. The biocatalytic reaction for dye decolorization using laccase occured in the biphasic medium, with the enzyme being "supported" in the IL-rich phase and the dye and degradation products being enriched in the polymer-rich phase. An initial screening of the laccase activity in aqueous solutions of ABS constituents, namely cholinium dihydrogen citrate ([Ch][DHC]), cholinium dihydrogen phosphate ([Ch][DHP]), cholinium acetate ([Ch][Acet]), polypropylene glycol 400 (PPG 400), polyethylene glycol 400 (PEG 400) and K₂ HPO₄ was carried out. Compared to the buffered control, a relative laccase activity of up to 170%, 257%, and 530% was observed with PEG 400, [Ch][DHP], and [Ch][DHC], respectively. These ABS constituents were then investigated for the in situ enzymatic biodegradation of the Remazol Brilliant Blue R (RBBR) dye. At the optimized conditions, the ABS constituted by PPG 400 at 46 wt% and [Ch][DHC] at 16 wt% leads to the complete degradation of the RBBR dye, further maintaining the enzyme activity. This ABS also allows an easy immobilization, recovery, and reuse of the biocatalyst for six consecutive reaction cycles, achieving a degradation yield of the dye of 96% in the last cycle. In summary, if properly designed, high enzymatic activities and reaction yields are obtained with ABS as liquid supports, while simultaneously overcoming the safety and environmental concerns of conventional organic solvents used in liquid-liquid heterogeneous reactions, thus representing more sustainable biocatalytic processes.

Effects of Ionic Liquids on Metalloproteins

In the past decade, innovative protein therapies and bio-similar industries have grown rapidly. Additionally, ionic liquids (ILs) have been an area of great interest and rapid development in industrial processes over a similar timeline. Therefore, there is a pressing need to understand the structure and function of proteins in novel environments with ILs. Understanding the short-term and long-term stability of protein molecules in IL formulations will be key to using ILs for protein technologies. Similarly, ILs have been investigated as part of therapeutic delivery systems and implicated in numerous studies in which ILs impact the activity and/or stability of protein molecules. Notably, many of the proteins used in industrial applications are involved in redox chemistry, and thus often contain metal ions or metal-associated cofactors. In this review article, we focus on the current understanding of protein structure-function relationship in the presence of ILs, specifically focusing on the effect of ILs on metal containing proteins.