Application of Ionic Liquids in Biotechnology

Bioseparation processes are a relevant part of modern biotechnology, particularly regarding the development of efficient and biocompatible methods for the separation and purification of added-value biologically active compounds. In this field, ionic liquids (ILs) have been proposed, either in liquid–liquid extractions, in which non-water miscible ILs or aqueous biphasic systems (ABS) formed by ILs can be used, or in solid–liquid extractions, in which they are covalently attached to create supported IL phases (SILPs). Aprotic ILs possess unique properties, such as non-volatility and designability, which are valuable in their use in bioseparation processes. In this chapter, we summarize and discuss bioseparation processes based on ILs, including both liquid–liquid and solid–liquid extractions, applied to amino acids and proteins. The most recent and remarkable advances in this area are emphasized, and improvements brought by the use of ILs properly discussed. New insights and envisaged directions with IL-based bioseparation processes are suggested.

Following the appearance of ionic liquids (ILs) and deep eutectic solvents (DESs), natural deep eutectic solvents (NADESs) have emerged as a new type of truly green solvents with many excellent advantages such as cheapness, sustainability, biocompatibility, environmental friendliness, and, in particular, remarkable solubilizing power and outstanding designability. Although only at an early stage, research on NADESs has started to blossom with exponential growth, showing attractive and promising potentials for applications in various areas. In this chapter we focus on an introduction to what is currently known about NADESs: their formation, structure and roles in nature, their physical/chemical properties, their toxicity and biodegradability, and, more importantly, their beneficial applications in biotechnology.

Ionic liquids (ILs), a potentially attractive “green,” recyclable alternative to environmentally harmful volatile organic compounds, have been increasingly exploited as solvents and/or cosolvents and/or reagents in a wide range of applications, including pretreatment of lignocellulosic biomass for further processing. The enzymatic delignification of biomass to degrade lignin, a complex aromatic polymer, has received much attention as an environmentally friendly process for clean separation of biopolymers including cellulose and lignin. For this purpose, enzymes are generally isolated from naturally occurring fungi or genetically engineered fungi and used in an aqueous medium. However, enzymatic delignification has been found to be very slow in these conditions, sometimes taking several months for completion. In this chapter, we highlight an environmentally friendly and efficient approach for enzymatic delignification of lignocellulosic biomass using room temperature ionic liquids (ILs) as (co)solvents or/and pretreatment agents. The method comprises pretreatment of lignocellulosic biomass in IL-aqueous systems before enzymatic delignification, with the aim of overcoming the low delignification efficiency associated with low enzyme accessibility to the solid substrate and low substrate and product solubilities in aqueous systems. We believe the processes described here can play an important role in the conversion of lignocellulosic biomass—the most abundant renewable biomaterial in the world—to biomaterials, biopolymers, biofuels, bioplastics, and hydrocarbons.

The use of whole-cell biocatalysis in ionic liquid (IL)-containing systems has attracted increasing attention in recent years. Compared to bioreactions catalyzed by isolated enzymes, the major advantage of using whole cells in biocatalytic processes is that the cells provide a natural intracellular environment for the enzymes to function with in situ cofactor regeneration. To date, the applications of whole-cell biocatalysis in IL-containing systems have focused on the production of valuable compounds, mainly through reduction, oxidation, hydrolysis, and transesterification reactions. The interaction mechanisms between the ILs and biocatalysts in whole-cell biocatalysis offer the possibility to effectively integrate ILs with biotransformation. This chapter discusses these interaction mechanisms between ILs and whole-cell catalysts. In addition, examples of whole-cell catalyzed reactions with ILs will also be discussed.

Biopolymer-based composite materials have many potential applications in biomedical, pharmaceutical, environmental, biocatalytic, and bioelectronic fields, owing to their inherent biocompatibility and biodegradability. When used as solvents, ionic liquids can be used to fabricate biopolymers such as polysaccharides and proteins into various forms, including molded shapes, films, fibers, and beads. This article summarizes the processes for preparing biopolymer-based composite materials using ionic liquids. The processes include biopolymer dissolution using ionic liquids, regeneration of the biopolymer by an anti-solvent, formation of shapes, and drying of the regenerated biopolymer. In particular, the preparation and applications of biopolymer blend-based composite materials containing two or more biopolymers are addressed.

Chitin isolated through microwave-assisted dissolution using ionic liquids is a high molecular weight (MW) polymer that can be manufactured into materials of different architectures (e.g., fibers, films, microspheres, nanostructured materials) to be used as wound care dressings, drug delivery devices, scaffolds, etc. However, because of differences from traditional isolation methods and, thus, differences in polymer length and degree of deacetylation, it could exhibit bio-related properties that differ from those of traditionally ‘pulped’ chitin. Here we present the initial assessments of bio-related chitin properties in order to provide a useful scientific basis for clinical applications: biocompatibility, cytotoxicity (intracutaneous reactivity), wound healing efficacy, histological evaluation of the wounds treated with chitin dressing, and antibacterial activity. We also provide the studies that outline potential applications of chitin as a raw polymer for preparation of biomaterials.

In this chapter, preparation, basic properties, and some applications of ionic liquids composed of naturally-derived ions are summarized. There are many candidate ions in nature suitable for ionic liquid preparation. Physicochemical properties and preparation of some ionic liquids based on carboxylate anions, cholinium cation, and even amino acids are mentioned. Some interesting applications based on these ionic liquids composed of naturally-derived ions are also briefly introduced.

This chapter focuses on recent advances in the use of ionic liquids as additives and solvents in protein applications. The solvent properties of ionic liquids can be tuned by the appropriate selection of cation and anion. The effects of different kinds of ionic liquids on protein stability and refolding behavior have been investigated and reported. The ionic liquid properties affect the intermolecular interactions of proteins, inducing different formations and folding behavior. These effects also vary with the concentration of ionic liquids. Although many of the associated mechanisms are not completely clear, some of this behavior may be attributed to the kosmotropicity of the ions and their Hofmeister effects.

Plants contain many kinds of natural organic compounds, and their compounds possess many useful properties. Natural organic compounds are important for the development of medicines, pesticides, fragrances, cosmetics, and synthetic chemicals. In this chapter, we introduce efficient methods for extraction and isolation of valuable natural organic compounds from various plant leaves by using cellulose-dissolving ionic liquids. High-polarity ionic liquids, which can dissolve cellulose, contribute to the extraction of natural organic compounds from plant leaves probably by breaking down plant cell walls, which are composed of cellulose, hemicellulose, and lignin. Extraction and isolation of shikimic acid from ginkgo leaves, caffeoylquinic acids from sweet potato leaves, and neral and geranial (which combine to form citral) from lemon myrtle leaves were performed. Ionic liquids can achieve extraction rates greater than those achieved with water and other organic solvents.

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Ionic liquids provide challenges and opportunities for sustainable industrial developments. However, the toxic impacts of ionic liquids reported by many researchers cannot be overlooked. Therefore, in this chapter, we introduce the antimicrobial activities of ionic liquids in bioprocesses and, in greater detail, we discuss their environmental impacts, including the toxicity, biodegradability, bioaccumulation, and mobility of ionic liquids. We believe that this presented information will support colleagues engaged in ionic liquid–related fields.