Abstract
Over the past decade, a variety of ionic liquids have emerged as greener solvents for use in the chemical manufacturing industries. Their unique properties have attracted the interest of chemists worldwide to employ them as replacement for conventional solvents in a diverse range of chemical transformations including biotransformations. Biocatalysts are often regarded as green catalysts compared to conventional chemical catalysts in organic synthesis owing to their properties of low toxicity, biodegradability, excellent selectivity and good catalytic performance under mild reaction conditions. Similarly, a selected number of specific ionic liquids can be considered as greener solvents superior to organic solvents owing to their negligible vapor pressure, low flammability, low toxicity and ability to dissolve a wide range of organic and biological substances, including proteins. A combination of biocatalysts and ionic liquids thus appears to be a logical and promising opportunity for industrial use as an alternative to conventional organic chemistry processes employing organic solvents. This article provides an overview of recent developments in this field with special emphasis on the application of more sustainable enzyme-catalyzed reactions and separation processes employing ionic liquids, driven by advances in fundamental knowledge, process optimization and industrial deployment.
Highlights
As a consequence of rapid developments in many fields of synthetic organic chemistry, researchers from both academia and industry have to pay much greater attention to the detrimental effects of chemicals and chemistry processes on the environment
The number of issued or pending patent applications mirrors a similar trend. The importance of this rapidly growing field of research has been documented by various authors, including the different research groups of Sheldon et al, Kragl et al and Goto et al, highlighting practical developments, as well as providing compilations of data for different ionic liquids/enzyme combinations [13,24,25,26,33,34,35,36,37,38,39,40,41]. These works have summarized different facets of the use of biocatalysts in ionic liquids, wherein key issues related to the effects of ionic liquids on the structure, activity and stability of enzymes have been explored and the impact of the water content in the ionic liquid assessed, together with several biocatalytic reactions employing a range of different enzymes and ionic liquid combinations for the design of reaction systems, including biocatalyst recovery, product isolation and choice of biphasic systems
Similar strategies can be forecasted as apparent from our recent work with biphasic biocatalytic conversion of xylan, the second most abundant biomaterial found in nature after cellulose, using recombinantly expressed, thermostable xylanases, genetically engineered to have high activity in a variety of non-polar ionic liquids, leading to the production of a range of chemical intermediates that can be directly recovered from the aqueous phase in continuous processes [98]
Summary
As a consequence of rapid developments in many fields of synthetic organic chemistry, researchers from both academia and industry have to pay much greater attention to the detrimental effects of chemicals and chemistry processes on the environment. These works have summarized different facets of the use of biocatalysts in ionic liquids, wherein key issues related to the effects of ionic liquids on the structure, activity and stability of enzymes have been explored and the impact of the water content in the ionic liquid assessed, together with several biocatalytic reactions employing a range of different enzymes and ionic liquid combinations for the design of reaction systems, including biocatalyst recovery, product isolation and choice of biphasic systems In this current article, an overview of innovations that have been developed in this field over the last decade is presented with a focus on the synthetic chemistry outcomes and benefits derived from carry out biocatalytic reactions in suitable ionic liquids. An overview of the application of a special class of biodegradable ion-based liquids, known as deep eutectic solvents, in biocatalysis, and recent adaptations of the use of ionic liquids to whole-cell biocatalysis, which from a green chemical perspective have potential for new applications in chemical manufacturing, medicine and the environmental sciences are provided
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