Chiral Polyol Synthesis Catalyzed by a Thermostable Transketolase Immobilized on Layered Double Hydroxides in Ionic liquids Ghina Ali, [a, b] Thomas Moreau, [a, b] Claude Forano,* [a, b] Christine Mousty, [a, b] Vanessa Prevot, [a, b] Franck Charmantray, [a, b] and Laurence Hecquet* [a, b] This manuscript is dedicated to Wolf-Dieter “Woody” Fessner on the occasion of his 60 th birthday. Introduction Among the challenges in the application of enzymes on a large scale and in industry, particular attention has been paid to the use of ionic liquids (ILs) as an attractive alternative to hazardous volatile organic solvents. [1, 2] ILs, based on anion and cation associations, are liquid from room temperature to 150– 200 8C and display unique features that make them suitable as solvents or cosolvents for a wide range of applications, such as electrochemistry, catalysis, organic and inorganic synthesis, en- gineering, and analysis. [3] In biocatalysis, ILs offer advantages over conventional organ- ic solvents or aqueous media. It is reported that ILs can induce better enzyme activity, [4] high conversion rates [5] and enantiose- lectivity, [6] changes in substrate specificity, and increased sub- strate solubility. [7] One of the main interests in ILs is their ability to enhance the solubility of substrates and/or products, al- though their efficiency is a trade-off between substrate dissolu- tion and the maintenance of enzyme activity. However, many authors have evidenced increased performance if biotransfor- mations proceed in ILs. [8] ILs have been investigated mainly in enzymatic reactions that involve polar substrates, such as amino acids or carbohy- drates in a low-water environment, and hydrolytic enzymes, typically, esterases, lipases, and proteases. [6, 9–13] It was shown that the biocatalytic activity was retained even at low water contents. Nonhydrolytic enzymes, particularly oxidoreductases, such as dehydrogenases, [14–17] peroxidases, [18] laccases, [19, 20] and oxygenases, [21, 22] have also been evaluated in aqueous IL mix- tures to test their catalytic activity and stability. Many factors affect enzyme activity and stability in ILs, espe- cially the intrinsic physical and chemical properties of ILs, such as polarity, hydrophobicity, and viscosity. More particularly, enzyme stability and activity in aqueous IL mixtures are strong- ly dependent on water activity and kosmotropic versus chao- tropic ion properties. Their roles on the protein surface energy or interactions with unfolded proteins affect biocatalytic per- formance. The immobilization of the enzyme in a protective matrix is an alternative process to stabilize enzyme activity. [23, 24] To overcome enzyme inactivation in IL media and improve activity, various methods, reviewed recently by Zhao, [25] have been studied, such as enzyme immobilization, enzyme modifi- cation with polyethylene glycol, water in IL microemulsions, the use of additives, and the design of IL structures. The com- bination of immobilization and a nonconventional solvent In this work we set out to study the activity of a thermostable Transketolase (TK) from Geobacillus stearothermophilus (TK gst ) in an ionic liquid as cosolvent, which has never been investigated before with this enzyme. 1-Butyl-3-methylimidazolium chloride ([BMIm][Cl]) in the range 30–50 % in water maintained the total activity of TK gst and increased the reaction rate in the presence of pentoses as acceptor substrates, particularly d-ribose. To improve the synthetic process, TK gst was immobi- lized on an inorganic support, layered double hydroxides (LDHs), with excellent immobilization yield and catalytic activi- ty using a simple, eco-compatible, efficient coprecipitation pro- cedure. The biohybrid MgAl@TK gst was tested in 30 % [BMIm] [Cl] for the synthesis of a rare, very costly commercially avail- able sugar, d-sedoheptulose, which was obtained in one step from d-ribose with an isolated yield of 82 %. This biohybrid was reusable over four cycles with no loss of enzymatic activi- ty. The particular activity of free and immobilized TK gst in [BMIm][Cl] holds promise to extend the applications of TK gst in other ionic liquids and unusual media in biocatalysis. [a] Dr. G. Ali, Dr. T. Moreau, Prof. C. Forano, Dr. C. Mousty, Dr. V. Prevot, Dr. F. Charmantray, Prof. L. Hecquet Institut de Chimie de Clermont-Ferrand Clermont UniversitØ, UniversitØ Blaise Pascal BP 10448 63000 Clermont-Ferrand (France) E-mail : laurence.hecquet@univ-bpclermont.fr claude.forano@univ-bpclermont.fr [b] Dr. G. Ali, Dr. T. Moreau, Prof. C.Forano, Dr. C. Mousty, Dr. V. Prevot, Dr. F. Charmantray, Prof. L. Hecquet CNRS, UMR 6296 ICCF 63177 Aubire (France) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cctc.201500524. ChemCatChem 2015, 7, 3163 – 3170 # 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 3163 Full Papers DOI: 10.1002/cctc.201500524