The development of novel green solvents has been one of the hottest subjects in green chemistry. Deep eutectic solvents (DESs) have logically and naturally emerged in the search for more biocompatible and biodegradable solvents. In this study, some basic physical properties, including viscosity, conductivity and density, of twenty DESs prepared from choline chloride and various hydrogen bond donors were investigated systematically. In addition, the biocompatibility of the tested DESs was qualitatively and quantitatively evaluated using two gram-positive (Staphylococcus aureus and Listeria monocytogenes) and two gram-negative (Escherichia coli and Salmonella enteritidis) bacteria. A Closed Bottle Test was used to assess the biodegradability of these DESs. The results demonstrated that these choline chloride-based DESs were excellent solvents with extremely low toxicity and favorable biodegradability. Finally, DESs were used to extract a flavonoid (rutin) from the flower buds of Sophora japonica. An extraction efficiency of 194.17±2.31 mg·g −1 was achieved using choline chloride/triethylene glycol containing 20% water. The excellent properties of DESs indicate their potential as promising green solvents for the extraction of rutin with favorable prospects for wide use in the field of green technology. acid, levulinic acid, malonic acid, malic acid, citric acid, tartaric acid, xylose, sucrose, fructose, glucose, and maltose (all ≥99% mass fraction purity) were all purchased from Tianjin Kermel Chemical Reagent Co., Ltd. (Tianjin, China). Rutin (≥98% mass fraction purity) was purchased from Shanghai Yuanye Biotechnology Co., Ltd. (Shanghai, China). S. japonica bud was purchased from ZhanJiang Yizhou Medicines Co., Ltd. (Guangdong, China). All other chemicals were of analytical grade.Preparation of DESs. DESs were synthesized by mixing choline chloride and HBDs at a defined molar ratio (see Table 1) and heating at 100 °C for 2-4 h at an atmospheric pressure under constant stirring until a stable homogeneous liquid was formed. 21 Sugar-based DESs were prepared using the same conditions but under a nitrogen atmosphere. All the prepared DESs were allowed to cool to room temperature and dried in a vacuum oven at 50 °C for 24 h.The solvents were stored in sealed laboratory vials and kept in a desiccator. Physical Properties. The water contents of the samples were measured using a Metrohm Karl-Fischer (model 890) titrator. The viscosities of the DESs were measured with a HAAKE RheoStress 600 at 100 Hz from 25-80 °C at a rate of 5 °C min −1 . The conductivity of all samples was measured with a conductivity meter (Shanghai Leici DDS-307A) at a preset temperature.The densities of all samples were determined using a 5 cm 3 pycnometer calibrated with deionized water at 30 °C. As for the determination of viscosities, conductivity and densities, all the DESs except sugar-based DESs were dried at 100 °C to minimize the water content. All measurements were performed at constant temperature. The relative standard deviation for all th...

Deep eutectic solvents (DESs) are eutectic mixtures of salts and hydrogen bond donors with melting points low enough to be used as solvents. DESs have proved to be a good alternative to traditional organic solvents and ionic liquids (ILs) in many biocatalytic processes. Apart from the benign characteristics similar to those of ILs (e.g., low volatility, low inflammability and low melting point), DESs have their unique merits of easy preparation and low cost owing to their renewable and available raw materials. To better apply such solvents in green and sustainable chemistry, this review firstly describes some basic properties, mainly the toxicity and biodegradability of DESs. Secondly, it presents several valuable applications of DES as solvent/co-solvent in biocatalytic reactions, such as lipase-catalyzed transesterification and ester hydrolysis reactions. The roles, serving as extractive reagent for an enzymatic product and pretreatment solvent of enzymatic biomass hydrolysis, are also discussed. Further understanding how DESs affect biocatalytic reaction will facilitate the design of novel solvents and contribute to the discovery of new reactions in these solvents.

What is the most significant result of this study? The most importanto bservation of this study is the biocata-lyst-Meyerozyma guilliermondii SC1103-since the cells of this yeast are much more tolerant to 5-hydroxymethylfurfural (HMF) compared to microbesr eported previously.I na ddition, the efficiency of the biocatalytic HMF reduction as well as its selectivity are very high. What new scientific questions/problems doest his work raise? We think that one of the new scientific questionsm ay be the mechanism by which this yeast strain can tolerate high levels of HMF.U nderstandingt his mechanism will provideu seful in-formationf or the rational modificationo ft he strains for various applications involving HMF. What is the story behindt he cover? The yeast train plays ad ominant role in the biocatalytic reduction of HMF,w hich earned the title of the conductor.G lucose, fructose(the precursors for the synthesis of HMF), HMF,a nd 2,5-bis(hydroxymethyl)furan act as the piano players. So we named this cover image "TheConductor and Its Players". Invited for this month'sc over is the group of Min-Hua Zong at South ChinaU niversity of Technology.T he image shows the selectives ynthesis of 2,5-bis(hydroxymethyl)furan from 5-hydroxymethylfurfural (HMF) using highly HMF-tolerantw hole cells.

Use of deep eutectic solvents (DESs) to improve biocatalytic asymmetric reduction of 3-chloropropiophenone to (S)-3-chloro-1-phenylpropanol catalyzed by whole-cell of Acetobacter sp. CCTCC M209061 was successfully performed. The cells immobilized on PVA-sodium sulfate exhibited markedly enhanced stability. Diverse DESs as co-solvents manifested significantly different influences on the reaction. Among them, the DES choline chloride/urea ([ChCl][U]) showed the best biocompatibility and moderately increased the cell member permeability, as demonstrated by MAR and flow cytometry assays, and consequently gave the best results. For the bioreduction conducted in the [ChCl][U]-containing system, the optimum [ChCl][U] content, substrate concentration, glucose concentration, pH and temperature were 5% (v/v), 10.0 mmol/L, 60 mmol/L, 5.5 and 30 °C, respectively. Under the optimized conditions, the obtained yield and product e.e. were 82.3% and above 99.0% at a reaction time of 6 h, respectively, and the productivity was 1.37 mmol/L/h. The efficient whole-cell biocatalytic process proved to be feasible on a 500-mL preparative scale. Moreover, the combination of water-immiscible ionic liquid C 4 MIM·PF 6 with [ChCl][U] in a biphasic system further enhanced substrate concentration (16.0 mmol/L), product yield (93.3%) and productivity (1.87 mmol/L/h) significantly, showing to be very promising for biocatalytic synthesis of (S)-3-chloro-1-phenylpropanol with immobilized Acetobacter sp. CCTCC M209061 cells.Acetobacter sp. CCTCC M209061, isolated from Chinese kefir grains by our group, was used as an efficient biocatalyst for highly enantioselective anti-Prelog reduction of prochiral ketones. 11Over the last several years, deep eutectic solvents (DESs) have been considered as another promising alternative to conventional ionic liquids (ILs) as green solvents. 12, 13 DESs are eutectic mixtures composed of two or three cheap and safe components which could associate with each other through hydrogen bond interactions. 14 These solvents not only share the similar characteristics with ILs such as low vapor pressure, non-flammability, thermal stability, but also have some special virtues including relatively low cost, good sustainability, biocompatibility and biodegradability. 15,16 Most importantly, the formation of these solvents is very simple and needs no further purification steps. Up to now, there appears to be some researches related to the applications of DESs as co-solvents in biocatalytic reactions, especially in enzyme-catalyzed reactions. [17][18][19] However, few accounts were published about whole-cell biocatalysis in a In the present study, we attempted for the first time to use various DESs as co-solvents in aqueous system to improve the biocatalytic asymmetric reduction of CPE with immobilized Acetobacter sp. CCTCC M209061 cells (Scheme 1). The biocompatibility of these DESs with the cells and their effects on the cell member integrity were investigated systematically as well as several influential factors on the react...

Magnetic cellulose nanocrystals (MCNCs) were prepared and used as an enzyme support for immobilization of Pseudomonas cepacialipase (PCL). PCL was successfully immobilized onto MCNCs (PCL@MCNC) by a precipitation-cross-linking method. The resulting PCL@MCNC with a nanoscale size had high enzyme loading (82.2 mg enzyme/g) and activity recovery (95.9%). Compared with free PCL, PCL@MCNC exhibited significantly enhanced stability and solvent tolerance, due to the increase of enzyme structure rigidity. The observable optimum pH and temperature for PCL@MCNC were higher than those of free PCL. PCL@MCNC manifested relatively higher enzyme-substrate affinity and catalytic efficiency. Moreover, PCL@MCNC was capable of effectively catalyzing asymmetric hydrolysis of ketoprofenethyl ester with high yield of 43.4% and product e.e. of 83.5%. Besides, immobilization allowed PCL@MCNC reuse for at least 6 consecutive cycles retaining over 66% of its initial activity. PCL@MCNC was readily recycled by magnetic forces. Remarkably, the as-prepared nanobiocatalyst PCL@MCNC is promising for biocatalysis.