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Deep eutectic solvents (DES) have emerged as promising solutions in many areas of chemistry. DES have many of the advantages of ionic liquids (e.g., low vapor pressure, nonflammability, tunability, etc.) but have lower costs, straightforward syntheses, and are often biodegradable. In this minireview, we discuss briefly the applications of DES in areas such as biotransformations, organocatalysis, and combinations of these that lead to multistep processes. DES can be used as solvents, cosolvents, performance additives for bio- and organocatalysis, tools to anchor organocatalysts selectively, or for extraction/separation. Several DES have been used both as solvents and organocatalysts at the same time. Given their promising features, it may be expected that many applications in these areas will appear in the coming years. [ABSTRACT FROM AUTHOR]

Benzaldehyde lyase (BAL) results in an efficient biocatalyst for the umpolung carboligation of furfural, HMF, and mixtures of them, leading to blended C10–C12 platform chemicals. Subsequently, the mixing and gentle heating (＜100 °C) of the formed hydroxy-ketone with choline chloride leads to the formation of a novel biomass-derived deep-eutectic-solvent. [ABSTRACT FROM AUTHOR]

Recent years have witnessed the use of different ionic liquids for biomass processing, either at the level of lignocellulose pre-treatment, to fractionate biomass in its main components, separating hemicellulose and lignin from cellulose, or directly in cellulose decrystallization by dissolving it in the ionic liquid and subsequent precipitation by adding anti-solvents. Yet, most of the ILs employed in these strategies (e.g. imidazolium-based solvents) are (still) expensive for such applications, and provide discussable ecological footprints. In an attempt to combine the highly useful generated knowledge with novel neoteric solvents with improved properties, economics, availability and ecology, several new trends have appeared in these areas during recent years. They comprise the use of switchable ILs, based on strong organic bases and CO2, the application of distillable ILs, as well as the use of bio-based and low-cost ILs and deep-eutectic-solvents (DES), e.g. choline chloride-based derivatives. Apart from other emerging uses, for all these solvents some preliminary applications in biomass processing involving pretreatments, cellulose dissolution and other applications have been successfully reported. This Minireview contextualizes these recent trends and discusses them with emphasis on future use of them in biorefineries and biomass valorization. © 2013 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Hydrolases catalyze synthetic reactions in nonaqueous media, whereas they perform hydrolysis under aqueous solutions. An acyl transferase from Mycobacterium smegmatis (MsAcT) is able to catalyze synthetic reactions in buffer because of its highly hydrophobic active site, which enables efficient transesterification reactions even at 99.9 % v/v buffer solution. This unique feature of MsAcT among hydrolases may open new opportunities to conduct synthetic (bio)catalysis in aqueous media. With these goals in mind, this paper explores some evidence of such potential: MsAcT can perform enantioselective transesterifications (e.g., ( S)-2-octanol), which could be combined with other aqueous multistep (asymmetric) reactions; 5-hydroxymethylfurfural (HMF) can be esterified to produce more hydrophobic and easily extractable HMF esters (e.g., for downstream processing or wastewater treatment); and upon addition of dilute H2O2, MsAcT works efficiently as a perhydrolase to form in situ peracids-in bulk water-that can be used for oxidations (e.g., furfural to furoic acid oxidation). Overall, these and many other new applications can be envisaged by using MsAcT in aqueous solutions. [ABSTRACT FROM AUTHOR]

Furfural and 5-hydroxymethylfurfural (HMF) are important biomass-derived platform chemicals that can be obtained from the dehydration of lignocellulosic sugars. A possible route for the derivatization of furanics is their oxidation to afford a broad range of chemicals with promising applications (e.g., diacids, hydroxyl acids, aldehyde acids, monomers for novel polymers). Herein we explore the organic peracid-assisted oxidation of furanics under mild reaction conditions. Using lipases as biocatalysts, alkyl esters as acyl donors, and aqueous solutions of hydrogen peroxide (30 % v/ v) added stepwise, peracids are formed in situ, which subsequently oxidize the aldehyde groups to afford carboxylic acids with high yields and excellent selectivities. Furthermore, the use of an immobilized silica-based 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) affords the selective oxidation of the hydroxymethyl group of HMF to afford 2,5-diformylfuran. That product can be subsequently oxidized using again lipases for the in situ peracid formation to yield 2,5-furandicarboxylic acid, which is considered to be a key building block for biorefineries. These lipase-mediated reactions proceeded efficiently even with high substrate loadings under still non-optimized conditions. Overall, a proof-of-concept for the oxidation of furanics (based on in situ formed organic peracids as oxidants) is provided. [ABSTRACT FROM AUTHOR]

2-Methyl-tetrahydrofuran (2-MeTHF) can be derived from renewable resources (e.g., furfural or levulinic acid) and is a promising alternative solvent in the search for environmentally benign synthesis strategies. Its physical and chemical properties, such as its low miscibility with water, boiling point, remarkable stability compared to other cyclic-based solvents such as THF, and others make it appealing for applications in syntheses involving organometallics, organocatalysis, and biotransformations or for processing lignocellulosic materials. Interestingly, a significant number of industries have also started to assess 2-MeTHF in several synthetic procedures, often with excellent results and prospects. Likewise, preliminary toxicology assessments suggest that the use of 2-MeTHF might even be extended to more processes in pharmaceutical chemistry. This Minireview describes the properties of 2-MeTHF, the state-of-the-art of its use in synthesis, and covers several outstanding examples of its application from both industry and academia. [ABSTRACT FROM AUTHOR]

Abstract: Lipase-catalyzed esterifications in biphasic media (heptane–water, 1:1) were conducted by using Thermomyces lanuginosus lipase (TLL) as biocatalyst. Different carboxylic acids (from acetic to lauric) were thus esterified with 1-butanol at different pH values (2–10). For all carboxylic acids tested, pH optima for the enzymatic esterifications were ca. 3–5, in clear agreement with previous literature, and quite different from optima pH of TLL in hydrolytic reactions (8–11). Interestingly, the interval of pH in which TLL was active in esterifications, varied markedly depending on the carboxylic acid. Thus, for long-chain acids (i.e. lauric), such pH interval was much wider than for short-chain carboxylic acids (i.e. acetic). To understand this effect, simple pK a values of carboxylic acids, retrieved from open literature, are not sufficient, since those values are measured in pure water. When a second phase is added, aspects related to partition coefficient of each carboxylic acid need to be considered as well, thus leading to the apparent pK a concept. Herein we performed theoretical calculations to obtain such app pK a of each carboxylic acid. When such calculations were compared with the pH interval, a clear correlation was observed. Overall, results confirm that lipases accept only the protonated form of the carboxylic acid (R–COOH) during esterifications in biphasic media. [Copyright &y& Elsevier]

Background: Biomass recalcitrance towards pretreatment and further processing can be related to the compositional and structural features of the biomass. However, the exact role and relative importance to those structural attributes has still to be further evaluated. Herein, ten different types of biomass currently considered to be important raw materials for biorefineries were chosen to be processed by the recently developed, acid-catalyzed OrganoCat pretreatment to produce cellulose-enriched pulp, sugars, and lignin with different amounts and qualities. Using wet chemistry analysis and NMR spectroscopy, the generic factors of lignocellulose recalcitrance towards OrganoCat were determined. Results: The different materials were processed applying different conditions (e.g., type of acid catalyst and temperature), and fractions with different qualities were obtained. Raw materials and products were characterized in terms of their compositional and structural features. For the first time, generic correlation coefficients were calculated between the measured chemical and structural features and the different OrganoCat product yields and qualities. Especially lignin-related factors displayed a detrimental role for enzymatic pulp hydrolysis, as well as sugar and lignin yield exhibiting inverse correlation coefficients. Hemicellulose appeared to have less impact, not being as detrimental as lignin factors, but xylan-O-acetylation was inversely correlated with product yield and qualities. Conclusion: These results illustrate the role of generic features of lignocellulosic recalcitrance towards acidic pretreatments and fractionation, exemplified in the OrganoCat strategy. Discriminating between types of lignocellulosic biomass and highlighting important compositional variables, the improved understanding of how these parameters affect OrganoCat products will ameliorate bioeconomic concepts from agricultural production to chemical products. Herein, a methodological approach is proposed. [ABSTRACT FROM AUTHOR]

A non-innocent biogenic solvent? The use of Cyrene™ as solvent in biocatalysis may be advantageous. Its ability to form geminal diols and Cygnet-type structures leads to solvent gradients with tailored polarities, offering promising options for enzymatic processes (from its use in aqueous media as co-solvents, to synthetic purposes as non-conventional media). [Display omitted] • Cyrene is useful as organic solvent for lipophilizations enzymatic reactions. • The immobilized CALB is active in Cyrene, yielding up to ∼ 10 g product L−1. • CALB-CLEA remain stable in Cyrene, enabling its use along several catalytic cycles. • CALB displays hydrolytic reactions using Cyrene as cosolvent. • CALB-CLEA remain fully active over 6 cycles at 30 % v/v Cyrene. An emerging biogenic aprotic solvent is the cellulose-derived dihydrolevoglucosenone, or 6,8-dioxabicyclooctanone (Cyrene™). This paper explores the use of Cyrene in lipase-catalyzed biotransformations, both in aqueous solutions – as co-solvent – as well as non-conventional media for synthesis. Cyrene is useful as organic solvent for lipophilizations using benzoic acid and glycerol as a model system for substrates with unpaired solubilities. The immobilized lipase B from Candida antarctica is active in Cyrene, yielding up to ∼ 10 g product L−1. Interestingly, crosslinked aggregates immobilized lipases (CLEA) remain significantly stable in Cyrene, enabling its use along several catalytic cycles. Cyrene is highly hygroscopic and forms geminal-diol structures with water, leading to solvent mixtures with a (tailored) gradient of polarities, what may be promising for biocatalysis in aqueous solutions. CALB displays hydrolytic reactions with different proportions of Cyrene as cosolvent, and CLEA derivatives remain fully active over 6 cycles at 30 % v/v Cyrene. [ABSTRACT FROM AUTHOR]

[Display omitted] • Lipase from Pseudomonas stutzeri was immobilized through cross-linking aggregates. • The new derivative is active in a synthesis reaction using DES as reaction media. • The biocatalyst is stable and can be reused several times. • Cross-linking aggregates are a simple tool to obtain active biocatalysts in DES. The use of deep eutectic solvents (DES) with buffer as cosolvent (up to 10 % v/v) leads to low-viscous media in which lipases can perform synthetic reactions, instead of hydrolysis. This paper explores the immobilization of Pseudomonas stutzeri lipase (TL) in cross-linking aggregates (CLEA) to deliver robust derivatives that are active in media like choline chloride – glycerol DES with buffer as cosolvent. While the free TL enzyme was markedly inactive in these media, TL-CLEA derivatives perform esterifications and can be reused several times. Overall, results are consistent with previous experiments reported for other lipases in these DES-water media and confirm that CLEA immobilization turns out a very useful and straightforward alternative for generating active (bio)catalysts for DES-aqueous media systems. Immobilized systems open the possibility of performing continuous processes in low-viscous DES-buffer media. [ABSTRACT FROM AUTHOR]

The valorization of lignin-derived feedstocks by catalytic means enables their defunctionalization and upgrading to valuable products. However, the development of productive, safe, and low-waste processes remains challenging. This paper explores the industrial potential of a chemoenzymatic reaction performing the decarboxylation of bio-based phenolic acids in wet cyclopentyl methyl ether (CPME) by immobilized phenolic acid decarboxylase from Bacillus subtilis, followed by a base-catalyzed acylation. Key-to-success is the continuous control of water activity, which fluctuates along the reaction progress, particularly at high substrate loadings (triggered by different hydrophilicities of substrate and product). A combination of experimentation, thermodynamic equilibrium calculations, and MD simulations revealed the change in water activity which guided the integration of water reservoirs and allowed process intensification of the previously limiting enzymatic step. With this, the highly concentrated sequential two-step cascade (400 g·L–1) achieves full conversions and affords products in less than 3 h. The chemical step is versatile, accepting different acyl donors, leading to a range of industrially sound products. Importantly, the finding that water activity changes in intensified processes is an academic insight that might explain other deactivations of enzymes when used in non-conventional media. Lignin-derived phenolic acids can be upgraded to styrene derivatives through chemoenzymatic processes, however, the scale-up of such processes remains challenging. Here, the authors find that controlling the water activity during the decarboxylation of bio-based phenolic acids, including through the integration of a water reservoir, enables high conversions and efficient reaction times, that can be combined with a versatile acyl donor substrate scope. [ABSTRACT FROM AUTHOR]

• Lipase-CLEA aggregates can be efficiently immobilized in Lentikats®, leading to a highly robust biocatalyst. • The new biocatalyst can be used in low viscous non-conventional Deep Eutectic Solvent – Buffer systems. • The new biocatalyst displays outstanding stability and straightforward recovery. The immobilization of lipases in cross linked aggregates (CLEA) leads to a robust biocatalyst that remains very stable in low viscous non-conventional Deep Eutectic Solvents – Buffer mixtures. To reinforce that stability, and to facilitate the biocatalyst recovery, this paper explores the immobilization of Lipase-CLEA derivatives in Lentikats®. This double immobilization can be successfully used in esterifications in DES-buffer media, using substrates of unpaired solubilities (e.g. benzoic acid and glycerol), in batch and continuous processes, and reaching full conversion. Under these conditions, the derivatives display an improved stability (compared to the Lipase-CLEA derivatives) and enable the reuse of the reaction media in continuous devices for at least 6 cycles under non-optimized conditions, accumulating 10 g product L−1, enhancing the productivity, and opening exciting future options for sustainable chemistry. [ABSTRACT FROM AUTHOR]

Highlights • Low viscous DES-water blends can be used in continuous processes for biocatalysis. • The pH control increases the conversion, using DES in a fed-batch reactor. • Fed-batch reactor reached the highest concentration of product 33 g/L. • The semicontinuous and continuous bioreactors reached similar productivities. • Biocatalyst stability was high in a packed-bed reactor, without loss for 10 days. Abstract This work explores for the first time the use of Deep Eutectic Solvents (DES) with phosphate buffer 100 mM pH 7 as cosolvent (10% v/v) in biocatalytic reactions in fed-batch and packed-bed bioreactors. The lipase-catalyzed esterification of glycerol and benzoic acid is studied, as it involves two substrates with different polarities (for which DES are needed). In the fed-batch bioreactor, the highest conversion (90%) was obtained at a substrate flow rate of 0.01 mL/min. The fed-batch operation increased the conversion by 59% compared to the batch mode. Regarding productivity, semi-continuous and continuous bioreactors showed analogous results. Upon recirculation of the reaction media in the continuous bioreactor, a conversion of 67% was achieved in 7 cycles of operation. The stability of the biocatalyst in the packed-bed bioreactor decreased only 2% in 10 days, demonstrating the attractiveness that low viscous DES-water mixtures with continuous processes may have. [ABSTRACT FROM AUTHOR]

Lignin is the major aromatic biopolymer in nature, and it is considered a valuable feedstock for the future supply of aromatics. Hence, its valorisation in biorefineries is of high importance, and various chemical and enzymatic approaches for lignin depolymerisation have been reported. Among the enzymes known to act on lignin, β-etherases offer the possibility for a selective cleavage of the β-O-4 aryl ether bonds present in lignin. These enzymes, together with glutathione lyases, catalyse a reductive, glutathione-dependent ether bond cleavage displaying high stereospecificity. β-Etherases and glutathione lyases both belong to the superfamily of glutathione transferases, and several structures have been solved recently. Additionally, different approaches for their application in lignin valorisation have been reported in the last years. This review gives an overview on the current knowledge on β-etherases and glutathione lyases, their biochemical and structural features, and critically discusses their potential for application in biorefineries. [ABSTRACT FROM AUTHOR]

Highlights: [•] Chitosan-aerogels catalyze biodiesel-type transesterifications. [•] Chitosan is presently a waste that can be valorized. [•] Other polysaccharides (e.g. alginic acid) may be used as catalysts as well. [Copyright &y& Elsevier]