Combination of deep eutectic solvent and ionic liquid to improve biocatalytic reduction of 2-octanone with Acetobacter pasteurianus GIM1.158 cell

Influence of deep eutectic solvents on redox biocatalysis involving alcohol dehydrogenases

Redox biocatalysis plays an increasingly important role in modern organic synthesis. The recent integration of novel media such as deep eutectic solvents (DESs) has significantly impacted this field of chemical biology. Alcohol dehydrogenases (ADHs) are important biocatalysts where their unique specificity is used for enantioselective synthesis. This review explores aspects of redox biocatalysis in the presence of DES both with whole cells and with isolated ADHs. In both cases, the presence of DES has a significant influence on the outcome of reactions albeit via different mechanisms. For whole cells, DES was shown to be a useful tool to direct product formation or configuration - a process of solvent engineering. Whole cells can tolerate DES as media components for the solubilization of hydrophobic substrates. In some cases, DES in the growth medium altered the enantioselectivity of whole cell transformations by solvent control. For isolated enzymes, on the other hand, the presence of DES promotes substrate solubility as well as enhancing enzyme stability and activity. DES can be employed as a smart solvent or smart cosubstrate particularly for cofactor regeneration purposes. From the literatures examined, it is suggested that DES based on choline chloride (ChCl) such as ChCl:Glycerol (Gly), ChCl:Glucose (Glu), and ChCl:1,4-butanediol (1,4-BD) are useful starting points for ADH-based redox biocatalysis. However, each specific reaction will require optimisation due to the influence of several factors on biocatalysis in DES. These include solvent composition, enzyme source, temperature, pH and ionic strength as well as the substrates and products under investigation.

Biobased natural deep eutectic system as versatile solvents: Structure, interaction and advanced applications

The increasing emphasis on the development of green replacements to traditional organic solvents and ionic liquids (ILs) can be attributed to the rising concerns over human health and detrimental impacts of conventional solvents towards the environment. A new generation of solvents inspired by nature and extracted from plant bioresources has evolved over the last few years, and are referred to as natural deep eutectic solvents (NADES). NADES are mixtures of natural constituents like sugars, polyalcohols, sugar-based alcohols, amino acids and organic acids. Interest in NADES has exponentially grown over the last eight years, which is evident from an upsurge in the number of research projects undertaken. NADES are highly biocompatible as they can be biosynthesized and metabolized by nearly all living organisms. These solvents pose several noteworthy advantages, such as easy synthesis, tuneable physico-chemical properties, low toxicity, high biodegradability, solute sustainability and stabilization and low melting point. Research on the applicability of NADES in diverse areas is gaining momentum, which includes as - media for chemical and enzymatic reactions; extraction media for essential oils; anti-inflammatory and antimicrobial agent; extraction of bioactive composites; as chromatographic media; preservatives for labile compounds and in drug synthesis. This review gives a complete overview of the properties, biodegradability and toxicity of NADES which we propose can assist in further knowledge generation on their significance in biological systems and usage in green and sustainable chemistry. Information on applications of NADES in biomedical, therapeutic and pharma-biotechnology fields is also highlighted in the current article along with the recent progress and future perspectives in novel applications of NADES.

Enhanced whole-cell biotransformation of 3-chloropropiophenone into 1-phenyl-1-propanone by hydrogel entrapped Chlorella emersonii (211.8b)

OBJECTIVES

This study focuses on dehalogenation of halogenated organic substrate (3-Chloropropiophenone) using both free and hydrogel entrapped microalgae Chlorella emersonii (211.8b) as biocatalyst. We aimed at successful immobilization of C. emersonii (211.8b) cells and to assess their biotransformation efficiency.

RESULTS

Aquasorb (entrapping material in this study) was found to be highly biocompatible with the cellular growth and viability of C. emersonii. A promising number of entrapped cells was achieved in terms of colony-forming units (CFUs = 2.1 × 10⁴) per hydrogel bead with a comparable growth pattern to that of free cells. It was determined that there is no activity of hydrogenase that could transform 1-phenyl-2-propenone into 1-phenyl-1-propanone because after 12 h the ratio between two products (0.36 ± 0.02) remained constant throughout. Furthermore, it was found that the entrapped cells have higher biotransformation of 3-chloropropiophenone to 1-phenyl-1-propanone as compared to free cells at every interval of time. 1-phenyl-2-propenone was excluded from the whole-cell biotransformation as it was also found in the control group (due to spontaneous generation).

CONCLUSION

Hence, enhanced synthesis of 1-phenyl-1-propanone by entrapped Chlorella (211.8b) can be ascribed to either an enzymatic activity (dehalogenase) or thanks to the antioxidants from 211-8b, especially when they are in immobilized form. The aquasorb based immobilization of microalgae is highly recommended as an effective tool for exploiting microalgal potentials of biocatalysis specifically when free cells activities are seized due to stress.

The study and application of biomolecules in deep eutectic solvents

Deep eutectic solvents offer stimulating possibilities for biomolecular stabilization and manipulation, biocatalysis, bioextraction, biomass processing, and drug delivery and therapy.

Biocatalyzed Redox Processes Employing Green Reaction Media

The application of biocatalysts to perform reductive/oxidative chemical processes has attracted great interest in recent years, due to their environmentally friendly conditions combined with high selectivities. In some circumstances, the aqueous buffer medium normally employed in biocatalytic procedures is not the best option to develop these processes, due to solubility and/or inhibition issues, requiring biocatalyzed redox procedures to circumvent these drawbacks, by developing novel green non-conventional media, including the use of biobased solvents, reactions conducted in neat conditions and the application of neoteric solvents such as deep eutectic solvents.

Using Choline Chloride-Based DESs as Co-Solvent for 3,5-Bis(trifluoromethyl) Acetophenone Bioreduction with Rhodococcus erythropolis XS1012

(S)-3,5-Bistrifluoromethylphenyl ethanol((S)-BTPE) is a key pharmaceutical intermediate of the NK-1 receptor antagonist. The asymmetric bioreduction of 3,5-bis(trifluoromethyl) acetophenone (BTAP) to (S)-BTPE using Rhodococcus erythropolis XS1012 has been established in a phosphate buffer system. To overcome the problem of unsatisfactory yields at high substrate concentration, deep eutectic solvents (DESs) have been introduced to the buffer system. After screening 13 kinds of choline chloride-based DESs, [choline chloride][urea] ([ChCl][U]) showed great influence on the cell activity and significantly increased the cell membrane permeability. Subsequently, some major parameters for this reaction were determined. A remarkable (S)-BTPE yield of 91.9% was gained at 150 mM substrate concentration under optimized reaction conditions with >99.9% product enantioselectivity. Compared to reduction in a buffer system, the developed [ChCl][U]-containing system increased the yield from 82.6% to 91.9%. It maintains a yield of 80.7% with the substrate concentration up to 300 mM, compared to only 63.0% in buffer system. This study demonstrated that [ChCl][U] is a feasible co-solvent to improve the bioreduction process.

The Versatile Applications of DES and Their Influence on Oxidoreductase-Mediated Transformations

In the last decade, new types of solvents called deep eutectic solvents (DES) have been synthesized and commercialized. Among their main advantages, they can be eco-friendly and are easy to synthesize at different molar ratios depending on the desired solvent properties. This review aims to show the different uses of DES in some relevant biocatalytic redox reactions. Here we analyze oxidoreductase-mediated transformations that are performed in the presence of DES and compare them with the ones that avoided those solvents. DES were found to present advantages such as the increase in the product yield and enantiomeric excess in many reactions.

Recent developments in biocatalysis in multiphasic ionic liquid reaction systems

Ionic liquids are well known and frequently used 'designer solvents' for biocatalytic reactions. This review highlights recent achievements in the field of multiphasic ionic liquid-based reaction concepts. It covers classical biphasic systems including supported ionic liquid phases, thermo-regulated multi-component solvent systems (TMS) and polymerized ionic liquids. These powerful concepts combine unique reaction conditions with a high potential for future applications on a laboratory and industrial scale. The presence of a multiphasic system simplifies downstream processing due to the distribution of the catalyst and reactants in different phases.

Innovative aspects of protein stability in ionic liquid mixtures

Mixtures of ionic liquids (ILs) have attracted our attention because of their extraordinary performances in extraction technologies and in absorbing large amount of CO₂ gas. It has been observed that when two or more ILs are mixed in different proportions, a new solvent is obtained which is much better than that of each component of ILs from which the mixture is obtained. Within a mixture of ILs, several unidentified interactions occur among several ions which give rise to unique solvent properties to the mixture. Herein, in this review, we have highlighted the utilization of the advantageous properties of the IL mixtures in protein stability studies. This approach is exceptional and opens new directions to the use of ILs in biotechnology.

Asymmetric Chemoenzymatic Reductive Acylation of Ketones by a Combined Iron-Catalyzed Hydrogenation-Racemization and Enzymatic Resolution Cascade

A general and practical process for the conversion of prochiral ketones into the corresponding chiral acetates has been realized. An iron carbonyl complex is reported to catalyze the hydrogenation-dehydrogenation-hydrogenation of prochiral ketones. By merging the iron-catalyzed redox reactions with enantioselective enzymatic acylations a wide range of benzylic, aliphatic and (hetero)aromatic ketones, as well as diketones, were reductively acylated. The corresponding products were isolated with high yields and enantioselectivities. The use of an iron catalyst together with molecular hydrogen as the hydrogen donor and readily available ethyl acetate as acyl donor make this cascade process highly interesting in terms of both economic value and environmental credentials.