Catalysts

36 pages, 4326 KiB

Open AccessEditor’s ChoiceReview

The Role of Yeast-Surface-Display Techniques in Creating Biocatalysts for Consolidated BioProcessing

by Ian Dominic Flormata Tabañag, I-Ming Chu, Yu-Hong Wei and Shen-Long Tsai

Catalysts 2018, 8(3), 94; https://doi.org/10.3390/catal8030094 - 25 Feb 2018

Cited by 18 | Viewed by 7607

Climate change is directly linked to the rapid depletion of our non-renewable fossil resources and has posed concerns on sustainability. Thus, imploring the need for us to shift from our fossil based economy to a sustainable bioeconomy centered on biomass utilization. The efficient [...] Read more.

Climate change is directly linked to the rapid depletion of our non-renewable fossil resources and has posed concerns on sustainability. Thus, imploring the need for us to shift from our fossil based economy to a sustainable bioeconomy centered on biomass utilization. The efficient bioconversion of lignocellulosic biomass (an ideal feedstock) to a platform chemical, such as bioethanol, can be achieved via the consolidated bioprocessing technology, termed yeast surface engineering, to produce yeasts that are capable of this feat. This approach has various strategies that involve the display of enzymes on the surface of yeast to degrade the lignocellulosic biomass, then metabolically convert the degraded sugars directly into ethanol, thus elevating the status of yeast from an immobilization material to a whole-cell biocatalyst. The performance of the engineered strains developed from these strategies are presented, visualized, and compared in this article to highlight the role of this technology in moving forward to our quest against climate change. Furthermore, the qualitative assessment synthesized in this work can serve as a reference material on addressing the areas of improvement of the field and on assessing the capability and potential of the different yeast surface display strategies on the efficient degradation, utilization, and ethanol production from lignocellulosic biomass. Full article

(This article belongs to the Special Issue Immobilized Biocatalysts)

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32 pages, 4795 KiB

Open AccessEditor’s ChoiceReview

The Design of MnO_x Based Catalyst in Post-Plasma Catalysis Configuration for Toluene Abatement

by Zhiping Ye, Jean-Marc Giraudon, Nathalie De Geyter, Rino Morent and Jean-François Lamonier

Catalysts 2018, 8(2), 91; https://doi.org/10.3390/catal8020091 - 23 Feb 2018

Cited by 42 | Viewed by 8817

Abstract

This review provides an overview of our present state of knowledge using manganese oxide (MnO_x)-based catalysts for toluene abatement in PPC (Post plasma-catalysis) configuration. The context of this study is concisely sum-up. After briefly screening the main depollution methods, the principles [...] Read more.

This review provides an overview of our present state of knowledge using manganese oxide (MnO_x)-based catalysts for toluene abatement in PPC (Post plasma-catalysis) configuration. The context of this study is concisely sum-up. After briefly screening the main depollution methods, the principles of PPC are exposed based on the coupling of two mature technologies such as NTP (Non thermal plasma) and catalysis. In that respect, the presentation of the abundant manganese oxides will be firstly given. Then in a second step the main features of MnO_x allowing better performances in the reactions expected to occur in the abatement of toluene in PPC process are reviewed including ozone decomposition, toluene ozonation, CO oxidation and toluene total oxidation. Finally, in a last part the current status of the applications of PPC using MnO_x on toluene abatement are discussed. In a first step, the selected variables of the hybrid process related to the experimental conditions of toluene abatement in air are identified. The selected variables are those expected to play a role in the performances of PPC system towards toluene abatement. Then the descriptors linked to the performances of the hybrid process in terms of efficiency are given and the effects of the variables on the experimental outcomes (descriptors) are discussed. The review would serve as a reference guide for the optimization of the PPC process using MnO_x-based oxides for toluene abatement. Full article

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28 pages, 6004 KiB

Open AccessFeature PaperEditor’s ChoiceReview

One-Pot Combination of Metal- and Bio-Catalysis in Water for the Synthesis of Chiral Molecules

by Nicolás Ríos-Lombardía, Joaquín García-Álvarez and Javier González-Sabín

Catalysts 2018, 8(2), 75; https://doi.org/10.3390/catal8020075 - 10 Feb 2018

Cited by 48 | Viewed by 7621

Abstract

During the last decade, the combination of different metal- and bio-catalyzed organic reactions in aqueous media has permitted the flourishing of a variety of one-pot asymmetric multi-catalytic reactions devoted to the construction of enantiopure and high added-value chemicals under mild reaction conditions (usually [...] Read more.

During the last decade, the combination of different metal- and bio-catalyzed organic reactions in aqueous media has permitted the flourishing of a variety of one-pot asymmetric multi-catalytic reactions devoted to the construction of enantiopure and high added-value chemicals under mild reaction conditions (usually room temperature) and in the presence of air. Herein, a comprehensive account of the state-of-the-art in the development of catalytic networks by combining metallic and biological catalysts in aqueous media (the natural environment of enzymes) is presented. Among others, the combination of metal-catalyzed isomerizations, cycloadditions, hydrations, olefin metathesis, oxidations, C-C cross-coupling and hydrogenation reactions, with several biocatalyzed transformations of organic groups (enzymatic reduction, epoxidation, halogenation or ester hydrolysis), are discussed. Full article

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11 pages, 1863 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

New Trendy Magnetic C-Scorpionate Iron Catalyst and Its Performance towards Cyclohexane Oxidation

by Ana P. C. Ribeiro, Inês A. S. Matias, Elisabete C. B. A. Alegria, Ana M. Ferraria, Ana M. Botelho do Rego, Armando J. L. Pombeiro and Luísa M. D. R. S. Martins

Catalysts 2018, 8(2), 69; https://doi.org/10.3390/catal8020069 - 08 Feb 2018

Cited by 14 | Viewed by 4563

Abstract

For the first time, a magnetic C-scorpionate catalyst was prepared from the iron(II) complex [FeCl₂{κ³-HC(pz)₃}] (pz = pyrazol-1-yl) and ferrite, using the sustainable mechanochemical synthetic procedure. Its catalytic activity for the cyclohexane oxidation with tert-butyl hydroperoxide [...] Read more.

For the first time, a magnetic C-scorpionate catalyst was prepared from the iron(II) complex [FeCl₂{κ³-HC(pz)₃}] (pz = pyrazol-1-yl) and ferrite, using the sustainable mechanochemical synthetic procedure. Its catalytic activity for the cyclohexane oxidation with tert-butyl hydroperoxide (TBHP) was evaluated in different conditions, namely under microwave irradiation and under the effect of an external magnetic field. The use of such magnetic conditions significantly shifted the catalyst alcohol/ketone selectivity, thus revealing a promising, easy new protocol for tuning selectivity in important catalytic processes. Full article

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21 pages, 4778 KiB

Open AccessEditor’s ChoiceArticle

1,3-Diene Polymerization Mediated by Homoleptic Tetramethylaluminates of the Rare-Earth Metals

by Christoph O. Hollfelder, Lars N. Jende, Dominic Diether, Theresa Zelger, Rita Stauder, Cäcilia Maichle-Mössmer and Reiner Anwander

Catalysts 2018, 8(2), 61; https://doi.org/10.3390/catal8020061 - 03 Feb 2018

Cited by 22 | Viewed by 5278

Abstract

During the past two decades homoleptic tetramethylaluminates of the trivalent rare-earth metals, Ln(AlMe₄)₃, have emerged as useful components for efficient catalyst design in the field of 1,3-diene polymerization. Previous work had focused on isoprene polymerization applying Ln(AlMe₄) [...] Read more.

During the past two decades homoleptic tetramethylaluminates of the trivalent rare-earth metals, Ln(AlMe₄)₃, have emerged as useful components for efficient catalyst design in the field of 1,3-diene polymerization. Previous work had focused on isoprene polymerization applying Ln(AlMe₄)₃ precatalysts with Ln = La, Ce, Pr, Nd, Gd and Y, in the presence of Et₂AlCl as an activator. Polymerizations employing Ln(AlMe₄)₃ with Ln = La, Y and Nd along with borate/borane co-catalysts [Ph₃C][B(C₆F₅)₄], [PhNMe₂H][B(C₆F₅)₄] and [B(C₆F₅)₃] were mainly investigated for reasons of comparison with ancillary ligand-supported systems (cf. half-sandwich complexes). The present study investigates into a total of eleven rare-earth elements, namely Ln = La, Ce, Pr, Nd, Gd, Tb, Dy, Ho, Y, Er and Lu. A full overview on the polymerization behavior of Ln(AlMe₄)₃ in the presence of perfluorinated borate/borane cocatalysts and R₂AlCl-type activators (R = Me, Et) is provided, probing the monomers isoprene and 1,3-butadiene (and preliminary ethylene). Virtually complete cis-1,4-selectivities are obtained for several catalyst/cocatalyst combinations (e.g., Gd(AlMe₄)₃/Me₂AlCl, >99.9%). Insights into the ‘black box’ of active species are obtained by indirect observations via screening of pre-reaction time and cocatalyst concentration. The microstructure of the polydienes is investigated by combined ¹H/¹³C NMR and ATR-IR spectroscopies. Furthermore, the reaction of [LuMe₆(Li(thf)_x)₃] with AlMe₃ has been applied as a new strategy for the efficient synthesis of Lu(AlMe₄)₃. The solid-state structures of Gd(AlMe₄)₃ and Tb(AlMe₄)₃ are reported. Full article

(This article belongs to the Special Issue Catalysts for the Controlled Polymerization of Conjugated Dienes)

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12 pages, 2297 KiB

Open AccessFeature PaperEditor’s ChoiceCommunication

Whole-Cell Biocatalyst for Chemoenzymatic Total Synthesis of Rivastigmine

by Paola Vitale, Filippo Maria Perna, Gennaro Agrimi, Isabella Pisano, Francesco Mirizzi, Roberto Vito Capobianco and Vito Capriati

Catalysts 2018, 8(2), 55; https://doi.org/10.3390/catal8020055 - 31 Jan 2018

Cited by 45 | Viewed by 6567

Abstract

Biocatalytic processes are increasingly playing a key role in the development of sustainable asymmetric syntheses, which are central to pharmaceutical companies for the production of chiral enantiopure drugs. This work describes a simple and economically viable chemoenzymatic process for the production of ( [...] Read more.

Biocatalytic processes are increasingly playing a key role in the development of sustainable asymmetric syntheses, which are central to pharmaceutical companies for the production of chiral enantiopure drugs. This work describes a simple and economically viable chemoenzymatic process for the production of (S)-rivastigmine, which is an important drug for the treatment of mild to moderate dementia of the Alzheimer’s type. The described protocol involves the R-regioselective bioreduction of an aromatic ketone by Lactobacillus reuteri DSM 20016 whole cells in phosphate buffered saline (PBS) (37 °C, 24 h) as a key step. Biocatalytic performance of baker’s yeast whole cells in water and in aqueous eutectic mixtures have been evaluated and discussed as well. The route is scalable, environmentally friendly, and the target drug is obtained via four steps in overall 78% yield and 98% ee. Full article

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10 pages, 1006 KiB

Open AccessEditor’s ChoiceArticle

Genetically Fused T4L Acts as a Shield in Covalent Enzyme Immobilisation Enhancing the Rescued Activity

by Matteo Planchestainer, David Roura Padrosa, Martina Letizia Contente and Francesca Paradisi

Catalysts 2018, 8(1), 40; https://doi.org/10.3390/catal8010040 - 20 Jan 2018

Cited by 11 | Viewed by 5261

Abstract

Enzyme immobilisation is a common strategy to increase enzymes resistance and reusability in a variety of excellent ‘green’ applications. However, the interaction with the solid support often leads to diminished specific activity, especially when non-specific covalent binding to the carrier takes place which [...] Read more.

Enzyme immobilisation is a common strategy to increase enzymes resistance and reusability in a variety of excellent ‘green’ applications. However, the interaction with the solid support often leads to diminished specific activity, especially when non-specific covalent binding to the carrier takes place which affects the delicate architecture of the enzyme. Here we developed a broadly applicable strategy where the T4-lysozyme (T4L) is genetically fused at the N-terminus of different enzymes and used as inert protein spacer which directly attaches to the carrier preventing shape distortion of the catalyst. Halomonas elongata aminotransferase (HEWT), Bacillus subtilis engineered esterase (BS2m), and horse liver alcohol dehydrogenase (HLADH) were used as model enzymes to elucidate the benefits of the spacer. While HEWT and HLADH activity and expression were diminished by the fused T4L, both enzymes retained almost quantitative activity after immobilisation. In the case of BS2m, the protective effect of the T4L effectively was important and led to up to 10-fold improvement in the rescued activity. Full article

(This article belongs to the Special Issue Immobilized Biocatalysts)

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16 pages, 4240 KiB

Open AccessEditor’s ChoiceArticle

“Deceived” Concentrated Immobilized Cells as Biocatalyst for Intensive Bacterial Cellulose Production from Various Sources

by Nikolay Stepanov and Elena Efremenko

Catalysts 2018, 8(1), 33; https://doi.org/10.3390/catal8010033 - 18 Jan 2018

Cited by 25 | Viewed by 5758

Abstract

A new biocatalyst in the form of Komagataeibacter xylinum B-12429 cells immobilized in poly(vinyl alcohol) cryogel for production of bacterial cellulose was demonstrated. Normally, the increased bacteria concentration causes an enlarged bacterial cellulose synthesis while cells push the polysaccharide out to pack themselves [...] Read more.

A new biocatalyst in the form of Komagataeibacter xylinum B-12429 cells immobilized in poly(vinyl alcohol) cryogel for production of bacterial cellulose was demonstrated. Normally, the increased bacteria concentration causes an enlarged bacterial cellulose synthesis while cells push the polysaccharide out to pack themselves into this polymer and go into a stasis. Immobilization of cells into the poly(vinyl alcohol) cryogel allowed “deceiving” them: bacteria producing cellulose pushed it out, which further passed through the pores of cryogel matrix and was accumulated in the medium while not covering the cells; hence, the latter were deprived of a possible transition to inactivity and worked on the synthesis of bacterial cellulose even more actively. The repeated use of immobilized cells retaining 100% of their metabolic activity for at least 10 working cycles (60 days) was performed. The immobilized cells produce bacterial cellulose with crystallinity and porosity similar to polysaccharide of free cells, but having improved stiffness and tensile strength. Various media containing sugars and glycerol, based on hydrolysates of renewable biomass sources (aspen, Jerusalem artichoke, rice straw, microalgae) were successfully applied for bacterial cellulose production by immobilized cells, and the level of polysaccharide accumulation was 1.3–1.8-times greater than suspended cells could produce. Full article

(This article belongs to the Special Issue Immobilized Biocatalysts)

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8 pages, 1882 KiB

Open AccessFeature PaperEditor’s ChoiceCommunication

Relationships between Substrate Promiscuity and Chiral Selectivity of Esterases from Phylogenetically and Environmentally Diverse Microorganisms

by Cristina Coscolín, Mónica Martínez-Martínez, Jennifer Chow, Rafael Bargiela, Antonio García-Moyano, Gro E. K. Bjerga, Alexander Bollinger, Runar Stokke, Ida H. Steen, Olga V. Golyshina, Michail M. Yakimov, Karl-Erich Jaeger, Alexander F. Yakunin, Wolfgang R. Streit, Peter N. Golyshin and Manuel Ferrer

Catalysts 2018, 8(1), 10; https://doi.org/10.3390/catal8010010 - 05 Jan 2018

Cited by 8 | Viewed by 4673

Abstract

Substrate specificity and selectivity of a biocatalyst are determined by the protein sequence and structure of its active site. Finding versatile biocatalysts acting against multiple substrates while at the same time being chiral selective is of interest for the pharmaceutical and chemical industry. [...] Read more.

Substrate specificity and selectivity of a biocatalyst are determined by the protein sequence and structure of its active site. Finding versatile biocatalysts acting against multiple substrates while at the same time being chiral selective is of interest for the pharmaceutical and chemical industry. However, the relationships between these two properties in natural microbial enzymes remain underexplored. Here, we performed an experimental analysis of substrate promiscuity and chiral selectivity in a set of 145 purified esterases from phylogenetically and environmentally diverse microorganisms, which were assayed against 96 diverse esters, 20 of which were enantiomers. Our results revealed a negative correlation between substrate promiscuity and chiral selectivity in the evaluated enzymes. Esterases displaying prominent substrate promiscuity and large catalytic environments are characterized by low chiral selectivity, a feature that has limited commercial value. Although a low level of substrate promiscuity does not guarantee high chiral selectivity, the probability that esterases with smaller active sites possess chiral selectivity factors of interest for industry (>25) is significantly higher than for promiscuous enzymes. Together, the present study unambiguously demonstrates that promiscuous and selective esterases appear to be rare in nature and that substrate promiscuity can be used as an indicator of the chiral selectivity level of esterases, and vice versa. Full article

(This article belongs to the Special Issue Biocatalysis and Biotransformations)

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