Affinity partitioning of yeast and horse liver alcohol dehydrogenases in polyethylene glycol-dyes/dextran two-phase systems

Summary Affinity partition of yeast and horse liver alcohol dehydrogenases (ADH) in two-phase systems containing polyethylene glycol (PEG)-dyes is most effective using Cu(II) complexes of Light resistant yellow 2KT and Red-violet 2KT. The effects of NaCl, NAD and chelating agents (imidazole and adenine) on the partitioning of ADH's were studied. It was shown that two-phase systems containing dyes in the top and bottom phases with different affinity to yeast ADH are promising for the extraction of enzyme from crude extract.     

Immobilised metal ion affinity chromatography purification of alcohol dehydrogenase from baker’s yeast using an expanded bed adsorption system

Alcohol dehydrogenase (ADH) from solutions of homogenised packed bakers’ yeast has been successfully purified using immobilised metal-ion affinity chromatography in an expanded bed. Method scouting carried out using pure ADH solutions loaded onto 5-ml HiTrap columns charged with Zn²⁺, Ni²⁺ and Cu²⁺ and eluted using 0–50 mM EDTA gradient found that charging with Zn²⁺ gave the highest recovery and the lowest EDTA concentration required for elution. These results were used to develop a protocol for the expanded bed system and further tested using clarified yeast homogenate loaded onto XK16/20 packed beds (approximately 30 ml) packed with Chelating Sepharose FastFlow matrix in order to determine the optimum elution conditions using EDTA. The ADH was found to elute at 5 mM EDTA and the dynamic and total binding capacities of Streamline chelating for ADH were found to be 235 U/ml and 1075 U/ml matrix, respectively. Expanded bed work based on a step EDTA elution protocol demonstrated that ADH could be successfully eluted from unclarified homogenised bakers’ yeast diluted to 10 mg/ml total protein content with a recovery of 80–100% that was maintained over five consecutive runs with a vigorous clean-in-place procedure between each run.     

InBr3-catalyzed reduction of ketones with a hydrosilane: deoxygenation of aromatic ketones and selective synthesis of secondary alcohols and symmetrical ethers from aliphatic ketones

An InBr₃-Et₃SiH reducing system was developed to selectively convert aliphatic ketones to a variety of secondary alcohols in moderate to good yields. An initial mixing of InBr₃ and PhSiH₃ was followed by the addition of aliphatic ketones and a solvent to afford the symmetrical ether derivatives.     

Asymmetric reduction of ketones using recombinant E. coli cells that produce a versatile carbonyl reductase with high enantioselectivity and broad substrate specificity

The gene encoding a versatile biocatalyst that shows high enantioselectivity for a variety of ketones, SCR (Saccharomyces cerevisiae carbonyl reductase), has been identified, cloned, and expressed in Escherichia coli. Two types of expression systems with high NADPH-regenerating capacities have been constructed. One is the tandem system, where the genes encoding SCR and GDH (glucose dehydrogenase) are located in the same plasmid, and the other is the two-plasmid system, where each of the SCR and GDH genes is located in separate plasmids that can coexist in one E. coli cell. Asymmetric reduction of ketones with the recombinant E. coli cells gave synthetically useful 20 alcohols, 11 of which were enantiomerically pure. The productivity of one of these products was as high as 41 g/L.     

Enclosing the nitrogen cycle: Ammonia synthesis by NOx reduction

Nitrogen cycling (N₂-NO_x-NH₃) is essential for maintaining life as it is crucial in fertilizers and nucleic acids. However, the current NH₃ synthesis (N₂-to-NH₃) for fertilizers and energy requires large amounts of fossil fuels and greenhouse gas emissions, compromising its eco-economic significance. Meanwhile, approaches like selective catalytic reaction are applied to neutralize the toxic NO_x into N₂ but call for value-added NH₃ as the reduction agent. In this regard, directly converting harmful NO_x, one of the major environmental pollutants, into NH₃ is a promising way to balance the nitrogen cycle eco-friendly, which is still in its infancy. Recently, the electrocatalytic NO_x reduction reaction (NO_xRR) unveiled a potential route for the NO_x-to-NH₃ conversion. This review presents the latest progress in the electrocatalytic NO_xRR in reaction mechanism and catalysts design. It will provide a comprehensive understanding to guide future research in NO_xRR, aiming to offer sustainable chemistry and energy feedstocks for the carbon-zero economy.     

TMDS-Pd/C: a convenient system for the reduction of acetals to ethers

A simple and practical procedure for the reduction of acetals to ethers is described. It is based on the use of a 1,1,3,3-tetramethyldisiloxane (TMDS)-Pd/C system in the presence of a Brønsted acid as the co-catalyst. The reaction occurs under mild conditions and ethers are obtained in high yields.     

Enzymatic reduction of ribonucleotides: biosynthesis pathway of deoxyribonucleotides

Ribonucleotide reductases are enzymes that synthesize the deoxyribonucleotides required for the replication of DNA in dividing cells. They thus have a key function for the growth of microorganisms and of all plant and animal tissues. The enzymes reduce all four purine and pyrimidine ribonucleotides (as the 5′-diphosphates or triphosphates) with direct substitution of the 2′-hydroxyl group by hydrogen. The physiological reducing agents are the mercapto groups of thioredoxins, a group of small proteins, which are regenerated from the oxidized form by NADPH-dependent thioredoxin reductases. There are two known types of ribonucleotide reductases (I and II), which catalyze hydrogen transfer with the aid of protein-bound iron ions or of 5′-deoxyadenosylcobalamin (coenzyme B₁₂); free radicals can be detected in both cases. The enzymes are regulated by effector nucleotides. There may exist a homeostatic mechanism, which guarantees the supply of DNA precursors to the cell.     

A mild titanium-based system for the reduction of amides to aldehydes

A mild method for the reduction of amides to aldehydes using 1,1,3,3-tetramethyldisiloxane/titanium(IV) isopropoxide reducing system is described. The reaction occurs under mild conditions and allows the reduction of aromatic as well as aliphatic, tertiary amides to the corresponding aldehydes, in good yields. This methodology was extended to the reduction of aromatic secondary and primary amides to the corresponding aldehydes.     

Simultaneous reduction of nitro- to amino-group in the palladium-catalyzed Suzuki cross-coupling reaction

An efficient method for palladium-catalyzed Suzuki cross-coupling reaction with simultaneous reduction of nitro- to amino-group has been developed. This method allows nitro-substituted aryl halides to readily react with arylboronic acids, to afford aryl substituted aniline in low to excellent yields. The reaction was catalyzed by Pd(OAc)₂ (3 mol %) at 150 °C under atmospheric pressure in the presence of K₂CO₃ (3 equiv) in DMF/H₂O (5/1).     

Iron-catalyzed selective reduction of nitro compounds to amines

An efficient reduction of the nitro group with a catalytic amount of Fe(acac)₃ and TMDS in THF at 60 °C affording the corresponding amine is described.     

Recent advances on deoximation: From stoichiometric reaction to catalytic reaction

Recent advances on the deoximation reactions are reviewed in this review. It was shown that catalytic deoximation with molecular oxygen as the mild oxidant should be the developing trend of the reaction.     

Alcohol reduction of enamines

Primary or secondary alcohols will reduce enamines to their corresponding saturated amines when heated in a microwave apparatus at a temperature of 160 °C for a period of one hour.     

Membrane-bound dehydrogenases from Gluconobacter sp.: Interfacial electrochemistry and direct bioelectrocatalysis

Although membrane-bound dehydrogenases isolated from Gluconobacter sp. (mainly PQQ-dependent alcohol and fructose dehydrogenase) have been used for preparing diverse forms of bioelectronic interfaces for almost 2 decades, it is not an easy task to interpret an electrochemical behaviour correctly. Recent discoveries regarding redox properties of membrane-bound dehydrogenases along with extensive investigations of direct electron transfer (DET) or direct bioelectrocatalysis with these enzymes are summarized in this review. The main aim of this review is to draw general conclusions about possible electronic coupling paths of these enzymes on various interfaces via direct electron transfer or direct bioelectrocatalysis. A short overview of the metabolism and respiration chain in Gluconobacter relevant to interfacial electrochemistry is given. Biosensor devices based on DET or direct bioelectrocatalysis using membrane-bound dehydrogenases from Gluconobacter sp. are described briefly with the emphasis given on practical applications of preparing enzymatic biofuel cells. Moreover, interfacial electrochemistry of Gluconobacter oxydans related to the construction of microbial biofuel cells is also discussed.     

A novel application of horseradish peroxidase: Oxidation of alcohol ethoxylate to alkylether carboxylic acid

A novel application of horseradish peroxidase （HRP） in the oxidation of alcohol ethoxylate to alkylether carboxylic acid in the present of H2O2 was reported in this paper. We propose the mechanism for the catalytic oxidation reaction is that the hydrogen transfers from the substrate to the ferryl oxygen to form the α-hydroxy carbon radical intermediate. The reaction offers a new approach for further research structure and catalytic mechanism of HRP and production of alkylether carboxylic acid.     

Study of the responses of a gas chromatography—reduction gas detector system to gaseous hydrocarbons under different conditions

The response of a reduction gas detector (RGD) to C₂-C₆ alkenes, C₂-C₆ alkanes, isoprene and benzene has been investigated using gas chromatography (GC) with a packed column. The RGD is considerably more sensitive to alkenes than is the flame ionization detector. The detection limit of this present GC/RGD system for alkenes is about 0.01 ng. It has much greater sensitivity to alkenes than to alkanes. Its sensitivity increases with increasing HgO bed temperature, but its selectivity towards alkenes decreases at the same time. The selectivity of the RGD may not be significant for much heavier molecules. The sensitivity of the RGD is inversely proportional to the carrier gas flow rate through the HgO bed. The baseline of the system increases significantly with increasing oven temperature.     

An alternative route to tethered Ru(II) transfer hydrogenation catalysts

A new route towards a series of tethered η⁶-arene/Ru(II) catalysts for use in the transfer and pressure hydrogenation of ketones and aldehydes to alcohols is reported. The route proceeds through the formation of an amide from the diamine precursor, followed by reduction, rather than the direct alkylation of the diamine. This has the advantage that dialkylation of the amine is avoided during the synthesis. Through this new route, both racemic and enantiomerically-pure η⁶-arene/Ru(II) tethered catalysts can be prepared in high yield.     

Highly selective reduction of nitrobenzenes to azoxybenzenes with a copper catalyst

A convenient protocol for highly selective delivery of azoxybenzenes from reduction of nitrobenzenes was developed by utilizing a copper catalyst. A variety of functional groups and substitution were well tolerated.     

Rapid identification of new bacterial alcohol dehydrogenases for (R)- and (S)-enantioselective reduction of ss-ketoesters

New bacterial alcohol dehydrogenases with high and complementary enantioselectivity for the reduction of ethyl 3-keto-4,4,4-trifluorobutyrate 1 and methyl 3-keto-3-(3'-pyridyl)-propionate 3 have been rapidly identified by use of a new methodology consisting of preselection of microorganisms based on degradation ability and high-throughput screening with a miniaturized system coupled with fast analysis of enantioselectivities.     

A fast route to obtain manganese spinel nanoparticles by reduction of K-birnessite

The K-birnessite (K_xMnO₂·yH₂O) reduction reaction has been tested in order to obtain manganese spinel nanoparticles. The addition of 0.25 weight percent of hydrazine hydrate, the reducing agent, during 24 hours is efficient to transform the birnessite powder in a hausmanite Mn₃O₄ powder. Well crystallised square shape nanoparticles are obtained. Different birnessite precursors have been tested and the reaction kinetics is strongly correlated to the crystallinity and granulometry of the precursor. The effects of aging time and hydrazine hydrate amount have been studied. Well crystallised Mn₃O₄ is obtained in one hour. The presence of feitknechtite (MnO(OH)) and amorphous nanorods has been detected as an intermediate phase during birnessite conversion into hausmanite. The conversion mechanism is discussed.