Molar Conversion Research Articles

Characterization of three glutamate decarboxylases from Bacillus spp. for efficient \u03b3-aminobutyric acid production

BackgroundGamma-aminobutyric acid (GABA) is an important bio-product used in pharmaceuticals and functional foods and as a precursor of the biodegradable plastic polyamide 4. Glutamate decarboxylase (GAD) converts l-glutamate (l-Glu) into GABA via decarboxylation. Compared with other methods, develop a bioconversion platform to produce GABA is of considerable interest for industrial use.ResultsThree GAD genes were identified from three Bacillus strains and heterologously expressed in Escherichia coli BL21 (DE3). The optimal reaction temperature and pH values for three enzymes were 40 °C and 5.0, respectively. Of the GADs, GADZ11 had the highest catalytic efficiency towards l-Glu (2.19 mM− 1 s− 1). The engineered E. coli strain that expressed GADZ11 was used as a whole-cell biocatalyst for the production of GABA. After repeated use 14 times, the cells produced GABA with an average molar conversion rate of 98.6% within 14 h.ConclusionsThree recombinant GADs from Bacillus strains have been conducted functional identification. The engineered E. coli strain heterologous expressing GADZ1, GADZ11, and GADZ20 could accomplish the biosynthesis of l-Glu to GABA in a buffer-free reaction at a high l-Glu concentration. The novel engineered E. coli strain has the potential to be a cost-effective biotransformation platform for the industrial production of GABA.

Batch and continuous production of biolubricant from fusel oil and oleic acid: Lipase screening, reactor system development, and reaction optimization

Fusel oil was used as a source of isoamyl alcohol in the synthesis of biolubricant by esterification with oleic acid catalyzed by different sources of lipase immobilized on poly(styrene/divinylbenzene) copolymer resin. In preliminary tests, Rhizopus oryzae lipase showed satisfactory performance, providing high molar conversion of the starting materials (>90% in 24 h of reaction), and was selected for subsequent experiments. The optimal conditions for isoamyl oleate production by immobilized R. oryzae lipase were 1:1.5 ratio of fusel oil to oleic acid and reaction temperature of 45°C. Continuous runs were carried out in a two-stage packed-bed reactor coupled to a water extraction column filled with molecular sieves. Each reactor stage was loaded with 2.6 g of immobilized lipase and then fed with fusel oil and oleic acid at a 1:1.5 molar ratio in the presence of isooctane. The performance of the proposed system was tested at a space time of 10.2 h, resulting in a mean ester productivity of 292.20 ± 18.46 µmol g−1 min−1 and biocatalyst half-life of 179.6 h. The properties of purified samples were in accordance with standard requirements for biolubricants.

Synthesis and catalytic performance of Linde-type A zeolite (LTA) from coal fly ash utilizing microwave and ultrasound collaborative activation method

Pure LTA zeolites of high crystallinity have been synthesized from coal fly ash (CFA) by utilizing a method of microwave and ultrasound collaborative activation (MUCA) in situ for the first time. Compared to the activation method of only microwave or ultrasound, the MUCA have more efficient ability to dissolve silica-aluminum species from CFA while avoiding the digestion of other impurities, greatly reduced the energy consumption. While the liquid-solid ratio (LSR) of sodium hydroxide solution to CFA was 10 mL/g, the molar conversion rates of silicon and aluminum were 70.26% and 68.03%, respectively. Furthermore, with different LSR, pure LTA zeolite could be synthesized by adjusting the ratio of Si/Al. The CFA used in this paper contains Fe2O3 of about 12 wt percentage, and there have found almost no element of iron existing in the LTA zeolite products, indicating that the method of MUCA is suitable for the preparation of high purity zeolite. Finally, according to the mechanism of crystallization-dissolution-recrystallization, the morphology of LTA products could be well tuned by adjusting parameters such as LSR or crystallization time. The maximum BET surface area was 474 m2/g without additional calcium ion exchange steps by direct using of municipal water instead of deionized water, and the maximum CO2 adsorption capacity was 1.96 mol/g under 0 ℃. The mesoporous LTA zeolite also have been prepared just through the adjustment of crystallization time without addition of any other templates, the intramesopores of about 17 nm made greatly improvement in catalytic cracking of 1,3,5-tri-isopropylbenzene which is inaccessible to the conventional LTA micropores, and the conversion rate of 1,3,5-tri-isopropylbenzene reached to 25.40% as well as 11.05% of the selectivity of secondary cracking product benzene.

Biosynthesis of 3’-O-methylisoorientin from luteolin by selecting O-methylation/C-glycosylation motif

Glycosylation and methylation of flavonoids are the main types of structural modifications and can endow flavonoids with greater stability, bioactivity, and bioavailability. In this study, five types of O-methyltransferases were screened for producing O-methylated luteolin, and the biosynthesis strategy of 3’-O-methylisoorientin from luteolin was determined. To improve the production of 3’-O-methylluteolin, the S-adenosyl-l-methionine synthesis pathway was reconstructed in the recombinant strain by introducing S-adenosyl-l-methionine synthetase genes. After optimizing the conversion conditions, maximal 3’-O-methylluteolin production reached 641 ± 25 mg/L with a corresponding molar conversion of 76.5 %, which was the highest titer of methylated flavonoids reported to date in Escherichia coli. 3’-O-Methylluteolin (127 mg) was prepared from 250 mL of the broth by silica gel column chromatography and preparative HPLC with a yield of 79.4 %. Subsequently, we used the biocatalytic cascade of Gentiana triflora C-glycosyltransferase (Gt6CGT) and Glycine max sucrose synthase (GmSUS) to biosynthesize 3’-O-methylisoorientin from 3’-O-methylluteolin in vitro. By optimizing the coupled reaction conditions and using the fed-batch operation, maximal 3’-O-methylisoorientin production reached 226 ± 8 mg/L with a corresponding molar conversion of 98 %. Therefore, this study provides an efficient method for the production of novel 3’-O-methylisoorientin and the biosynthesis strategy for methylated C-glycosylation flavonoids by selective O-methylation/C-glycosylation motif on flavonoids.

Biomass of a Psychrophilic Fungus as a Biocatalyst for Efficient Direct Esterification of Citronellol

A biomass-bound lipase from psychrophilic Chrysosporium pannorum A-1 is an efficient biocatalyst for direct esterification of β-citronellol and acetic acid in an organic solvent. The biomass is effectively produced by fungal submerged culture at 20 ℃, which results in lower energy consumption during the production of biocatalyst. Supplementation of the culture medium with calcium carbonate together with olive oil contributed to a significant increase in the active biomass of mycelium in one batch culture and increased the efficiency of the biocatalyst. Biomass-bound lipase showed high catalytic activity in a broad temperature range of 30–60 °C and stability up to 70 °C. A maximum molar conversion value of 98% was obtained at 30 °C in n-hexane using a 2:1 alcohol-to-acid molar ratio and 3% w/v of the biocatalyst within 24 h. The high equimolar concentration of the substrates (200 mM) did not have an adverse effect on mycelial biomass activity. Dry mycelium of C. pannorum is a promising biocatalyst for large-scale biosynthesis of citronellyl acetate, given its low-cost production, high activity at low temperatures, and reusability in a minimum of seven 24-h biocatalytic cycles.

Lipase-Catalyzed Production of Sorbitol Laurate in a "2-in-1" Deep Eutectic System: Factors Affecting the Synthesis and Scalability.

Surfactants, such as glycolipids, are specialty compounds that can be encountered daily in cleaning agents, pharmaceuticals or even in food. Due to their wide range of applications and, more notably, their presence in hygiene products, the demand is continuously increasing worldwide. The established chemical synthesis of glycolipids presents several disadvantages, such as lack of specificity and selectivity. Moreover, the solubility of polyols, such as sugars or sugar alcohols, in organic solvents is rather low. The enzymatic synthesis of these compounds is, however, possible in nearly water-free media using inexpensive and renewable building blocks. Using lipases, ester formation can be achieved under mild conditions. We propose, herein, a “2-in-1” system that overcomes solubility problems, as a Deep Eutectic System (DES) made of sorbitol and choline chloride replaces either a purely organic or aqueous medium. For the first time, 16 commercially available lipase formulations were compared, and the factors affecting the conversion were investigated to optimize this process, owing to a newly developed High-Performance Liquid Chromatography-Evaporative Light Scattering Detector (HPLC-ELSD) method for quantification. Thus, using 50 g/L of lipase formulation Novozym 435® at 50 °C, the optimized synthesis of sorbitol laurate (SL) allowed to achieve 28% molar conversion of 0.5 M of vinyl laurate to its sugar alcohol monoester when the DES contained 5 wt.% water. After 48h, the de novo synthesized glycolipid was separated from the media by liquid–liquid extraction, purified by flash-chromatography and characterized thoroughly by one- and two-dimensional Nuclear Magnetic Resonance (NMR) experiments combined to Mass Spectrometry (MS). In completion, we provide initial proof of scalability for this process. Using a 2.5 L stirred tank reactor (STR) allowed a batch production reaching 25 g/L in a highly viscous two-phase system.

Orientin and vitexin production by a one-pot enzymatic cascade of a glycosyltransferase and sucrose synthase

Orientin and vitexin, important components of bamboo-leaf extracts, are C-glycosylflavones which exhibit a number of interesting biological properties. In this work, we developed an efficient biocatalytic cascade for orientin and vitexin production consisting of Trollius chinensis C-glycosyltransferase (TcCGT) and Glycine max sucrose synthase (GmSUS). In order to relieve the bottleneck of the biocatalytic cascade, the biocatalytic efficiency, reaction condition compatibilities and the ratio of the enzymes were determined. We found that the specific activity of TcCGT was significantly influenced by enzyme dose and Triton X-100 or Tween 20 (0.2%). Co-culture of BL21-TcCGT-Co and BL21-GmSUS-Co affected the catalytic efficiency of TcCGT and GmSUS, and the maximum orientin production rate reached 47 μM/min at the inoculation ratio of 9:1. The optimal pH and temperature for the biocatalytic cascade were pH 7.5 and 30 °C, respectively. Moreover, the high dose of the enzymes can improve the tolerance of biocatalytic cascade to substrate inhibition in the one-pot reaction. By using a fed-batch strategy, maximal titers of orientin and vitexin reached 7090 mg/L with a corresponding molar conversion of 98.7% and 5050 mg/L with a corresponding molar conversion of 97.3%, respectively, which is the highest titer reported to date. Therefore, the method described herein for efficient production of orientin and vitexin by modulating catalytic efficiencies of enzymes can be widely used for the C-glycosylation of flavonoids.

Inhibitory effect of alkyl groups on N-nitrosamine formation from secondary and tertiary alkylamines with monochloramine

N -nitrosamines are contaminants of emerging concern, and controlling these chemicals in potable water and recycled water for potable reuse has become important for protecting public health. This study aimed to evaluate the influence of the alkyl chain lengths of N -nitrosamine precursors (secondary and tertiary amines) on the formation of N -nitrosamines via chloramination. The molar conversion efficiency from dimethylamine, an N -nitrosodimethylamine (NDMA) precursor, to NDMA (0.67%) was greater than that from diethylamine, an N -nitrosodiethylamine (NDEA) precursor, to NDEA (0.38%). Similarly, the molar conversion efficiency from trimethylamine to NDMA (0.92%) was greater than from triethylamine to NDEA (0.33%). Interestingly, a considerable difference in molar conversion efficiencies were observed for tertiary amines with the N , N -dialkyl- α -arylamine structure: the molar conversion efficiencies from N , N -dimethylbenzylamine and N , N -diethylbenzylamine to NDMA and NDEA were 50.2% and 1.7%, respectively. These results indicate that amines with ethyl groups have lower potentials for producing the corresponding N -nitrosamines than those with methyl groups. These differences in yields between amines with methyl and ethyl groups can be explained by the difference in electron density in the nitrogen atom of the amine, which influences the protonation of the amine and stabilization of intermediate species. These findings could be useful for enhancing source control of water and wastewater by regulating runoff or industrial wastewater containing high concentrations of specific N -nitrosamine precursors. • Formation of four N -nitrosamines from the secondary and tertiary amines were tested. • The molar conversion of amines having ethyl group were lower than those of methyl group. • Benzylamines had higher molar conversion values in comparison with simple alkylamines. • Longer alkyl chains in amines suppressed N -nitrosamine formation reactions.

Fine tuning the glycolytic flux ratio of EP-bifido pathway for mevalonate production by enhancing glucose-6-phosphate dehydrogenase (Zwf) and CRISPRi suppressing 6-phosphofructose kinase (PfkA) in Escherichia coli

BackgroundNatural glycolysis encounters the decarboxylation of glucose partial oxidation product pyruvate into acetyl-CoA, where one-third of the carbon is lost at CO2. We previously constructed a carbon saving pathway, EP-bifido pathway by combining Embden-Meyerhof-Parnas Pathway, Pentose Phosphate Pathway and “bifid shunt”, to generate high yield acetyl-CoA from glucose. However, the carbon conversion rate and reducing power of this pathway was not optimal, the flux ratio of EMP pathway and pentose phosphate pathway (PPP) needs to be precisely and dynamically adjusted to improve the production of mevalonate (MVA).ResultHere, we finely tuned the glycolytic flux ratio in two ways. First, we enhanced PPP flux for NADPH supply by replacing the promoter of zwf on the genome with a set of different strength promoters. Compared with the previous EP-bifido strains, the zwf-modified strains showed obvious differences in NADPH, NADH, and ATP synthesis levels. Among them, strain BP10BF accumulated 11.2 g/L of MVA after 72 h of fermentation and the molar conversion rate from glucose reached 62.2%. Second, pfkA was finely down-regulated by the clustered regularly interspaced short palindromic repeats interference (CRISPRi) system. The MVA yield of the regulated strain BiB1F was 8.53 g/L, and the conversion rate from glucose reached 68.7%.ConclusionThis is the highest MVA conversion rate reported in shaken flask fermentation. The CRISPRi and promoter fine-tuning provided an effective strategy for metabolic flux redistribution in many metabolic pathways and promotes the chemicals production.

Immobilization of Thermostable β-Glucosidase and α-l-Rhamnosidase from Dictyoglomus thermophilum DSM3960 and Their Cooperated Biotransformation of Total Flavonoids Extract from Epimedium into Icaritin

The thermostable GH3 family β-glucosidase DthBgl3 and thermostable GH78 family α-l-rhamnosidase DthRha from Dictyoglomus thermophilum DSM3960 were successfully immobilized by industrial amino resin 1000NH. The optimal reaction temperature and pH of 1000NH-DthBgl3 was 85 °C and pH 5.0. Over 65% residual enzyme activity maintained for 1000NH-DthBgl3 after a 3-h incubation under 85 °C, while about 20% residual enzyme activity maintained for free DthBgl3. The optimal reaction temperature and pH of 1000NH-DthRha was 95 °C and pH 6.5. Over 90% residual enzyme activity maintained for 1000NH-DthRha after a 3-h incubation under 90 °C, while about 22% residual enzyme activity maintained for free DthRha. Meanwhile, immobilized 1000NH-DthBgl3 and 1000NH-DthRha were successfully and could completely transform all major ingredient of 10 g/L total flavonoids extract from Epimedium (TFEE) into icaritin. After 15 cycles (45 h) of repeated use at 85 °C, 3 U 1000NH-DthBgl3 showed a molar conversion rate of 73.12%, initial activity of 30.09% and productivity of 124 mg/L/h, while 15 U 1000NH-DthRha showed a molar conversion rate of 88.50%, initial activity of 85.31% and productivity of 75 mg/L/h after ten cycles (60 h) of repeated use at 85 °C. The cooperation of two immobilized enzymes showed a molar conversion rate of 87.21% and productivity of 141 mg/L/h after 15 cycles of repeated use at 85 °C. This is the first report on immobilization of two thermostable glycosidases from thermophilic bacteria and their cooperated biocatalysis of all major ingredients of TFEE into icaritin with high productivity under a high substrate concentration.

Identification and Characterization of an Efficient Phenylalanine Ammonia-Lyase from Photorhabdus luminescens.

A putative aromatic amino acid ammonia-lyase gene (named Pl-pal) was discovered in Photorhabdus luminescens DSM 3368. BLAST and phylogenetic analyses predicted that this enzyme is a histidine ammonia-lyase, whereas sequence alignment suggested that it is more likely a phenylalanine ammonia-lyase (PAL). This gene was amplified from P. luminescens and expressed in Escherichia coli BL21(DE3). The function of Pl-PAL (58 kDa) was characterized by in vitro enzymatic reactions with L-phenylalanine (L-Phe), L-tyrosine (L-Tyr), L-histidine (L-His), and L-tryptophan (L-Trp). Pl-PAL can convert L-Phe and L-Tyr to trans-cinnamic acid and p-coumaric acid, respectively, but had no function on L-His and L-Trp. The optimum temperature and pH were determined to be 40 °C and 11.0, respectively. Under the optimal conditions, Pl-PAL had a kcat/Km value of 0.52 s-1 mM-1 with L-Phe as the substrate, while only 0.013 s-1 mM-1 for L-Tyr. Therefore, the primary function of Pl-PAL was determined to be PAL. The Pl-pal-harboring E. coli strain was used as a whole-cell biocatalyst to produce trans-cinnamic acid from L-Phe. The overall molar conversion rate and productivity were 65.98% and 228.10 mg L-1 h-1, respectively, after the cells were repeatedly utilized 7 times. This work thus provides a promising strain for industrial production of trans-cinnamic acid.

Efficient single whole-cell biotransformation for L-2-aminobutyric acid production through engineering of leucine dehydrogenase combined with expression regulation

Leucine dehydrogenase (LDH) is widely used in the preparation of L-2-aminobutyric acid (L-2-ABA), however its wide application is limited by 2-ketobutyric acid (2-OBA) inhibition. Firstly, a novel high-throughput screening method of LDH was established, specific enzyme activity and 2-OBA tolerance of Lys72Ala mutant were 33.3% higher than those of the wild type. Subsequently, we constructed a single cell comprised of ivlA, EsldhK72A, fdh and optimized expression through fine-tuning RBS intensity, so that the yield of E. coli BL21/pET28a-R3ivlA-EsldhK72A-fdh was 2.6 times higher than that of the original strain. As a result, 150 g L-threonine was transformed to 121 g L-2-ABA in 5 L fermenter with 95% molar conversion rate, and a productivity of 5.04 g·L-1·h−1, which is the highest productivity of L-2-ABA currently reported by single-cell biotransformation. In summary, our research provided a green synthesis for L-2-ABA, which has potential for industrial production of drug precursors.

Sodium Ethoxide Concentrated Solution Synthesis at Ambient Temperature Using Sodium Hydroxide and Ethanol-90 in Excess

Sodium ethoxide is a specific chemical product of synthesis used in laboratory, thus its presence at the suppliers stays very periodic and on order. It was in that sense that this project to synthesize a concentrated solution of sodium ethoxide got off at ambient temperature, under normal atmospheric pressure in an uncovered beaker using ethanol 90% of purity and sodium hydroxide 99% of purity seeing that the ethanol molecules were in excess in comparison with sodium hydroxide molecules which quantities were all soluble in ethanol. The initial calculated pH was equal to 15.23. In addition, not only an extraction procedure of the concentrated sodium ethoxide was done but also a titration procedure of the concentrated sodium ethoxide solution by hydrochloric acid HCl-0.1N was established and permitted to evaluate kinetic parameters of this synthesis reaction on these experimental conditions. The evaluated molar conversion from the initial quantities of sodium hydroxide was 88.49% after 3h25mn of reaction. It was noticed that the formation of sodium ethoxide was initially very important and very speed confirming the negativity of its standard molar enthalpies. Thus, the initial speed formation of synthesized sodium ethoxide was approximately equal to 0.013 [[mol×l^-1×s^-1]. Once synthesized, the total crystallization of the concentrated sodium ethoxide was tried with an evaluation of its porosity by immersion in dichloromethane giving a value in the order of 54.60%.

Esterification of anthocyanins isolated from floral waste: Characterization of the esters and their application in various food systems

Anthocyanins were extracted from red rose petals collected from floral waste, and were esterified with fatty acids using the lipase Fermase CALB™ 10000 to enhance their lipophilicity. The process parameters for the extraction of anthocyanin were optimized for extraction time, nature of the solvent, substrate to solvent ratio, and concentration of citric acid. Anthocyanins were purified using resins. Acylated anthocyanins were primarily detected using TLC followed by confirmation using LC-MS analysis. Optimization of the reaction parameters was carried out by one-factor-at-a-time method using HPTLC. An optimized molar conversion of 63% of anthocyanins to its fatty acid esters was achieved in acetonitrile at 40 °C with a cyanidin:lauric acid molar ratio of 1:100 and an enzyme and molecular sieve load of 20 mg/mL and 100 mg/mL, respectively, in 24 h. The antioxidant activity of anthocyanin and its fatty acid esters assessed using DPPH, ABTS and FRAP assays showed retention in the activity upon acylation. The use of lauric acid esters of anthocyanins was studied as a colorant in emulsion-based foods such as cupcakes and sandwich biscuit cream (filling). The antioxidant effect of the esterified anthocyanins assessed by TGA, manifested improved stability on the thermo-oxidative lipid peroxidation of the biscuit cream. Anthocyanins and its fatty acid esters were also studied as pre-extrusion colorants in rice extrudates, where the esters showed superior color stability to thermal processing in comparison to anthocyanins. Anthocyanin fatty acid esters can thus find application in functional foods.

Effective Glycosylation of Cucurbitacin Mediated by UDP-Glycosyltransferase UGT74AC1 and Molecular Dynamics Exploration of Its Substrate Binding Conformations

Cucurbitacins, a group of diverse tetracyclic triterpenes, display a variety of biological effects. Glycosylation mediated by glycosyltransferases (UGTs) plays a vital role in structural and functional diversity of natural products and influences their biological activities. In this study, GT-SM, a mutant of UGT74AC1 from Siraitia grosvenorii, was chosen as a potential catalyst in glycosylation of cucurbitacins, and its optimal pH, temperature, and divalent metal ions were detected. This enzyme showed high activity (kcat/Km, 120 s−1 µM−1) toward cucurbitacin F 25-O-acetate (CA-F25) and only produced CA-F25 2-O-β-d-glucose which was isolated and confirmed by 1D and 2D nuclear magnetic resonance. A pathway for uridine diphosphate glucose (UDP-Glc) regeneration and cucurbitacin glycoside synthesis was constructed by combing GT-SM and sucrose synthase to cut down the costly UDP-Glc. The molar conversion of CA-F25 was 80.4% in cascade reaction. Molecular docking and dynamics simulations showed that CA-F25 was stabilized by hydrophobic interactions, and the C2-OH of CA-F25 showed more favorable catalytic conformation than that of C3-OH, explaining the high regioselectivity toward the C2-OH rather than the ortho-C3-OH of CA-F25. This work proved the important potential application of UGT74AC1 in cucurbitacins and provided an understanding of glycosylation of cucurbitacins.

Progress in the Free and Controlled Radical Homo- and Co-Polymerization of Itaconic Acid Derivatives: Toward Functional Polymers with Controlled Molar Mass Distribution and Architecture.

Polymeric derivatives of itaconic acid are becoming increasingly more interesting for research and industry because itaconic acid is accessible from renewable resources. In spite of the structural similarity of poly(itaconic acid derivatives) to poly(methacrylates), they are much less reactive, homopolymerize only sluggishly by free radical polymerization (FRP), and are often obtained with low molar masses and conversions. This has so far limited their use. The reasons for the low reactivity of itaconic acid derivatives (including itaconimides, diitaconates, and diitaconamides) are combined steric and electronic effects, as demonstrated by the body of literature on the FRP homopolymerization kinetics of these monomers which is summarized herein. These problems can be solved to a large extent by using controlled radical polymerization (CRP) techniques, notably atom transfer radical polymerization (ATRP) and reversible addition and fragmentation chain transfer radical polymerization (RAFT). By optimizing the reaction conditions for the ATRP and RAFT of itaconic acid derivatives, in particular the reaction temperature, linear relations between molar mass and conversion are obtained in many cases, and homopolymers with high molar masses and reasonably narrow polydispersity indices become accessible. This review presents the state-of-the-art FRP and CRP of itaconic acid derivatives, and highlights functional polymers obtained by these methods.

Implementation of Biocatalysis in Continuous Flow for the Synthesis of Small Cyclic Amines.

Significant progress has been made in establishing transaminases as robust biocatalysts for the green and scalable synthesis of a diverse range of chiral amines. However, very few examples on the amination of small cyclic ketones have been reported. Cyclic ketones are particularly challenging for transaminase enzymes because they do not display the well-defined small and large substituent areas that are characteristic for the bio- catalytic mechanism. In this work, we exploited the broad substrate scope of the (S)-selective transaminase from Halomonas elongata (HeWT) to develop an efficient biocatalytic system in continuous flow to generate a range of small cyclic amines which feature very often in pharmaceuticals and agrochemicals. [3] Tetrahydrofuran-3-one and other challenging prochiral ketones were rapidly (5-45 min) transformed to their corresponding amines with excellent molar conversion (94-99%) and moderate to excellent ee.

Amination of Cyclohexane by Dielectric Barrier Discharge Processing in a Continuous Flow Microreactor: Experimental and Simulation Studies

A miniaturized flow device has been developed to combine microfluidics technology and plasma process. In this microreactor, atmospheric pressure dielectric barrier discharges are generated in a gas in contact with a liquid phase. This study was conducted with plasma generated in ammonia in contact with a flow of liquid cyclohexane. Cyclohexylamine was synthesized with a good selectivity, and the process can be implemented to improve conversion and effectiveness. Numerical simulations confirmed that NH2 radicals are generated in the plasma and react with cyclohexyls radicals to achieve the reaction, giving a selectivity of 50% and a total molar conversion of 20% of cyclohexane. The effects of voltage and frequency on the selectivity and the experimental conversion rate were studied and discussed.

Whole-cell biocatalysis using the Acidovorax sp. CHX100 Δ6HX for the production of ω-hydroxycarboxylic acids from cycloalkanes

Omega hydroxycarboxylic acids (ω-HAs) possess two functional groups, a hydroxyl group and a carboxyl group, and are essential precursors for the production of biodegradable polyester polymers. In this work, an Acidovorax mutant was investigated as a whole-cell biocatalyst for the conversion of cycloalkanes to their respective ω-hydroxycarboxylic acids. This Acidovorax sp. strain CHX100 originated from a wastewater treatment plant and uses cyclohexane as the sole source of carbon and energy with excellent growth rates (0.199 h-1). The metabolic efficiency of Acidovorax CHX100 is based on a highly efficient enzyme cascade used for the mineralization of cyclohexane. A deletion of 6-hydroxyhexanoate dehydrogenase in the native cycloalkane pathway resulted in the Acidovorax sp. strain CHX100 Δ6HX mutant, which accumulated short ω-hydroxycarboxylic acids (C5 to C10) from cycloalkanes. This mutant transformed cyclopentane and cyclohexane (5 mM) to 5-hydroxypentanoic acid and 6-hydroxyhexanoic acid, respectively, with a molar conversion above 98% in 6 h. An elementary environmental and economical assessment based on E-factor and biocatalyst yield suggests the use of inexpensive electron donor and carbon sources, with subsequent efforts to minimize waste generation. Such an early-stage analysis highlights the main bottlenecks that need to be solved in developing a sustainable bioprocess.

Optimization Using Response Surface Methodology (RSM) for Biodiesel Synthesis Catalyzed by Radiation-Induced Kenaf Catalyst in Packed-Bed Reactor

In this study, continuous transesterification of refined palm oil by using radiation-induced kenaf denoted as anion exchange kenaf catalyst in a packed-bed reactor was developed. The application of full factorial design and response surface methodology (RSM) based on the central composite design (CCD) was used to design the process and analyzed the effect of reactor operating variables such as packed bed height, the molar ratio of oil to ethanol and volumetric flow rate on the production of fatty acid ethyl ester (FAEE). The statistical analysis results showed that all three operating parameters affect the reaction efficiency significantly. The optimum conditions were determined to be 9.81 cm packed bed height, a molar ratio at 1:50, and a volumetric flow rate of 0.38 mL min−1. Three tests were carried out to verify the optimum combination of process parameters. The predicted and actual values of molar conversion fatty acid ethyl ester (FAEE) molar conversion were 97.29% and 96.87%, respectively. The reusability of kenaf fiber-based catalysts is discussed with a specially highlighted on fiber dissolution, leaching, and fouling. Nevertheless, the impurities absorption properties of anion exchange kenaf catalyst towards biodiesel production could eventually simplify the biodiesel purification steps and cost. In sum, anion exchange kenaf catalyst shows the potential commercial applications to transesterification of FAEE in a packed-bed reactor.