High Conversion Yield Research Articles

Two-step physico-biological production of xylooligosaccharides from sugarcane leaves

The production of xylooligosaccharides (XOS) from sugarcane leaves (SCL) presents high potential to the nutraceutical industries as SCL are cheap and readily available. In this study, a two-step process using hydrothermal pretreatments and enzymatic hydrolysis are developed and optimized for XOS production to obtain high conversion yield and product specificity. Two operation methods for hydrothermal pretreatments, parr reactor, and microwave reactor were compared to extract xylan from SCL. Two hemicellulose enzymes, hemicellulase Amano and xylanase (X2753) were then tested for enzymatic hydrolysis of extracted xylan to XOS. Conditions with high conversion yield after pretreatments were found at 180 °C for 30 min (parr reactor) and 800 W for 8 min (microwave reactor): producing 4.95 mg/mL (22.11 %w/v) and 3.49 mg/mL (15.61 %w/v) XOS respectively. Subjection of derived liquor from hydrothermal pretreatment to enzymatic hydrolysis produced a maximum of 9.42 mg/mL (41.87 %w/v) and 7.81 mg/mL (34.71 %w/v) of XOS for hemicellulase Amano and xylanase (X2753) respectively. The hemicellulase resulted in XOS with degree of polymerization (DP) of 2–5 for the various pretreatment conditions whereas xylanase yielded XOS of DP 2 to 4. However, a negative effect on enzymatic hydrolysis was observed for microwave-assisted pretreated samples. This study revealed that combination of physico-biological methods on SCL could result in high XOS yield with distinct degree of polymerization.

Enhancing photocatalytic visible-light-driven oxidation of NOx over Mott-Schottky Ag/SnO2 nanorod heterojunctions

Nitrogen oxides (NOx) is formed by primary emission from diesel engine vehicles. In this study, we synthesized and applied the photocatalytic effect over Mott-Schottky Ag/SnO2 nanorod heterojunctions toward NOx removal under visible light. In detail, the presence of Ag NPs in the Ag/SnO2 nanorod heterojunction, the number of electrons participating in the catalysis is enhanced due to the localized surface plasmon resonance (LSPR) of Ag NPs. In addition, the potential of the reducing region of SnO2 is also changed, thereby creating favourable conditions for the photocatalysis. We determined that 1.5% Ag/SnO2 nanorod heterojunction is the best sample with NO (500 ppb) photodegradation efficiency of 50.64% under visible light irradiation. Moreover, Ag/SnO2 nanorod heterojunction has an excellent stability after undergoing five times recycling and is highly applicable in practical applications with a high NO degradation and low NO2 conversion yield. The Mott-Schottky plots, Tauc plots, and trapping tests were used to build the energy scheme of the Ag/SnO2 heterojunction.

Facile synthesis of functionalized polysiloxanes with nonconventional fluorescence by oxa-Michael addition reaction

ABSTRACTDeveloping a novel methodology for the synthesis of functionalized polysiloxanes is highly desirable because of their extensive applications in engineering, textile, construction, electronics, and medical systems. Herein we introduce the oxa-Michael addition reaction as an efficient methodology to prepare a series of functionalized polysiloxanes from hydroxyalkyl-containing polysiloxanes and vinyl monomers using phosphazene base as the catalyst. The effects of various factors, including reaction time, feed ratio and solvent, were explored in this reaction. It was found that the reaction can be carried out under mild reaction (room temperature in 6 h to 24 h) with moderate to high conversion yields (60% to 99%). In particular, vinyl monomers with strong electron-withdrawing groups (e.g., cyano and sulfone groups) have higher reactivity, and the functionalized polysiloxanes can be obtained quantitatively or near-quantitatively. Interestingly, their molecular weights determined by gel permeation chromatography (GPC) reveal that the Si-O-Si skeletons were attacked by phosphazene base and re-arranged during the reaction, thus leading to improved molecular weights and more uniform molecular weight distributions in the final products than the original polysiloxanes. Moreover, these polysiloxanes exhibited intriguing nonconventional fluorescence due to the presence of unique chromophores, and those containing cyano and sulfone groups particularly exhibit the best fluorescence performance. More organosilicon materials could be developed under this simple strategy.

Fabricating Pt0-acid synergy in Pt/Beta phenol hydrodeoxygenation catalysts via a surface modification strategy of Beta molecular sieves

As for metal/zeolite supported phenol hydrodeoxygenation catalysts, it is important to improve the dispersion of metallic sites and build synergistic relationship between metallic and acid sites. The current research proposes a surface modification strategy by introducing CTAB in the NaOH etching of Beta. CTAB interacts with crystal defects to inhibit excessive crystal destruction. Aluminum atoms are protected from being removed and acid sites are reserved. Generated silicon hydroxyl groups anchor Pt0 particles. Pt0 particles are spatial resisted on the internal surface of catalysts to activate C–O bonds of phenol. Preserved acid sites provide reactive sites for dehydration reaction of cyclohexanol on the external surface of Pt/Beta-H. The high phenol conversion (i.e., 92.26 %) and cyclohexane yield (i.e., 7.18 %) were obtained at 80 °C due to the functional synergistic effect between acid and Pt0 sites. Proposed surface modification strategy proposes references for the structure design and development of efficient phenolics hydrodeoxygenation catalysts.

Facile and Efficient Production of Biomass-Derived Isosorbide Dioxides via Epoxidation Using In situ-generated DMDO under Ultrasonication.

Herein, we present a facile synthetic process for producing biomass-derived isosorbide (ISB) dioxides using dimethyl dioxirane (DMDO) as an efficient oxidizing agent, which was generated in situ from acetone and KHSO5 . To achieve high conversion and product yield, the KHSO5 concentration, KHSO5 flow rate, and reaction temperature were optimized. Under the optimal conditions, rapid and efficient epoxidation using the in situ-generated DMDO was observed under ultrasonication, yielding the desired product within 35 min at 0 °C. This study offers a convenient and efficient method for generating biomass-derived ISB building blocks, which have significant potential for the fabrication of bioplastics.

Engineering Comamonas testosteroni for the production of 2-pyrone-4,6-dicarboxylic acid as a promising building block

BackgroundPlastics are an indispensable part of our daily life. However, mismanagement at their end-of-life results in severe environmental consequences. The microbial conversion of these polymers into new value-added products offers a promising alternative. In this study, we engineered the soil-bacterium Comamonas testosteroni KF-1, a natural degrader of terephthalic acid, for the conversion of the latter to the high-value product 2-pyrone-4,6-dicarboxylic acid.ResultsIn order to convert terephthalic acid to 2-pyrone-4,6-dicarboxylic acid, we deleted the native PDC hydrolase and observed only a limited amount of product formation. To test whether this was the result of an inhibition of terephthalic acid uptake by the carbon source for growth (i.e. glycolic acid), the consumption of both carbon sources was monitored in the wild-type strain. Both carbon sources were consumed at the same time, indicating that catabolite repression was not the case. Next, we investigated if the activity of pathway enzymes remained the same in the wild-type and mutant strain. Here again, no statistical differences could be observed. Finally, we hypothesized that the presence of a pmdK variant in the degradation operon could be responsible for the observed phenotype and created a double deletion mutant strain. This newly created strain accumulated PDC to a larger extent and again consumed both carbon sources. The double deletion strain was then used in a bioreactor experiment, leading to the accumulation of 6.5 g/L of product in 24 h with an overall productivity of 0.27 g/L/h.ConclusionsThis study shows the production of the chemical building block 2-pyrone-4,6-dicarboxylic acid from terephthalic acid through an engineered C. testosteroni KF-1 strain. It was observed that both a deletion of the native PDC hydrolase as well as a pmdK variant is needed to achieve high conversion yields. A product titer of 6.5 g/L in 24 h with an overall productivity of 0.27 g/L/h was achieved.

(Invited) Recent Development of Electrochemical Nitrate Reduction

Understanding the complexities of nitrogen cycle is critical because when the cycle is not in balance, excess reduced and oxidized nitrogen compounds could result in harmful impacts to life. Electrocatalytic conversion of waste nitrate (NO3 -) to benign dinitrogen (N2) and ammonia (NH3) fuel is an appealing strategy that may easily integrate with renewable energy. The process does not require chemical addition and thus requires operating costs lower than thermal routes. Nearly all nitrogen-based fertilizers rely on ammonia as a feedstock, and thus the demand for this chemical is heavily dependent on the global population and food demand. Over the next three decades, the global population will continue to dictate the market size and value for ammonia, which consequently will have a significant impact on our energy infrastructure. While electrochemical nitrogen reduction reaction (NRR) requires multiple proton and electron transfer process, ammonia production from nitrate reduction (NO3RR) is catalytic easier than NRR because the adsorbed/activated ion reactants (nitrate and nitrite) have an advantage of a lower dissociation energy for the N−O and N=O bonds (204 and 607 kJ mol-1) than that of N≡N bond (941 kJ mol-1). The synergistic effect between Cu and Pd has shown a high nitrate conversion yield and nitrogen selectivity. Engineering the Pd and Cu sites is critical but examination of the use of secondary metals in shape-controlled nanoparticle and atomic reconstruction are rare.Here, we controlled Cu surface coverage on Pd nanocube nanoparticle to steer the selectivity between nitrogen and ammonia. In addition, the engineered the atomic structure of Pd and Cu nanoparticles showed high nitrate conversion yield, excellent dinitrogen selectivity, and outstanding cyclic stability. This study provides insights into the rational design of NO3RR electrocatalyst for efficiently transforming nitrate into nitrogen and ammonia.

Pt-Loaded Nb─W Metal Composite Oxide for Selective Cleavage of Secondary C─O Bonds.

Selective hydrogenolysis of glycerol to 1,3-propanediol (1,3-PDO) is recognized as one of the most promising reactions for the valorization of biomass. Precise activation of C─O bonds of glycerol molecule is the key step to realize the high yield of catalytic conversion. Here, a Pt-loaded Nb-W composite oxides with crystallographic shear phase for the precise activation and cleavage of secondary C─O (C(2)─O) bonds are first reported. The developed Nb14 W3 O44 with uniform structure possesses arrays of W-O-Nb active sites that totally distinct from individual WOx or NbOx species, which is superior to the adsorption and activation of C(2)─O bonds. The Nb14 W3 O44 support with rich reversible redox couples also promotes the electron feedback ability of Pt and enhances its interaction with Pt nanoparticles, resulting in high activity for H2 dissociation and hydrogenation. All these favorable factors confer the Pt/Nb14 W3 O44 excellent performance for selective hydrogenolysis of glycerol to 1,3-PDO with the yield of 75.2% exceeding the record of 66%, paying the way for the commercial development of biomass conversion. The reported catalysts or approach can also be adopted to create a family of Nb-W metal composite oxides for other catalytic reactions requiring selective C─O bond activation and cleavage.

Direct and efficient conversion of cellulose to levulinic acid catalyzed by carbon foam-supported heteropolyacid with Brønsted–Lewis dual-acidic sites

This study aimed to produce bio-based levulinic acid (LA) via direct and efficient conversion of cellulose catalyzed by a sustainable solid acid. A carbon foam (CF)-supported aluminotungstic acid (HAlW/CF) catalyst with Brønsted–Lewis dual-acidic sites was creatively engineered by a hydrothermal impregnation method. The activity of the HAlW/CF catalyst was determined via the hydrolysis and conversion of cellulose to prepare LA in aqueous system. The cooperative effect of Brønsted and Lewis acids in HAlW/CF resulted in high cellulose conversion (89.4%) and LA yield (60.9%) at 180 °C for 4 h, which were greater than the combined catalytic efficiencies of single HAlW and CF under the same conditions. The HAlW/CF catalyst in block form exhibited superior catalytic activity, facile separation from reaction system, and favorable reusability. This work offers novel perspectives for the development of recyclable dual-acidic catalysts to achieve one-pot catalytic conversion of biomass to value-added chemicals.

Elucidating multi-scale deconstruction of bamboo crystalline cellulose by novel acetylcholine chloride based deep eutectic solvents for enhanced enzymatic hydrolysis

Exploration and application of novel and sustainable deep eutectic solvents (DESs) on lignocellulose pretreatment are promising approaches to efficient bioconversion. However, comprehensive understanding on efficient DESs selection and inner mechanisms of lignocellulose deconstruction are still limited. Herein, bio-based acetylcholine chloride (AChCl) was firstly utilized as hydrogen bond acceptor in cooperation with lactic acid, urea and glycerol respectively for microwave-assisted pretreatment on moso bamboo in short time. High enzymatic conversion yield of bamboo cellulose (∼85%) was achieved by lactic acid-AChCl DES due to its lower pH value and viscosity, followed by glycerol-AChCl and urea-AChCl DES. In addition to the features of proposed DESs, changed chemical and physical properties of highly recalcitrant bamboo biomass after pretreatments were systematically determined. Besides of great amount of lignin (∼90%)/ xylan (100%) removal, micro- to nano-scale variations of cellulose structures including more dissociated microfibrils, lowered crystallinity, and enlarged crystallite sizes all played key roles in promoting bioconversion yields. Moreover, the multi-factors contributing to improved hydrolysis performance were integrated to evaluate the effects of novel DESs pretreatments on lignocellulose deconstruction, which may provide new strategies on bioconversion enhancement and process optimization.

Deployment of integrated Power-to-X and CO2 utilization systems: Techno-economic assessment of synthetic natural gas and methanol cases

Achieving the climate neutrality requires decisive actions in curbing CO2 emissions. Various possible strategies can be exploited for this target such as boosting renewable sources, increasing energy efficiency for both conversion and utilisation steps, deploying Carbon Capture, Utilization and Storage (CCUS) applications. Power-to-X (P2X) and CO2 utilization technologies got significant attention as options to reduce fossil CO2 emissions and produce sustainable chemicals. This work assesses large-scale synthetic natural gas (SNG) and methanol production from renewable H2 and captured CO2 from a techno-economic perspective. Sizes of investigated systems are 500 MWth for the SNG case and 100000 t/y for the methanol case to be relevant from an industrial perspective. The assessed concepts were modelled and simulated in a thermally integrated design for optimization of the overall energy utilization. The key performance indicators were calculated based on overall mass & energy balances. As results show, the SNG and methanol production systems from green H2 and captured CO2 have high energy efficiency (e.g., about 54–58 %) and very high CO2 conversion yields (about 96–99 %). From an economic point of view, these solutions are not yet competitive to existing fossil-based systems (e.g., production costs are about 16 €/GJ for SNG and about 755 €/t for renewable methanol compared to average 10 €/GJ for natural gas and 450–500 €/t for fossil methanol).

Irreversible biosynthesis of D-Allulose from D-glucose in Escherichia coli through fine-tuning of carbon flux and cofactor regeneration engineering.

As a rare hexose with low calories and various physiological functions, D-allulose has drawn increasing attention. The current industrial production of D-allulose from D-fructose or D-glucose is achieved via epimerization based on the Izumoring strategy; however, the inherent reaction equilibrium during reversible reaction limits its high conversion yield. Although the conversion of D-fructose to D-allulose could be enhanced via phosphorylation-dephosphorylation mediated by metabolic engineering, biomass reduction and byproduct accumulation remain a largely unresolved issue. After modifying the glycolytic pathway of Escherichia coli and optimizing the whole-cell reaction condition, the engineered strain produced 7.57 ± 0.61 g L-1 D-allulose from 30 g L-1 D-glucose after 24 h of catalysis. By developing an ATP regeneration system for enhanced substrate phosphorylation, the cell growth inhibition was alleviated and D-allulose production increased by 55.3% to 11.76 ± 0.58 g L-1 (0.53 g g-1 ). Fine-tuning of carbon flux caused a 48% reduction in D-fructose accumulation to 1.47 ± 0.15 g L-1 . After implementing fed-batch co-substrate strategy, the D-allulose titer reached 15.80 ± 0.31 g L-1 (0.62 g g-1 ) with a D-glucose conversion rate of 84.8%. This study presented a novel strategy for high-yield D-allulose production from low-cost substrate. This article is protected by copyright. All rights reserved.

A process for p-hydroxystyrene production from glycerol based on cell-free biosynthesis system

As an essential chemical, p-hydroxystyrene has attracted much attention and is widely used in the field of semiconductors. However, the current production methods have some disadvantages, such as low molar conversion yield, p-hydroxystyrene toxicity, and high substrate cost. To overcome these problems, an five enzymes cell-free cascade, consisting of alditol oxidase from Streptomyces coelicolor A3 (ScALDO), dehydratase from Paralcaligenes ureilyticus (PuDHT), tyrosine phenol lyase from Citrobacter freundii (CfTPL), tyrosine ammonia lyase from Rhodotorula glutinis (RgTAL) and phenylacrylate decarboxylase from Enterobacter sp. (EsPAD), was constructed for the de novo biosynthesis of p-hydroxystyrene from glycerol. Through process strategy optimization, a molar conversion yield of more than 84.2% was finally obtained from 10 mM crude glycerol. It is worth mentioning that the reaction system performed an excellent titer using 50 mM crude glycerol, and the p-hydroxystyrene concentration reached 30.32 mM, which exceeded the maximum titer of fermentation. This showed that our system is robust to p-hydroxystyrene and crude glycerol. In addition, a ‘two-step purification process’ was designed to produce pure p-hydroxystyrene. This is the first study focused on the cell-free biosynthesis of p-hydroxystyrene, and the highest conversion yield and titer thus far was obtained for p-hydroxystyrene de novo biosynthesis.

Electrochemical conversion of natural graphite minerals into carbon nanostructures incorporated with Fe3Si for Li-ion storage application

Natural graphite mineral (NGM) is an abundant and low-cost carbon source with the potential of being employed as the precursor for producing high-quality carbon nanostructures for energy storage applications. In this article, one-pot electrochemical conversion of NGM into graphitic carbon nanostructures incorporated with Fe3Si nanocrystals with enhanced bulk electrical conductivity and Li-ion storage performance is reported. To this end, electrodes made of NGM are negatively polarized in molten LiCl-NaCl at 740 °C under various cathode current densities. At 1 A cm−2, the high-yield conversion of the mineral into carbon nanotubes (CNTs), nanofibers and onion-like carbon nanoparticles is realized. The product exhibits a specific electrical conductivity of 9.83 S m2 g−1, and the Li+ transfer resistance of 24 Ω. The Li-ion storage capacity of the material is evaluated to be high at 382 mAh g−1 after 220 Li-ion insertion and extraction cycles under the current density of 200 mA g−1, making the material an attractive low-cost candidate for the anode of lithium ion batteries. The ferromagnetic behavior of the nanostructured Fe3Si incorporated carbon is characterized by the saturation magnetization of 11.1 emu g−1, potentially promoting the recyclability of spent anode material. This article reports on the green and low-cost conversion of NGMs into nanostructured carbon materials with enhanced Li-ion storage performance.

Facile Synthesis, Characterization, and Photocatalytic Performance of BiOF/BiFeO3 Hybrid Heterojunction for Benzylamine Coupling under Simulated Light Irradiation

Under simulated light irradiation, the aerobic oxidation of benzylamine to N,N-benzylidenebenzylamine was carried out as a model reaction to investigate the photocatalytic activity of a hydrothermally prepared composite based on BiOF and BiFeO3 materials. The prepared photocatalysts were characterized using several spectroscopic techniques, such as powder X-ray diffraction (PXRD), diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and Fourier transform infrared spectroscopy (FTIR). Band gap analysis showed that the composite exhibits a band gap that lies in the UV region (3.5 eV). Nonetheless, pristine BiOF and BiFeO3 exhibited band gaps of 3.8 eV and 2.15 eV, respectively. N,N-benzylidenebenzylamine was selectively achieved with a high conversion yield of ~80% under atmospheric conditions in which the product was confirmed using 1H-NMR, 13C-NMR, and FTIR spectroscopic techniques. Various control experiments were conducted to further confirm the enhanced photocatalytic performance of the reported composite.

Sintering-free catalytic ammonia cracking by vertically standing 2D porous framework supported Ru nanocatalysts

Catalytic ammonia decomposition enables ammonia to be a hydrogen gas carrier for a carbon-free fuel economy. The challenge is to obtain high conversion yields and rates at low temperatures for a prolonged time. A promising approach is to engineer a catalyst support to minimize deleterious effects like sintering. Here, we compared a conventional 2D planar porous framework support with a vertically standing 2D structure to ascertain the effects of support geometry on the catalytic performance. The catalysts were made by loading ruthenium (Ru) nanoparticles onto the structures, and the catalytic activities were monitored by varying the ammonia (NH3) feeding rate and reaction temperature. Unlike the planar version, the vertically standing 2D support prevented nanoparticle aggregation, retained the original nanoparticle size, and showed an excellent hydrogen production rate (95.17 mmol gRu−1 min−1) at a high flow rate of 32,000 mL gcat−1 h−1 at a temperature of 450 °C.

Simultaneous reactions of sulfonation and condensation for high-yield conversion of polystyrene into carbonaceous material

Polystyrene (PS) was chemically treated with sulfuric acid to prepare stabilized precursors, which were converted into carbonaceous materials with high yield via subsequent carbonization. In addition to sulfuric acid, paraformaldehyde (PFA) was used to increase the crosslink density within the sulfonated PS chain networks by forming methylene bridges between phenyl rings via condensation. This transformed PS into a black glassy powder with increased crosslinking points. The carbon yield of the stabilized PS obtained after carbonization showed was considerably higher (45.3 wt%) than those of pristine PS (0 wt%) and sulfonated PS without PFA (22.4 wt%). This was attributed to its superior degree of crosslinks and the additional contribution of sulfur bridges to its thermal stability during carbonization. Further thermal treatment up to 2800 °C resulted in the formation of an intermediate structure between hard and soft carbons, which was directly revealed by microscopic images. These simultaneous reactions of sulfonation and condensation can be universally applied to various PS wastes, regardless of their shape and morphology. This suggests that the solid-to-solid transformation from PS to carbonaceous substances can be an effective and affordable method of upcycling general PS wastes.

Recent Approaches in the Synthesis of 5-Arylidene-2,4-thiazolidinedione Derivatives Using Knoevenagel Condensation

Abstract: 5-Arylidene-2,4-thiazolidinedione (5-A-TZD) is an emerging precursor molecule in medicinal chemistry for discovering multifunctional therapeutic agents. For synthesizing this precursor molecule, Knoevenagel Condensation (KC) is one of the most excellent tools in modern organic chemistry. The 5-A-TZD framework has a variety of therapeutic functions such as antidiabetic, anticancer, antimicrobial, and anti-inflammatory. As a result, several approaches and methods of KC have been established for the synthesis of this multifunctional precursor. However, the use of highly corrosive catalysts, prolonged reaction times, by-products formation, and poor product yields are the main drawbacks in 5-A-TZDs synthesis via KC. Therefore, several authors have been successfully established fast, effective, and environmentally sustainable protocols of KC using organic catalysts, inorganic catalysts, heterogeneous solid catalysts, ionic liquids (ILs), and bio-catalysts to synthesize 5-A-TZD derivatives with high conversion yield and selectivity. In this review, we have summarized the recent approaches for synthesizing 5-A-TZDs via KC and their therapeutic application as a precursor molecule in medicinal chemistry.

Engineering of Hydroxymandelate Oxidase and Cascade Reactions for High-Yielding Conversion of Racemic Mandelic Acids to Phenylglyoxylic Acids and (R)- and (S)-Phenylglycines

An alcohol oxidase (AOx) for the (S)-enantioselective oxidation of 4-hydroxymandelic acid (4-HMA) to 4-hydroxyphenylglyoxylic acid (4-HPGA) with enhanced activity was developed by directed evolution of hydroxymandelate oxidase (HMO) through three rounds of iterative saturation mutagenesis. The engineered HMO mutant A80G-T159S-T162Q (HMOTM) catalyzed the oxidation of (S)-4-HMA to 4-HPGA with a 23-fold enhancement in catalytic efficiency (kcat/KM). Substrate docking simulation on HMOTM suggested that A80G reoriented FMN, while T159S and T162Q formed hydrogen bonds with the carboxylic group of the substrate, thus facilitating substrate binding and catalysis. (S)-Enantioselective HMOTM was used together with mandelic acid racemase (MR) and catalase (KatE) to achieve high-yielding oxidation of rac-4-HMA to 4-HPGA with either purified enzymes (up to 93% yield and 426 mM) or Escherichia coli (HMC) cells expressing the three enzymes (up to 93% yield and 140 mM). The HMOTM-MR-KatE cascades were applied for the oxidation of seven other substituted MAs, producing the corresponding phenylglyoxylic acids with 90–99% conversions using purified enzymes or whole cells. Efficient conversion of racemic α-hydroxy acids to (S)- or (R)-α-amino acids was achieved by combining HMOTM-MR-KatE with (S)-enantioselective transaminase (EcαTA) or (R)-enantioselective transaminase (DpgAT), together with glutamate dehydrogenase (GluDH). Coupling of E. coli (HMC) with E. coli (E-G) expressing EcαTA and GluDH for one-pot biotransformation of five rac-MAs produced the corresponding (S)-phenylglycines (PGs) in 91–99% ee with 73–98% conversions. Using E. coli (HMC) and E. coli (D-G) expressing DpgAT and GluDH enabled the production of five (R)-PGs with 93–99% ee and 73–98% conversions from the corresponding rac-MAs. The engineered AOx, AOx-MR-KatE cascades, and AOx-MR-Kat-GluDH-(S)- or (R)-TA cascades provide useful tools for highly active and enantioselective oxidation of racemic hydroxyacids and high-yielding conversion of racemic hydroxyacids to ketoacids and enantiopure (S)- or (R)-aminoacids, respectively, which are challenging and useful chemical reactions.

Polybenzodiazine Aerogels: All-Nitrogen Analogues of Polybenzoxazines─Synthesis, Characterization, and High-Yield Conversion to Nanoporous Carbons

Tetrahydroquinazoline (THQ) was designed as an all-nitrogen analogue of main-stream benzoxazine monomers. THQ solutions in DMF gelled at 100 °C via HCl-catalyzed ring-opening polymerization to polybenzodiazine (PBDAZ) wet gels, which were dried in an autoclave with supercritical fluid CO2 to aerogels. These as-prepared PBDAZ-100 aerogels undergo ring-fusion aromatization at 240 °C under O2. This oxidized form is referred to as PBDAZ-240. Chemical identification of PBDAZ-100 and PBDAZ-240 relied on consideration of all nine possible polymerization pathways, in combination with elemental analysis, infrared and solid-state 13C NMR spectroscopy, and 15N NMR spectroscopy of aerogels from the selectively 15N-enriched THQ monomer. Fully oxidized PBDAZ-240 aerogels were carbonized at 800 °C under Ar to carbon aerogels with 61% w/w yield and with retention of the nanomorphology of the parent PBDAZ-100 aerogels. Direct pyrolysis of PBDAZ-100 at 800 °C, i.e., without prior oxidation, resulted in only 40% w/w yield and complete loss of the fine nanostructure. The evolution of PBDAZ-240 aerogels along pyrolysis toward carbonization was monitored using progressively higher pyrolysis temperatures from 300 to 800 °C under Ar. Aerogels received at 600 and 800 °C (referred to as PBDAZ-600 and PBDAZ-800, respectively) had relatively high surface areas (432 and 346 m2 g–1, respectively), a significant portion of which (79% in both materials) was assigned to micropores. The new polymer aerogels, together with polybenzoxazine aerogels, comprise a suitable basis set for comparing N-rich versus O-rich porous carbons as adsorbers.