Reaction Condition Optimization Research Articles

Sensitive fluorescent aptasensing of tobramycin on graphene oxide coupling strand displacement amplification and hybridization chain reaction

An ultrasensitive biosensor was designed and constructed for tobramycin detection. As a target recognition component, the DNA probe consists of an aptamer region for tobramycin binding and a template for amplification. In the absence of tobramycin, the probe was locked to form a stem–loop structure. In the presence of the target, the binding of tobramycin led to a conformational change in the probe. The released 3′ end was used as a primer for the strand displacement amplification (SDA) to produce a large amount of single-stranded trigger DNA, which then efficiently initiated the following hybridization chain reaction (HCR) to produce a long duplex DNA with many fluorophores. The signals were detected after the addition of graphene oxide (GO) to quench the fluorescence from excess hairpin DNA. Through sequence and reaction condition optimization, the biosensor exhibited high selectivity for tobramycin. The linearity range and limit of detection (LOD) were 0.5–30 nM and 0.06 nM, respectively. Moreover, the application of detecting tobramycin in milk and lake water samples showed that this method is reliable and could be further used in food safety control and environmental monitoring.

Sanitary Ware Waste as a Source for a Valuable Biodiesel Catalyst

Biofuel is a type of fuel that is made from biomass using modern techniques rather than the relatively slow geological processes that lead to the development of fossil fuels. In Europe, biodiesel is the most widely used biofuel. The sanitary ware industry generates a lot of hazardous waste, such as waste gypsum molds. These molds are broken, pulverized, and reacted with NaCO3 to make CaCO3, which is then heated to produce CaO. The resulting CaO catalyzes the reaction between waste frying oil and methanol for biodiesel synthesis. To evaluate the effect of reaction parameters on the production of biodiesel, the independent reaction parameters that were chosen are as follows: reaction temperature in the range 50–70°C, methanol to oil (M:O) molar ratio in the range 9–15, catalyst loading in the range 1–5%, and time in the range 2–6 hrs. The influence of the independent factors on the reaction-dependent responses was evaluated and it was found that reaction temperature and methanol-to-oil ratio have a major effect on the biodiesel yield. Reaction condition optimization has been studied to maximize biodiesel yield at minimum reaction conditions. The optimum process conditions are 93.4% biodiesel yield at an M:O molar ratio of 15 : 1, catalyst loading of 1%, reaction temperature of 53.6°C, and reaction time of 2 h. The results showed that resulted biodiesel catalyst (CaO) can be used one time; then, a fresh catalyst will be used.

Construction of efficient enzyme systems for preparing chiral ethyl 3-hydroxy-3-phenylpropionate

Ethyl 3-hydroxy-3-phenylpropionate (EHPP), (R)-EHPP or (S)-EHPP, is an important chiral intermediate for pharmaceuticals. Its synthesis from ethyl benzoyl acetate (EBA) by alcohol dehydrogenase is regarded as a green method. However, scarcely any alcohol dehydrogenase has been reported competent in asymmetric synthesis of chiral EHPP at high EBA loading. Present study developed two robust and efficient bio-catalysts Mu-S2 and Mu-R4 for preparation of (S)-EHPP and (R)-EHPP respectively by rational design of alcohol dehydrogenase PcSDR from Pedobacter chitinilyticus based on molecular dynamics (MD) simulation analysis. BtGDH, a glucose dehydrogenase from Bacillus toyonensis catalyzing the oxidation of glucose for cofactor regeneration, was co-expressed with the screened mutants to form enzyme systems Mu-S2-BtGDH and Mu-R4-BtGDH. After reaction condition optimization, Mu-S2-BtGDH and Mu-R4-BtGDH were efficient in the synthesis of (S)-EHPP (94% conv. and 99% e.e.) and (R)-EHPP (99% conv. and 98% e.e.) respectively in 100 mL scale under 500 mM of EBA loading in 10 h following a substrate continuous feeding mode. After purifying, the isolated yield for each EHPP enantiomer is > 93%. This work not only provides potential biocatalysts for the industrial production of (R)-EHPP and (S)-EHPP, but also enriches the constructure-function relationship of alcohol dehydrogenases.

Tributyl phosphate degradation and phosphorus immobilization by MnO2: Reaction condition optimization and mechanism exploration

The treatment of tributyl phosphate (TBP) extractant waste from specific industry, eg., nuclear industry, is a great challenge due to its stability and high environmental risk of phosphorus-containing species releasing. Inspired by chemical looping combustion (CLC) technology, a MnO2-assisted thermal oxidation strategy is proposed for TBP degradation and simultaneously P immobilization. Under recommended reaction conditions of 220 °C, 10 g MnO2 mL−1 TBP and 3 h reaction duration, a high P immobilization efficiency of 93.99% is achieved. Material characterization results indicate that P is mainly immobilized in the form of Mn2P2O7, which greatly reduces the environmental risk of P-containing species. TBP degradation intermediates are further identified by thermogravimetric-gas chromatography-mass spectrometry (TG-GC-MS), liquid chromatography-mass spectrometry (LC-MS) and gas chromatography-mass spectrometry (GC-MS), which facilitates understanding of reaction mechanisms as well as proposing possible pathways of TBP degradation. It is suggested that MnO2 provides essential oxygen as oxygen carrier for flameless combustion. Meantime, MnO2 reduction leads to the generation of Mn(III) species. The existence of oxygen vacancy in MnO2 also facilitates •O2- radical generation. Under flameless combustion and attacks of Mn(III) and •O2-, TBP is firstly degraded into intermediates and finally mineralized into CO2 and H2O, while P is mainly immobilized as pyrophosphate.

Studies on deactivation behavior of SO42−/ZrO2-SiO2 catalyst derived from C2F4 and C3F6 oligomers deposition

• Catalyst deactivation derived from oligomers deposition was discovered. • Oligomers deposition could be described with modified Voorhies equation. • Effects of reaction conditions and total acid sites on oligomers deposition were revealed. • Relationship between oligomers accumulation and catalytic decay factor was unraveled. Preparation of tetrafluoroethylene (C 2 F 4 , TFE) and hexafluoropropylene (C 3 F 6 , HFP) from decomposition of trifluoromethane (CHF 3 , R23), which is produced from methane via chlorination and followed fluorination, attracts researchers’ interest. However, the deposition of TFE and HFP oligomers will lead to catalyst deactivation. Herein, the TFE and HFP oligomers deposition and resulting deactivation behavior on SO 4 2− /ZrO 2 -SiO 2 catalyst series, with different Lewis and Brønsted acid site densities, were investigated using (modified) Voorhies equation. For that purpose, the Lewis and Brønsted acid site densities in these utilized catalysts were measured by employing pyridine IR spectroscopy in combination with pyridine titration method. And the amount of oligomers deposited on catalyst was determined by thermogravimetry (TG) analysis. The effects of reaction temperature, molar fraction of feedstock and amount of total acid sites on the oligomers accumulation were revealed, as well as the relationship between catalytic decay factor and amount of oligomers deposited on catalyst. The results showed that both Brønsted and Lewis acid sites were responsible for TFE and HFP oligomers formation and deposition. The oligomers deposition over time-on-stream obeyed the Voorhies equation modified with the variables of reaction temperature, molar fraction of feedstock and total acid sites in the case of feeding TFE, HFP or TFE-HFP mixture. With the obtained exponential relationship between amount of oligomers deposited on catalyst and catalytic decay factor, the catalyst deactivation process can be regularly described by the reaction temperature, molar fraction of feedstock and total acid sites in catalyst when feeding TFE, HFP and TFE-HFP mixture, which would be helpful for further catalyst modification and reaction condition optimization in the field of R23 transformation.

CRISPR/Cas12a-based biosensors for ultrasensitive tobramycin detection with single- and double-stranded DNA activators

In addition to its application in genome editing, the CRISPR/Cas system provides a new molecular tool for the construction of biosensor platforms due to its high target sequence specificity and programmability. To exploit the potential of the CRISPR/Cas system for detecting non-nucleic-acid targets, two ultrasensitive biosensors (sensor-ss and sensor-ds) consisting of allosteric aptamer probes integrated with the CRISPR/Cas12a system were designed and constructed for tobramycin detection. Both sensors utilized hairpin DNA containing a tobramycin aptamer sequence as the target recognition probe, which can respond to target binding and further produce signal transduction sequences. However, there are two differences between the sensors. First, in sensor-ss, single-stranded DNA was set to be the activator to trigger cutting activity (trans-cleavage) of CRISPR/Cas12a, leading to cleavage of the FQ-reporter (a short single-stranded DNA labeled with a fluorophore and quencher at each end) and increasing the fluorescent signal. However, double-stranded DNA containing a protospacer adjacent motif (PAM) site was produced in sensor-ds as the signal transduction sequence, which was recognized by CRISPR/Cas12a, resulting in the cleavage of the FQ-reporter. Second, sensor-ss involved a strand displacement amplification (SDA) reaction as the signal enhancement step, while no DNA amplification procedure was designed in sensor-ds. Through DNA sequence and reaction condition optimization, sensor-ds showed a linear relationship between the fluorescence response and tobramycin concentrations ranging from 10 to 300 pM with a limit of detection (LOD) as low as 3.719 pM. Although sensor-ss exhibited higher sensitivity (LOD = 1.542 pM) than sensor-ds, rapidly reaching the fluorescent signal saturation platform led to a narrow linear response range (5–30 pM). Moreover, our CRISPR/Cas12a-based assay can realize on-site detection by the naked eye readout under UV light. The constructed sensor-ds was also used to detect tobramycin in milk and lake water samples, and the results indicated that the detection system was reliable. The design strategy reported in this study could shed new light on CRISPR/Cas12a-based biosensor construction for small molecule detection.

NEXTorch: A Design and Bayesian Optimization Toolkit for Chemical Sciences and Engineering.

Automation and optimization of chemical systems require well-informed decisions on what experiments to run to reduce time, materials, and/or computations. Data-driven active learning algorithms have emerged as valuable tools to solve such tasks. Bayesian optimization, a sequential global optimization approach, is a popular active-learning framework. Past studies have demonstrated its efficiency in solving chemistry and engineering problems. We introduce NEXTorch, a library in Python/PyTorch, to facilitate laboratory or computational design using Bayesian optimization. NEXTorch offers fast predictive modeling, flexible optimization loops, visualization capabilities, easy interfacing with legacy software, and multiple types of parameters and data type conversions. It provides GPU acceleration, parallelization, and state-of-the-art Bayesian optimization algorithms and supports both automated and human-in-the-loop optimization. The comprehensive online documentation introduces Bayesian optimization theory and several examples from catalyst synthesis, reaction condition optimization, parameter estimation, and reactor geometry optimization. NEXTorch is open-source and available on GitHub.

Metal-Free C-H/C-H Coupling of 2H-Imidazole 1-Oxides with Polyphenols toward Imidazole-Linked Polyphenolic Compounds.

The methodology of nucleophilic substitution of hydrogen (SNH) was successfully applied as a convenient synthetic tool to afford azaheterocyclic derivatives of phenols of various architectures. A series of 26 novel imidazole-linked polyphenolic compounds were first prepared in 72-95% yields through the direct metal-free C-H/C-H coupling of polyphenols with 2H-imidazole 1-oxides. Comprehensive studies on the reaction condition optimization, scope, and limitations enabled the development of a straightforward method toward novel bifunctional derivatives bearing both phenolic and imidazole scaffolds of particular interest in the design of challenging molecules for versatile applications in medicinal chemistry and materials science.

Preparation of 191Os–phytate, an in-vivo radionuclide generator, for radiosynovectomy application

191Os is a parent radionuclide with a 15.4 d half-life. It decays by beta emission to 191mIr, which is a radionuclidewith a 4.96s half-life. It decays by the isomeric transition to stable 191Ir, emitting a 129-keV gamma photon. In thisstudy, 191Os–phytate was developed into an in-vivo radionuclide generator for simultaneous radiosynovectomy and imaging. 191Os-hexachloroosmate was used to prepare 191Os–phytate (100 μCi/50 μl) using reaction condition optimization followed by an intraarticular injection to rat knee joints. Also, its distribution and stability were assessed. The imaging of 191Os cation and 191Os–phytate was performed by SPCET. The 191Os–phytate complex was obtained at pH=5.5 with normal saline at room temperature. Radio-TLC showed an overall radiochemical yield of 95-98%. The complex was injected into the rats’ knees, and the whole injected dose remained at the injection site even three days after injection. Due to the stability and retention of the complex in joints approved by biodistribution and imaging studies, the complex is a potential in vivo generator for cavital radiosynovectomy of minor joints.

Membrane technologies in toilet urine treatment for toilet urine resource utilization: a review.

Membrane technologies have broad potential in methods for separating, collecting, storing, and utilizing urine collected from toilets. Recovering urine from toilets for resource utilization instead of treating it in a sewage treatment plant not only reduces extra energy consumption for the degradation of N and P but also saves energy in chemical fertilizer production, which will contribute to carbon emission reduction of 12.19–17.82 kg kgN−1 in terms of N alone. Due to its high efficiency in terms of volume reduction, water recycling, nutrient recovery, and pollutant removal, membrane technology is a promising technology for resource utilization from urine collected from toilets. In this review, we divide membrane technologies for resource utilization from urine collected from toilets into four categories based on the driving force: external pressure-driven membrane technology, vapor pressure-driven membrane technology, chemical potential-driven membrane technology, and electric field-driven membrane technology. These technologies influence factors such as: recovery targets and mechanisms, reaction condition optimization, and process efficiency, and these are all discussed in this review. Finally, a toilet with source-separation is suggested. In the future, membrane technology research should focus on the practical application of source-separation toilets, membrane fouling prevention, and energy consumption evaluation. This review may provide theoretical support for the resource utilization of urine collected from toilets that is based on membrane technology.

Reaction condition optimization for non-oxidative conversion of methane using artificial intelligence

Using machine learning and metaheuristic optimization, we optimize the reaction conditions for non-oxidative conversion of methane.

Computational and biological studies of novel thiazolyl coumarin derivatives synthesized through Suzuki coupling

The current investigation presents the synthesis, computational molecular-docking and biological activity studies of arylated thiazole coumarins. Aryl substituted thiazolyl coumarin derivatives were synthesized via Suzuki cross-coupling reaction. A detailed reaction condition optimization revealed that the Pd-PEPPSI-IPent precatalyst in only 2 mol% loading resulted in the desired product with high yield. The aim of this study was to examine the antimicrobial behavior of thiazole coumarin derivatives through in vitro and in silico studies. All the compounds showed activity against both antibacterial strains, Staphylococcus aureus and Escherichia coli, except 5d . Similarly, the compounds 5a , 5b , and 5d were found to be active against Trichoderma harzianum. The compound 5d of this series was found to have a higher activity with MIC 125 mg/ml against Trichoderma harzianum. Molecular studies showed the high activities of these compounds are due to the presence of strong H-bonding and π-π interaction with their respective targets. A good correlation was observed between computational and in vitro studies.

Studies on Biological Production of Isomaltulose Using Sucrose Isomerase: Current Status and Future Perspectives

Isomaltulose, as a safe sucrose substitute, is widely used as a functional sweetener due to its promising properties, such as slower digestion, prolonged energy release, and less cariogenicity. The transformation of sucrose to isomaltulose by free sucrose isomerase (SIase) or microbial cells harboring the SIase gene has received considerable attention in the industry. Heterologous expression of SIase in food-safe grade strains has become a hot topic due to its broad applicability in the food industry. Thanks to rapid developments in genetic engineering technology, SIases from different sources have been heterogeneously expressed in Escherichia coli, which significantly increased the enzyme’s titer. This review presents a systematic and detailed summary of the contemporary biotechnological approaches employed for isomaltulose production, including the source, structural determination, catalysis mechanism, heterologous expression, catalytic reaction condition optimization of SIase, and immobilization of cells. In addition, protein engineering, heterologous expression in food-grade safety strains, fermentation optimization strategies, and immobilization techniques of SIase are introduced in detail. Towards the end, the review is wrapped up with the concluding remarks, and future strategies are outlined for improving the biological production of isomaltulose. Summary of biological isomaltulose production from sucrose catalyzed by sucrose isomerase.

Synthesis of a Crizotinib Intermediate via Highly Efficient Catalytic Hydrogenation in Continuous Flow

Kilogram-scale highly selective catalytic hydrogenation of the aryl nitro group in the intermediate of crizotinib has been developed, which adopted continuous-flow technology with prepassivated Raney Ni as a catalyst at room temperature. According to the reaction condition optimization, side reactions such as dehalogenation, debenzylation, and reduction of other unsaturated functional groups were inhibited eminently. Moreover, catalytic hydrogenation of (R)-3-(1-(2,6-dichloro-3-fluorophenyl)ethoxy)-2-nitropyridine (compound I) afforded the desired product (R)-3-[1-(2,6-dichloro-3-fluorophenyl)ethoxy]pyridin-2-amine (compound II) with high selectivity (99.9%) and high conversion (99.5%). Finally, high-quality crizotinib was synthesized from intermediate II.

Development of real-time RT-PCR for N2 subtype avian influenza RNA-virus detection

Currently, N2 subtype avian influenza (AI) virus actively circulates in domestic and wild bird populations and is regularly detected in China, other Asian countries and Russia, particularly in combination with H9 hemagglutinin. Therefore, a method for rapid detection of the said infectious agent is urgently required. Data on oligonucleotide primer selection and reverse transcription real-time polymerase chain reaction condition optimization for N2 AI virus detection are presented in the paper. Modified primers and probe proposed by B. Hoffmann in 2006 as well as original primers and probes with the viruses available in the Laboratory working collection and selected during testing were assessed for N2 neuraminidase gene fragment amplification. Optimal concentrations of real-time RT-PCR master mix components and temperature-time mode were determined. Various combinations of primers were tested against ten N2 avian influenza virus isolates that genetically differed from each other in N gene. Nine viruses were isolated from birds in the Russian Federation regions and classified to different genetic groups. The real-time RT-PCR assay was tested for its specificity using AI virus isolates of different neuraminidase subtypes (H5N8, H3N6, H4N6, H5N1, H10N7) as well as samples containing other RNA-viruses: Newcastle disease virus, infectious bronchitis virus and infectious bursal disease virus. As a result of the testing, real-time RT-PCR conditions providing high sensitivity and specificity of the assay were selected and optimized.

Towards defect engineering in hexagonal MoS2 nanosheets for tuning hydrogen evolution and nitrogen reduction reactions

Combined computational and experimental approaches were used to evaluate defective 2H-MoS2 nanosheets for their activity and selectivity for hydrogen evolution reaction (HER) and nitrogen reduction reaction (NRR). Density functional theory calculations were used to understand the relationship between HER and NRR activity on the ideal basal MoS2 plane, seven grain-boundaries, ten single-/few-atom vacancies and anti-sites, and zigzag and armchair edge sites. The results confirm that 2H-MoS2 should contain several defects with high activity for HER: armchair and zigzag edges, VS vacancy, MoS2 anti-site, and S-S and Mo-Mo grain boundaries. Considering Gibbs free energy change for all the steps in the NRR mechanism and kinetic barriers for a key NRR step, we have found that activation of perspective NRR selective sites in 2H-MoS2, namely VMoS6 and clusters of S-vacancies, would require large overpotential, conditions at which HER dominates. The DFT conclusions are supported by the electrochemical studies of NRR activity and selectivity under aqueous conditions, which show an increase in NRR activity but a decrease in Faradaic efficiency as applied cell potential becomes more negative. The results of this work therefore highlight the challenges in activating natural 2H-MoS2 for NRR, which would require additional material engineering or reaction condition optimization as a way to suppress HER, decrease the NRR overpotential or preferentially both.

Heavy oil catalytic upgrading under methane environment: A small pilot plant evaluation

The effects of variable factors such as temperature, pressure, weight hourly space velocity (WHSV), catalyst regeneration and reaction time on catalytic upgrading of heavy oil under methane environment over Ag-Ga/HZSM-5 catalyst are evaluated by small pilot plant tests. The viscosity, TAN and average molecular weight of the heavy oil samples are notably reduced accompanied with a low olefin content after the catalytic upgrading. Methane incorporation to product molecules results in increased liquid product yield. The simulated distillation and compositional analysis results illustrate the conversion of resin and asphaltene components to small molecules. After the upgrading at 430 °C and 5 MPa, the percentage of gasoline content is increased to 17% from 3% in the feedstock, and the percentage of diesel fraction is increased to 27% from 21%. The percentage of light end volatiles is increased from 4.4% to 22.2%. During the catalytic upgrading, a higher temperature and pressure benefits the oil quality improvement and methane participation while maintaining the high liquid yield and low coke generating rate. Outstanding stability of the product oil samples is witnessed by comparing the products obtained at variable reaction time. A higher WHSV results in slightly compromised performance of the catalytic upgrading of heavy oil under methane. A positive effect of catalyst regeneration is witnessed. Stable oil quality from the upgrading process is observed when catalysts have been regenerated twice or more. The knowledge obtained in this study would benefit the potential industrial application of this innovative technology at larger scales and guide the further reaction condition optimization.

Virtual Reaction Condition Optimization based on Machine Learning for a Small Number of Experiments in High-dimensional Continuous and Discrete Variables

We examined a virtual simulation scheme for reaction condition optimization using machine learning for a small number of experiments with nine reaction conditions, consisting of five continuous and...

Reaction condition optimization and degradation pathway in wet oxidation of benzopyrazole revealed by computational and experimental approaches

The nitrogen heterocyclic compounds (NHCs) are very toxic and widely used in many industries, while the treatment of NHCs in wastewater has not attracted enough concern till now. Here we studied the complete degradation of a typical NHCs, benzopyrazole (BP), in wet oxidation. The effects of different operation parameters, such as stirring speed, temperature, reaction time and initial pH, on BP degradation and chemical oxygen demand (COD) removal were studied. BP was totally degraded and the COD removal efficiency achieved 76.7%, after 120 min reaction at 220 °C with initial pH 6.5. Meanwhile, 81.7% of the nitrogen from BP was removed from the solution. The toxicity of the BP solution was reduced by 95.2% after wet oxidation at 240 °C for 180 min. The influences of coexisted NO3−, CO32−, SO42− and PO43− ions were also investigated. With quantum chemical calculation and intermediates analysis by electrospray ionization mass spectrometry, a very detailed degradation pathway of BP in wet oxidation was proposed.

Thermodynamic study of direct amination of isobutylene to tert-butylamine

On basis of thermodynamic empirical equations, the thermodynamic parameters for the direct amination of isobutylene to tert-butylamine, an atomically economic and green chemical reaction, were calculated. In particular, the equilibrium conversion of isobutylene under various reaction conditions close to those used in industry was calculated and discussed. Isobutylene amination is a temperature sensitive reaction due to its exothermic nature and isobutylene equilibrium conversion decreases with temperature. However, kinetically, the amination reaction will be faster at a higher temperature. Thus, there must be an optimum temperature for the reaction. A high pressure and n(NH3)/n(i-C4H8) molar ratio promote the transformation of isobutylene to tert-butylamine. Developing a highly efficient catalyst under mild reaction conditions is preferred for the amination process. The reaction was investigated over a series of acidic zeolites. ZSM-11 zeolite exhibited the best performance with 14.2% isobutylene conversion (52.2% of the equilibrium conversion) and > 99.0% tert-butylamine selectivity. The effect of reaction conditions on the performance of the ZSM-11 catalyst agreed with the thermodynamic results, which provides guidance for further catalyst development and reaction condition optimization.