Reversible Step Research Articles

Effect of the post-gate annealing on the gate reliability of AlGaN/GaN HEMTs

In this paper, we investigated the effect of post-gate annealing (PGA) on reverse gate leakage and the reverse bias reliability of Al0.23Ga0.77N/GaN high electron mobility transistors (HEMTs). We found that the Poole–Frenkel (PF) emission is dominant in the reverse gate leakage current at the low reverse bias region (V th < V G < 0 V) for the unannealed and annealed HEMTs. The emission barrier height of HEMT is increased from 0.139 to 0.256 eV after the PGA process, which results in a reduction of the reverse leakage current by more than one order. Besides, the reverse step stress was conducted to study the gate reliability of both HEMTs. After the stress, the unannealed HEMT shows a higher reverse leakage current due to the permanent damage of the Schottky gate. In contrast, the annealed HEMT shows a little change in reverse leakage current. This indicates that the PGA can reduce the reverse gate leakage and improve the gate reliability.

Ruthenium(II)-Catalyzed Regioselective C-H Olefination of Aromatic Ketones and Amides with Allyl Sulfones.

A Ru(II)-catalyzed cross-dehydrogenative Heck-type olefination of arenes with allyl sulfones leveraging the assistance of weakly coordinating ketone and amide functional groups is reported. It features a distinct reactivity profile in comparison to other allylic congeners, where β-sulfonyl elimination was not detected. The ambiphilic nature of the allyl sulfone side chain has also been demonstrated through intramolecular aza-Michael addition and aldol condensation. Mechanistic studies indicated the involvement of a reversible metalation step, where β-hydride elimination takes place selectively from the benzylic position.

Stereoselective Installation of Five Contiguous Stereogenic Centers in a Double Aldol-Tishchenko Cascade and Evaluation of the Key Transition State through DFT Calculation.

The stereoselective formation of 5 contiguous chiral centers in a single pot reaction is demonstrated using an aldol, aldol–Tishchenko reaction of N-tert-butyl sulfinimines. One diastereoisomer (from 32 possibilities) predominates, and a series of cyclic and acyclic 3-amino-1,5-diol derivatives are synthesized in good yields (up to 80%) and excellent diastereoselectivities (up to >98:2 dr). Investigations support two reversible aldol steps, and multiple intermediates which are funnelled through a remarkably selective, irreversible, Tishchenko reduction, in a Curtin–Hammett phenomenon. DFT calculations using a disolvated (THF) model reveal the factors controlling stereoselectivity in the final irreversible Tishchenko step.

Synthesis of 1,2-Aminoalcohols through Enantioselective Aminoallylation of Ketones by Cu-Catalyzed Reductive Coupling.

Herein, we report the development of a catalytic enantioselective addition of N-substituted allyl equivalents to ketone electrophiles through use of Cu-catalyzed reductive coupling to access important chiral 1,2-aminoalcohol synthons in high levels of regio-, diastereo-, and enantioselectivity. Factors affecting enantioinduction are discussed including the identification of a reversible ketone allylation step that has not been previously reported in Cu-catalyzed reductive coupling.

Classification of slope area types and hydrocarbon accumulation rules in Wuerxun-Beier Depression

After more than 50 years of exploration and development, Wuerxun-Beier depression has entered a high exploration stage. It is more and more difficult to find large-scale structural reservoirs. Therefore, structural-lithologic reservoirs in slope areas have gradually become the focus of exploration. Based on the overall study and dissection of the depression, the geological differentiation characteristics of the large-scale slope area are discussed. According to the occurrence of the slope, the intensity of tectonic activity, the intensity of source supply and the pattern of synsedimentary fault combination, the slope zone in the study area can be divided into six types, namely, the steep slope with strong source along the fault step type, the compound fault step type of medium slope with strong source, the reverse fault step type of the gentle slope with strong source, and the weak supply type. Different types of slope have different sand control mechanisms and reservoir forming characteristics, such as the source gentle slope forward fault terrace type, the weak source gentle slope reverse fault terrace type and the weak source middle slope forward fault terrace type. Source supply intensity and slope dip control the development type of sedimentary system, the combination of synsedimentary faults and valleys controls the distribution characteristics of sedimentary system. Through exploration practice, significant discoveries have been made on the southwestern, southeastern and northern slopes of Beixi, Wuerxun-Beier depression, which confirms that the slope area is the main breakthrough direction for oil and gas exploration and large-scale reservoir increase in continental fault-depression lake basins.

Origin of Performances of Pt/Cu Single-Atom Alloy Catalysts for Propane Dehydrogenation

The propane dehydrogenation (PDH) reaction converts cheap propane to value-added propene. Pt-based catalysts show high performance in PDH, but suffer from coke formation and deactivation. Therefore, promoter, that is, a second metal component, is required to enhance its stability. Our previous study has constructed Pt/Cu single atom alloy (SAA) catalysts and achieved high PDH selectivity and anticoke ability. However, the nature of its high performance in PDH still remains to be revealed. This paper describes the origin of catalytic performance for Pt/Cu SAA in PDH via density functional theory (DFT) calculations and kinetic Monte Carlo (kMC) simulations. We constructed a complex reaction network with 54 reversible reaction steps, including adsorption, desorption, C–H bond breaking, and C–C bond cracking processes on the Pt/Cu SAA catalyst. The high selectivity of propene has been demonstrated because of the higher occurrence of propene formation and, simultaneously, the high energy barriers for deep dehydrogenation of propene. The lower coverages of the coke species origin from the deep dehydrogenation instead of the C–C bond cracking for Pt/Cu SAA catalyst, which is different from that proposed for Pt catalyst. The simulation suggests that hydrogen (H2) cofeeding can further reduce the surface coke species. Overall, the current study provides fundamental insights into the origin of high selectivity and anticoke ability to help the design of stable and high-performance Pt-based catalysts.

Current Frontiers in Pincer Chemistry

Ever since the introduction of the archetypal (bisphosphinomethyl)phenyl PCP pincer ligand by Shaw in 1976, the use of this class of tridentate ligands with a central phenyl moiety has found widespread utility in coordination chemistry and homogeneous catalysis. Initially, van Koten's definition of pincer ligands, which was inspired by the claws of the crab, only included rigid, meridionally binding, monoanionic ligands. The rapid growth in popularity of pincer chemistry in the 1990s can be associated with the modular tunability of the steric and electronic properties of these ligands, which can give pincer supported complexes enhanced chemical stability and well-defined reactivity. Consequently, the application of pincer supported complexes has had a significant impact on the advancement of key areas in small molecule activation and catalysis, such as C–H activation, olefin polymerization and cross-coupling. As of today, the term pincer ligand is used more broadly and now comprises a wide range of more or less flexible, neutral and charged, tridentate ligands with a large variety of central and flanking donor groups. While this development means that there is no longer a clear definition of a pincer ligand, the broadening of the field has allowed for the combination of new, chemically active functional groups with the beneficial structural properties of pincer ligands. Accordingly, the utility of pincer ligands was enhanced by the introduction of functional pincer ligands, which adopt active roles in chemical transformations, such as reversible electron and/or proton transfer steps, and extend pincer ligands beyond traditional inert auxiliary ligands. This conceptual advance has contributed to recent progress in many fields, like the renaissance of base metal catalysis, the use of non-innocent, redox active and cooperating ligands in catalysis, or the development of acceptorless de-/hydrogenation strategies for organic synthesis. This themed issue of the Zeitschrift für Anorganische und Allgemeine Chemie dedicated to Pincer Chemistry addresses three current focal areas in the field with contributions from leading groups in Asia, America, and Europe: (a) The synthesis of new pincer-type ligands, (b) the electronic structures of pincer supported complexes, and (c) the application of pincer ligated complexes in chemical transformations and catalysis. The work from Caulton et al., Huang et al., Langer and Vogt et al., Nishibayashi et al., Ozerov et al. and Walter et al. focuses on the development of synthetic methodologies towards new pincer platforms with respect to the central donor site, the connecting backbone, and the flanking “wings” of the ligands. These studies offer insight into the tunability of donor strength, rigidity and steric properties in pincer ligands. Contributions from Anderson et al., Kirchner et al., Milsmann et al. and Ray and Swart et al. disclose detailed spectroscopic and computational studies of iron and copper pincer complexes. Particular focus lies on their electronic structures, redox state assignments and control of accessible spin states and reactivity. Guan et al., Kuwata et al., Morris et al., Jones and Nachtigall et al. and Schneider et al. examined the proton/electron transfer model chemistry of complexes with proton responsive and redox active pincer ligands. These contributions are complemented by a systematic computational study from Pidko et al. that evaluates the effects of pincer substitution on metal-ligand cooperativity. Finally, Goswami et al. utilize such functional pincer ligands as hydrogen relays in transfer hydrogenation catalysis. These contributions reflect the current frontiers and the state-of-the-art in Pincer Chemistry and intend to stimulate the use pincer ligands in coordination chemistry and catalysis.

Understanding Reaction Networks through Controlled Approach to Equilibrium Experiments Using Transient Methods.

We report a combined experimental/theoretical approach to studying heterogeneous gas/solid catalytic processes using low-pressure pulse response experiments achieving a controlled approach to equilibrium that combined with quantum mechanics (QM)-based computational analysis provides information needed to reconstruct the role of the different surface reaction steps. We demonstrate this approach using model catalysts for ammonia synthesis/decomposition. Polycrystalline iron and cobalt are studied via low-pressure TAP (temporal analysis of products) pulse response, with the results interpreted through reaction free energies calculated using QM on Fe-BCC(110), Fe-BCC(111), and Co-FCC(111) facets. In TAP experiments, simultaneous pulsing of ammonia and deuterium creates a condition where the participation of reactants and products can be distinguished in both forward and reverse reaction steps. This establishes a balance between competitive reactions for D* surface species that is used to observe the influence of steps leading to nitrogen formation as the nitrogen product remains far from equilibrium. The approach to equilibrium is further controlled by introducing delay timing between NH3 and D2 which allows time for surface reactions to evolve before being driven in the reverse direction from the gas phase. The resulting isotopic product distributions for NH2D, NHD2, and HD at different temperatures and delay times and NH3/D2 pulsing order reveal the role of the N2 formation barrier in controlling the surface concentration of NHx* species, as well as providing information on the surface lifetimes of key reaction intermediates. Conclusions derived for monometallic materials are used to interpret experimental results on a more complex and active CoFe bimetallic catalyst.

Abstract 707: Detection of SARS-CoV-2 co-infections with seasonal respiratory viruses using a multiplexed amplicon NGS panel

Abstract The ongoing COVID-19 pandemic, caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has affected everyone around the world. Most symptoms of COVID-19 overlap with symptoms of the flu and the common cold. With the approaching flu season, early and accurate detection of these viruses are critical not only to slow the spread of SARS-CoV-2, but also to ensure that patients receive the appropriate care based on their diagnosis, and to keep the healthcare system from becoming overloaded. We designed a next-generation sequencing (NGS) assay to detect the SARS-CoV-2, influenza A H1N1, influenza A H3N2, influenza B, RSV A, and RSV B viruses, and to allow for surveillance and subtype identification. The primers for this multiplex PCR-based method interrogate nearly every gene of each virus. Subsequent sequencing enables not only virus detection but also co-infection detection for these respiratory viruses. In addition, sequencing of virus-positive samples makes it possible to use this assay for mutation and strain analysis. Using the CleanPlex target enrichment technology, we prepared targeted amplicon libraries with human total RNA (50ng) spiked with SARS-CoV-2 synthetic RNA, influenza A synthetic RNA, influenza B synthetic RNA, RSV A RNA, and RSV B RNA (100-10,000 viral genome copies), either individually or in combination. The NGS library preparation protocol includes a reverse transcription step to generate cDNA, followed by a multiplexed PCR step for specific amplification of viral targets. A critical subsequent background cleaning step removes non-specific PCR products, and a final PCR adds sample indices and Illumina sequencing adapters to complete the NGS library preparation. Libraries were sequenced on the Illumina iSeq100 platform, and sequencing metrics as well as virus characterization were determined using Paragon Genomics's bioinformatics pipeline. Each sample was sequenced at 1,000 average paired-end reads per amplicon. After aligning sequencing reads to each viral genome, we were able to detect nearly every gene of each virus with high specificity. At viral loads of 10,000 copies, 96-100% of amplicons were covered at &amp;gt;100X, and mapped to the intended virus species as well as to the intended subtypes for influenza A and RSV. The assay also accurately identified co-infected samples, which contained equal copies of SARS-CoV-2 and influenza (either A H1N1, A H3N2, or B). In summary, the assay detects multi-target respiratory viruses with high accuracy and specificity. We plan to expand on our findings for this assay's performance with additional targets, co-infection studies and mutational analysis studies. Citation Format: Lucie S. Lee, Rounak Feigelman, David Debruyne, Julia Spencer, Chenyu Li, Zhitong Liu, Guoying Liu. Detection of SARS-CoV-2 co-infections with seasonal respiratory viruses using a multiplexed amplicon NGS panel [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 707.

Assembly factors chaperone ribosomal RNA folding by isolating helical junctions that are prone to misfolding

While RNAs are known to misfold, the underlying molecular causes have been mainly studied in fragments of biologically relevant larger RNAs. As these small RNAs are dominated by secondary structures, misfolding of these secondary structures remains the most-explored cause for global RNA misfolding. Conversely, how RNA chaperones function in a biological context to promote native folding beyond duplex annealing remains unknown. Here, in a combination of dimethylsulfate mutational profiling with sequencing (DMS-MaPseq), structural analyses, biochemical experiments, and yeast genetics, we show that three-helix junctions are prone to misfolding during assembly of the small ribosomal subunit in vivo. We identify ubiquitous roles for ribosome assembly factors in chaperoning their folding by preventing the formation of premature tertiary interactions, which otherwise kinetically trap misfolded junctions, thereby blocking further progress in the assembly cascade. While these protein chaperones act indirectly by binding the interaction partners of junctions, our analyses also suggest direct roles for small nucleolar RNAs (snoRNAs) in binding and chaperoning helical junctions during transcription. While these assembly factors do not utilize energy to ameliorate misfolding, our data demonstrate how their dissociation renders reversible folding steps irreversible, thereby driving native folding and assembly and setting up a timer that dictates the propensity of misfolded intermediates to escape quality control. Finally, the data demonstrate that RNA chaperones act locally on individual tertiary interactions, in contrast to protein chaperones, which globally unfold misfolded proteins.

The kinetics modeling and reactor simulation of propylene chlorination reaction process

AbstractThe kinetics experiments of fast reaction process of propylene chlorination at low temperature (30–90°C) and high temperature (420–480°C) are respectively conducted, and the corresponding reaction mechanisms and kinetics models are proposed. The radical mechanism at high temperature and the molecular mechanism at low temperature are found to be most likely with the experimental results. Specifically, the kinetics model, firstly considering the reversible reaction step of forming C3H6Cl· and direct hydrogen abstraction of forming C3H5·, shows better agreement with the experimental data. Furthermore, the critical reaction temperature Tcritical is firstly proposed to determine the dominant reaction mechanism in different conditions, and correspondingly the combination method of the high‐temperature and low‐temperature kinetics models has been adopted for tubular reactor simulation, which can reasonably reflect the influence of wide variation range of temperature in the reactor and guide the industrial reactor design in the further work.

Design and Electrochemical Investigation of Ureido-Sulfonamidic Receptors for Phosphates

Anions play an important role in biological systems. At the same time, many of them are the major environmental pollutants and substances endangering living organisms [1]. For these purposes the anion recognition, elimination and sensing would find application in many branches including application in medicine or environmental chemistry. Suitable examples of anion pollutants are phosphates, which could cause eutrophication of water and they are also known for their limited removal from body fluids, which could lead to serious health problems. Therefore, the aim of our research group is the design and preparation of anionic receptors with suitable binding sites to bind these anions.In the first step of our synthesis a series of substituted nosylamidic intermediates (fig. a, b) was prepared. These substances are suitable precursors for the synthesis of novel receptors bearing ureido functions (fig. c). The sulfonamidic motif itself is known as a neutral donor of hydrogen bond. Hence for better understanding of the behaviour of the final urea receptors, the properties of intermediate molecules were studied by various physicochemical techniques including spectroscopic and electrochemical methods.Spectroscopic methods were used to evaluate the binding ability of this motif and to determine its acid-basic properties. Electrochemical methods (represented by polarography and cyclic voltammetry with mercury dropping or hanging electrodes in dimethylformamide with Bu4N PF6 as electrolyte) were chosen because the nitro groups in our intermediate molecules are not only important substituents enabling continuation in synthesis, but also electrochemical "probes" reflecting the properties of the parent molecule. Their reduction in aprotic media is generally known after the first one-electron reversible reduction step where a stable radical anion is formed, a three-electron irreversible process follows resulting in the corresponding hydroxylamine [2]. However, the reduction pattern of the series (b) is totally different: After the first irreversible step (theoretically involving 4/5 of electron) a one-electron reversible reduction takes place followed by a multielectron process. This behaviour can be explained by using autoprotonation mechanism [3] where the acidic hydrogen of the sulfonamidic group is involved.Then our attention focused on final receptors (fig c). It was shown, that sulfonamidic moiety can be utilized as an electron-withdrawing group useful to enhance the anion complexation properties of urea-based receptors. On the other hand, it brings an inherent predisposition for deprotonation in the presence of more basic anions. In order to shift the deprotonation/complexation equilibrium in favour of the complexation, the receptors were derivatized by electron-donating groups like –OCH3 at sulfonamidic moiety. The binding for this receptor was evaluated in a competitive solvent (DMSO) by using NMR titration experiments. The experimental results show a considerable selectivity of our receptor to phosphates compared to another biologically important anions such as Cl-, NO3 - and HSO4 - [4].Based on these results, the prepared receptors appear to be suitable motifs for binding phosphate anions. In order to take advantage of their binding capabilities, these molecules need to be attached to the surface of a suitable molecular carrier. The formation of these functional materials (in our case especially dendrimers) is also associated with the need to design and optimize methods to describe anion binding ability, as well as the possibility to recycle the prepared materials. This was the reason for which it seems to be interesting to consider the presence of an electrochemical “probe” also in the final molecular receptors. The redox transformation of such a probe should fundamentally affect the complexing abilities of the receptor and allow targeted degradation of the complex. Acknowledgements: The work was supported by the grant number 18-12150S and 20-07833S.

Versatile and flexible microfluidic qPCR test for high-throughput SARS-CoV-2 and cellular response detection in nasopharyngeal swab samples.

The emergence and quick spread of SARS-CoV-2 has pointed at a low capacity response for testing large populations in many countries, in line of material, technical and staff limitations. The traditional RT-qPCR diagnostic test remains the reference method and is by far the most widely used test. These assays are limited to a few probe sets, require large sample PCR reaction volumes, along with an expensive and time-consuming RNA extraction step. Here we describe a quantitative nanofluidic assay that overcomes some of these shortcomings, based on the BiomarkTM instrument from Fluidigm. This system offers the possibility of performing 4608 qPCR end-points in a single run, equivalent to 192 clinical samples combined with 12 pairs of primers/probe sets in duplicate, thus allowing the monitoring of SARS-CoV-2 including the detection of specific SARS-CoV-2 variants, as well as the detection other pathogens and/or host cellular responses (virus receptors, response markers, microRNAs). The 10 nL-range volume of BiomarkTM reactions is compatible with sensitive and reproducible reactions that can be easily and cost-effectively adapted to various RT-qPCR configurations and sets of primers/probe. Finally, we also evaluated the use of inactivating lysis buffers composed of various detergents in the presence or absence of proteinase K to assess the compatibility of these buffers with a direct reverse transcription enzymatic step and we propose several protocols, bypassing the need for RNA purification. We advocate that the combined utilization of an optimized processing buffer and a high-throughput real-time PCR device would contribute to improve the turn-around-time to deliver the test results to patients and increase the SARS-CoV-2 testing capacities.

Role of Intracellular Distribution of Feline and Bovine SAMHD1 Proteins in Lentiviral Restriction.

Human SAMHD1 (hSAM) restricts lentiviruses at the reverse transcription step through its dNTP triphosphohydrolase (dNTPase) activity. Besides humans, several mammalian species such as cats and cows that carry their own lentiviruses also express SAMHD1. However, the intracellular distribution of feline and bovine SAMHD1 (fSAM and bSAM) and its significance in their lentiviral restriction function is not known. Here, we demonstrated that fSAM and bSAM were both predominantly localized to the nucleus and nuclear localization signal (11KRPR14)-deleted fSAM and bSAM relocalized to the cytoplasm. Both cytoplasmic fSAM and bSAM retained the antiviral function against different lentiviruses and cytoplasmic fSAM could restrict Vpx-encoding SIV and HIV-2 more efficiently than its wild-type (WT) protein as cytoplasmic hSAM. Further investigation revealed that cytoplasmic fSAM was resistant to Vpx-induced degradation like cytoplasmic hSAM, while cytoplasmic bSAM was not, but they all demonstrated the same in vitro dNTPase activity and all could interact with Vpx as their WT proteins, indicating that cytoplasmic hSAM and fSAM can suppress more SIV and HIV-2 by being less sensitive to Vpx-mediated degradation. Our results suggested that fSAM- and bSAM-mediated lentiviral restriction does not require their nuclear localization and that fSAM shares more common features with hSAM. These findings may provide insights for the establishment of alternative animal models to study SAMHD1 in vivo.

Improvement in the sensitivity of viroid detection by adapting the reverse transcription step in one-step RT-qPCR assays

Over the course of developing and applying a new real-time PCR assay for the detection of the newly described apple chlorotic fruit spot viroid (ACFSVd), slight modifications of the reverse transcription (RT) step were found to improve significantly the detection limit of the assay. To prove this hypothesis, three different one-step RT-qPCR kits for the detection of three plant viroids and three plant viruses were compared. The results showed both extension of the RT reaction time from 10 or 15 min–30 min or the increase in reaction temperature from 49 to 52 °C for the cDNA synthesis step results in a 10 times higher sensitivity for potato spindle tuber viroid and apple scar skin viroid one-step RT-qPCR assay and 45 higher sensitivity for ACFSVd one-step RT-qPCR assay. No variation in the detection limit was observed when the modifications were tested on tomato brown rugose fruit virus, plum pox virus and tomato ringspot virus assays. This finding is highly valuable for the investigation of viroids in general and could contribute to enhance sensitivity in their detection and to benefit regulatory outcomes for national plant protection organisations.

Evaluation of a New Histoplasma spp. Quantitative RT-PCR Assay

Laboratory diagnosis of histoplasmosis is based on various methods, including microscopy, culture, antigen, and DNA detection of Histoplasma capsulatum var. capsulatum or Histoplasma capsulatum var. duboisii. To improve sensitivity of existing real-time quantitative PCR (qPCR) assays, we developed a new RT-qPCR assay that allows amplification of whole nucleic acids of Histoplasma spp. validated on suspected cases. The limit of detection was 20 copies, and the specificity against 114 fungal isolates/species was restricted to Histoplasma spp. Whole nucleic acids of 1319 prospectively collected consecutive samples from 907 patients suspected of having histoplasmosis were tested routinely between May 2015 and May 2019 in parallel with standard diagnostic procedures performed in parallel. Forty-four had proven histoplasmosis attributable to H. capsulatum var. capsulatum (n = 40) or H.capsulatum var. duboisii (n = 4) infections. The results of RT-qPCR were positive in 43 of 44 patients (97.7% sensitivity) in at least one specimen. Nine of 863 cases (99% specificity) were RT-qPCR positive and therefore classified as possible cases. RT-qPCR was positive in 13 of 30 (43.3%) blood samples tested in proven cases. A positive RT-qPCR result in blood was significantly associated with H. capsulatum var. capsulatum progressively disseminated histoplasmosis with a positive RT-qPCR result in 92.3% of the immunocompromised patients with disseminated disease. This new Histoplasma RT-qPCR assay enabling amplification of H. capsulatum var. capsulatum and H. capsulatum var. duboisii is highly sensitive and allows the diagnosis of histoplasmosis advantageously from blood and bronchoalveolar lavage fluid.

Selective synthesis of γ-valerolactone from levulinic and formic acid over ZnAl mixed oxide

After testing different mixed oxides, a very promising catalyst to obtain γ-valerolactone from levulinic acid and formic acid is proposed in this work: a ZnAl hydrotalcite-derived material. Optimum conditions (T = 140 °C, FA/LA = 5/1, aqueous phase stirred batch reactor) excel results previously proposed in the literature, combining high activity (>87%) and selectivity (90% GVL yield) with remarkable stability, the reaction being performed at mild conditions and using a highly available and cheap catalyst.A detailed mechanistic with its kinetic study was accomplished for this optimum catalyst, considering that formic acid decomposition is the limiting step following a second–order kinetic, and the FA dehydration to AL is a pseudo-first–order reversible step. Angelica-lactone is identified as the main by–product and the precursor for the formation of light organic deposits, the main responsible for the slight deactivation observed during the experiments in absence of reactivation procedure.

The Effect of Flow Swing on Waterflood Under Oil-Wet Conditions: A Pore-Level Study

The stability of the waterfront in a heterogeneous porous medium and in the absence of gravity effects is controlled by capillary and viscous forces. Under oil-wet conditions, waterflood is a drainage process and the displacement front advances in zones with larger pores where capillary forces are lower, and the rate of displacement is higher compared to zones with smaller pores. Hence, in a waterflood process, a transition zone is formed where the water saturation gradually decreases from a trailing front to the leading end of advanced water fingers. In a heterogeneous medium, oil–water capillary pressure fluctuates due to variations of pore sizes in flooding paths. The difference in the capillary pressures between leading and trailing zones can help with the stability of the waterfront when the capillary pressure in frontal zones is increased by displacing oil through smaller pores. However, this mechanism creates a limited pressure gradient in the oil phase, so the waterfront instabilities continue to grow, especially at the adverse mobility ratio and high displacement rates. In this study, different oil samples with low, medium and high viscosities are displaced by water in an oil-wet medium containing pore-level heterogeneities. Herein, the effect of flow swing, which is introduced to the direction of oil–water displacement, on waterflood performance is investigated. Under flow-swing conditions, we reverse the fluid flow direction periodically; however, the overall volume of injected water is maintained the same for all scenarios by adjusting the periods of the forward and reverse steps. The flow reversal promotes the refill of water paths with oil, hence attenuating the advanced fingers. Consequently, the sweep efficiency of waterflood is improved and higher oil sweep efficiency is obtained at the time of breakthrough. The flow-swing mechanism is more effective when oscillations of capillary pressure result in a faster flow of oil between trailing and leading zones, thus decreasing the waterfront instabilities. The new process can be optimized and utilized at larger scales for improving the sweep efficiency of flooding operations.

Influence of Nanoconfinement on the Hydrogen Release Processes from Sodium Alanate

Sodium alanate (NaAlH4) is a prospective H2 storage material for stationary and mobile applications, as NaAlH4 contains 7.4 wt% of H2, and it is possible to do multiple H2 release and accumulation cycles. Nanoconfinement is a potential solution to enhance the H2 release properties of NaAlH4. To optimize the supporting material and the synthesis method used for the nanoconfinement of NaAlH4, a better understanding of the influence of nanoconfinement on the H2 release processes is necessary. Thus, the H2 release from bulk, purely nanoconfined, and intermediate NaAlH4 is measured at different temperature ramp rates, and the characteristic parameters for each hydrogen release process are determined. Activation energies for each process are determined using the Kissinger method, and the effect of nanoconfinement on the activation energies is analysed. The impact of nanoconfinement on the H2 release processes from NaAlH4 and the limitations of each process in case of bulk and nanoconfined NaAlH4 are presented and discussed. Nanoconfinement of NaAlH4 decreases activation energies of the initial reversible H2 release steps to between 30 and 45 kJ mol−1 and increased the activation energy of the last irreversible H2 release step to over 210 kJ mol−1.

Primer ID Next-Generation Sequencing for the Analysis of a Broad Spectrum Antiviral Induced Transition Mutations and Errors Rates in a Coronavirus Genome.

Next generations sequencing (NGS) has become an important tool in biomedical research. The Primer ID approach combined with the MiSeq platform overcomes the limitation of PCR errors and reveals the true sampling depth of population sequencing, making it an ideal tool to study mutagenic effects of potential broad-spectrum antivirals on RNA viruses. In this report we describe a protocol using Primer ID sequencing to study the mutations induced by antivirals in a coronavirus genome from an in vitro cell culture model and an in vivo mouse model. Viral RNA or total lung tissue RNA is tagged with Primer ID-containing cDNA primers during the initial reverse transcription step, followed by two rounds of PCR to amplify viral sequences and incorporate sequencing adaptors. Purified and pooled libraries are sequenced using the MiSeq platform. Sequencing data are processed using the template consensus sequence (TCS) web-app. The Primer ID approach provides an accurate sequencing protocol to measure mutation error rates in viral RNA genomes and host mRNA. Sequencing results suggested that β-D-N4-hydroxycytidine (NHC) greatly increased the transition substitution rate but not the transversion substitution rate in the viral RNA genomes, and cytosine (C) to uridine (U) was found as the most frequently seen mutation.