Dehydration Pathway Research Articles

Surface reactions of ethanol on UO2 thin film. Dehydrogenation and dehydration pathways

The reaction of ethanol has been investigated on a UO2 thin film by temperature programmed desorption. Two channels for ethanol desorption are identified. The first, in the 250–500 K region, is coverage dependent while the second with a maximum peak temperature (Tp) at ca. 630 K is not. The desorption energy, Ed, of the second channel is found to be equal to ca. 150 kJ/mol with a prefactor of 1012 s−1 and a desorption order n = 2. This is attributed to surface ethoxides re-combinative desorption. This second desorption channel is accompanied by the desorption of acetaldehyde (and hydrogen) and ethylene (and water). Acetaldehyde (CH3CHO) desorption, produced by the dehydrogenation of ethoxides, was sensitive to surface coverage. Tp changed from 640 K at θ = 0.06 to 610 K at θ = 1, while ethylene (CH2CH2) desorption, produced by the dehydration of ethoxides did not shift. The molar ratio of these two products (CH3CHO/CH2CH2) of 0.8 is similar to that previously found on a UO2(1 1 1) single crystal and fits with the UO bonding nature that contains a non-negligible fraction of covalency.

Genome-Wide Identification and Characterization of Diterpenoid Pathway CYPs in Andrographis paniculata and Analysis of Their Expression Patterns under Low Temperature Stress

Andrographis paniculata is known for its diterpenoid medicinal compounds with antibacterial and anti-inflammatory properties. However, it faces production and cultivation challenges due to low temperatures (LTs). Cytochrome P450 monooxygenases (CYPs) are key enzymes in diterpenoid accumulation. Nevertheless, the functions and LT-related expression patterns of diterpenoid pathway CYPs in Andrographis paniculata remain poorly understood. In this study, 346 CYPs were discovered in Andrographis paniculata. Among them, 328 CYPs belonged to 42 known subfamilies. The remaining 17 CYPs might have represented novel subfamilies unique to this species. A total of 65 candidate CYPs associated with diterpenoid modification were identified. Of these, 50 were transmembrane proteins, and 57 were localized to chloroplasts. The CYP71 subfamily was the most abundant and had the highest motif diversity. Promoters of all candidate CYPs commonly contained elements responsive to gibberellins (GAs), methyl jasmonate (MeJA), and abiotic stresses. Notably, the XP_051152769 protein, corresponding to a CYP gene over 40,000 bp in length, featured an extraordinarily long intron (40,751 nts). Functional elements within this intron were related to LT, GAs, and dehydration pathways. Based on the promoter element arrangement and subfamily classification, 10 representative candidate CYPs were selected. Under LT stress, significant expression changes were observed in three representative CYPs: CYP71D, ent-kaurenoic acid oxidase (KAO), and ent-kaurene oxidase (KO). KAO and KO were significantly upregulated during early LT stress. KAO and KO interacted with each other and jointly interacted with GA20OX2-like. CYP71D acted as a negative response factor to LT stress. Among the 37 proteins interacting with CYP71D, 95% were CYPs. This study provides a critical preliminary foundation for investigating the functions of diterpenoid pathway CYPs in Andrographis paniculata, thereby facilitating the development of LT-tolerant cultivars.

Elucidating enantioselective fate and sensitive biomarkers in zebrafish of chiral pesticide fenpropidin: Insights into metabolic pathways and hazard assessment

Fenpropidin (FPD), a widely utilized chiral fungicide, has been detected in aquatic environments. This study systematically evaluated the bioaccumulation, depuration, biotransformation, and sensitive biomarkers of FPD enantiomers in zebrafish to assess their environmental risks. Compared with S-FPD, R-FPD demonstrated a higher rate of enrichment and an increased level of bioaccumulation. The half-lives of R-FPD and S-FPD were 0.49 ± 0.01 and 0.91 ± 0.02 days at 0.05 mg/L and 1.65 ± 0.01 and 1.85 ± 0.03 days at 0.5 mg/L. Nontarget metabolism analysis identified nine metabolites, primarily formed through hydroxylation, oxidation, dehydration, glutathione conjugation, and glucuronidation pathways. Some metabolites exhibited high toxicity, underscoring the necessity for continuous monitoring of their toxicological effects and environmental fate in risk assessments. The toxicity of S-FPD in zebrafish was 1.21 times greater than that of R-FPD. Furthermore, this study identified sensitive markers for the enantiomers at both protein and transcriptional levels using an integrated biomarker response approach. S-FPD exhibited increased sensitivity to apoptosis and metabolic gene expression, while R-FPD showed greater sensitivity to antioxidant kinase activity. These findings facilitate timely monitoring of environmental pollution caused by FPD enantiomers. This study provides critical insights for assessing potential risks associated with pesticide exposure to human health.

Cysteine Radical and Glutamate Collaboratively Enable C-H Bond Activation and C-N Bond Cleavage in a Glycyl Radical Enzyme HplG.

Hydroxyprolines are abundant in nature and widely utilized by many living organisms. Isomerization of trans-4-hydroxy-d-proline (t4D-HP) to generate 2-amino-4-ketopentanoate has been found to need a glycyl radical enzyme HplG, which catalyzes the cleavage of the C-N bond, while dehydration of trans-4-hydroxy-l-proline involves a homologous enzyme of HplG. Herein, molecular dynamics simulations and quantum mechanics/molecular mechanics (QM/MM) calculations are employed to understand the reaction mechanism of HplG. Two possible reaction pathways of HplG have been explored to decipher the origin of its chemoselectivity. The QM/MM calculations reveal that the isomerization proceeds via an initial hydrogen shift from the Cγ site of t4D-HP to a catalytic cysteine radical, followed by cleavage of the Cδ-N bond in t4D-HP to form a radical intermediate that captures a hydrogen atom from the cysteine. Activation of the Cδ-H bond in t4D-HP to bring about dehydration of t4D-HP possesses an extremely high energy barrier, thus rendering the dehydration pathway implausible in HplG. On the basis of the current calculations, conserved residue Glu429 plays a pivotal role in the isomerization pathway: the hydrogen bonding between it and t4D-HP weakens the hydroxyalkyl Cγ-Hγ bond, and it acts as a proton acceptor to trigger the cleavage of the C-N bond in t4D-HP. Our current QM/MM calculations rationalize the origin of the experimentally observed chemoselectivity of HplG and propose an H-bond-assisted bond activation strategy in radical-containing enzymes. These findings have general implications on radical-mediated enzymatic catalysis and expand our understanding of how nature wisely and selectively activates the C-H bond to modulate catalytic selectivity.

Bvp4c approach and duality of hybrid nanofluid over extending and contracting sheet with chemical reaction and cross-diffusion effects

Heat transfer has a major effect on material selection and mechanical efficiency. The importance of peristaltic fluid motion in transmitting heat is obvious in the domains of biomedical research through the processes of metabolic heat generation, blood transportation, capillary dehydration, thermal control, and bio-heat exchange pathways. The present work aims to explore the computational and theoretical evaluation of hybrid nanofluid (HNF)-suspended Cu and Al2O3 nanoparticles in water in the presence of chemical reaction, Lorentz force and ross-diffusion. The fundamental flow system based on Navier-Stokes in terms of partial differential equations is converted to dimensionless nonlinear ordinary differential equations via similarity transformations. The transformed ODEs are computationally solved by bvp4c approach. Dual solutions have been observed for emerging factors, so stability examinations are implemented to find the stable solution. Based on eigenvalues, it is witnessed that smallest positive eigenvalues indicates the stable while negative depicts the unstable solutions. The influences of involved factors on the flow characteristics are depicted through graphs and tables. The confirmation of the present analysis is done with the published study. Decreasing behavior is investigated for both branches of velocity as the M is improved while f′(η) is an increasing function of K. From this analysis it is reported that θ(η) is directly proportional to R, Q and Q1. Increasing phenomena is reported for θη and ϕη profiles as the quantities of Ec are augmented from 0.1 to 1. The conclusions of this theoretical analysis have impending applications in numerous fields such as technological devices, solar cooling and heating systems for cars, surfactants, lubricating qualities, hybrid generators, metallic welding process, and the production of medical equipment.

Statistically driven automated method for catalytic glucose conversion optimisation.

A statistically driven, automated approach to optimize glucose transformations to platform chemicals, methyl lactate and levulinic acid, is reported. The combination of a robotic synthesis platform with design of experiments methods enabled efficient and precise modelling of glucose conversion catalysed by SnCl4·5H2O with 0-100% H2O and methanol as a cosolvent. Using this strategy, optimal reaction conditions within the available reaction space were identified in 58 runs, showcasing the excellent efficiency of this method in producing high yields of methyl lactate (75.9%) and levulinic acid (64.5%) in independent reactions via distinct retro-aldol condensation and dehydration pathways, respectively.

Boosting 3-acetamido-5-acetylfuran production from N-acetyl-D-glucosamine in γ-valerolactone by a dissolution-dehydration effect

Chitin biorefinery offers a unique opportunity to sustainably produce highly-valued organonitrogen compounds such as the versatile pharmaceutical precursor 3-acetamido-5-acetylfuran (3A5AF), bypassing the Haber process and mitigating the consumption of fossil feedstocks. However, the reported protocols engaged large quantities of toxic organic solvents and required harsh conditions. In this work, a highly efficient catalytic system has been developed in the nontoxic, biobased γ-valerolactone (GVL) solvent under relatively mild conditions. 3A5AF was selectively obtained with an unprecedent yield of 75.3% at 140 °C for 2 h by adding NH4SCN and HCl. The high yielding was exclusively promoted by a dissolution-dehydration effect. Based on the UPLC-TOF-MS and NMR analyses, the presence of NH4SCN has induced a very rapid NAG conversion possibly by coordinating with the acetamido group and the hydroxyl groups, and the 3A5AF product was obtained in a subsequent dehydration pathway from NAG with the Chromogen I and Chromogen III as the intermediates.

Structural basis for ion selectivity in potassium-selective channelrhodopsins

KCR channelrhodopsins (K+-selective light-gated ion channels) have received attention as potential inhibitory optogenetic tools but more broadly pose a fundamental mystery regarding how their K+ selectivity is achieved. Here, we present 2.5-2.7Å cryo-electron microscopy structures of HcKCR1 and HcKCR2 and of a structure-guided mutant with enhanced K+ selectivity. Structural, electrophysiological, computational, spectroscopic, and biochemical analyses reveal a distinctive mechanism for K+ selectivity; rather than forming the symmetrical filter of canonical K+ channels achieving both selectivity and dehydration, instead, three extracellular-vestibule residues within each monomer form a flexible asymmetric selectivity gate, while a distinct dehydration pathway extends intracellularly. Structural comparisons reveal a retinal-binding pocket that induces retinal rotation (accounting for HcKCR1/HcKCR2 spectral differences), and design of corresponding KCR variants with increased K+ selectivity (KALI-1/KALI-2) provides key advantages for optogenetic inhibition invitro and invivo. Thus, discovery of a mechanism for ion-channel K+ selectivity also provides a framework for next-generation optogenetics.

Tea-based biochar-mediated changes in cation diffusion homeostasis in rice grown in heavy metal (loid) contaminated mining soil

Foreseeable future scenarios highlight the urgency of applying eco-safe avoidance methods or tolerance to heavy metal(loid) (HM) stress in agricultural production areas of contamination. The analyses show that the Ni, Mn, As, and Cr concentrations detected in the soils of the paddy fields in the Black Sea region vary between 123.60 and 263.30; 687–1271; 8.90–14.50; 162.00–340.00 mg kg−1 proving high accumulation of Ni, Mn, As, Cr in rice. Overconsumption of rice farmed extensively on these soils might also lead to human HM-related health problems. Therefore, in the current study, the approach of using tea-based biochar (BC) proven to have one of the most significant potentials as a soil amendment to reduce HM transmission to in-vitro-grown rice plants was investigated in the soil medium naturally contaminated with HMs. The tea-BC was produced from readily available local black tea waste of a conventional fermentation process and applied in the in-vitro experiments. Among the tested doses examined, 1% tea-BC showed a more positive effect on rice plant growth and development characterized by a better relative growth rate (59.7 and 84 mg g−1 d−1 for root and shoot tissues), photosynthetic pigment intactness (62.48 μg mL−1), cellular membrane integrity (93%), and relative water (96%) than the other rates (0% BC, 3%BC, 5%BC). The mRNA expression data highlights the probability of a cation diffusion facilitator (CDF) (OsMTP11) in concert with catalase isozyme (CATa) and dehydration-responsive element binding protein (DREB1a) linking the HM detoxification, oxidative defense, and dehydration pathways with the help of tea-BC. At the optimum concentration (1%BC), this approach might reduce HM accumulation levels of crops planted in HM-contaminated farmlands.

B–O Oligomers or Ring Species in AlB2: Which is More Selective for Propane Oxidative Dehydrogenation?

B-based catalysts are widely studied in the oxidative dehydrogenation of propane (ODHP) owing to their high selectivity. Correspondingly, two species, B–O oligomers and rings, have been recognized as active centers in B-based catalysts. To answer the essential question of whether B–O oligomers or ring species are more selective for ODHP, two AlB2 catalysts enriched with B–O rings (R-AlB2) and abundant B(OH)xO3–x oligomers (O-AlB2) were designed and compared herein. When tested in ODHP, R-AlB2 exhibits an olefin yield of 30.2% at 500 °C, which is 2.3 times that of O-AlB2. Additionally, R-AlB2 was stable for up to 200 h without deterioration. Multiple characterizations, including in situ Fourier transform infrared spectroscopy and theoretical calculations, demonstrate that B–O rings are more advantageous for producing propylene (C3=) via a dehydration pathway with lower energy barriers and ethylene (C2=) via two other reaction pathways (direct cracking of propane and oxidative coupling of methyl) B(OH)xO3–x is primarily responsible for producing few C3=.

ANALYSIS OF CATALYTIC BEHAVIOR OF RHENIUM PROMOTED PT/TIO2 CATALYST IN ERYTHRITOL HYDROGENOLYSIS

Rhenium modified Pt/TiO2 catalyst has been tested during erythritol (ERY) hydrogenolysis reaction in a slurry reactor. N2 physisorption, temperature programmed reduction and CO chemisorption characterizations were performed. After reduction treatment, Pt species were fully reduced with a dispersion of 26% whereas Re species remained partially oxidized. ERY may convert through four pathways: isomerization, dehydration and C-O or C-C hydrogenolysis. Pt-Re/TiO2 was active and selective to butanetriols and butanediols formation. The influence of temperature (423–498 K) and reactant concentrations (15-35 barH2 and 0.2-0.6 MERY) on catalytic activity and products distribution were evaluated; the activation energy and the reaction orders for each route were estimated. Dehydration pathway displayed the highest activation energy whereas isomerization showed the lowest value. The order to ERY and H2 were 0.23 and 0.97 respectively, for C-O hydrogenolysis route and is consistent with two different mechanisms proposed for the removal of primary or secondary OH group.

Selectivity of Ethanol Conversion on Al/Zr/Ce Mixed Oxides: Dehydration and Dehydrogenation Pathways Based on Surface Acidity Properties

AbstractZirconia‐alumina mixed oxides (Zr+Ce)O2−Al2O3 with various mol. ratios (5, 10, 20, 50, and 75 % alumina) were prepared using the sol‐gel method. The catalysts were characterised via XRD, SEM, DTA/TG, BET, and FT‐IR spectroscopy. The acidities of the catalysts were measured through the absorption of anthraquinone and pyridine probe molecules using EPR and IR spectroscopy, respectively. Catalytic activity and selectivity were investigated for ethanol conversion to acetaldehyde, ethylene, and diethyl ether, which were used as model reactions to identify surface‐active sites. The relationship between the surface structure and the dehydration/dehydrogenation activity was evaluated. Diethyl ether formation is promoted by the presence of the ZrO2 tetragonal phase at a low ZrO2/Al2O3 ratio in the sample composition, at which the Lewis acid site has an aluminum‐oxygen environment. The reaction mechanism was also discussed. In the low‐temperature reaction region, dehydrogenation competes with dehydration; ethylene and acetaldehyde share a common reactive intermediate.

Biofuel characteristics of chars produced from rapeseed, whitewood, and seaweed via thermal conversion technologies – Impacts of feedstocks and process conditions

Understanding the suitability of different conversion technologies for different types of biomass feedstocks is crucial in delivering the full valorisation of different types of biomass feedstocks. Optimal valorisation pathways can be identified by investigating the formation of products and the most efficient application technologies of these products. This is therefore novel research reporting an extensive comparative study on the biomass processing pathways (hydrothermal conversion, pyrolysis, and torrefaction) for three distinct biomass feedstocks (Rapeseed residue, Whitewood, Seaweed–Laminaria Digitata) to optimise char formation under a wide range of processing conditions and their biofuel characteristics in the bioenergy applications. The results demonstrates that Whitewood gradually decomposes during all three conversion processes to produce chars (hydrochars/biochars) that have a lower O/C-H/C ratio as process temperature increases. The char formation from Whitewood follows the dehydration process in the Van Krevelen diagram. Char formation from Rapeseed residue and L. digitata via pyrolysis also follows a similar dehydration and demethanation pathway at higher temperatures (550 °C for Rapeseed residue and 400 °C for L. digitata). However, char formation from Rapeseed residue and L. digitata via hydrothermal conversion predominantly follows the decarboxylation pathway producing structures with a higher H/C ratio and lower O/C ratio. The intrinsic reactivity analysis of these chars showed that the temperature of initial weight loss and the onset of ignition for the raw biomass sample was shifted to a higher temperature for the chars produced by hydrothermal conversion or pyrolysis, regardless of biomass feedstocks. The chars produced from Whitewood (with hydrothermal conversion, pyrolysis and torrefaction) and Rapeseed residue (with pyrolysis) have a potential application in bioenergy production due to the significant enhancement of char products. However, the chars produced from L. digitata appear less promising for bioenergy applications due to relatively low energy yield, carbon recovery, inferior char structures and a high inherent ash content.

Catalytic effects on decomposition of formic acid in the atmosphere – A kinetic and thermochemical investigation

Gas-phase unimolecular decomposition of formic acid via (a) decarboxylation and (b) dehydration pathways is explored using density functional theory. A significant reduction in the activation energies of the decomposition pathways is noticed with the assistance ofwater, organic and inorganic acids as well assulphuric acid –water complex. Dehydration is the preferred route for catalytic pathways except for the water-assistance. Cooperative effect in the sulphuric acid - water complex is proposed to be the reason behind the lowest activation barrier of this system.

Differential metabolic profiles of ginsenosides in artificial gastric juice using ultra-high-pressure liquid chromatography coupled with linear ion trap-Orbitrap mass spectrometry.

Ginsenosides have poor oral bioavailability and undergo rapid biological transformation in the complex gastrointestinal environment. Most studies on the metabolism of ginsenosides have focused on gut bacteria, yet gastric juice remains a nonnegligible factor. Metabolic profiles of ginsenoside monomers formed in artificial gastric juice were separately investigated and qualitatively identified using ultra-high-pressure liquid chromatography coupled with linear ion trap-Orbitrap mass spectrometry (UHPLC-LTQ-Orbitrap MSn ). A common pattern of their metabolic pathways was established, showing that ginsenosides were transformed via deglycosylation, hydration, and dehydration pathways. Two major structure types, 20(S), 20(R)-protopanaxatriols and 20(S), 20(R)-protopanaxadiols, basically shared similar transformation pathways and yielded deglycosylated, hydrated, and dehydrated products. Fragmentation patterns of major ginsenosides were also discussed. Consequently, gastric juice, as the primary link in ginsenoside metabolism and as important as the intestinal flora, produces considerable amounts of degraded ginsenosides, providing a partial explanation for the low bioavailabilities of primary ginsenosides.

Recent Advances in Anode Electrocatalysts for Direct Formic Acid Fuel Cell-II-Platinum-Based Catalysts.

Platinum-based catalysts have a long history of application in formic acid oxidation (FAO). The single metal Pt is active in FAO but expensive, scarce, and rapidly deactivates. Understanding the mechanism of FAO over Pt important for the rational design of catalysts. Pt nanomaterials rapidly deactivate because of the CO poisoning of Pt active sites via the dehydration pathway. Alloying with another transition metal improves the performance of Pt-based catalysts through bifunctional, ensemble, and steric effects. Supporting Pt catalysts on a high-surface-area support material is another technique to improve their overall catalytic activity. This review summarizes recent findings on the mechanism of FAO over Pt and Pt-based alloy catalysts. It also summarizes and analyzes binary and ternary Pt-based catalysts to understand their catalytic activity and structure relationship.

Perovskite Supported Catalysts for the Selective Oxidation of Glycerol to Tartronic Acid

Exceptional selectivity of LaMnO3 perovskite supported Au catalysts for the oxidation of glycerol to the dicarboxylate tartronic acid is reported. Through using monometallic Au, Pt or bimetallic Au:Pt nanoparticles the tartronic acid yield could be altered significantly, with a maximum yield of 44% in 6 h with Au/LaMnO3 and 80% within 24 h. These LaMnO3 supported catalysts were compared with conventionally TiO2 supported catalysts, which at comparable reaction conditions produced lactic acid, via a dehydration pathway, in high yield and a maximum tartronic acid yield of only 9% was observed. The LaMnO3 catalysts produced minimal lactic acid regardless of the supported metal, showing that the support structure influences the prevalence of dehydration and oxidation pathways. The choice of metal nanoparticle influenced product selectivity along the oxidation pathway for both LaMnO3 and TiO2 supported catalysts. Au catalysts exhibited a higher selectivity to tartronic acid, whereas AuPt catalysts produced glyceric acid and Pt catalysts produced predominantly C–C scission products.Graphical

A highly dispersed Ni3P/HZSM-5 catalyst for hydrodeoxygenation of phenolic compounds to cycloalkanes

A highly dispersed Ni3P/HZSM-5 catalyst was prepared by deposition-precipitation of Ni species followed by electroless plating and thermal treatment, and characterized by means of XRD, ICP, N2 physical adsorption, TEM, XPS, NH3-TPD, and CO chemisorption. Electroless plating reaction takes place in an aqueous solution under mild conditions, facilitating the high dispersion of the formed Ni3P particles. XRD measurements illustrated the lamellar nickel phyllosilicate was produced at the first step of deposition-precipitation, amorphous Ni-P was formed in the subsequent electroless plating, and highly dispersed Ni3P crystallites were generated in thermal treatment. TEM observation demonstrated that the average particle size of Ni3P crystallites in the prepared Ni3P/HZSM-5 catalyst was 4.3 nm. Bifunctional Ni3P/HZSM-5 was investigated in hydrodeoxygenation (HDO) of phenolic compounds, including phenol, m-cresol, and guaiacol. Ni3P/HZSM-5 exhibited high catalytic performance in HDO with enhanced hydrogenation and dehydration pathway.

Engineering O-O Species in Boron Nitrous Nanotubes Increases Olefins for Propane Oxidative Dehydrogenation.

Boron nitride (BN) has been widely studied as an efficient catalyst for oxidative propane dehydrogenation (OPDH). Oxygen-containing boron species (e.g., BO·, B(OH)xO3-x) are generally considered as the active centers in BN for OPDH. Here, we show an effective progressive substitution strategy toward the development of boron-oxygen-nitrogen nanotubes (BONNTs) enriched with O-O species as a highly active, selective, and stable catalyst for OPDH. At 525 °C, an olefin yield of 48.6% is achieved over BONNTs with a propane conversion of 64.4%, 2.8 times that of boron nitrogen nanotubes (BNNTs). Even after reaction for 150 h (475 °C), BONNTs exhibit good olefin yield. Both the B(OH)xO3-x and O-O species that coexist in the BONNT catalyst are demonstrated as active centers, which differs from the B(OH)xO3-x one in BNNTs. Based on catalytic results, propane and oxygen alternate treatment experiments, and theoretical calculations, the O-O center is more favorable for producing both propylene (C3=) and ethylene (C2=), which experiences a dehydration pathway and two possible reaction paths with a lower energy barrier to yield olefins, while B(OH)xO3-x is mainly responsible for producing few C3=.

Selectivity of Ethanol Conversion on Al-Zr-Ce Mixed Oxides: Dehydration and Dehydrogenation Pathways Based on Surface Acidity Properties

Selectivity of Ethanol Conversion on Al-Zr-Ce Mixed Oxides: Dehydration and Dehydrogenation Pathways Based on Surface Acidity Properties