Search Results (43)

Oxidative dehydrogenation (ODH) of ethanol to acetaldehyde is an important production process. However, it still suffers from low deactivation, selectivity, and high costs. Herein, we developed a new strategy for preparing mesoporous nitrogen-doped carbon catalysts by carbonization of phenolic resin with silica as a hard template. The catalyst demonstrated an impressive acetaldehyde selectivity of over 76% at 270 °C for 25 h during the ODH of ethanol to acetaldehyde. Mechanistic studies have shown that the two carbon atoms in adjacent C=O groups are replaced by nitrogen atoms in the N₀-Gra-O structural unit. The C=O functional group on the surface of the catalyst is the active center for the ODH of ethanol to acetaldehyde, and the introduction of nitrogen atoms can reduce the adsorption capacity of acetaldehyde molecules at the active site (ΔG values can be reduced by 0.11–0.45 eV), enabling rapid desorption of the product and avoiding the problem of excessive oxidation, thereby improving the selectivity of acetaldehyde. This work reveals the structure–activity relationship between active sites and selective regulation of nitrogen-doped carbon-based catalysts for the ODH of ethanol, providing a theoretical basis for the development of efficient non-metallic carbon-based catalysts. Full article

Hydrogenation and dehydrogenation reactions are fundamental in chemistry and essential for all living organisms. We employ density functional theory (DFT) to understand the reaction mechanism of the oxidative dehydrogenation (ODH) of the pyridyl-amine complex [Fe^IIIL³]³⁺ (L³, 1,9-bis(2′-pyridyl)-5-[(ethoxy-2″-pyridyl)methyl]-2,5,8-triazanonane) to the mono-imine complex [Fe^IIL⁴]²⁺ (L⁴, 1,9-bis(2′-pyridyl)-5-[(ethoxy-2″-pyridyl)methyl]-2,5,8-triazanon-1-ene) in the presence of dioxygen. The nitrogen radical [Fe^IIL³_N8•]²⁺, formed by deprotonation of [Fe^IIIL³]³⁺, plays a crucial role in the reaction mechanism derived from kinetic studies. O₂ acts as an oxidant and is converted to H₂O. Experiments with the deuterated ligand L³ reveal a primary C-H kinetic isotope effect, k^CH/k^CD = 2.30, suggesting C-H bond cleavage as the rate-determining step. The DFT calculations show that (i) ³O₂ abstracts a hydrogen atom from the α-pyridine aliphatic C-H moiety, introducing a double bond regio-selectively at the C₇N₈ position, via the hydrogen atom transfer (HAT) mechanism, (ii) O₂ does not coordinate to the iron center to generate a high-valent Fe oxo species observed in enzymes and biomimetic complexes, and (iii) the experimental activation parameters (ΔH^≠ = 20.38 kcal mol⁻¹, ΔS^≠ = −0.018 kcal mol⁻¹ K⁻¹) fall within in the range of values reported for HAT reactions and align well with the computational results for the activated complex [Fe^IIL³_N8•]²⁺···³O₂. Full article

This study aimed to evaluate the effect of production system and lactation stage (LS) on the yield, centesimal composition, and fatty acid profile of milk from Holstein–Friesian cows. A total of 539 milk samples were collected in winter from cows in six certified organic dairy herds (ODHs) and eight conventional dairy herds (CDHs). The samples were collected randomly from up to 30% of cows at a given stage of lactation (7–45, 46–90, 91–135, 136–180, 181–225, 226–270, 271–315, and 316–360 days after calving). Milk samples were analyzed for proximate composition and the concentrations of fatty acids. The average daily milk yield was 11.4 kg higher (p < 0.01) in CDHs than in ODHs (28.1 kg vs. 16.7 kg). The concentrations of milk fat, protein, and lactose were also higher in CDHs than in ODHs. The fatty acid profile of milk fat was more desirable in ODHs than in CDHs (higher concentrations of polyunsaturated fatty acids (PUFAs), including n-3 PUFAs, trans-vaccenic acid, linolenic acid, and conjugated linoleic acid, and a higher desaturase index). Milk yield decreased (the decrease was more pronounced in ODHs), the concentrations of milk constituents increased, and the proportion of short-chain fatty acids in milk fat decreased (p < 0.05) with advancing lactation. Full article

Understanding population structure is a priority for evaluating population dynamics of commercially fished cephalopods under fishing pressure and environmental changes. This study employed a multidisciplinary approach to clarify the population structure of Loliolus (Nipponololigo) uyii, a common squid in inshore fisheries. Sampling was conducted multiple times to cover the distribution range across the East China Sea and South China Sea. High haplotype diversity was revealed by three gene markers (COI, 16S and ODH). Two geographical clades with significant genetic differentiation were divided through phylogenetic trees and haplotype networks. The boundary between the two clades is delineated by the Dongshan population in the southern East China Sea. Furthermore, the neutrality tests and mismatch analysis suggested that L. (N.) uyii populations may have undergone population expansion. Correspondingly, statolith differences in lateral dome and posterior indentation, along with high classification success, further supported the genetic division. The overall difference in statolith shape also efficiently identified seasonal groups in the Beibu Gulf lacking genetic differentiation. This result offers new insights into the influence of genetic and environmental factors on statolith shape. The integrated results provide a comprehensive understanding of the population structure of L. (N.) uyii, laying the foundation for resource development and the conservation of the species. Full article

This study considers the development of a kinetic model for the n-butane oxidative dehydrogenation (ODH) to C₄-olefins using a VO_x/MgO−γAl₂O₃ catalyst. The prepared catalyst contained 5 wt% V on an MgO modified γAl₂O₃ support. The developed catalyst exhibited both weak and medium acid sites, as revealed by NH₃-temperature-programmed desorption. TPR/TPO analyses also indicated that 73% of the loaded VO_x was reducible. Kinetic experiments were conducted in a fluidized CREC Riser Simulator at temperatures ranging from 475–550 °C and residence times of 5–20 s. An optimal C₄-olefin selectivity of 86% was achieved at 500 °C and 10 s, with this selectivity then decreasing at higher temperatures and longer residence times. The kinetic model developed involved a Langmuir–Hinshelwood-type of kinetics that incorporated cracking, oxydehydrogenation, and complete oxidation reactions. Model parameters were determined by fitting experimental data with kinetic parameters established with narrow 95% confidence intervals and low cross-correlation. Full article

Poly-γ-glutamic acid (γ-PGA) is an attractive biopolymer for medical, agri-food, and environmental applications. Although microbial synthesis by Bacilli fed on waste streams has been widely adopted, the obtainment of efficient sustainable production processes is still under investigation by bioprocess and metabolic engineering approaches. The abundant glycerol-rich waste generated in the biodiesel industry can be used as a carbon source for γ-PGA production. Here, we studied fermentation performance in different engineered Bacillus subtilis strains in glycerol-based media, considering a swrA⁺ degU32^Hy mutant as the initial producer strain and glucose-based media for comparison. Modifications included engineering the biosynthetic pgs operon regulation (replacing its native promoter with P_hyspank), precursor accumulation (sucCD or odhAB deletion), and enhanced glutamate racemization (racE overexpression), predicted as crucial reactions by genome-scale model simulations. All interventions increased productivity in glucose-based media, with P_hyspank-pgs ∆sucCD showing the highest γ-PGA titer (52 g/L). Weaker effects were observed in glycerol-based media: ∆sucCD and P_hyspank-pgs led to slight improvements under low- and high-glutamate conditions, respectively, reaching ~22 g/L γ-PGA (26% increase). No performance decrease was detected by replacing pure glycerol with crude glycerol waste from a biodiesel plant, and by a 30-fold scale-up. These results may be relevant for improving industrial γ-PGA production efficiency and process sustainability using waste feedstock. The performance differences observed between glucose and glycerol media also motivate additional computational and experimental studies to design metabolically optimized strains. Full article

Ammonia is a major water quality factor influencing the survival and health of shrimp, among which the gill is the main effector organ for ammonia toxicity. In this study, we chose two types of Litopenaeus vannamei that were cultured in 30‰ seawater and domesticated in 3‰ low salinity, respectively, and then separately subjected to ammonia stress for 14 days under seawater and low-salinity conditions, of which the 3‰ low salinity-cultured shrimp were domesticated from the shrimp cultured in 30‰ seawater after 27 days of gradual salinity desalination. In detail, this study included four groups, namely the SC group (ammonia-N 0 mg/L, salinity 30‰), SAN group (ammonia-N 10 mg/L, salinity 30‰), LC group (ammonia-N 0 mg/L, salinity 3‰), and LAN group (ammonia-N 10 mg/L, salinity 3‰). The ammonia stress lasted for 14 days, and then the changes in the morphological structure and physiological function of the gills were explored. The results show that ammonia stress caused the severe contraction of gill filaments and the deformation or even rupture of gill vessels. Biochemical indicators of oxidative stress, including LPO and MDA contents, as well as T-AOC and GST activities, were increased in the SAN and LAN groups, while the activities of CAT and POD and the mRNA expression levels of antioxidant-related genes (nrf2, cat, gpx, hsp70, and trx) were decreased. In addition, the mRNA expression levels of the genes involved in ER stress (ire1 and xbp1), apoptosis (casp-3, casp-9, and jnk), detoxification (gst, ugt, and sult), glucose metabolism (pdh, hk, pk, and ldh), and the tricarboxylic acid cycle (mdh, cs, idh, and odh) were decreased in the SAN and LAN groups; the levels of electron-transport chain-related genes (ndh, cco, and coi), and the bip and sdh genes were decreased in the SAN group but increased in the LAN group; and the level of the ATPase gene was decreased but the cytc gene was increased in the SAN and LAN groups. The mRNA expression levels of osmotic regulation-related genes (nka-β, ca, aqp and clc) were decreased in the SAN group, while the level of the ca gene was increased in the LAN group; the nka-α gene was decreased in both two groups. The results demonstrate that ammonia stress could influence the physiological homeostasis of the shrimp gills, possibly by damaging the tissue morphology, and affecting the redox, ER function, apoptosis, detoxification, energy metabolism, and osmoregulation. Full article

This paper presents two novel formulations for scheduling problems, namely order-position hybrid formulation (OPH) and order-disjunctive hybrid formulation (ODH), which extend and combine parts of existing formulation strategies. The first strategy (OPH) is based on sequence position and linear ordering formulations, adding relationships between constraints that allow relaxing some decision variables. The second approach (ODH) is based on linear ordering and disjunctive formulations. In this work, we prove ODH to be the most efficient formulation known so far. The experiments have been carried out with a large set of problems, which consider single machines and identical parallel machines. Computational results show that OPH is better than the rest of the existing formulations for the case of weighted completion objectives, while ODH turns out to be the best approach for most scenarios studied. Full article

(S)-Atenolol ((S)-2-(4-(2-Hydroxy-3-(isopropylamino)propoxy)phenyl)acetamide) has been synthesized in >99% enantiomeric excess (ee) with the use of Candida antarctica lipase B from Syncozymes (Shanghai, China), in a kinetic resolution of the corresponding racemic chlorohydrin. A catalytic amount of base was used in deprotonation of the phenol building block. The enantiopurity of the chlorohydrin building block remained unchanged upon subsequent amination to yield the final drug. All four steps in the synthesis protocol have been optimized compared to previously reported methods, which makes this new protocol more sustainable and in accordance with green chemistry principles. The overall yield of (S)-atenolol was 9.9%, which will be further optimized. Full article

The oxidative dehydrogenation (ODH) of alkanes, whereby hydrogen is removed to form unsaturated compounds, is an important process, particularly in the petrochemical industry. The ODH of lighter alkanes (C3–C6) is well-reported in the literature, and while there are several reports on the ODH of n-octane (C8), there is no reported review of the important findings in the literature. This review discusses the gas-phase ODH of n-octane occurring at high temperatures (300–550 °C). The mechanisms via which the n-octane ODH of occurs are also briefly discussed. The oxidants (mainly O₂ and CO₂) and catalysts (supported and unsupported metal oxides) are discussed as well as the effect of these and the temperature on the type of products formed and their various distributions. Furthermore, the review looks at the acid–base and redox properties of the catalysts and how they affect product formation. Some challenges as well as perspectives of the ODH process are also highlighted. Full article

This study evaluates the effectiveness of fluidizable VO_x/MgO-γAl₂O₃ catalysts for C₄-olefin production via n-butane oxidative dehydrogenation (BODH). Catalysts were prepared via vacuum incipient wetness impregnation and then characterized by employing several techniques such as BET (Brunauer–Emmett–Teller) method, XRD (X-ray diffraction), LRS (laser Raman spectroscopy), XPS (X-ray photoelectron spectroscopy), TPR/TPO (temperature-programmed reduction/temperature-programmed oxidation), NH₃-TPD (temperature-programmed desorption), NH₃ -desorption kinetics and pyridine-FTIR. The BET analysis showed the prepared catalysts’ mesoporous structure and high surface areas. The XRD, LRS and XPS established the desirable presence of amorphous VO_x phases. The TPR/TPO analyses corroborated catalyst stability over repeated reduction and oxidation cycles. The NH₃-TPD and NH₃ desorption kinetics showed that the catalysts had dominant moderate acidities and weak metal-support interactions. In addition, Pyridine-FTIR showed the critical influence of Lewis acidity. The VO_x/MgO-γAl₂O₃ catalysts were evaluated for BODH using a fluidized CREC Riser Simulator, operated under gas-phase oxygen-free conditions, at 5 to 20 s reaction times, and at 450 °C to 600 °C temperatures. The developed VO_x/MgO-γAl₂O₃ catalysts demonstrated performance stability throughout multiple injections of butane feed. Catalyst regeneration was also conducted after six consecutive BODH runs, and the coke formed was measured using TOC (Total Organic Carbon). Regarding the various BODH catalyst prepared, the 5 wt% V-doped MgO-γAl₂O₃ yielded in a fluidized CREC Riser Simulator the highest selectivity for C₄-olefins, ranging from 82% to 86%, alongside a butane conversion rate of 24% to 27%, at 500 °C and at a 10 s reaction time. Full article

The microbial contamination of food poses a threat to human health. Chestnut shells, which are byproducts of chestnut processing, contain polyphenols that exert various physiological effects, and thus have the potential to be used in food preservation. This study investigates the bacteriostatic effect and mechanism(s) of the action of chestnut shell polyphenols (CSPs) on three food-spoilage bacteria, namely Bacillus subtilis, Pseudomonas fragi, and Escherichia coli. To this end, the effect of CSPs on the ultrastructure of each bacterium was determined using scanning electron microscopy and transmission electron microscopy. Moreover, gene expression was analyzed using RT-qPCR. Subsequent molecular docking analysis was employed to elucidate the mechanism of action employed by CSPs via the inhibition of key enzymes. Ultrastructure analysis showed that CSPs damaged the bacterial cell wall and increased permeability. At 0.313 mg/mL, CSPs significantly increased the activity of alkaline phosphatase and lactate dehydrogenase, as well as protein leakage (p < 0.05), whereas the activity of the tricarboxylic acid (TCA) cycle enzymes, isocitrate dehydrogenase and α-ketoglutarate dehydrogenase, were inhibited (p < 0.05). The expression levels of the TCA-related genes gltA, icd, sucA, atpA, citA, odhA, IS178_RS16090, and IS178_RS16290 are also significantly downregulated by CSP treatment (p < 0.05). Moreover, CSPs inhibit respiration and energy metabolism, including ATPase activity and adenosine triphosphate (ATP) synthesis (p < 0.05). Molecular docking determined that proanthocyanidins B1 and C1, the main components of CSPs, are responsible for the antibacterial activity. Therefore, as natural antibacterial substances, CSPs have considerable potential for development and application as natural food preservatives. Full article

Co/TiO₂ catalysts with different cobalt loadings (3.8, 7.5 and 15 wt%) were prepared by impregnation method of Co(NO₃)₂ 6H₂O over titania. Samples containing Co(NO₃)₂·6H₂O and TiO₂ in stoichiometric proportions in order to obtain CoTiO₃ and Co₂ TiO₄ phases were also synthesized. The effect of the calcination treatment at two different temperatures, 550 and 1150 °C, was investigated. Characterizations by several techniques, such as XRD, UV–vis–NIR, DRS, Raman and XPS, were carried out. XRD showed the coexistence of three phases: CoTiO₃; Co₂TiO₄ and Co₃O₄ after calcination at 550 °C, while calcination at high temperature (1150 °C) led to single-phase systems (CoTiO₃ or Co₂TiO₄). Diffuse reflection and XPS spectroscopy showed that divalent cobalt occupies octahedral sites in the ilmenite phase, and both tetrahedral and octahedral sites in the spinel phase. The catalytic performances of the prepared catalysts were evaluated in the oxidative dehydrogenation reaction (ODH) of ethane to ethylene, as a function of the Co content for Co/TiO₂ catalysts and as a function of the calcination temperatures for the CoTiO₃ and Co₂TiO₄ phases. Co(7.5)/TiO₂ was the most active, although the conversion of ethane decreased in the first 150 min of the reaction, reaching values comparable to those of Co₂TiO₄ and CoTiO₃; however, Co(7.5)/TiO₂ was confirmed as having the best selectivity to ethylene in comparison with the bulk phases, CoTiO₃ and Co₂TiO₄. The influence of the reaction mixture composition, specifically the presence of water, at different percentages, was investigated. There is a decrease in the overall ethane conversion and an increase in the ethylene selectivity when the percentage of water increases. This behavior can likely be attributed to an increase in the surface concentration of hydroxyl species (OH), resulting in heightened surface acidity. Full article

Oxidative dehydrogenation (ODH) is an alternative for styrene (ST) production compared to the direct dehydrogenation process. However, ODH with O₂ or CO₂ suffers from either over-oxidation or endothermic property/low ethylbenzene conversion. Herein, we proposed an ODH process with a CO₂-O₂ mixture atmosphere for the efficient conversion of ethylbenzene (EB) into styrene. A thermoneutral ODH is possible by the rationalizing of CO₂/O₂ molar ratios from 0.65 to 0.66 in the temperature range of 300 to 650 °C. K modification is favorable for ethylbenzene dehydrogenation, and 10%K/CeO₂ achieved the highest ethylbenzene dehydrogenation activity due to the enhanced oxygen mobility and CO₂ adsorbability. The catalyst achieved 90.8% ethylbenzene conversion and 97.5% styrene selectivity under optimized conditions of CO₂-4O₂ oxidation atmosphere, a temperature of 500 °C, and a space velocity of 5.0 h⁻¹. It exhibited excellent catalytic and structural stability during a 50 h long-term test. CO₂ induces oxygen vacancies in ceria and promotes oxygen exchange between gaseous oxygen and ceria. The ethylbenzene dehydrogenation in CO₂-O₂ follows a Mars-van Krevelen (MvK) reaction mechanism via Ce³⁺/Ce⁴⁺ redox pairs. The proposed ODH strategy by using oxygen vacancies enriched catalysts offers an important insight into the efficient dehydrogenation of ethylbenzene at mild conditions. Full article

Porous organic cages (POCs) are a new subclass of porous materials, which are constructed from discrete cage molecules with permanent cavities via weak intermolecular forces. In this study, a novel chiral stationary phase (CSP) has been prepared by chemically binding a [4 + 6]-type chiral POC (C₁₂₀H₉₆N₁₂O₄) with thiol-functionalized silica gel using a thiol-ene click reaction and applied to HPLC separations. The column packed with this CSP presented good separation capability for chiral compounds and positional isomers. Thirteen racemates have been enantioseparated on this column, including alcohols, diols, ketones, amines, epoxides, and organic acids. Upon comparison with a previously reported chiral POC NC1-R-based column, commercial Chiralpak AD-H, and Chiralcel OD-H columns, this column is complementary to these three columns in terms of its enantiomeric separation; and can also separate some racemic compounds that cannot be separated by the three columns. In addition, eight positional isomers (iodoaniline, bromoaniline, chloroaniline, dibromobenzene, dichlorobenzene, toluidine, nitrobromobenzene, and nitroaniline) have also been separated. The influences of the injection weight and column temperature on separation have been explored. After the column has undergone multiple injections, the relative standard deviations (RSDs) for the retention time and selectivity were below 1.0 and 1.5%, respectively, indicating the good reproducibility and stability of the column for separation. This work demonstrates that POCs are promising materials for HPLC separation. Full article