Search Results (641)

High-energy-density fuels (HEDFs) have garnered considerable interest in aerospace fields, primarily due to their superior density and volumetric net heat of combustion (NHOC) compared with traditional petroleum-based fuels. Strained polycyclic hydrocarbons are regarded as one of the most crucial categories of HEDF. As an isomer (C₁₀H₁₆) of JP-10, the target compound is composed of two cyclopropyl rings and one cyclobutyl ring connected in a linear manner. Notably, intramolecular H-migration reactions of peroxyl radicals derived from strained polycyclic hydrocarbons (C₁₀H₁₅OO•) are of great significance for establishing the reaction mechanism of high-energy-density fuels over a broad temperature range. In this work, the intramolecular H-migration kinetics of C₁₀H₁₅OO• with distinct cis and trans configurations are investigated by quantum chemical calculations. Geometry optimization and frequency calculations are carried out for all species using the M06-2X/6-311++G(d,p) level of theory, while single-point energy calculations are performed at the CBS-QB3 level. Our calculated results demonstrate that different types of intramolecular H-migration reactions exhibit significant differences in barrier heights. Based on the ring structures where the reaction centers are located, these reactions can be classified into three categories: the lowest barriers correspond to H-migration reactions occurring between the central cyclopropyl ring and the terminal cyclobutyl ring; the highest barriers correspond to H-migration reactions confined entirely within the terminal cyclobutyl ring; and the barriers for H-migration reactions occurring between the terminal cyclopropyl ring and the central cyclopropyl ring lie between the above two. High-pressure-limit rate constants for 33 elementary reactions are determined in the temperature range of 500 to 2500 K based on the conventional transition-state theory (TST) and expressed in the modified Arrhenius form. Full article

Porous coordination polymers, alternatively known as metal–organic framework (MOF) nanoparticles, have acquired increasing significance in nanomaterials science, especially with the increased importance and versatility in catalysis. The complex structures of MOFs allow the incorporation of metal nodes, enclosing substrates, and functional linkers, thus enabling synergistic structural and functional engineering to produce capable catalytic active sites that provide solutions to decrease human activities in designing new organic reactions. Recently, Cu-MOF-mediated organic reactions hold a significant promise to substitute homogenous and heterogeneous catalysts due to their promising structural features such as tailorable porous structures, high-density catalytic active sites and surface area, sufficient framework stability, minimal leaching, and facile recovery and recyclability. This review emphasizes the significance of Cu-MOFs in synthetic chemistry, in particular, in the synthesis of organic compounds. It examines their applicability in hydrogenation, oxidation, cross-coupling/condensation reactions, functionalization at terminal alkenes and alkynes, intramolecular C-H amination, and other multicomponent reactions. In addition to these organic transformations, recent progress in Cu-MOF-catalyzed CO₂ electroreduction and nitrate reduction is also briefly described. Subsequently, the state-of-the-art synthetic methods of certain decorated Cu-MOFs are thoroughly elaborated as well as the essential structural parameters that govern the stability and recyclability of MOFs in organic transformations. This focused examination of Cu-MOFs is expected to provide useful information for future research endeavors in the field of MOF catalytic applications. Full article

Cellulose is the most promising abundant renewable polymer material with the highest potential for the future low-carbon biorefineries. However, its utilization in industry is limited by the structural recalcitrance as a result of organization of crystalline domains, fibrillar architecture hierarchy and intramolecular and intermolecular hydrogen bonding which is responsible for access restriction for the catalysts and consequent cleavage of the glycosidic bonds. Therefore, efficient depolymerization of cellulose is of paramount importance as a step in biomass conversion into the low molecular products. In this review, the recent advances in cellulose depolymerization are discussed. The chemical, enzymatic, thermal, thermochemical, mechanochemical, oxidative and hybrid catalytic method is thoroughly discussed. Attention is paid to the mechanism of the depolymerization reaction steps as glycosidic bond activation as hydrolytic, radical mediated, and energy assisted pathways. Selectivity and conversion efficiency based on substrate morphology, solvent system and catalyst design are also discussed. Further, there is a comparison of key performance metrics which are relevant for the industrial process as product yield, carbon efficiency, energy demand, stability of the catalyst, solvent recyclability and impact to the environmental lifecycle. The pros and cons of the various methods are also represented. Processes based on mineral acids enable rapid conversion. However, they suffer from corrosion, waste handling issues and degradation by-products. On the other hand, enzymatic depolymerization processes offer relatively high selectivity but they are limited in terms of feedstock sensitivity and slow reaction kinetics. The downstream valorization mechanisms are also described with the result being that no single available technology is capable of satisfying all industrial requirements. Thus, future progress expects integrated circular processes where advanced catalysis, process intensification and digital optimization strategies take place. Full article

This review highlights the recent advances in the synthesis of 1,4-diazatriphenylenes and their various structural analogs. It focuses on several methodologies, including condensation reactions and intramolecular cyclizations of 2,3-di(het)aryl-substituted pyrazine derivatives. These methods exploit either oxidative photocyclization (the Mallory reaction), intramolecular cyclodehydrogenation (the Scholl reaction), or intramolecular S_N^H reactions (nucleophilic aromatic substitution of hydrogen) involving 2-bis(het)aryl-substituted 1,4-diazine derivatives. Additionally, the review explores the potential applications of these compounds as fluorescent and/or semiconducting materials in organic electronics, as well as their role in coordination chemistry and biological issues. It summarizes the literature from 2018 to March 2026, complementing the data discussed in our previous review. Full article

In this work, we investigated the incorporation of a fluorescent side group, fluorescein octyl ester (FOE), in benzodithiophene-based donor–acceptor terpolymers as a strategy to modulate excited-state behavior. Three FOE-containing terpolymers (P2-iIa-c), obtained at different polymerization times, were systematically evaluated against an analogous material without the fluorescent pendant unit (P1-iI). Thermal analysis revealed good thermal stability and an increase in glass transition temperature upon FOE incorporation, suggesting restricted segmental mobility and increased conformational constraints within the conjugated backbone. Optical characterization showed distinct absorption spectra with reaction time and shorter fluorescence lifetimes for the FOE-containing materials, consistent with the presence of additional excited-state deactivation pathways and intramolecular energy transfer processes within the terpolymer backbone. An approximate estimation of energy transfer efficiencies (≈60–65%) suggested that such processes may be operative within the system. Cyclic voltammetry measurements showed only minor variations in HOMO and LUMO energy levels between P1-iI and P2-iIa-c series, indicating that the conjugated backbone predominantly determined the frontier orbital energies despite side chain modification. Furthermore, photocurrent measurements from the bilayer device configuration exhibited a systematic increase in photocurrent for the FOE-containing material, supporting the role of excitonic modulation, rather than significant changes in interfacial energetic alignment. These results suggest that fluorescent side chain incorporation provides an effective strategy for regulating exciton dynamics while maintaining the electronic structure of the donor–acceptor terpolymer. Full article

The pyrolysis of polypropylene (PP) microplastics offers a potential route to convert plastic waste into fuel-range hydrocarbon mixtures and chemical feedstocks. However, the elementary radical pathways underlying the formation of medium-chain hydrocarbon fragments remain insufficiently resolved. In this study, a representative isotactic PP oligomer model (C₄₅H₉₂) was evaluated using a comparative density functional theory (DFT) framework. The main mechanistic analysis was based on M06-2X, ωB97X-D, and M11 calculations combined with the def2-TZVP basis set, whereas LANL2DZ was retained only as a lower-cost comparative level during reaction-pathway exploration. Thermochemical profiles were evaluated over a temperature range of 298–923 K. Three selected pathways involving mid-chain homolytic cleavage, intramolecular hydrogen transfer (backbiting), radical rearrangement, and β-scission were examined. Within the selected reaction set, Route 1 exhibited a comparatively more favorable thermochemical profile than Routes 2 and 3 and provided a mechanistically plausible sequence toward medium-chain hydrocarbon fragments. The −TΔS contribution strongly influenced the calculated Gibbs free-energy profiles because fragmentation increases the number of molecular species under the ideal-gas thermochemical approximation. Accordingly, the ΔG values were interpreted comparatively and were not treated as direct evidence of spontaneous fragmentation under condensed-phase pyrolysis conditions or as quantitative predictions of experimental product selectivity. Differences among the evaluated functionals further indicate that the relative description of radical intermediates and transition-state regions is method-dependent. These results provide a molecular-level framework for future studies integrating quantum-chemical calculations, microkinetic modeling, and experimental product characterization. Full article

Ferrocenium-catalyzed transformations provide a practical and sustainable approach to propargylic substitution reactions. Herein, we investigate the ring-opening of cyclopropyl-substituted propargylic alcohols with alcohol nucleophiles, catalyzed by ferrocenium tetrafluoroborate ([FeCp₂][BF₄]) to afford synthetically valuable enyne ethers. Mechanistic studies using GC and NMR spectroscopy reveal that the reaction proceeds via initial formation of a ring-closed propargylic ether intermediate, which subsequently undergoes ring opening to the enyne ether. Experimental evidence supports a carbocationic pathway in which the ferrocenium cation promotes ionization to a stabilized cyclopropyl ether intermediate, followed by intramolecular, ferrocenium-assisted cyclopropyl ring opening to the enyne product. Reaction rates and product distributions are strongly influenced by temperature and solvent polarity, with polar solvents and elevated temperatures favoring ring opening. At room temperature, the ring-closed substitution product predominates, whereas efficient formation of enynes occurs at 65 °C. The reaction progresses faster in a polar solvent, indicating an ionic mechanism. Studies employing substrates containing substituted cyclopropyl rings demonstrated pronounced regioselectivity during nucleophilic ring opening with alcohols, with preferential cleavage of the bond between the two substituted carbon atoms. This selectivity is consistent with partial positive-charge stabilization in the transition state. The corresponding enyne ether products were isolated in 98–31% isolated yields, in most cases as a single regio- and E/Z stereoisomer (5 h at 45 °C, 5 mol% [FeCp₂][BF₄] catalyst load, six equivalents alcohol nucleophile). The ferrocenium-catalyzed cyclopropyl ring opening establishes a convenient method for accessing enyne motifs, which are important structural units in organic synthesis and medicinal chemistry. Full article

The use of water as a nucleophile in catalytic asymmetric reactions remains a significant challenge, primarily due to its intrinsically low nucleophilicity and small size, which make precise control over both reactivity and stereoselectivity particularly difficult. To address this issue, we developed a CPA-catalyzed asymmetric hydrolysis system, successfully achieving the efficient and highly stereoselective transformation of 4H-oxazines with water. Under this catalytic system, the initial formation of chiral α-bromo ketones is followed by their in situ conversion through reduction and intramolecular S_N2 reactions, directly affording valuable chiral bromo alcohols and chiral oxazolone derivatives in high yields with excellent enantioselectivity. Full article

Hydrogen sulfide (H₂S) is a toxic and biologically relevant gas, necessitating sensitive and interference-resistant detection methods for environmental monitoring. Here, we develop a donor–acceptor molecular platform incorporating a polarized conjugated double bond bridge and demonstrate its application, using YG2 as the representative probe, as a dual-peak ratiometric UV–Vis sensor for H₂S. UV–Vis spectroscopy, supported by ¹H NMR analysis, indicates HS^--induced interaction with the conjugated linkage, leading to disruption of π-conjugation, suppression the intramolecular charge-transfer (ICT) band at 409 nm, and enhancing the locally excited (LE) band at 279 nm. The ratiometric parameter log(Abs₂₇₉/Abs₄₀₉) affords a linear response over the concentration range of 1.0 × 10⁻⁶–1.0 × 10⁻⁴ M with a detection limit of 8.3 × 10⁻⁷ M, providing approximately an order-of-magnitude improvement in analytical sensitivity compared with single-wavelength methods, and the reaction reaches completion within ~10 s. YG2 exhibits excellent selectivity toward H₂S over common anions and enables accurate quantification in real water samples, with recoveries of 95.43–105.86% and relative standard deviations (RSDs) of 0.56–9.58%. These results suggest that YG2 is a rapid, self-calibrating, and spectroscopically interpretable ratiometric probe suitable for reliable H₂S detection in complex aqueous environments. Full article

This study used UV-Vis absorption spectroscopy to investigate the interactions of flavonoids—baicalein (with ortho-dihydroxyl on the A-ring) and apigenin (with 4′-monohydroxyl on the B-ring)—with metal ions (Co²⁺, Ce⁴⁺) and membrane–mimetic systems (CTAB/SDS micelles, liposomes, vesicles). It revealed how flavonoid spectral properties related to molecular structure and microenvironment. Key findings were as follows: pH affected absorption spectra by altering phenolic hydroxyl protonation. Metal chelation depended on hydroxyl position: baicalein’s A-ring ortho-dihydroxyl formed a stable charge-transfer complex with Cu²⁺. In acidic medium, apigenin reduced Ce(IV) more effectively than baicalein, which contradicted the classic antioxidant role of ortho-dihydroxyl groups. This showed that reaction microenvironments could change hydroxyl reactivity and electron transfer paths. Membrane–mimetic systems (liposomes/vesicles) raised apparent pKa, enhanced solubility and stability. The study first quantified distinct ΔpKa values for different flavonoids (e.g., quercetin vs. baicalein), which were linked to intramolecular H-bonding and membrane preference. Quercetin’s B-ring ortho-dihydroxyl enabled the formation of hydrophobic interfacial anions in nanocarriers under alkaline pH, ensuring high stability. Kaempferol showed sustained leakage. These findings provided a basis for structure-guided flavonoid carrier design, bioavailability, and antioxidant delivery. By integrating reaction microenvironment, membrane interface effects, and carrier stability, this work clarified flavonoid bioactivity mechanisms and supported targeted delivery strategies. Full article

Herein, starting from (R)-(+)-α-methylbenzylamine, we report an efficient synthesis and full characterization of a new (R)-3-(1-hydroxyethylidene)-1-(1-phenylethyl)piperidine-2,4-dione, a new tetramic acid analog. The key steps involved a non-classical Corey–Chaykovsky intramolecular cyclization reaction to access the corresponding zwitterion, followed by a sequential desulfurization/reduction and condensation procedure. The titled product was obtained in five steps, and the desired product 7 with an overall 58% yield. Full article

The Pschorr reaction is a radical-mediated intramolecular cyclization involving diazonium salts, affording five-, six- and seven-membered fused polycyclic and heterocyclic rings, discovered by R. Pschorr in the late nineteenth century. Over the years, this classic reaction has played an important role in ring-forming reactions. In 2009 we reviewed the progress in the field. The intervening years have witnessed major advances in the application of Pschorr reaction that are mediated by various metals, by photocatalysis, and by ionic liquids, leading to the development of new and improved methods for the synthesis of diverse bioactive heterocycles. The notable progress in the field since our 2009 review provided the impetus to summarize, discuss, and put these advances in perspective. Full article

This study employs molecular dynamics simulations to investigate the influence of functionalized UiO-66 materials (with -H, -NH₂, -NO₂, and -(OH)₂ groups) on the adsorption and diffusion behaviors of ethanol and waste oil before transesterification reactions. A multi-scale modeling approach, including a three-layer interfacial model, surface adsorption, and intra-framework adsorption, was utilized to systematically evaluate the effects of functionalization on structural properties, molecular diffusion, adsorption performance, and interfacial interactions. The simulation results reveal that functionalization enhances the intrinsic diffusivity of the metal–organic framework but generally suppresses the diffusion of ethanol and waste oil. The -(OH)₂ group exhibits the most significant diffusion hindrance due to steric effects and strong hydrogen bonding. Adsorption of waste oil is dominated by coordination and hydrophobic interactions, while ethanol adsorption relies on hydrogen bonding. Within the framework, functionalization does not improve ethanol adsorption capacity; instead, pristine UiO-66 shows the highest uptake due to its optimal pore size. Adsorption energy calculations on the (002) surface indicate that the -NO₂ group exhibits the strongest affinity for oleic acid, owing to its strong electronegativity and synergistic effects with metal sites. For polyunsaturated fatty acids, adsorption performance depends critically on the compatibility between the hydrophobic pore environment and molecular conformation. Ethanol adsorption is governed primarily by hydrogen bonding and metal coordination. This study provides molecular-level insights into the structure–function relationships governing pre-reaction adsorption and mass transport mechanisms of functionalized UiO-66 in transesterification reactions, providing a theoretical foundation for the rational design of efficient pre-reaction microenvironments in biodiesel catalysts. Full article

C. pseudotuberculosis is a Gram-positive pathogenic bacterium that infects various animals, causing diseases such as caseous lymphadenitis, leading to significant economic losses in the livestock industry and posing zoonotic risks. This study targeted the conserved gyrA gene fragment of this bacterium, designed specific primers, optimized the reaction system and conditions, and established a high-resolution melting curve (HRM) detection method with potential utility for preliminary molecular screening. Validation showed that this method exhibits strong specificity, producing specific amplification only for the target biovars. The melting temperatures (Tm values) for the two biovars were 86.16 ± 0.05 °C and 86.92 ± 0.05 °C, respectively, allowing clear differentiation. It demonstrated high sensitivity, with minimum detection limits of 28 copies/μL and 25 copies/μL for standard plasmids of the ovis and equi biovars, respectively. The method also showed good reproducibility, with intra- and inter-batch coefficients of variation both below 1.0%. Applied to 133 clinical nasal swab samples from goats in Fujian Province, the method detected a positivity rate of 19.5% and indicates that a biovar equi-like gene fragment was detected in goat nasal swabs from Fujian Province via molecular screening. The HRM method developed in this study is sensitive, specific, simple, and cost-effective, enabling rapid detection and biovar differentiation of C. pseudotuberculosis. It is suitable for large-scale clinical sample screening and provides an efficient technical approach for epidemiological monitoring and precise control of the disease. Full article

Better understanding the controlling factors of shale oil quality including density and viscosity plays a key role in exploring these unconventional pay zones efficiently and profitably. The shale oil extracted from the middle Permian Lucaogou Formation (P₂l) of Santanghu Basin becomes denser and more viscous from the Tiaohu Sag to Malang Sag. It has been proven that oil quality is negatively correlated with saturated hydrocarbon content and positively correlated with aromatic/resin content. However, the underlying controls at the molecular levels are not yet clear. In order to reveal the fundamental controls, shale oil samples with varying density and viscosity were collected from these two sags, and molecular compositions of these samples were analyzed by using gas chromatography–mass spectrometry (GC–MS) for the saturated and aromatic hydrocarbons and electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT–ICR MS) for heteroatom hydrocarbons in resin fraction. Thereafter, correlation analysis was performed between oil density and viscosity and geochemical parameters associated with saturated, aromatic and NSO-containing compounds. The experimental results indicate that the oil thermal maturity levels play a major role, since both density and viscosity present significant negative correlations (correlation coefficient > 0.5) with the maturity parameters of n-alkanes, terpanes, steranes and triaromatic steranes. Organic facies also play a partial role as indicated by the significant positive correlations between density and viscosity and the parameters of tricyclic terpanes, dibenzothiophene/phenanthrene, and methylated phenanthrenes. In resin fraction, density presents better correlations with acid compounds, including O_x (x = 5–9), N₁O_x (x = 0–2) and N₂O₃ species, and viscosity shows better correlations with basic N-containing compounds (N₁O₁, N₁O₃, and N₂O₁ species) and S-containing compounds (N₁S₁ and O₁S₁ species). This indicates that the cross-linking by acid oxygen-containing compounds and the intramolecular and intermolecular forces induced by basic N-containing compounds and sulfur-containing compounds play an important role in directing the P₂l shale oil quality. Moreover, the ratios of specific species with low-to-high double bond equivalents (DBEs) and the homologues with low molecular weight to high molecular weight both present significant negative correlations with density and saturated and aromatic maturity parameters. This highlights the effects of bond cleavage, cyclization and aromatization reactions with elevated thermal maturity in enhancing oil quality in the targeted pay zones. Most P₂l shale oil sources were deposited under the reducing lacustrine setting, containing mainly Type I/II kerogens. Shale oils from Tiaohu Sag are more matured than those from Malang Sag, which is supposed to be responsible for the better oil quality in Tiaohu Sag. This study provides the supporting evidence for regulating shale oil quality in the Santanghu Basin at the molecular levels, and should be helpful in identifying the sweet spots of shale oil plays in this area. Full article