Search Results (110)

Phthalic acid esters (PAEs), ubiquitously employed as a plasticizer, have been classified as priority environmental pollutants because of their persistence, bioaccumulation, and endocrine-disrupting properties. As a characterized PAE-degrading strain of marine origin, Mycolicibacterium phocaicum RL-HY01 utilizes di-(2-ethylhexyl) phthalate (DEHP) as its sole carbon and energy source. Genome sequencing and RT-qPCR analysis revealed a previously uncharacterized hydrolase gene (dehpH) in strain RL-HY01, which catalyzes ester bond cleavage in PAEs. Subsequently, recombinant expression of the cloned dehpH gene from strain RL-HY01 was established in Escherichia coli BL21(DE3). The purified recombinant DehpH exhibited optimal activity at 30 °C and pH 8.0. Its activity was enhanced by Co²⁺ and tolerant to most metal ions but strongly inhibited by EDTA, SDS, and PMSF. Organic solvents (Tween-80, Triton X-100, methanol, ethanol, isopropanol, acetone, acetonitrile, ethyl acetate, and n-hexane) showed minimal impact. Substrate specificity assay indicated that DehpH could efficiently degrade the short and long side-chain PAEs but failed to hydrolyze the cyclic side-chain PAE (DCHP). The kinetics parameters for the hydrolysis of DEHP were determined under the optimized conditions, and DehpH had a V_max of 0.047 ± 0.002 μmol/L/min, K_m of 462 ± 50 μmol/L, and k_cat of 3.07 s⁻¹. Computational prediction through structural modeling and docking identified the active site, with mutagenesis studies confirming Ser228, Asp324, and His354 as functionally indispensable residues forming the catalytic triad. The identification and characterization of DehpH provided novel insights into the mechanism of DEHP biodegradation and might promote the application of the target enzyme. Full article

The photochemistry of 1,3,4-oxadiazoles remains poorly understood, despite their recognized importance in medicinal chemistry and materials science. In this work, we report a detailed matrix-isolation study of 2-amino-5-(4-methoxyphenyl)-1,3,4-oxadiazole, combining low-temperature infrared spectroscopy with broadband UV photolysis and quantum chemical calculations. Theoretical analysis predicts the gas-phase molecule to exist exclusively as the amino tautomer, populating two nearly isoenergetic conformers (anti and syn) defined by the relative orientation of the amino and methoxy groups. Experimental IR spectra of the compound isolated in Ar and Xe matrices at 15 K confirm sole trapping of the amino tautomer. Annealing of the Xe matrix to the highest achievable temperature induced no detectable spectral changes, consistent with the predicted isoenergetic character of the conformers. Upon broadband UV irradiation (λ > 200 nm), the compound undergoes ring opening through N−N and C−O bond cleavages, paralleling the behavior of unsubstituted 1,3,4-oxadiazole system. Isocyanates emerge as the predominant photoproducts from these photochemical pathways. Additionally, spectroscopic evidence supports an alternative reaction pathway involving early-stage amino−imino tautomerization, followed by ring-opening of the imino tautomer through isocyanic acid extrusion, leading to the formation of a nitrilimine intermediate. This reactive species subsequently photorearranges into a carbodiimide via a diazirine-mediated pathway. All photoproducts were unambiguously identified through their distinct IR signatures, supported by quantum chemical calculations and reference data from structurally related systems. These findings provide unprecedented insight into the photochemical behavior of substituted 1,3,4-oxadiazoles and unveil new reaction pathways modulated by substituent effects, expanding the understanding of their photoreactivity. Full article

Herein a rapid, metal-free, and highly efficient synthesis of aryl ynamides from aryl alkynyl acids has been described. This approach, utilizing tertiary amines as an amino source via metal-free C-N cleavage, enabled the construction of a diverse range of aryl ynamides with medium to excellent yields (33 examples, up to 95% yield). This reaction exhibits significantly enhanced efficiency compared to the conventional stepwise approach involving aryl alkynyl acids and secondary amines. It can be successfully scaled up, providing a practical and environmentally benign strategy for alkynamide synthesis. Full article

Cyclohexane-containing semi-aromatic polyamides (c-SaPA) exhibit excellent comprehensive properties. Existing studies predominantly focus on synthesis and modification, while fundamental investigations into pyrolysis mechanisms remain limited, which restricts the development of advanced materials for high-performance applications such as automotive and energy systems. This study employs Reactive Force Field Molecular Dynamics (ReaxFF-MD) simulations to establish a pyrolysis model for poly(terephthaloyl-hexahydro-m-xylylenediamine) (PHXDT), systematically probing its pyrolysis kinetics and evolutionary pathways under elevated temperatures. The simulation results reveal an activation energy of 107.55 kJ/mol and a pre-exponential factor of 9.64 × 10¹³ s⁻¹ for the pyrolysis process. The primary decomposition pathway involves three distinct stages. The first is initial backbone scission generating macromolecular fragments, followed by secondary fragmentation that preferentially occurs at short-chain hydrocarbon formation sites alongside radical recombination. Ultimately, the process progresses to deep dehydrogenation, carbonization, and heteroatom elimination through sequential reaction steps. Mechanistic analysis identifies multi-pathway pyrolysis involving carboxyl/amide bond cleavage and radical-mediated transformations (N-C-O, C-C-O, OH· and H·), yielding primary products including H₂, CO, H₂O, CH₃N, C₂H₂, and C₂H₄. Crucially, the cyclohexane structure demonstrates preferential participation in dehydrogenation and hydrogen transfer reactions due to its conformational dynamic instability and low bond dissociation energy, significantly accelerating the rapid generation of small molecules like H₂. Full article

Ammonia is a promising hydrogen storage material because it is easy to store and decompose into CO_X-free hydrogen. A Ru-based catalyst exhibits good catalytic performance in ammonia decomposition, and enhancing the interaction between the Ru atoms and the support is an important way to further improve its catalytic activity. In this study, CeO₂ was prepared by calcination using a cerium-based metal–organic framework (MOF) as the precursor, and the number of oxygen vacancies on the surface of CeO₂ was regulated by hydrogen reduction. The XPS and Raman results showed that abundant oxygen vacancies were formed on the surface of these CeO₂, and their number increased with an increase in the reduction time. The Ru/CeO₂-4 h catalyst, using CeO₂ reduced for 4 h as the support, exhibited good catalytic activity in ammonia decomposition, reaching 98.9% ammonia conversion and 39.74 mmol g_cat⁻¹ min⁻¹ hydrogen yield under the condition of GHSV = 36,000 mL g_cat⁻¹ h⁻¹ at 500 °C. The XAFS results demonstrated that Ru was stably anchored with oxygen vacancies on the surface of CeO₂ via Ru-O-Ce bonds. Density functional theory calculations further showed that these bondings lower the reaction energy barrier for N-H bond cleavage, thereby significantly enhancing the catalytic activity. Full article

Gossypol is a polyphenolic toxic compound present in cotton plants. To determine whether the candidate cytochrome P450BM3 enzymes could reduce gossypol in vitro, functional recombinant cytochrome P450BM3 enzymes were successfully expressed in E. coli. Site-directed mutagenesis generated mutants (R162H, R162K, Q129H, Q129N) to explore structural determinants of catalytic efficiency. Both wild-type P450BM3 and mutants exhibited significant ability to reduce gossypol levels, with R162H and R162K showing 33.4% and 24.2% reduced catalytic efficiency compared with the wild-type enzyme, respectively. Q129H and Q129N mutants maintained comparable catalytic efficiency to the wild type. Metabolomic profiling revealed two distinct reducing pathways catalyzed by wild-type P450BM3 and its mutants (R162H/Q129H), involving decarboxylation, hydroxylation, and C-C bond cleavage. This study demonstrated the feasibility of P450BM3 as a highly efficient biocatalyst for reducing gossypol levels, speculated that Arg162 might be a critical active residue, and hypothesized the potential pathways by which P450BM3 catalyzes the reduction of gossypol content, thereby providing a theoretical foundation for the enzymatic reduction of gossypol. Full article

This research work focuses on the chemical recycling of a Carbon Fiber-Reinforced Composite (CFRC) manufactured through a vacuum-assisted resin infusion (VARI) process, characterized by a high Young’s modulus of approximately 7640 MPa. The recycling reaction was performed using a mixture of eco-sustainable solvents, composed of acetic acid and hydrogen peroxide, and was conducted at three different temperatures (70, 80, and 90 °C). The reaction yield values, evaluated with an innovative approach that involved the use of thermogravimetric analysis (TGA), confirmed the importance to recycle at a temperature corresponding to the glass transition temperature (Tg = 90.3 °C) of the resin. Spectroscopic investigations highlighted that the chemical bond cleavage occurred through the selective breaking of the C-N bonds of the cross-linked matrix structure, allowing the recovery of both the reinforcing phase of the epoxy matrix and the initial oligomers/monomers of the epoxy matrix. The morphological and electrical investigations carried out on the recovered fibers further confirmed the efficiency of the recycling process conducted at the highest explored temperature, allowing the recovery of cleaner fibers with an electrical conductivity value (8.04 × 10² S/m) closer to that of virgin fibers (2.20 × 10³ S/m). The proposed strategy is a true challenge in terms of saving energy, solving waste disposal problems, preserving the earth, and preventing the depletion of planet resources. Full article

The conversion of methane (CH₄) to methanol (CH₃OH) under mild conditions remains a significant challenge in catalysis. In this study, we introduce a method to adjust the surface valence states of copper species in Cu-ZSM-5 catalysts by annealing under different atmospheres (N₂, air, and H₂). Among these, the 10% Cu-ZSM-5 catalyst calcined in H₂ showed outstanding performance, achieving a methanol productivity of 8.08 mmol/(g_cat·h) and 91% selectivity at 70 °C and 3 MPa using H₂O₂ as the oxidant. Comprehensive characterization revealed that H₂ annealing optimized the Cu surface to a lower valence state (predominantly Cu⁺), enhancing CH₄ adsorption and promoting H₂O₂ activation to generate ·OH and ·CH₃ radicals, which drive selective CH₃OH formation. In situ DRIFTS and radical trapping experiments further confirmed the critical role of Cu⁺ in facilitating C-H bond cleavage and suppressing overoxidation. Full article

In this work, we studied the main decomposition reactions on the ground state of nitromethane (CH₃NO₂) with the CASPT2 approach. The energetics of the main elementary reactions of the title molecule have been analyzed on the basis of Gibbs free energies obtained from standard expressions of statistical thermodynamics. In addition, we describe a mapping method (orthogonalized 3D representation) for the potential energy surfaces (PESs) by defining an orthonormal basis consisting of two $R^n$ orthonormal vectors (n, internal degrees of freedom) that allows us to obtain a set of ordered points in the plane (vector subspace) spanned by such a basis. Geometries and harmonic frequencies of all species and orthogonalized 3D representations of the PESs have been computed with the CASPT2 approach. It is found that all of the analyzed kinetically controlled reactions of nitromethane are endergonic. For such a class of reactions, the dissociation of nitromethane into CH₃ and NO₂ is the process with the lower activation energy barrier (ΔG); that is, the C-N bond cleavage is the most favorable process. In contrast, there exists a dynamically controlled process that evolves through a roaming reaction mechanism and is an exergonic reaction at high temperatures: CH₃NO₂ → [CH₃^…NO₂]* → [CH₃ONO]* → CH₃O + NO. The above assertions are supported by CASPT2 mappings of the potential energy surfaces (PESs) and classical trajectories obtained by “on-the fly” CASSCF molecular dynamics calculations. Full article

The role of halogen bonding (HaB) in the reactions of N-chlorosuccinimide (SimCl), a versatile reagent in organic synthesis, was investigated through experimental and computational analyses of its interactions with halides. The reactions of SimCl with Br⁻ or I⁻ resulted in the crystallization of HaB complexes of chloride with N-iodosuccinimide (SimI) or N-bromosuccinimide (SimBr). Computational analysis revealed that halogen rearrangements, which occurred even at −73 °C, were facilitated by halogen bonding. The dissociation of SimCl∙Y⁻ (Y = I or Br) complexes into a Sim⁻ + ClY pair (followed by the rotation and re-binding of the interhalogen molecules) bypassed the formation of the high-energy Sim⁻ + Cl⁺ pair and drastically (about tenfold) reduced the dissociation energy of the N–Cl bond. Furthermore, while the dissociation energy of individual SimCl is higher (and its HaB is weaker) compared to that of SimI or SimBr, the dissociation of the N-Cl bond in SimCl∙Y⁻ requires less energy than in the complexes of SimBr or SimI. The facile cleavage of such bonds in HaB complexes explains the high reactivity of SimCl and its effectiveness as a halogenating agent. Full article

Inorganic/organic composite passivation film can significantly improve the corrosion resistance performance of hot-dip Al-Zn-coated steel. However, yellowing of the passivation film always leads to obvious performance degradation in corrosion resistance. Investigating the yellowing mechanism of the passivation film and its impact on corrosion resistance would provide a foundation for enhancing its yellowing resistance property. This study primarily focuses on the yellowing mechanism of the passivation film based on the copolymer of N-vinylpyrrolidone and N-vinylcaprolactam. It is found that the oxidation and semi-carbonization of butyramide and valeroamide generated by C–N bond cleavage in the copolymer at high temperatures are responsible for the yellowing of the passivation film. The cracking of the passivation film caused by yellowing degree exposes more of the bare Al-Zn coating, further accelerating the degradation in the corrosion resistance. Additionally, it is observed that the impact of yellowing on the corrosion resistance is negligible when the color difference (ΔE*) caused by yellowing is less than 3.0, whereas ΔE* values above 3.0 result in rapid degradation in the corrosion resistance of the passivation film. The formula y = 0.77 − 0.07x + 0.023x² + 0.0039x³ effectively expresses the relationship between corrosion area (y) and ΔE* (x) (R² = 0.995). Full article

In this study, we present the HOAc-catalyzed selective cleavage of the C=C double bond of enaminones, enabling the formation of a new C–N bond and a new C=N bond for the one-pot synthesis of 2-substituted 3,4-dihydroquinazolines directly from ynones and 2-(aminomethyl)anilines. This method operates in ethanol under transition-metal-free and oxidant-free conditions, offering a sustainable and efficient approach for the synthesis of 3,4-dihydroquinazolines with broad functional group tolerance. 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

Polyester-based polyurethane coatings were widely used in automotive, industrial, construction, and plastics industries due to their excellent mechanical properties, adhesion, and relatively outstanding oil and chemical resistance. In these coatings, the type and ratio of polyester and isocyanate curing agents influenced the cohesion energy, hydrogen bonding, crystallinity, crosslinking density, molecular weight, and morphology of the polyurethane at the microscopic level, thereby affecting the macroscopic mechanical properties, electrical performance, and environmental resistance of the material. However, there was limited systematic research on the effect of crosslinking density on the properties of polyester-based polyurethanes. In this study, an HTP-1 system was composed of neopentyl glycol (NPG) and phthalic anhydride (PA), and an HTP-2 system was composed of neopentyl glycol (NPG), hexahydrophthalic anhydride (HHPA), and adipic acid (AA). A series of polyesters (HTPs) were synthesized by adding polyols with different functional groups and adjusting their proportions in the system. The synthesized polyester was characterized using FT-IR, GPC, and DSC, and then cured with polyisocyanate curing agent N3390 to prepare the coating. The following properties of the films were evaluated: adhesion, impact resistance, pencil hardness, gloss, flexibility, oil resistance, and weather resistance. The results showed that in the HTP-1 system, the introduction of dipentaerythritol resulted in a polyester with a broad molecular weight distribution at high hydroxyl values, with a maximum PDI of 12.66 and a glass transition temperature (Tg) reaching 40.19 °C. The polyesters prepared by introducing three types of multifunctional polyols into the HTP-1 system exhibited good impact resistance, adhesion, and hardness. At low hydroxyl values, the coatings demonstrated good flexibility, but due to the lower crosslinking density, the oil resistance was poor. As the hydroxyl value increased, flexibility decreased, while oil resistance improved. In the HTP-2 system, coatings prepared with three different multifunctional polyols showed good impact resistance, flexibility, and hardness at low hydroxyl values but poor adhesion and oil resistance. As the hydroxyl value increased, adhesion improved from grade 1 to grade 0, and oil resistance improved for coatings prepared with trimethylolpropane and ditrimethylolpropane. However, the oil resistance of coatings prepared with dipentaerythritol decreased. Regarding weather resistance, the HTP-1-series resins primarily exhibited the cleavage of -CH₂ groups, while the HTP-2-series resins showed the cleavage of C-N bonds. Overall, the HTP-2 series resins demonstrated better weather resistance. In the high-hydroxyl-value HTP-2 system, the incorporation of trimethylolpropane or ditrimethylolpropane has been shown to produce coatings that achieve a balance among mechanical properties, flexibility, and oil resistance. This finding provides valuable insights for the design and development of high-performance polyester-based polyurethane coatings. Full article

A palladium-catalyzed aromatic dual C-H acylations followed with intramolecular cyclizations have been developed by the assistance of bidentate N-(quinolin-8-yl)benzamide. This tandem process involves the formation of three new chemical bonds, providing access to novel quinoline-substituted hydroxyl isoindolones skeleton under simple reaction conditions. The deuterium-labeled competition reaction has revealed that C-H bond cleavage is the turnover limiting step. Full article