Search Results (289)

Density functional theory (DFT) calculations elucidate the mechanism of diastereoselective cyclization of 2-picoline with 1,5-hexadiene catalyzed by a cationic half-sandwich scandium complex. The catalytic cycle proceeds through four key stages: formation of active species, initial alkene insertion, cis-selective cyclization, and protonation. Central to the mechanism is the dual role of 2-picoline, which initially coordinates as a supporting ligand to facilitate C–H activation and regioselective 1,2-insertion but must dissociate to enable stereocontrol. The mono(2-picoline)-coordinated complex C3 is identified as the thermodynamically favored active species. C–H activation reactivity follows the trend: ortho-C(sp²)–H (2-picoline-free) > ortho-C(sp²)–H (2-picoline-coordinated) > benzylic C(sp³)–H (2-picoline-free) > benzylic C(sp³)–H (2-picoline-coordinated), a preference governed by a wider C_α–Sc–C_α′ angle and shorter Sc···X (X = C_α, C_α′, H) distances that enhance scandium–substrate interaction. Subsequent 1,5-hexadiene insertion proceeds with high 1,2-regioselectivity through a picoline-assisted pathway. The stereoselectivity-determining step reveals a mechanistic dichotomy: while picoline coordination is essential for initial activation, its dissociation is required for intramolecular cyclization. This ligand displacement avoids prohibitive steric repulsion in the transition state, directing the reaction exclusively toward the cis-cyclized product. The cycle concludes with a sterically accessible mono-coordinated protonation. This work establishes a “ligand-enabled then ligand-displaced” mechanism, highlighting dynamic substrate coordination as a critical design principle for achieving high selectivity in rare-earth-catalyzed C–H functionalization. Full article

The color and scent of flowers are vital ornamental attributes influenced by a complex interaction of metabolic and transcriptional mechanisms. Comparative analyses were performed to determine the molecular rationale for these features in Hydrangea arborescens, between the white-flowered variety ‘Annabelle’ (An) and its pink-flowered variant ‘Pink Annabelle’ (PA). Gas chromatography–mass spectrometry (GC–MS) detected 25 volatile organic compounds (VOCs) in ‘An’ and 21 in ‘PA’, with 18 chemicals common to both types. ‘An’ exhibited somewhat higher VOC diversity, whereas ‘PA’ emitted much bigger quantities of benzenoid and phenylpropanoid volatiles, including benzaldehyde, benzyl alcohol, and phenylethyl alcohol, resulting in a more pronounced floral scent. UPLC–MS/MS metabolomic analysis demonstrated obvious clustering of the two varieties and underscored the enrichment of phenylpropanoid biosynthesis pathways in ‘PA’. Transcriptomic analysis revealed 11,653 differentially expressed genes (DEGs), of which 7633 were elevated and linked to secondary metabolism. Key biosynthetic genes, including PAL, 4CL, CHS, DFR, and ANS, alongside transcription factors such as MYB—specifically TRINITY_DN5277_c0_g1, which is downregulated in ‘PA’ (homologous to AtMYB4, a negative regulator of flavonoid biosynthesis)—and TRINITY_DN23167_c0_g1, which is significantly upregulated in ‘PA’ (homologous to AtMYB90, a positive regulator of anthocyanin synthesis), as well as bHLH, ERF, and WRKY (notably TRINITY_DN25903_c0_g1, highly upregulated in ‘PA’ and homologous to AtWRKY75, associated with jasmonate pathway), demonstrating a coordinated activation of color and fragrance pathways. The integration of metabolomic and transcriptome data indicates that the pink-flowered ‘PA’ variety attains its superior coloring and aroma via the synchronized transcriptional regulation of the phenylpropanoid and flavonoid pathways. These findings offer novel molecular insights into the genetic and metabolic interplay of floral characteristics in Hydrangea. Full article

To explore the aging mechanism of (Styrene Butadiene Styrene) and CR (Crumb Rubber) composite-modified asphalt in a multi-source environment, the characteristics of functional group changes in the infrared spectroscopy of SBS and CR modifiers as well as their single and composite modified asphalts under thermal, UV, and coupled aging were tested using Attenuated Total Reflection–Fourier Transform Infrared Spectroscopy (ATR-FTIR) technology. It was found that SBS and CR modifiers exhibited significant yellowing degradation after aging due to high-energy effects, causing abstraction of α-hydrogen from polybutadiene via oxidation, initiating radical chain reactions. The addition of SBS and CR to asphalt significantly increased the absorption peaks of 966 cm⁻¹ polybutadiene and 699 cm⁻¹ polystyrene. However, certain labile bonds in the modified asphalt, such as the C-H bond, C-C bond, and C=C double bond in polycyclic aromatic hydrocarbons, were easily broken to produce reactive free radicals under aging, which reacted chemically with other components to produce new sulfoxide and carbonyl groups. Overall, the aging reaction of the asphalt was a dual sequential oxidation process. Under normal temperature conditions in the early stage, a large number of sulfoxides were oxidized. In the later stage of the reaction, as the concentration and persistence of active free radicals increased, the oxidation reaction of the asphalt benzyl carbon also enhanced significantly, ultimately generating carbonyls. Full article

Aeschynomene indica L. has become a problematic weed in the upland direct-seeding rice fields of the lower Yangtze River region, China, leading to substantial yield reductions. A comprehensive understanding of its seed germination ecology and response to herbicides is crucial for developing effective control strategies. This study examined the effects of major environmental factors including temperature, light, pH, salt stress, osmotic potential, and burial depth on seed germination of A. indica and assessed the efficacy of 20 commonly used herbicides in rice under controlled conditions. Results revealed that germination was highly sensitive to temperature, with optimum constant and alternating temperatures of 35 °C and 40/30 °C (day/night), respectively, both achieving germination rates above 90%. The seeds were non-photoblastic, maintaining a high germination rate of 83.33% under complete darkness. Germination remained consistently high across a broad pH range from 4 to 9, with rates ranging from 83.33% to 96.67%. Salt and osmotic stresses markedly suppressed germination, with EC₅₀ values of 195.08 mmol·L⁻¹ NaCl and −0.43 MPa, respectively. Seedling emergence decreased significantly with increasing burial depth, with no emergence occurring at depths greater than 7 cm. The EC₅₀ for emergence was 4.21 cm. Among the herbicides screened, saflufenacil and mesotrione were the most effective pre-emergence treatments, with GR₅₀ values of 5.38 and 12.02 g ai ha⁻¹, respectively. Florpyrauxifen-benzyl and fluroxypyr-meptyl exhibited the highest post-emergence activity, with GR₅₀ values of 0.20 and 19.69 g ai ha⁻¹, respectively. These results underscore the high ecological adaptability of A. indica to paddy fields conditions and provide a scientific foundation for integrating chemical control with cultural practices such as deep tillage into sustainable weed management systems for paddy fields. Full article

The pyridylamines 2,6-Me₂C₆H₃NHCR₂-C₅H₅H-2 (R = H, L¹H; Me, L²H) on treatment with Me₃Al (one equivalent) afforded the complexes [Al(Me)₂(L¹)] (1) and [Al(Me)₂L²] (2), respectively. Use of excess L¹H led to [Al(Me)(L¹)₂] (3). The molecular structures of 1–3 are reported, and the three complexes, as well as the parent compounds L¹H and L²H, have been screened, in the presence of benzyl alcohol (BnOH), as catalysts for the ring opening polymerization (ROP) of ε-caprolactone and δ-valerolactone. Results revealed that these ROPs proceed in a controlled nature (Đ ≤ 1.33 for ε-CL and ≤1.48 for δ-VL) in the process without catalyst deactivation, whilst the products formed were predominantly linear with OBn/OH end groups; L¹H and L²H exhibited little or no activity. Full article

Based on comprehensive experimental datasets—proximate/ultimate analyses, XPS, solid-state ¹³C NMR, and Raman spectroscopy—we constructed and optimized a compositionally faithful macromolecular model of SG coking coal. Using density-functional theory (DFT) calculations, we simulated electrostatic-potential (ESP) fields and frontier molecular orbitals (FMO) to probe elementary oxidation steps relevant to combustion, and focused on how heteroatom speciation and carbon ordering govern site-selective reactivity. Employing multi-peak deconvolution and parameter synthesis, we obtained an aromatic fraction f_a = 76.56%, a bridgehead-to-periphery ratio X_BP = 0.215, and Raman indices I_D1/I_G ≈ 1.45 (area) with FWHM(G) ≈ 86.7 cm⁻¹; the model composition C₁₉₀H₁₄₄N₂O₂₁S and its predicted ¹³C NMR envelope validated the structural assignment against experiment. ESP–FMO synergy revealed electron-rich hotspots at phenolic/ether/carboxyl and thiophenic domains and electron-poor belts at H-terminated edges/aliphatic bridges, rationalizing carbon-end oxidation of CO, weak electrostatic steering by O₂/CO₂, and a benzylic H-abstraction → edge addition → O-insertion/charge-transfer sequence toward CO₂/H₂O, with thiophenic sulfur comparatively robust. We quantified surface functionalities (C–O 65.46%, O–C=O 24.51%, C=O 10.03%; pyrrolic/pyridinic N dominant; thiophenic-S with minor oxidized S) and determined a naphthalene-dominant, stacked-polyaromatic architecture with sparse alkyl side chains after Materials Studio optimization. The findings are significant for mechanistic understanding and control of coking-coal oxidation, providing actionable hotspots and a reproducible workflow (multi-probe constraints → model building/optimization → DFT reactivity mapping → spectral back-validation) for blend design and targeted oxidation-inhibition strategies. Full article

The combination of multicomponent reactions with post-transformation processes is a powerful strategy for the rapid synthesis of structurally complex polyheterocycles. Herein, we describe the preparation of the novel compound 2-benzyl-6-(3-((7-chloroquinolin-4-yl)amino)propyl)-3-morpholino-7-(4-(pyridin-2-yl)phenyl)-6,7-dihydro-5H-pyrrolo[3,4-b]pyridin-5-one via a sequence that combines an Ugi-Zhu reaction with a cascade process (aza-Diels–Alder/N-acylation/aromatization) under microwave irradiation in chlorobenzene using ytterbium (III) triflate (Yb(OTf)₃) as the catalyst. The method provided the target polyheterocycle in 75% yield and 85% atom economy. Structural characterization was performed by 1D (¹H and ¹³C) and 2D (COSY, HSQC and HMBC) NMR spectroscopy, and the molecular mass was confirmed by high-resolution mass spectrometry (HRMS). These results illustrate the effectiveness of MCR as powerful synthetic tools for expanding chemical diversity. Full article

The importance of 1,2,4-triazole derivatives in modern pharmaceuticals is very high. They find their application in drug therapy as antifungal, antifungal agents (fluconazole, intraconazole). It is worth noting that some 1,2,4-triazole compounds are used in therapy for the treatment of Alzheimer’s disease, and new, more effective pharmacophores are being sought to create drugs for neurodegenerative diseases. We propose a modernized method for obtaining a new bis(1,2,4-triazole) derivative using the recyclization reaction of 4-hydroxy-2,5-disubstituted-1,3-6H-oxazin-6-ones with a bisnucleophilic reagent, which was m-phenylenedihydrazine. The method of preparation described in the literature did not lead to the expected products, so it was necessary to select new reaction conditions. 1,1′-(benzene-1,3-diyl)bis[5-benzyl-3-(4-nitrophenyl)-1H-1,2,4-triazole] was obtained by recyclization of 4-hydroxy-2-(4-nitrophenyl)-5-phenyl-6H-1,3-oxazin-6-one with m-phenylenedihydrazine dihydrochloride in absolute methanol in the presence of sodium methoxide for 48 h. The structure of the compound was confirmed by ¹H, ¹³C NMR spectroscopy, and mass spectrometry. Antifungal and antibacterial activities were determined by serial dilutions using meat-peptone broth and Sabouraud medium. The yield based on 4-hydroxy-2-(4-nitrophenyl)-5-phenyl-6H-1,3-oxazin-6-one was 76%. The obtained compound exhibited antimicrobial activity against Staphylococcus aureus with a minimum inhibitory concentration of 62.5 μg/mL and 125 μg/mL against Candida albicans. Full article

A series of five cobalt(II) complexes, dichloro-bis(1-benzyl-benzimidazole)-cobalt(II) (1a), dichloro-bis[1-(4-fluorobenzyl)-benzimidazole]-cobalt(II) (1b), dichloro-bis((Z)-1-styryl-benzimidazole)-cobalt(II) (1c), dichloro-bis[(Z)-1-(2-fluorostyryl)-benzimidazole]-cobalt(II) (1d) and dichloro-bis(1-cinnamyl-benzimidazole)-cobalt(II) (1e), were evaluated in ethylene dimerization. Four of these complexes were described for the first time and fully characterized by IR, elemental analysis, mass and NMR spectroscopy. In the solid state, the cobalt atom exhibited a typical tetrahedral geometry and was found to be coordinated to two chlorine atoms and two benzimidazole rings. In the presence of 20 bar of ethylene and diethylaluminium chloride as a co-catalyst, the complex with styryl substituents on the benzimidazole rings, complex 1c, exhibited the highest activity with a turnover frequency of 3430 mol(ethylene)·mol(Co)⁻¹·h⁻¹. Full article

Viologens are promising candidates for next-generation electrochromic devices due to their reversible color changes, low operating voltages, and structural tunability. However, their practical performance is often constrained by limited color range, stability issues, and poor charge delocalization. In this study, we present a detailed density functional theory (DFT) and time-dependent DFT (TD-DFT) investigation of asymmetric viologens based on the Benzyl-4,4′-dipyridyl-R (BnV-R) framework. A series of electron-donating and electron-withdrawing substituents (CN, COOH, PO₃H₂, CH₃, OH, NH₂) were introduced via either benzyl or phenyl linkers. Geometry optimizations for neutral, radical cationic, and dicationic states were performed at the CAM-B3LYP/6-31+G(d,p) level with C-PCM solvent modeling. Electronic structure, frontier orbital distributions, and redox potentials were correlated with substituent type and linkage mode. Natural Bond Orbital analysis showed that electron-withdrawing groups stabilize reduced states, while electron-donating groups enhance intramolecular charge transfer and switching kinetics. TD-DFT calculations revealed significant bathochromic and hyperchromic shifts dependent on substitution patterns, with phenyl linkers promoting extended conjugation and benzyl spacers minimizing aggregation. Radical cation stability, quantified via ΔE_red and comproportionation constants, highlighted cyano- and amine-substituted systems as particularly promising. These insights provide predictive design guidelines for tuning optical contrast, coloration efficiency, and electrochemical durability in advanced electrochromic applications. Full article

A novel inclusion complex of a fluorinated pyrazolopiperidine derivative (5-benzyl-7-(2-fluorobenzylidene)-2,3-bis(2-fluorophenyl)-3,3a,4,5,6,7-hexahydro-2H-pyrazolo [4,3-c]pyridine hydrochloride, PP·HCl) with β-cyclodextrin (PPβCD) was designed, synthesized, and characterized as a potential therapeutic agent for chemotherapy-induced myelosuppression and lymphopenia. Encapsulation of PP within β-cyclodextrin increased aqueous solubility by approximately 3.4-fold and improved dissolution rate by 2.8-fold compared with the free compound. Structural analysis using IR, ^1H/^13C NMR, and TLC confirmed the formation of a stable 1:1 host–guest complex, and the disappearance of free PP signals further supported complete encapsulation. In vivo evaluation in a cyclophosphamide-induced myelosuppression model demonstrated that PPβCD accelerated hematopoietic recovery, restoring leukocyte and erythrocyte counts 35–40% faster than methyluracil, without any signs of systemic toxicity. These findings indicate that β-cyclodextrin complexation significantly enhances solubility, dissolution, and biological efficacy of the pyrazolopiperidine scaffold, supporting further preclinical development of PPβCD as a supportive therapy for chemotherapy-related hematological complications. Full article

In this contribution, two silsesquioxane–cyclopentadienyl titanium complexes featuring one or two chloride ancillary ligands, [Ti(η⁵-C₅H₄SiMeO₂Ph₇Si₇O₁₀-κO)Cl₂] (1) and [Ti(η⁵-C₅H₄SiMe₂OPh₇Si₇O₁₁-κ²O₂)Cl] (2), were synthesized and evaluated in the Ziegler–Natta polymerization of styrene and the ring-opening polymerization (ROP) of L-lactide, respectively. Complex 1, activated with methylaluminoxane (MAO), catalyzed the syndiotactic polymerization of styrene with turnover frequencies up to 28 h⁻¹, affording polymers with narrow dispersity, low number-average molecular weights (M_n = 5.2–8.2 kDa), and high stereoregularity, as confirmed by ¹³C NMR. Complex 2, in combination with benzyl alcohol, promoted the ring-opening polymerization of L-lactide in solution at 100 °C, achieving conversions up to 95% with good molecular weight control (M_n close to theoretical, Đ = 1.19–1.32). Under melt conditions at 175 °C, it converted up to 3000 equiv. of monomer within 1 h. Kinetic analysis revealed first-order dependence on monomer concentration. The results highlight the ability of these complexes to produce syndiotactic polystyrene with narrow molecular weight distributions and to catalyze controlled ROP of L-lactide under both solution and melt conditions. Computational studies provided insight into key structural and energetic features influencing reactivity, offering a framework for further catalyst optimization. This work broadens the application scope of silsesquioxane–cyclopentadienyl titanium complexes and supports their potential as sustainable and versatile catalysts for both commodity and biodegradable polymer synthesis. Full article

Rosa bracteata J.C.Wendl. is a thorny, clump-forming or trailing perennial evergreen shrub native to China. The current analysis was designed to explore the chemical constituents and determine the in vitro antimicrobial, cytotoxic, and antioxidant properties of the essential oils (EOs) of the stems, leaves, and flowers of Rosa bracteata for the first time. The chemical composition of the essential oils obtained through hydro-distillation was characterized by means of gas chromatography–mass spectrometry (GC–MS) and gas chromatography with a flame ionization detector (GC–FID). Thirty-seven, thirty-six, and forty-two constituents were identified from leaf oil (LEO), stem oil (SEO), and flower oil (FEO), representing 96.3%, 95.9%, and 97.4% of the total oil constituents, respectively. The LEO was mainly composed of 1-pentadecene, α-cadinol, and hexadecanoic acid. However, the main identified components of SEO were (E)-nerolidol, phytol, and benzyl benzoate, and the main components of the flower oil were ethyl octanoate, octanoic acid, and α-cadinol. All of the EOs exhibited antibacterial activities against both Gram-positive and Gram-negative bacteria with MIC values ranging from 40.00 to 640.00 μg/mL. In addition, the checkerboard method demonstrates potent synergistic effects of Rosa bracteata EOs when combined with commercial antibiotics (chloramphenicol and streptomycin). In the MTT test, SEO (IC₅₀: 37.91 ± 2.10 to 51.15 ± 6.42 μg/mL) showed stronger cytotoxic activity against four cancer cell lines (MCF-7, A549, HepG2, and HCT-116) during the incubation time of 48 h in comparison to the EOs isolated from the other plant parts. Overall, these findings reveal the chemical composition and significant bioactivity of R. bracteata EOs for the first time, suggesting their potential as promising natural agents for therapeutic applications, especially in combination therapies to combat antibiotic resistance. Full article

This work reports the crystallographic study of two benzenesulfonamides, 1 ((E)-N-benzyl-3-((benzylimino)methyl)-4-hydroxybenzenesulfonamide) and 2 (N-benzyl-3-(3-(N-benzylsulfamoyl)-2-oxo-2H-chromene-6-sulfonamide). These compounds share structural features with belinostat, an FDA-approved histone deacetylase (HDAC) inhibitor used in the treatment of peripheral T-cell lymphoma. Compound 1 contains one sulfonamide group, meanwhile compound 2 contains two sulfonamide moieties and presents four independent molecules in its unit cell. The crystal packing of 1 and 2 is mainly governed by N–H···O=S hydrogen bonding interactions. π → π* and n → π* stacking interactions also contribute to the molecular assembly. Hirshfeld surface (HS) analysis was carried out to further examine the intermolecular interactions of compounds 1 and 2, revealing that N–H∙∙∙O and C–H∙∙∙O hydrogen bonding interactions, along with O∙∙∙H/H∙∙∙O interactions, are the strongest contributors to the individual surfaces. Interaction energy analysis was also performed to evaluate the relative strength and nature of the intermolecular contacts. Additionally, molecular docking studies of compounds 1 and 2 were performed on the crystal structure of the enzyme HDAC2, an enzyme overexpressed in several cancers, particularly breast cancer. The results revealed that both compounds exhibit a binding mode and binding energies similar to those of belinostat, suggesting their potential as novel therapeutic agents. Full article

A transition metal-free synthesis of 1,2,5-trisubstituted 1H-indoles by a deprotonation–S_NAr cyclization sequence from 1-aryl-2-(2-fluoro-5-nitrophenyl)ethan-1-one (deoxy-benzoin) Schiff bases is reported. The starting deoxybenzoins were prepared by Friedel-Crafts acylation of activated aromatic compounds by 2-(2-fluoro-5-nitrophenyl)acetyl chloride with AlCl₃ or the corresponding acid with (CH₃SO₂)₂O. The Schiff bases were generated by slow distillation of toluene (18–24 h) from a heated solution of each deoxybenzoin (1 equiv) with a benzyl- or phenethylamine, a high-boiling aliphatic amine, or an aniline derivative (5 equiv). Subsequent addition of N,N-dimethylformamide, 2 equiv of anhydrous K₂CO₃, and heating at 90–95 °C for 18–24 h completed the synthesis. Benzyl-, phenethyl-, and high-boiling amines gave excellent yields while the heating requirements for the initial condensation made volatile aliphatic amines difficult to use and gave low yields. Aniline reactivities correlated with substituent-derived base strength, although modified conditions allowed some yields to be improved. Several anticipated competing processes had minimal impact on the outcome of the cyclizations. Full article