Search Results (372)

Catalytic upgrading of pyrolysis oils is an important step for producing replacement hydrocarbon-rich liquid biofuels from biomass and can help to advance pyrolysis technology. Catalysts play a pivotal role in influencing the selectivity of chemical reactions leading to the formation of main compounds in the final upgraded liquid products. The present work involved a systematic study of solvent-free catalytic reactions of cyclohexanone in the presence of hydrogen gas at 160 °C for 3 h in a batch reactor. Cyclohexanone can be produced from biomass through the selective hydrogenation of lignin-derived phenolics. Three types of catalysts comprising undoped NbOPO₄, 10 wt% NiO/NbOPO₄, and 30 wt% NiO/NbOPO₄ were studied. Undoped NbOPO₄ promoted both aldol condensation and the dehydration of cyclohexanol, producing fused ring aromatic hydrocarbons and hard char. With 30 wt% NiO/NbOPO₄, extensive competitive hydrogenation of cyclohexanone to cyclohexanol was observed, along with the formation of C₆ cyclic hydrocarbons. When compared to NbOPO₄ and 30 wt% NiO/NbOPO₄, the use of 10 wt% NiO/NbOPO₄ produced superior selectivity towards bi-cycloalkanones (i.e., C₁₂) at cyclohexanone conversion of 66.8 ± 1.82%. Overall, the 10 wt% NiO/NbOPO₄ catalyst exhibited the best performance towards the production of precursor compounds that can be further hydrodeoxygenated into energy-dense aviation fuel hydrocarbons. Hence, the presence and loading of NiO was able to tune the activity and selectivity of NbOPO₄, thereby influencing the final products obtained from the same cyclohexanone feedstock. This study underscores the potential of lignin-derived pyrolysis oils as important renewable feedstocks for producing replacement hydrocarbon solvents or feedstocks and high-density sustainable liquid hydrocarbon fuels via sequential and selective catalytic upgrading. Full article

Fused and spiro nitrogen-containing heterocycles play an important role as structural motifs in numerous biologically active natural products and pharmaceuticals. The review summarizes various approaches to the synthesis of three-, four-, five-, and six-membered fused and spiro heterocycles with one or two nitrogen atoms. The assembling of the titled compounds via cycloaddition, oxidative cyclization, intramolecular ring closure, and insertion of sextet intermediates—carbenes and nitrenes—is examined on a vast number of examples. Many of the reactions proceed with high regio-, stereo-, or diastereoselectivity and in excellent, up to quantitative, yield, which is of principal importance for the synthesis of chiral drug-like compounds. For most unusual and hardly predictable transformations, the mechanisms are given or referred to. Full article

The reaction of either the L (2S3R) or D (2R3S) enantiomers of H₂N-C*H(R)CO₂⁻ (R = -C*H(OH)CH₃ or -C*H(OH)CH(CH₃)₂) and the L (2S) or D (2R) enantiomers of H₂N-C*H(C(CH3)₂OH)CO₂⁻ with imidazole-4-carboxaldehyde and nickel(II) acetate in methanol yields a single stereoisomer of an oxazolidine. There is retention of chirality on ring positions 4 and 5 (if C_β is chiral) of the oxazolidine, C_α and C_β of the parent amino acid, and transfer of chirality to the newly generated stereogenic centers, ring positions 3, the amino acid nitrogen atom, N_AA, and 2, the aldehyde carbon atom, C_ald. Specifically, when C_α has an S configuration, both N_AA and C_ald are formed as R. Likewise, a C_α which is R results in both N_AA and C_ald being formed as S. For example, the reaction of L threonine (C_α is S and C_β is R) with 4-imidazolecarboxaldehyde in the presence of nickel(II) gives the facial Λ NiL₂, where L is (2R, 3R, 4S, 5R) 4-carboxylato-5-methyl-2-(4-imidazolyl)-1,3-oxazolidine. The same reaction with D threonine produces the enantiomeric Δ complex of (2S, 3S, 4R, 5S) 4-carboxylato-5-methyl-2-(4-imidazoyl)-1,3-oxazolidine. The high stereospecificity is thought to be based on the fused three-ring structure of the characterized nickel complexes in which the hydrogen atoms of C_α, N_AA, and C_ald must be cis to one another. Identical reactions occur with 2-pyridine carboxaldehyde and LT or DT. In contrast, the reactions of L allo threonine (2S3S) and the primary alcohols, L or D serine, give the conventional meridionally coordinated aldimine product. Full article

Wireless structural health monitoring is needed for machine elements of which the working motions prevent wired monitoring. Rotating machine shafts are such elements. Wired monitoring of the rotating shaft requires making significant changes to the shaft structure, primarily drilling a hole in the longitudinal axis of the shaft and installing a slip ring assembly at the end of the shaft. Such changes to the shaft structure are not always possible. This paper proposes the use of piezoelectric energy harvesting from a rotating shaft to power wireless temperature monitoring of the shaft surface. The main components of presented wireless temperature monitoring are three piezoelectric composite patches, three thermal fuses, a system for storing and distributing the harvested energy, and a radio transmitter. This article contains the results of experimental research of such wireless monitoring on a dedicated laboratory stand. This research included four connections of piezoelectric composite patches: delta, star, parallel, and series for different capacities of a storage capacitor. Based on experimental results, three parameters that influence the frequency of sending data packets by the presented wireless temperature monitoring are identified: amplitude of stress in the rotating shaft, rotation speed of the shaft, and the capacity of a storage capacitor. Full article

This fundamental understanding of molecular structure–NLO property relationships provides critical design principles for next-generation optical limiting materials, quantum photonic devices, and ultrafast nonlinear optical switches, addressing the growing demand for high-performance organic optoelectronic materials in laser protection and photonic computing applications. In this study, it was observed that selenophene-incorporated fused D-A-D architectures exhibit a remarkable enhancement in two-photon absorption characteristics. By strategically modifying the heteroatomic composition of the Y6-derived fused-ring core, replacing thiophene (BDS) with selenophene (BDSe), the optimized system achieves unprecedented NLO performance. BDSe displays a nonlinear absorption coefficient (β) of 3.32 × 10⁻¹⁰ m/W and an effective two-photon absorption cross-section (σ_TPA) of 2428.2 GM under 532 nm with ns pulse excitation. Comprehensive characterization combining Z-scan measurements, transient absorption spectroscopy, and DFT calculations reveals that the heavy atom effect of selenium induces enhanced spin–orbit coupling, optimized intramolecular charge transfer dynamics and stabilized excited states, collectively contributing to the superior reverse saturable absorption behavior. It is believed that this molecular engineering strategy establishes critical structure–property relationships for the rational design of organic NLO materials. Full article

Pyrazolopyridines and pyrazolopyrimidines are 5:6 aza-fused N-heteroaromatic compounds (NHACs) comprising a pyrazole ring fused to a pyridine or pyrimidine ring. They exhibit dipolar behavior due to their π-excessive and π-deficient characteristics conferred by their five- and six-membered rings. These features favor their stability, reactivity, and structural diversity, offering numerous modular and functional derivatives (e.g., pyrazolo[1,2-a]pyridines, pyrazolo[1,5-a]pyrimidines, etc.). They have been utilized to obtain relevant chemicals in pharmaceuticals, photophysics, industry, and materials science; thus, their synthesis is highly desirable for discovering novel or improved applications. Therefore, this review focuses on recent advances in the synthesis and applications of these compounds, considering reports from the last decade (2015–2024), with particular emphasis on photophysics, as they contain dipolar 5:6 aza-fused rings as essential scaffolds for this purpose. Full article

Naturally occurring antioxidants have attracted significant research interest, owing to their radical scavenging ability that can be improved via structural modifications. In this study, aromaticity-extended resveratrol analogues (3–5) containing chalcogens were designed and synthesized using ring closure and Horner–Wadsworth–Emmons reactions. The antioxidant activities of the derivatives were evaluated using 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABST) assay. All resveratrol derivatives (3–5) exhibited higher radical scavenging activities than resveratrol 1 and analogue 2, with benzoselenophene-conjugated derivative 5 demonstrating the highest activity. The improved antioxidant performance of the resveratrol derivatives was attributed to the extended π conjugation resulting from the incorporation of fused rings, benzoheteroles. Additionally, the integration of benzoheteroles into resveratrol contributed to an efficient reduction in HOMO-LUMO gaps. This study demonstrates that aromaticity extension by introducing benzofuran, benzothiophene, and benzoselenophene is a feasible strategy for improving the antioxidant activity of naturally occurring oxidants. Full article

Oil seals are vital components in industrial production, necessitating high-precision 3D reconstruction for automated geometric measurement and quality inspection. High-quality point cloud completion is integral to this process. However, existing methods heavily rely on large datasets and often yield sub-optimal outcomes—such as distorted geometry and uneven point distributions—under limited sample conditions, constraining their industrial applicability. To address this, we propose a point cloud completion network that integrates a dynamic weighted fusion of multi-scale features with Transformer enhancements. Our approach incorporates three key innovations: a multi-layer perceptron fused with EdgeConv to enhance local feature extraction for small-sample oil seal rings, a dynamic weighted fusion strategy to adaptively optimize global feature integration across varying missing rates of oil seal rings, and a Transformer-enhanced multi-layer perceptron to ensure geometric consistency by linking global and local features. These innovations collectively enable high-quality point cloud completion for small-sample oil seal rings, achieving significant improvements at a 25% missing rate, reducing CD by 46%, EMD by 49%, and MMD by 74% compared to PF-Net. Experiments on the ShapeNet-Part dataset further validate the model’s strong generalizability across diverse categories. Experimental results on the industrial oil seal ring dataset and the small-sample ShapeNet sub-dataset show that our approach exhibits highly competitive performance compared to existing models. Full article

Kapakahines A–G are natural products isolated from the marine sponge Carteriospongia sp., characterized by complex molecular architectures composed of fused rings and diverse functional groups. Preliminary studies have indicated that some of these peptides may exhibit cytotoxic and antitumor activities, which has prompted interest in further exploring their chemical and pharmacokinetic properties. Computational chemistry—particularly Conceptual Density Functional Theory (CDFT)-based Computational Peptidology (CP)—offers a valuable framework for investigating such compounds. In this study, the CDFT-CP approach is applied to analyze the structural and electronic properties of Kapakahines A–G. Alongside the calculation of global and local reactivity descriptors, predicted ADMET (Absorption, Distribution, Metabolism, Excretion, and Toxicity) profiles and pharmacokinetic parameters, including pKa and LogP, are evaluated. The integrated computational analysis provides insights into the stability, reactivity, and potential drug-like behavior of these marine-derived cyclopeptides and contributes to the theoretical groundwork for future studies aimed at optimizing their bioactivity and safety profiles. Full article

A facile and efficient synthesis of functionalized 1,4-benzodiazepine derivatives under mild conditions was developed. The CuI/N,N-dimethylglycine-catalyzed intramolecular cross-coupling reaction of 1-(2-bromobenzyl)azetidine-2-carboxamides proceeded smoothly under mild conditions to provide 1,4,9,10a-tetrahydroazeto[1,2-a]benzo[e][1,4]diazepin-10(2H)-ones. The resulting azetidine-fused 1,4-benzodiazepine compounds underwent consecutive N-methylation with methyl triflate and the opening of the four-membered heterocyclic ring by NaN₃, KCN and PhSNa to produce diverse 1,4-benzodiazepine derivatives in good to excellent yields. Upon treatment with methyl chloroformate, on the other hand, the 1,4,9,10a-tetrahydroazeto[1,2-a]benzo[e][1,4]diazepin-10(2H)-ones were straightforwardly converted into 2-chloroethyl-substituted 1,4-benzodiazepine derivatives. Full article

A series of porphyrinoids fused to highly electron-withdrawing bis(thiadiazolo)benzene units have been prepared and spectroscopically characterized. These structures have modified chromophores and exhibit large bathochromic shifts. The nickel(II), copper(II) and zinc complexes of a bis(thiadiazolo)benzoporphyrin were prepared, and these showed strong absorptions above 600 nm that shifted to longer wavelengths with increasing atomic number for the coordinated metal cations. Although the investigated porphyrinoids were poorly soluble, proton NMR data could be obtained, and these demonstrated that the structures possess global aromatic character. This was confirmed with nucleus-independent chemical shift (NICS) calculations and anisotropy of induced current density (AICD) plots. The AICD plots also demonstrate that the fused heterocyclic unit is disconnected from the porphyrinoid π-system, and in this respect, it differs from phenanthroline-fused porphyrinoids as it shows the presence of extended conjugation pathways. Full article

Cyclacenes with the general formula C_4nH_2n are cyclic analogs of acenes. Acenes are well-known for their high reactivity, which increases with the number of fused benzene rings. The cyclic strain, absence of a Clar sextet, and diradical or polyradical nature are expected to render cyclacenes highly reactive under ambient conditions. Their primary decomposition pathway is anticipated to involve dimerization or polymerization. We explore the reaction pathway of the [_π4_s + _π4_s] dimerization of [n]-cyclacenes for 6 ≤ n ≤ 20 by density functional theory (DFT) using spin-unrestricted and thermally-assisted-occupation (TAO) formalisms. Computational analysis predicts a stepwise reaction mechanism that starts with the formation of a van der Waals complex and proceeds through a transition state to an intermediate with a single new C–C bond and two unsaturated valences. A subsequent second transition state results in the formation of the dimerization product. However, for smaller cyclacenes (n < 10), neither the van der Waals complex nor the first transition state is involved, and the intermediate is formed without a barrier. The largest [20]-cyclacene investigated exhibits the highest barriers for these processes. However, with a barrier as low as 3.9 kcal/mol at the UB3LYP-D3(BJ)/6-31G(d) level of theory, dimerization is anticipated to occur very rapidly. Full article

Nitrogen-containing heterocycles are fundamental scaffolds in organic chemistry, particularly due to their prevalence in pharmaceuticals, agrochemicals and materials science. Among them, five-membered rings, containing two nitrogen atoms in adjacent positions—such as pyrazoles, pyrazolines and indazoles—are especially significant due to their versatile biological activities and structural properties, which led to the search for greener, faster and more efficient methods for their synthesis. Conventional batch synthesis methods, while effective, often face challenges related to reaction efficiency, scalability and safety. Flow chemistry has emerged as a powerful alternative, offering enhanced control over reaction parameters, improved safety profiles and opportunities for scaling up synthesis processes efficiently. This review explores the impact of flow chemistry on the synthesis of these pivotal heterocycles, highlighting its advantages over the conventional batch methods. Although indazoles have a five-membered ring fused with a benzene ring, they will also be considered in this review due to their biological relevance. Full article

B30.2 domains, sometimes referred to as PRY/SPRY domains, were originally identified by sequence profiling methods at the gene level. The B30.2 domain comprises a concanavalin A-like fold consisting of two twisted seven-stranded anti-parallel β-sheets. B30.2 domains are present in about 150 human and 700 eukaryotic proteins, usually fused to other domains. The B30.2 domain represents a scaffold, which, through six variable loops, binds different unrelated peptides or endogenous low-molecular-weight compounds. At the cellular level, B30.2 proteins engage in supramolecular assemblies with important signaling functions. In humans, B30.2 domains are often found in E3-ligases, such as tripartite motif (Trim) proteins, SPRY domain-containing SOCS box proteins, Ran binding protein 9 and −10, Ret-finger protein-like, and Ring-finger proteins. The B30.2 protein recognizes the target and recruits the E2-conjugase by means of the fused domains, often involving specific adaptor proteins. Further well-studied B30.2 proteins are the methyltransferase adaptor protein Ash2L, some butyrophilins, and Ryanodine Receptors. Although the affinity of an isolated B30.2 domain to its ligand might be weak, it can increase strongly due to avidity effects upon recognition of oligomeric targets or in the context of macromolecular machines. Full article