Search Results (73)

In this work, the metal salts were introduced into the resin-solvent gel system to leverage their ortho-substitution effect, thereby accelerating the polymerization-induced phase separation process. Subsequent in-situ carbonization resulted in the preparation of porous carbon materials with three-dimensional interconnected pores. By precisely tuning the parameters of the resin-solvent-metal ion system, control over the pore structure of the porous carbon was achieved, with a porosity range of 16.5% to 66.5% and a pore diameter range of 8 to 248 nm. The addition of metallic salts can simply and effectively increase the pore structure after carbonization, making the infiltration of molten silicon easier. This is beneficial to the joining process of silicon carbide ceramics. Based on these findings, a high-reliability joining technique for large-sized (135 mm × 205 mm) silicon carbide ceramics was developed. The resulting interlayer was dense and defect-free, exhibiting a joining strength of 309 ± 33 MPa and a Weibull modulus of 10.67. These results highlight the critical role of structured porous media in advancing the field of large-sized ceramic joining. Full article

The rearrangement of a total of 56 members of 22 series of orthogonally protected N-alkyl arylsulphonamides of general structure 4-XC₆H₄SO₂NR¹CO₂R² [X = H, CH₃, F, Cl, Br, CH₃O, CN, CF₃ or C(CH₃)₃; R¹ = CH₃, CH₂CH₃, CH₂CH₂CH₃, CH(CH₃)₂ or CH₂CH(CH₃)₂; R² = CH₃, C₂H₅ or C(CH₃)₃] when treated with lithium di-isopropylamide in tetrahydrofuran at −78 °C has been studied. The competition between directed ortho metalated rearrangement, to form 4-X-2-(R²O₂C)C₆H₃SO₂NHR¹ and the production of a substituted saccharin, is strongly influenced by the size of R¹ and R², especially in the series with X = CH₃. When R¹ = CH₃ or to a lesser degree, C₂H₅, formation of the saccharin competes to a significant extent, especially when the migrating group is CO₂CH₃ or CO₂C₂H₅. In contrast, when R¹ is a larger alkyl group, particularly if it is branched at either the α- or β-carbon atom [CH(CH₃)₂ or CH₂CH(CH₃)₂], the increased steric hindrance essentially prevents cyclisation, thus facilitating rearrangement to 4-X-2-(R²O₂C)C₆H₃SO₂NHR¹ in high yield. The size of the migrating CO₂R² group also exerts an effect on the competition between the reactions: when R² = C(CH₃)₃, clean rearrangement is possible even when R¹ = CH₃ in each series of X. These results have implications for further elaboration and rearrangement of 4-X-2-(R²O₂C)C₆H₃SO₂NHR¹ in order to prepare substituted saccharins containing a 6-CO₂R³ group. Full article

Azulene-based polycyclic hydrocarbons have garnered much attention as potential materials for organic optoelectronic devices and as molecular models for graphene nanosheets with structural defects. Although various methods for ring fusions to an azulene core have been established for ring fusions to an azulene core, efficient synthetic methodologies for ortho- and peri-fusion to an azulene core are still lacking, which hinders the investigation of the effect of the ortho- and peri-fusion on the electronic properties of the embedded azulene core. Herein, we describe the synthesis and characterization of quinoxaline-fused cyclopenta[cd]azulene 4 as a new ortho- and peri-fused azulene derivative. The target molecule 4 was successfully synthesized in four steps from 4-methylazulene. The ring annulation decreased the lowest excitation energy compared with that of azulene and its structural isomer 5 and led to multiple reversible reduction processes. Characterization of the molecular geometry and optoelectronic properties of 4 revealed that the embedded azulene core preserves its original aromaticity, while the fused quinoxaline acts as a nucleophilic and basic site. These features suggest that 4 could serve as a metal ligand, a near-infrared absorber, and a component in organic functional devices. Full article

Background/Objectives: Perilla frutescens has historically been used to protect against inflammation and redox stress. This has been partly attributed to its high polyphenolic content; however, polyphenolic components in Perilla extract remain incompletely defined. This study aimed to characterise the polyphenolic composition in Perilla extract and evaluate its effect on the transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2), regulating antioxidant defenses during inflammation and oxidative stress. Methods: Hot water extraction from Perilla leaves was followed by fractionation using four solvents of different polarity, namely methanol, butanol, ethyl acetate and ether. The polyphenolic composition of these fractions was analysed using RP-HPLC, and some of these compounds were quantified. The total phenolic, flavonoid, and ortho-diphenolic contents of each Perilla fraction were determined. The antioxidant activity was assessed using metal cation reduction and radical scavenging assays. A dual-luciferase assay using a human NQO1 ARE-luciferase reporter plasmid was employed to quantify Nrf2 activation by the Perilla fractions. Results: HPLC analysis identified 35 polyphenolic compounds, with the highest phenolic content present in the polar fractions and rosmarinic acid being the major constituent. Radical scavenging tests (DPPH and ABTS) confirmed the highest antioxidant capacity in the polar fractions. On cells in vitro, the methanol Perilla fraction displayed the strongest antioxidant activity, showing up to a 1.5-fold increase in human NQO1 ARE-luciferase reporter induction. Conclusions: This study has shown that Perilla extract contains a diversity of polyphenolic compounds contributing to its potent antioxidant effects, with methanol and butanol being the most efficient extraction solvents. While rosmarinic acid is expected to be the major contributor towards providing protection against inflammation and redox stress, further work is required on the synergystic effects between different polyphenols. Full article

The coordination modes of several ortho-substituted benzoates towards the copper(II) centre are investigated. The coordination environment of the metal ion includes nitrogen atoms from 2,2′-bipyridine (bipy) or 1,10-phenanthroline (phen) and occasionally oxygen atoms from coordinated water, ethanol molecules, or nitrate ions. The compounds are investigated by a variety of spectroscopic methods and by single-crystal X-ray diffraction. Although the reaction scheme involved equimolar amounts of the reactants, cationic dinuclear compounds with a metal/benzoate/diimine ratio of 2:3:2 have been realized, cationic in nature regardless of the counter anion used. Furthermore, the carboxylate moieties display a range of twisting relative to the orientation of the benzene ring to which they are attached. Full article

This work aims to amplify the fluorescence of (Z)-4-hetarylidene-5(4H)-oxazolones 1 by suppression of the hula-twist non-radiative deactivation pathway by C^N-orthopalladation of the 4-hetarylidene ring. Different (Z)-4-hetarylidene-2-phenyl-5(4H)-oxazolones, 1a–1c, prepared by the Erlenmeyer–Plöchl method, have been studied. The orthopalladation of (Z)-2-phenyl-4-(5-thiazolylmethylene)-5(4H)-oxazolone (1a) takes place by C-H bond activation of the H4 of the heterocycle and C^N-chelation, giving the dinuclear trifluoroacetate derivative 2a. By further metathesis of bridging ligands in 2a, complexes containing the orthometalated oxazolone and a variety of ligands 3a–5a, were prepared. The study of the photophysical properties of 1a–5a shows that the bonding of the Pd metal to the 4-hetaryliden-5(4H)-oxazolone does not promote, in these cases, an increase in fluorescence. Interestingly, the orthopalladation of (Z)-2-phenyl-4-(4-thiazolylmethylene)-5(4H)-oxazolone (1b) gives orthopalladated 2b, where the incorporation of the Pd to the oxazolone takes place by C-H bond activation of the ortho-H2 of the 2-phenyl group, ring opening of the oxazolone heterocycle and simultaneous N,N-bonding of the N atoms of the thiazole ring and the generated benzamide fragment. This N^N^C-tridentate dianionic bonding mode is obtained for the first time in oxazolones. Despite a similar lock of the hula-twist deactivation, 2b does not show fluorescence. Full article

Upon exposure to irradiation, trans-cinnamic acid can dimerize, producing truxinic and truxillic acids, regioisomers distinguished by the relative arrangement of acid and phenyl groups on the formed cyclobutane ring. Solid-state dimerization, governed by Schmidt’s specified conditions, hinges on the initial molecular setup. This study endeavors to manipulate the reaction’s outcome in the solid state. To achieve this, the target molecule was paired with metals (Ag, Cu) to modify molecular orientation in the solid. Investigated derivatives included para-hydroxy-trans-cinnamic acid, ortho-methoxy-trans-cinnamic acid, ortho-ethoxy-trans-cinnamic acid, and ortho-chloro-trans-cinnamic acid. Despite easy synthesis of all complexes, only the complex between Ag and ortho-chloro-trans-cinnamic acid exhibits photoreactivity, mirroring the outcome of the metal-free derivative. Thus, while this approach has the potential to alter the photobehavior of cinnamic acid derivatives, obtaining the desired structure will require extensive screening to identify an appropriate metal complex. Full article

(1) Background: The most important part of an orthodontic attachment (bracket or tube) is the tube or slot for the insertion of the orthodontic wire. Aligning teeth along the archwire according to angular values preadjusted in the bracket slots (or tubes) requires a very precise size accordance between the archwires and slots. The aim of this study was to perform a nanotomographic analysis of the geometric features of molar tubes for direct bonding in terms of their dimensions and angles of their inner walls and analyze the presence of metallurgic imperfections. (2) Methods: Orthodontic tubes (n = 100) for upper right first molars from five different manufacturers (3M-Victory Series, Adenta-Bond Sing, Dentaurum-Ortho Cast M, GC-L LP, and ORMCO-Accent), 20 tubes each, were subjected to nanotomographic analysis. Measurements of the inner channel of the tubes, angles between the walls, and analysis of metallurgic imperfections were performed using high-resolution computed tomography. (3) Results: height measurements differed by 4–14% from ideal values declared by manufacturers, whereas the angles ranged from reducing by a maximum 1% comparing to values declared (hypodivergent walls) to increasing by a maximum 4.5% (divergent walls). (4) Conclusions: 1. The sizes of channels measured were slightly larger than those declared by manufacturers. 2. Slight deviations in wall parallelism and angles between the walls were found. 3. Some tubes were characterized by manufacturing defects of the metal. 4. Efforts should be made to further improve the production process of orthodontic attachments. Full article

C-H borylation is a powerful strategy for the construction of C-B bonds due to the synthetic versatility of C-B bonds. Various transition metals affect the powerful functionalization of C-H bonds, of which Ir is the most common. Substrate-directed methods have enabled directed Ir-catalyzed C-H borylation at the ortho position. Amongst the powerful directing groups in Ir-catalyzed C-H borylation are N-containing carbocyclic systems. This review covers substrate-directed Ir-catalyzed ortho-C-H borylation of aromatic C(sp2)-H bonds in N-containing carbocyclic compounds, such as anilines, amides, benzyl amines, hydrazones, and triazines. Full article

Piezoelectric micromachined ultrasound transducers (PMUTs) have gained significant popularity in the field of ultrasound ranging and medical imaging owing to their small size, low power consumption, and affordability. The scar-free “MIS” (micro-hole inter-etch and sealing) process, a novel bulk-silicon manufacturing technique, has been successfully developed for the fabrication of pressure sensors, flow sensors, and accelerometers. In this study, we utilize the MIS process to fabricate cavity diaphragm structures for PMUTs, resulting in the formation of a flat cavity diaphragm structure through anisotropic etching of (111) wafers in a 70 °C tetramethylammonium hydroxide (TMAH) solution. This study investigates the corrosion characteristics of the MIS technology on (111) silicon wafers, arranges micro-pores etched on bulk silicon around the desired cavity structure in a regular pattern, and takes into consideration the distance compensation for lateral corrosion, resulting in a fully connected cavity structure closely approximating an ortho-hexagonal shape. By utilizing a sputtering process to deposit metallic molybdenum as upper and lower electrodes, as well as piezoelectric materials above the cavity structure, we have successfully fabricated aluminum nitride (AlN) piezoelectric ultrasonic transducer arrays of various sizes and structures. The final hexagonal PMUT cells of various sizes that were fabricated achieved a maximum quality factor (Q) of 251 and a displacement sensitivity of 18.49 nm/V across a range of resonant frequencies from 6.28 MHz to 11.99 MHz. This fabrication design facilitates the achievement of IC-compatible and cost-effective mass production of PMUT array devices with high resonance frequencies. Full article

Current research on synthetic and naturally occurring phenolic compounds is centered around their prominent antioxidant properties. Since reactive oxygen (ROS) and nitrogen (RNS) species cause considerable damage to cellular components upon their overproduction, associated with the pathogenesis of degenerative, cardiovascular and oncological diseases, antioxidants may reduce the risk of developing such conditions. Because hydroxyl, amino and sulfhydryl groups present in their structure, antioxidants may function as hydrogen atom and electron donors, as well as metal-reducing and metal-chelating agents. We synthesized phenolic Schiff bases from 4,6-di-tert-butyl-2,3-dihydroxybenzaldehyde; ortho-, meta- and para-mercaptoanilines; and 2,2′- and 4,4′-disulfanediyldianilines. Their antioxidant properties were studied in a 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical-scavenging assay. Full article

The oxygenation of cells and tissues and acidification of the cellular endolysosomal system are among the major factors that ensure normal functioning of an organism and are violated in various pathologies. Recording of these parameters and their changes under various conditions is an important task for both basic research and clinical applications. In the present work, we utilized internalizable dual pH/O₂ lifetime sensor (Ir-HSA-FITC) based on the covalent conjugation of human serum albumin (HSA) with fluorescein isothiocyanate (FITC) as pH sensor and an orthometalated iridium complex as O₂ sensor. The probe was tested for simultaneous detection of acidification level and oxygen concentration in endolysosomes of endometrial mesenchymal stem/stromal cells (enMSCs) cultivated as 2D monolayers and 3D spheroids. Using a combined FLIM/PLIM approach, we found that due to high autofluorescence of enMSCs FITC lifetime signal in control cells was insufficient to estimate pH changes. However, using flow cytometry and confocal microscopy, we managed to detect the FITC signal response to inhibition of endolysosomal acidification by Bafilomycin A1. The iridium chromophore phosphorescence was detected reliably by all methods used. It was demonstrated that the sensor, accumulated in endolysosomes for 24 h, disappeared from proliferating 2D enMSCs by 72 h, but can still be recorded in non-proliferating spheroids. PLIM showed high sensitivity and responsiveness of iridium chromophore phosphorescence to experimental hypoxia both in 2D and 3D cultures. In spheroids, the phosphorescence signal was detected at a depth of up to 60 μm using PLIM and showed a gradient in the intracellular O₂ level towards their center. Full article

In this paper, a review on Pd(II), Pd(III), and Pd(IV) cyclometallated compounds with 2-arylpyridines (2-phenylpyridine, 2-benzylpyridine, 2-benzoylpyridine, 2-phenoxypyridine, 2-phenylsulfanylpyridine, 2-anilinopyridine, 2-(naphth-1-yl)pyridine, 2-(naphth-2-yl)pyridine, and their derivatives) and their analogues (2-phenylquinoline and 7,8-benzoquinoline) with 174 references is presented. A total of 672 species, containing κ²-N(1),C(6′)*-palladium (Pd(II), Pd(III), Pd(IV)) or analogous moiety (i.e., chelated by nitrogen of the pyridine-like ring and the deprotonated ortho-carbon of the phenyl-like ring) and thus possessing a character intermediate between metal complexes and organometallics, studied in the years 1980–2023 by NMR spectroscopy and/or single crystal X-ray diffraction (202 X-ray structures, for 186 species), are described. The biological or catalytic activity and luminescence properties of these species, as well as their possible applications as advanced materials were studied and are also quoted. Full article

The association of the V-prep and a resin-modified glass ionomer cement (RMGIC) has shown to be a suitable alternative for the orthodontic bracket bonding procedure in vitro. The aim of this study was to evaluate over eighteen months the clinical bonding failure and survival rates of the conventional bonding technique using the Transbond XT (3M Unitek, Monrovia, CA, USA) and the RMGIC Fuji Ortho LC (GC Corporation, Tokyo, Japan) prepared with the V-prep. Therefore, one operator using the straight-wire technique bonded two hundred metallic brackets to upper and lower premolars of twenty-five patients requiring an orthodontic treatment. The randomized trial was a single-blind design in a split-mouth comparison. Each patient was randomly allocated one of the two bonding systems for each premolar on each side of the mouth. The bonding and rebonding techniques were standardized throughout the trial and bond failure was recorded each month for a period of eighteen months. The survival rates of the brackets were estimated by Kaplan–Meier and log-rank test (p < 0.05). A total of 200 orthodontic brackets were included in the study with a significant lower failure rate of 9.0% for the V-prep and RMGIC compared to 25.0% for the conventional bonding technique (p < 0.05). A higher survival rate was observed for the V-prep and RMGIC (16.36 months) over the conventional bonding technique (13.95 months) (p < 0.05). Lower premolar bonding failure was higher than upper premolar for both bonding techniques. The V-prep followed by RMGIC, with enamel surface protection abilities, can be used as an alternative bonding technique in an orthodontic treatment. Full article

The formation mechanisms of pyrochlore-type Bi₂Co_1/2Cr_1/2Nb₂O_9+Δ (space group Fd-3m, a = 10.4838(8) Å), in the temperature range from 400 to 1050 °C were studied by employing X-ray diffraction, scanning electron microscopy and energy-dispersive spectroscopy. An extensive reaction between the binary metal oxides was found to begin at temperatures above 550 °C, following the transition of monoclinic α-Bi₂O₃ into a tetragonal β-Bi₂O₃ polymorph. The synthesis process occurs in several stages when Bi-rich intermediate products (Bi₆CrO₁₂, Bi₆Cr₂O₁₅, and Bi₅Nb₃O₁₅) transform into bismuth-depleted BiNbO₄ and a chromium–cobalt spinel is formed. The formation of a single pyrochlore phase occurs at the final reaction stage at 1050 °C via the doping of bismuth ortho-niobate, BiNbO₄, by the transition metal cations. The observed mechanism is essentially similar to the mechanism of tantalate-based phases except for the formation of Bi₅Nb₃O₁₅ at the intermediate reaction stages. Full article