In-Situ Synthesis and Characterization of Nanocomposites in the Si-Ti-N and Si-Ti-C Systems

The pyrolysis (1000 °C) of a liquid poly(vinylmethyl-co-methyl)silazane modified by tetrakis(dimethylamido)titanium in flowing ammonia, nitrogen and argon followed by the annealing (1000–1800 °C) of as-pyrolyzed ceramic powders have been investigated in detail. We first provide a comprehensive mechanistic study of the polymer-to-ceramic conversion based on TG experiments coupled with in-situ mass spectrometry and ex-situ solid-state NMR and FTIR spectroscopies of both the chemically modified polymer and the pyrolysis intermediates. The pyrolysis leads to X-ray amorphous materials with chemical bonding and ceramic yields controlled by the nature of the atmosphere. Then, the structural evolution of the amorphous network of ammonia-, nitrogen- and argon-treated ceramics has been studied above 1000 °C under nitrogen and argon by X-ray diffraction and electron microscopy. HRTEM images coupled with XRD confirm the formation of nanocomposites after annealing at 1400 °C. Their unique nanostructural feature appears to be the result of both the molecular origin of the materials and the nature of the atmosphere used during pyrolysis. Samples are composed of an amorphous Si-based ceramic matrix in which TiN_xC_y nanocrystals (x + y = 1) are homogeneously formed “in situ” in the matrix during the process and evolve toward fully crystallized compounds as TiN/Si₃N₄, TiN_xC_y (x + y = 1)/SiC and TiC/SiC nanocomposites after annealing to 1800 °C as a function of the atmosphere.     

A modified route to unsymmetrically substituted triphenylenes,new functionalised derivatives and twins,and the smallest reported triphenylene mesogen

ABSTRACT

We report the unexpected observation of columnar mesophase formation in a simple 2,7-dibromotetramethoxytriphenylene – by far the most lightly substituted discotic mesogen in this class. This derivative was prepared alongside the 3,6-dibromotriphenylene isomer to demonstrate an alternative, modified synthetic strategy that permits late-stage interchange of alkyl chain substituents. The new method is employed alongside the original route to deliver several new materials, including a conjugated ferrocene–triphenylene–ferrocene triad, a BODIPY–triphenylene–BODIPY triad and a new nematic twin linked through imine bridges.     

MXene-based composite electrodes for efficient electrochemical sensing of glucose by non-enzymatic method

A recently discovered 2D transition titanium metal carbides also called as MXenes (Ti₃C₂T_x)-based nanocomposite was prepared with Cu₂O through wet precipitation technique, and these materials were further developed as the electrode for sensing glucose by chronoamperometry technique. The prepared MXene-Cu₂O (Ti₃C₂T_x-Cu₂O) nanocomposite was characterized by XRD, FTIR, UV–Vis spectroscopy, FE-SEM, EDAX, and Raman spectroscopy. Morphological studies of the composites revealed that the micro-octahedral shape of Cu₂O is distributed on the surface of MXene with size larger than bare Cu₂O. Further, the prepared composite material was fabricated as a sensing probe, and the electrochemical activities were examined by cyclic voltammetric analysis (CV) and chronoamperometric (CA) methods. From the CV and CA investigation, the current response was higher for the composite than the bare material (Cu₂O & MXene) in the presence of glucose. The amperometric investigation of MXene-Cu₂O composite for the detection of glucose shows a broad linear range (0.01–30 mM) with a sensitivity of 11.061/μAmM cm^?2 and a detection limit of 2.83 μM. Further, the fabricated sensor exhibits good selectivity with interfering species like NaCl, fructose, sucrose, urea, ascorbic acid, lactose, short response time, stability, good reproducibility, and compatibility with human serum sample. From the investigation, the prepared MXene-Cu₂O composite is a good candidate for the direct detection of glucose molecules and is also well suitable for clinical diagnosis.     

Intermolecular cyclization of cinnamoyl isothiocyanate: A new synthetic entry for pyrimidine,triazine, and triazole candidates

An efficient and facile protocol for the synthesis of azine and azole ring systems was reported. Whereas, reaction of cinnamoyl isothiocyanate with N-nucleophile containing compounds (namely, p-aminophenol (2), N¹-phenylbenzene-1,4-diamine (5) and p-aminoacetophenone (8)) tolerated thiourea derivatives 3, 6, and 9, respectively. The later compounds underwent intramolecular cyclization upon treatment with EtONa to give pyrimidinethiones 4, 7, and 10, respectively, in moderate yield (74–79%). Compound 9 underwent intramolecular cyclization and condensation upon reaction with NaOH and benzaldehyde to give pyrimidinethione 12. Thiosemicarbazides 14 and 19 were obtained through reaction of heteroallen 1 with 2,4-dinitrophenylhydrazine 13 and hydrazone 18, respectively. Compound 14 was cyclized to pyrimidinethione 15 and triazine derivatives 17 through its reaction with EtONa at room temperature and refluxing temperature, respectively. Finally, base mediated and oxidative cyclization of thiourea derivative 19 with EtONa, Br₂/AcOH, and Pb(OAc)₂ afforded thiadiazole 20, benzothiazolotriazole 21, and triazolethione 22 derivatives, respectively.     

Pharmacoinformatics-based identification of transmembrane protease serine-2 inhibitors from Morus Alba as SARS-CoV-2 cell entry inhibitors

Molecular Diversity - Transmembrane protease serine-2 (TMPRSS2) is a cell-surface protein expressed by epithelial cells of specific tissues including those in the aerodigestive tract. It helps the...     

In quest of reversibility of Friedel-Crafts acyl rearrangements in the pyrene series

Friedel-Crafts acyl rearrangements in PPA of diacetylpyrenes (80–120 °C), dibenzoylpyrenes (80–200 °C), and bis(4-flurobenzoyl)pyrenes (80–120 °C) and Scholl reactions in AlCl₃/NaCl of dibenzoylpyrenes (140–200 °C) have been studied. The substrates were 1-AcPY, 2-AcPY, 1,3-Ac₂PY, 1,6-Ac₂PY, 1,8-Ac₂PY, 2,7-Ac₂PY, 1-BzPY, 1,6-Bz₂PY, 1,8-Bz₂PY, 1-4FBzPY, 1,6-4FBz₂PY, 1,8-4FBz₂PY. The mixtures of pyrene, 1-AcPY, 2-AcPY, 1,3-Ac₂PY, 1,6-Ac₂PY, 1,8-Ac₂PY, and 2,7-Ac₂PY were separated by HPLC. The following reversible intermolecular isomerizations were established: 1,6-Ac₂PY ? 1,8-Ac₂PY, 1,6-Bz₂PY ? 1,8-Bz₂PY, and 1,6-4'FBz₂PY ? 1,8-4'FBz₂PY, albeit not in high yields. The results substantiate Gore’s 1955 proposition that “The Friedel–Crafts acylation reaction of reactive aromatic hydrocarbons is a reversible process.” The isomerizations reported here differ from the few previously reported completely reversible intramolecular Friedel-Crafts acyl rearrangements. At ≥ 140 °C, in PPA and in AlCl₃/NaCl, 1,6-Bz₂PY and 1,8-Bz₂PY underwent a highly regioselective double Scholl reaction to give pyranthrone (3) and deacylations to 1-BzPy (and pyrene), followed by mono-Scholl reactions to give 8H-dibenzo[def,qr]chrysen-8-one (1), and 11H-indeno[2,1-a]pyren-11-one (2). The formation of 3 and not the expected tribenzo[a,ghi,o]perylene-7,16-dione (4) from 1,8-Bz₂PY indicates that 1,8-Bz₂PY has first undergone isomerization to 1,6-Bz₂PY. The present study confirms the linkage between Friedel-Crafts acyl rearrangements and the Scholl reaction.

     

Response of multiwall carbon nanotubes to impact loading

Dynamic behaviors of multiwall carbon nanotubes (MWCNTs) with finite length are investigated using an analytical method. Multiple elastic shells and linearized model of van der Waals forces are used for development a comprehensive continuum dynamic model of MWCNTs. By applying Laplace transform, analytical solution for thin and thick MWCNTs under dynamic loading are obtained. Dynamic responses of 3-, 9-, and 11-layer MWCNTs under external pressure shock are examined and accuracy of results are verified by comparison the results with those obtained by numerical methods. Both displacement and stress analysis are performed for layers of MWCNTs and frequencies of oscillations are obtained. Also, effects of axial wave created by external pressure shock are studied in MWCNTs with two-dimensional analyses. Dynamic responses of MWCNTs with initial axial displacement are also proposed and the propagation of the axial wave through the length of tubes is illustrated. Furthermore, wave propagation velocity is found by analysis of time history diagram.     

Numerical investigation of drag and heat reduction in hypersonic spiked blunt bodies

In this investigation, the effects of spike as retractable drag and aerodynamic heating reduction into the reentry Earth’s atmosphere for hemispherical body flying at hypersonic flow have been numerically studied. This numerical solution has been carried out for different length, shapes and nose configuration of spike. Additional modifications to the tip of the spike are investigated in order to obtain different bow shocks, including no spike, conical, flat and hemispherical aerodisk mounted. Unsteady compressible 3-D Navier–Stokes equations are solved with k ? ω (SST) turbulence model for a flow over a forward facing spike attached to a heat shield for a free stream Mach number of 6. The obtained numerical results are compared with the experimental ones, and the results shows acceptable verification. This analysis shows that the aerodisk is more effective than aerospike. The designs produced 60 and 15 % reduction in drag and wall temperature responses, respectively.     

First-principles study of metal-semiconductor contact between MX2 (M = Nb,Pt; X = S,Se) monolayers

First principles calculations are performed to investigate the structural and electronic properties of MX₂ (M = Nb, Pt; X = S, Se) monolayers and their van der Waals (vdW) heterostructures. The dynamical stability of monolayers and vdW heterostructures is confirmed by binding energy and phonon spectra. An indirect band gap nature is found for PtS₂ and PtSe₂ monolayers while NbS₂, NbSe₂ and all vdW heterostructures are metals. The intrinsic electronic properties of both NbX₂ and PtX₂ are well preserved due to weak vdW contact. It is demonstrated that a p-type Schottky contact with a small barrier height is formed at NbX₂-PtX₂ interface. The zero tunnel barrier and higher potential drop across the interface in these contacts imply large transfer of charge carriers across the interface, making them potential candidates in nanoelectronic device applications.