Tetrapyrrole bizirconium complexes as active catalysts for ethylene polymerization

Ethylene polymerization was carried out by using a group of new dizirconium(IV) tetrapyrrole complexes as catalysts and MAO as co-catalyst under 1 atmosphere pressure of ethylene gas at 25 and 40°C. The highest value of catalyst activity was obtained at 40°C by using bizirconium complexes including one calix[4]pyrrole between two zirconium centers and two terminal chlorines, while zirconium(IV) complexes with coordinated THF, almost have not catalytic activity. The maximum catalytic activity mounted to 830 kg/mol·bar·h by Zr₂(Cy₄ Pyr ₄)Cl₄. The results show that the structure of the coordination sphere of zirconium(IV) has great influence on the rate of polymerization, molar masses of forming polymer, and its molecular mass distribution.     

Charged lepton production from iron induced by atmospheric neutrinos

The charged current lepton production induced by neutrinos in ⁵⁶Fe nuclei has been studied. The calculations have been done for the quasielastic as well as the inelastic reactions assuming Δ-dominance and take into account the effect of Pauli blocking, Fermi motion and the renormalization of weak transition strengths in the nuclear medium. The quasielastic production cross-sections for lepton production are found to be strongly reduced due to nuclear effects, while there is about 10% reduction in the inelastic cross-sections in the absence of the final-state interactions of the pions. The numerical results for the momentum and angular distributions of the leptons averaged over the various atmospheric-neutrino spectra at the Soudan and Gran Sasso sites have been presented. The effect of nuclear-model dependence and the atmospheric-flux dependence on the relative yield of μ to e has been studied and discussed.     

Exploring the interaction between “site-markers,aspirin and esterase-like activity” ternary systems on the human serum albumin: direct evidence for modulation of catalytic activity of the protein in different inhibition modes

Albumin which is the most abundant drug carrier protein in plasma controls the distribution aspect of drug pharmacokinetics. The aim of this study has been to elucidate the concurrent binding behavior of indomethacin/ibuprofen/heme to HSA under the effect of aspirin-mediated protein acetylation and also to explore the esterase-like catalytic property of the unmodified/modified proteins, as binary or ternary systems, by using various spectroscopic and molecular docking techniques. We found that aspirin-based modification of HSA affects the protein conformation as well as ligand binding at sites I–III. Decrease in pNPA-mediated esterase activity of HSA in different reversible inhibition modes, upon the protein–ligand interactions, was also documented, an issue that may receive considerable attention for computational prodrug design in near future.     

Investigation of thermal,mechanical, and electrical properties of novel polyurethanes/high molecular weight polybenzoxazine blends

In order to prepare tough polyurethane (PU) electrical insulator with improved thermal stability and electrical insulating properties, high molecular weight polybenzoxazine precursor was mixed and co‐cured with crosslinkable urethane prepolymers. Polybenzoxazine precursor (Bmda) was synthesized from reaction of bisphenol‐A, methylenedianiline, and paraformaldehyde. Epoxy‐terminated polyurethanes (EPU1‐4) were prepared by the reaction of glycidol with NCO‐terminated urethane oligomers. The oligomers were prepared from different molecular weight versions of polycaprolactone polyol (CAPA) and hexamethylene diisocyanate. Blends were prepared through thermal treatment of equal weights of two precursors dissolved in chloroform. Optimum curing condition was determined by DSC and DMTA analysis and measurement of the gel content for cured samples. Viscoelastic, thermal, mechanical, and electrical properties of cured samples were investigated and structure–property relationship was established. Copyright © 2008 John Wiley & Sons, Ltd.     

Design and synthesis of novel thiourea metal complexes with controllable antibacterial properties

A new bidentate O,S donor thiourea ligand (L¹), namely N‐(2‐hydroxyethyl)‐N′‐2‐chlorobenzoylthiourea, and its oxazolidine derivative (L²) were synthesized. Derivative L² was used for the preparation of Ni(L²)₂ and Cu(L²)₂ complexes. The compounds were investigated using X‐ray crystallography and Fourier transform infrared, ¹H NMR and UV–visible spectroscopies. Single‐crystal X‐ray analysis showed strong hydrogen bonding interactions between carbonyl oxygen and N(10) ─ H in the L¹ ligand. In addition, the antibacterial activities of these compounds were evaluated against Gram‐positive and Gram‐negative bacteria, measured using the colony count method. The Cu(L²)₂ complex exhibited a significant antibacterial activity while the activity of the other compounds was much lower. Finally, the relationship between the structure and antibacterial properties of these compounds was investigated using highest occupied and lowest unoccupied molecular orbital energies calculated by density functional theory method based on the 6‐31G*/LANL2DZ basis set.     

Zinc chloride catalyzed three-component Ugi reaction: synthesis of N-cyclohexyl-2-(2-hydroxyphenylamino)acetamide derivatives

The ability of zinc chloride as a catalyst to promote the three-component Ugi reaction of 2-aminophenols, aliphatic or aromatic aldehydes, and cyclohexyl isocyanide in methanol at room temperature is described. The N-cyclohexyl-2-(2-hydroxyphenylamino) amide products are obtained in high yields. When N,N-dimethylformamide dimethyl acetal and triethyl orthoformate, as two new components of the three-component Ugi reaction are used instead of the aldehyde the reaction gives N-cyclohexyl-2-(dimethylamino)-2-(2-hydroxyphenylamino)acetamide and N-cyclohexyl-2-(2-hydroxyphenylamino)-2-ethoxyacetamide derivatives, respectively.     

High‐Performance Platinum‐Free Dye‐Sensitized Solar Cells with Molybdenum Disulfide Films as Counter Electrodes

By using a radio‐frequency sputtering method, we synthesized large‐area, uniform, and transparent molybdenum disulfide film electrodes (1, 3, 5, and 7 min) on transparent and conducting fluorine‐doped tin oxide (FTO), as ecofriendly, cost‐effective counter electrodes (CE) for dye‐sensitized solar cells (DSSCs). These CEs were used in place of the routinely used expensive platinum CEs for the catalytic reduction of a triiodide electrolyte. The structure and morphology of the MoS₂ was analyzed by using Raman spectroscopy, X‐ray diffraction, and X‐ray photoemission spectroscopy measurements and the DSSC characteristics were investigated. An unbroken film of MoS₂ was identified on the FTO crystallites from field‐emission scanning electron microscopy. Cyclic voltammetry, electrochemical impedance spectroscopy, and Tafel curve measurements reveal the promise of MoS₂ as a CE with a low charge‐transfer resistance, high electrocatalytic activity, and fast reaction kinetics for the reduction of triiodide to iodide. Finally, an optimized transparent MoS₂ CE, obtained after 5 min synthesis time, showed a high power‐conversion efficiency of 6.0 %, which comparable to the performance obtained with a Pt CE (6.6 %) when used in TiO₂‐based DSCCs, thus signifying the importance of sputtering time on DSSC performance.     

Impact of Surface Defects on LaNiO3 Perovskite Electrocatalysts for the Oxygen Evolution Reaction

Perovskite oxides are regarded as promising electrocatalysts for water splitting due to their cost-effectiveness, high efficiency and durability in the oxygen evolution reaction (OER). Despite these advantages, a fundamental understanding of how critical structural parameters of perovskite electrocatalysts influence their activity and stability is lacking. Here, we investigate the impact of structural defects on OER performance for representative LaNiO₃ perovskite electrocatalysts. Hydrogen reduction of 700 °C calcined LaNiO₃ induces a high density of surface oxygen vacancies, and confers significantly enhanced OER activity and stability compared to unreduced LaNiO₃; the former exhibit a low onset overpotential of 380 mV at 10 mA cm⁻² and a small Tafel slope of 70.8 mV dec⁻¹. Oxygen vacancy formation is accompanied by mixed Ni²⁺/Ni³⁺ valence states, which quantum-chemical DFT calculations reveal modify the perovskite electronic structure. Further, it reveals that the formation of oxygen vacancies is thermodynamically more favourable on the surface than in the bulk; it increases the electronic conductivity of reduced LaNiO₃ in accordance with the enhanced OER activity that is observed.     

Stability and Catalytic Performance of Single-Atom Supported on Ti2CO2 for Low-Temperature CO Oxidation: A First-Principles Study

Based on first-principles calculations, the potential of Ti₂CO₂ monolayer (MXene) as a single-atom catalyst (SAC) support for 3d transition metal (TM) atoms (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn) is studied for CO oxidation. We first screen the support effect according to the stability of a single metal atom and find that Sc and Ti supported on Ti₂CO₂ have stronger adsorption energy than the cohesive energy of their bulk counterparts and therefore, we selected Sc and Ti supported on Ti₂CO₂ for further catalytic reactions. The stability and the potential catalytic reactivity are verified by electronic structure and charge transfer analysis. Both Eley–Rideal (ER) and Langmuir–Hinshelwood (LH) mechanisms are considered in this study, and lower energy barriers of 0.002 and 0.37 eV were found in the ER mechanism compared to the LH mechanism, which are 0.25 and 0.34 eV for Sc and Ti catalysts, respectively. Moreover, kinetic ER and LH mechanisms are favorable for both Sc- and Ti/Ti₂CO₂ because of the comparable energy barrier to other metals and SAC supported on 2D materials. However, Ti/Ti₂CO₂ catalyst is thermodynamically unfavorable. Based on these calculations, we propose that Sc supported on Ti₂CO₂ is the best catalyst for CO-oxidation. The current study not only broadens the scope of the single-atom Sc catalyst but also extends the consideration of MXene support for catalyst optimization.     

Thermal performance of micro-polymers containing nano-solid structures during transport phenomenon

Journal of Thermal Analysis and Calorimetry - The inclusion of solid nano-structures in the liquid changes its rheology and hence its thermal performance. This article considers the impact of...