Influence of copper substitution on the interaction of ethylene over iron clusters: a theoretical study

We report the results of density functional theory (DFT) calculations of ethylene adsorption over the most stable pure and bimetallic clusters of Fe(n)Cu(m) (2 ≤ m+n ≤ 4), in two adsorption modes of π and di-σ. Our results show that the quality of interaction of ethylene with iron center in bimetallic clusters of iron-copper is characteristically different from what is found over pure iron. Over the range of our studies for dimers, trimers, and tetramers, whether for π or di-σ mode, alloying iron clusters results in a substantial improvement in adsorption of ethylene over cluster and exhibits a notable increase in binding and interaction energies compared with pure iron clusters. One of the interesting features of this adsorption is that ethylene never orients toward di-σ mode for Cu-Cu or Fe-Cu bonds, and π orientation is strongly preferred. Ethylene adsorption in di-σ coordination is accompanied by the sever restructuring, larger deformation energy, and the larger interaction energy. In the next part, we answer this question of how electronic perturbations induced by copper atoms can enhance the activity of iron toward ethylene. This interpretation is done within the framework of natural bond orbital (NBO) and natural resonance theory (NRT) analyses. Different reaction pathways detected by NRT analysis (donor-acceptor, metallacyclic, and carbanion) reveal interesting aspects of differences between the nature of metal-alkene coordination in bimetallic and purely metallic clusters.     

Synthesis and characterization of lead oxide nano-powders by sol–gel method

Our goal in this research was to obtain lead oxide nano-powders by sol–gel method. In this method, lead oxide nano-powders were synthesized through the reaction of citric acid (C₆H₇O₈·H₂O) solution and lead acetate [Pb(C₂H₃O₂)₂] solution as stabilizer and precursor, respectively. The effect of different parameters including calcination temperature, (molar ratio of citric acid to lead acetate) and drying conditions were investigated. The prepared lead oxide nano-powders were characterized by FT-IR spectroscopy, X-ray diffraction, thermogravimetric analysis and scanning electron microscopy. The prepared PbO samples consist of the particles in the range of 50–120 nm or the thick plate like structures with thickness of 53 nm depending on the drying conditions.     

Dual thermo- and pH-sensitive poly(2-hydroxyethyl methacrylate-co-acrylic acid)-grafted graphene oxide

A two-step modification was used to attach atom transfer radical polymerization (ATRP) initiator onto graphene oxide surface. ATRP polymerization of 2-hydroxyethyl methacrylate (HEMA) was performed via “grafting from” approach. Due to uncontrolled ATRP of acrylic acid (AA), the Br-terminated P(HEMA) chains were converted to reversible addition–fragmentation chain transfer agent and polymerization of AA was done. The structure of modified nanosheets was characterized using X-ray diffraction analysis, Raman spectroscopy, proton nuclear magnetic resonance, scanning electron microscopy, and etc. These nanosheets showed dual pH- and thermo-sensitive properties as measured by UV–visible spectroscopy in different pH (2–13) and temperature (15–55 °C) values. Generally, UV absorbance of P(HEMA-co-AA)-grafted nanosheets was higher than P(HEMA)-grafted nanosheets. Also, it seems that the poly(acrylic acid) block induces more pH sensitivity behavior than P(HEMA) block. Lower critical solution temperature of polymer-grafted nanosheets were shifted to higher temperature when chain extension was performed.     

Passive walking biped robot model with flexible viscoelastic legs

Nonlinear Dynamics - To simulate the complex human walking motion accurately, a suitable biped model has to be proposed that can significantly translate the compliance of biological structures. In...     

N-Sulfonic acid poly(4-vinylpyridinium) chloride as a highly effcient and reusable catalyst for the Biginelli reaction简

A mild, simple and efficient procedure for the preparation of 3,4-dihydropyrimidin-2（1H）-ones and -thiones is described using N-sulfonic acid poly（4-vinylpyridinium） chloride （NSPVPC） as a heterogeneous and efficient catalyst under solvent-free conditions. Simple methodologies, easy work-up procedure, easy preparation of the catalyst, excellent yields and very short reaction times are among the other advantages of this work. Further, the catalyst can be reused and recovered for several times without significant decrease in its activity.     

Vanadium Hydrogen Sulfate (I): Chemoselective Trimethylsilylation of Alcohols and Deprotection of Trimethylsilyl Ethers

Trimethylsilylation of alcohols with hexamethyldisilazane (HMDS) catalyzed by V(HSO₄)₃ under mild and completely heterogeneous reaction condition is reported. The method is highly chemoselective for the protection of alcohols in the presence of phenols, amines and thiols. Also, the deprotection of trimethylsilyl ethers is performed in the presence of V(HSO₄)₃ at room temperature in good to high yields.     

Polycarbonate-coated magnetic nanoparticles for the extraction of imipramine and its primary metabolite from urine

This study introduces a reliable and inexpensive magnetic dispersive solid phase extraction to extract imipramine and its primary metabolite (desipramine) from urine samples. To accomplish this aim, Fe₃O₄ magnetic nanoparticles were synthesized by sonication, subsequently, polycarbonate was precipitated gradually onto the surface of them to form the adsorbent. Extraction recoveries of 85% and 76%, enrichment factors of 57 and 51, limits of detection of 2.5 and 2.8 μg/L, and limits of quantification of 8.3 and 9.3 μg/L were obtained for imipramine and desipramine under the optimal conditions, respectively. In addition, relative standard deviations for intra- (n = 6) and inter-day (n = 5) precisions at two concentrations (50 and 100 μg/L of each analyte) were less than or equal to 4%. Short extraction time, good repeatability, high enrichment factors, and simplicity are the main advantages of the proposed method.     

An investigation into the role of polarity of diamines in controlling the electron migration mechanism of photoluminescent poly(amide–imide)s

Several diamines with remarkable different polarities were used to produce photoactive poly(amide–imide)s (PAI)s in a quantitative yield. The absorption, fluorescence and photophysical properties of series of poly(amide–imide)s containing fused aromatic systems as energy donor and energy acceptor with different diamines cores are described. Poly(amide–imide)s exhibit broad fluorescent characteristic, and its fluorescent intensity is related to the intermolecular chain–chain or chain–solvent interaction. The fluorescence spectra confirmed an efficient singlet–singlet energy transfer between fused aromatic systems. The self-quenching mechanism was studied according to the specific behavior of these polymers in different solvents. The self-quenching rate constant for the association reaction in the excited state (Kq) could be measured from the Stern–Volmer equation. The kind of fused system and diamines show different electron migration mechanisms and photoluminescent properties in the singlet-excited states. By using the exothermic energy transfer as a function of diamine polarity, the electron transfer mechanism was evaluated for aromatic poly(amide–imide)s. In principle, the fluorescence energy is absorbed by different (PAI)s and raises the molecules to one of its excited states. Afterwards this excitation energy transfers through the different relaxation channels, i.e. columbic or exchange energy transfer.