Computational study of cyclohexanone-monomer co-initiation mechanism in thermal homo-polymerization of methyl acrylate and methyl methacrylate

This paper presents a systematic computational study of the mechanism of cyclohexanone-monomer co-initiation in high-temperature homopolymerization of methyl acrylate (MA) and methyl methacrylate (MMA). Previous experimental studies of spontaneous thermal homopolymerization of MA and MMA showed higher monomer conversion in the presence of cyclohexanone than xylene. However, these studies did not reveal the initiation mechanism(s) or the initiating species. To identify the initiation mechanism and the initiating species, we explore four different mechanisms, (1) Kaim, (2) Flory, (3) α-position hydrogen transfer, and (4) Mayo, using first-principles density functional theory (DFT) and second-order M?ller-Plesset perturbation theory (MP2) calculations. Transition-state geometries for each mechanism are determined using B3LYP/6-31G* and assessed with MP2/6-31G*. Activation energies and rate constants are calculated using transition-state theory. The harmonic oscillator approximation and tunneling corrections are applied to compute the reaction rate constants. This study indicates that α-position hydrogen transfer and Mayo mechanisms have comparable barriers and are capable of generating monoradicals for initiating polymerization of MA and MMA; these two mechanisms can cause cyclohexanone-monomer co-initiation in thermal polymerization of MA and MMA.     

A chemometrics approach for simultaneous determination of cyanazine and propazine based on a carbon paste electrode modified by a molecularly imprinted polymer

In a completely rational and designed approach, simultaneous determination of cyanazine and propazine in environmental and food samples was performed using a molecularly imprinted polymer modified carbon paste electrode (MIP-CPE) and partial least squares. The MIP-CPE designed is based on the theoretical studies functioned as a selective recognition element and pre-concentrator agent for cyanazine and propazine. Fractional factorial and central composite designs were performed to recognize, and subsequently optimize, the variables affecting the cathodic stripping voltammetric currents for the analytes. The important variables were identified to be accumulation potential with optimum values of -0.45 and -0.44 V and pH with optimum values of 2.40 and 2.34 for cyanazine and propazine, respectively. Exploration of the overall optimum conditions for simultaneous determination of cyanazine and propazine resulted in accumulation potential of -0.44 V and pH of 2.4. Dynamic linear ranges of 0.05-9.00 μmol L(-1) and 0.01-1.00 μmol L(-1) and detection limits of 0.010 and 0.001 μmol L(-1) were obtained for cyanazine and propazine, respectively. The results of the application of the proposed method on the simultaneous determination of cyanazine and propazine in foodstuffs and environmental samples were satisfactory.     

Design of ionic liquid 3-methyl-1-sulfonic acid imidazolium nitrate as reagent for the nitration of aromatic compounds by in situ generation of NO(2) in acidic media

3-Methyl-1-sulfonic acid imidazolium nitrate ([Msim]NO(3)) as a new Br?nsted acidic ionic liquid and nitrating agent was prepared and used for the efficient nitration of aromatic compounds (even aniline derivatives). The dramatic effect of this reagent by in situ generation of nitrogen dioxide as a radical on aromatic compounds to give nitroarenes has been studied.     

Fabrication of highly efficient dye-sensitized solar cell and CO2 reduction photocatalyst using TiO2 nanoparticles prepared by spin coating-assisted sol–gel method

A sol?Cgel method was applied for fabrication of nanocrystalline anatase TiO₂ thin films on ITO glass substrates and followed by rapid thermal annealing for application as the work electrode for dye-sensitized solar cells (DSSC). TiO₂ nanoparticles were characterized by X-ray diffraction (XRD) pattern and scanning electron microscopy (SEM) and the absorption of dye on the TiO₂ electrode was shown by UV?Cvis spectroscopy. By controlling different parameters including numbers of coated layers, the gap between two electrodes, sensitization time, and light source power, TiO₂-based solar cells with high efficiency was achieved. The results show that a five time spin-coated TiO₂ electrode with applying sealant and sensitization time of 24?h in N3 dye under illumination of 100?W?cm^?2 tungsten lamp give the optimum power conversion efficiency (??) of 6.61%. The increases in thickness of TiO₂ films by increasing the numbers of coated layers can improve adsorption of the N3 dye through TiO₂ layers to increase the open-circuit voltage (V _oc). However, short-circuit photocurrents (J _sc) of DSSCs with a one-coated layer of TiO₂ films are smaller than those of DSSCs with five-coated layer of TiO₂ films. It could be due to the fact that the increased thickness of TiO₂ thin films also resulted in a decrease in the transmittance of TiO₂ thin films. Also, this electrode was employed to photoreduce CO₂ with H₂O under tungsten lamp as light source.     

Eremostachiin: a new furanolabdane diterpene glycoside from Eremostachys glabra

The reversed-phase preparative HPLC analysis of the methanol extract of the rhizomes of Eremostachys glabra (Lamiaceae) led to the isolation of two furanolabdane diterpene glycosides, phlomisoside II, and beta-D-glucopyranosyl-(1-->2)-beta-D-glucopyranosyl ester of phlomisoic acid (named eremostachiin), the latter being a novel natural product. The structure of the new compound has been elucidated unambiguously by HRMS and a series of 1D- and 2D-NMR spectroscopic techniques. The free radical scavenging activity of these compounds was assessed using the DPPH assay.     

A novel chelating acid-assisted thermolysis procedure for preparation of tin oxide nanoparticles

Pure tin dioxide (SnO₂) nanoparticles were synthesized via thermolysis of tin phthalate and tin oxalate in the presence of oleic acid (OA) as solvent. Oleic acid (OA) was employed as an organic solvent, which can be applied to control particle growth and to stabilize the particles. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) spectroscopy. The orthorhombic phase SnO₂ nanoparticles with average size about 12 nm were synthesized through thermolysis of tin phthalate in the presence of oleic acid.     

Stacky abelianization of algebraic groups

We prove a conjecture of Drinfeld regarding restriction of central extensions of an algebraic group G to the commutator subgroup. As an application, we construct the “true commutator” of G. The quotient of G by the action of the true commutator is the universal commutative group stack to which G maps.     

Morphologies and magnetic properties of FeCo nanoparticles modulated by changing the types of ligands of Co

A new way of preparing FeCo nanoparticles has been developed using the co-precipitation technique based on the appropriate Co precursors of different types of ligands. These new precursors have been prepared by the reaction of cobalt acetate with three various coordination compositions for forming cobalt complex types. This technique provides proper control on nanoparticle size distribution after annealing to 500 °C. The variation of the magnetic properties with the type of ligands of Co can arise from the changes of the microstructures and crystalline anisotropies. Maximum coercivity values of 480 Oe were obtained. It is found that the precursors with special structures can prevent from agglomeration without presence of any surfactants.     

Control of the supercontinuum spectrum bandwidth and emission efficiency for intense-isolated sub 40-as pulse generation by using a coherent superposition of states

We present a systematic study for generation of intense and short single as pulse in pre-excited He-ionic medium with the use of a same-frequency laser field synthesis. By preparing He+ ions in a coherent superposition of the ground and excited states, a depth of spectral modulation efficiently decreases and the efficiency of harmonic plateau increases. By means of optimizing the laser parameters, the broadband XUV supercontinuum achieve by the superposition state scheme. It shows that by increasing the harmonic order of the supercontinuum, emission efficiency increases. The detailed view shows that the short-trajectory contributes to each supercontinuous harmonic and long-trajectory fully suppresses. Finally, by superposing some properly selected harmonics from optimal spectrum, an intense and almost transform-limited isolated 38-as pulse can be generated without phase compensation. A single isolated 5-as pulse can be achieved after phase compensation. These results are explained by using classical and quantum time-frequency analyses.