An efficient and facile regioselective synthesis of new substituted (E)-1-(3-aryl-7,8-dihydrocinnoline-5(6H)-ylidene)hydrazines and (1E,2E)-1,2-bis(3-aryl-7,8-dihydrocinnoline-5(6H)-ylidene)hydrazines

A study concerning the new substituted cinnoline synthesis is described. The use of a one-pot three-component method allows a simple regioselective and efficient synthesis of cinnoline derivatives via reaction of arylglyoxals with 1,3-cyclohexanedione and dimedone in the presence of hydrazine hydrate.     

Thermal Degradation Behavior and Kinetic Analysis of Ultra High Molecular Weight Polyethylene Based Multi-Walled Carbon Nanotube Nanocomposites Prepared Via in-situ Polymerization

Thermal degradation behavior of multi-wall carbon nanotubes (MWCNTs)/ultra high molecular weight polyethylene (UHMWPE) nanocomposites, with different nanotubes contents (0.5, 1.5 and 3.5 wt%) prepared via in-situ polymerization technique have been investigated using thermal gravimetric analysis (TGA). TGA spectra revealed that these nanocomposites had enhanced thermal stability and no significant mass loss (<0.4 wt%) occurred up to 350°C. Thermal degradation of these UHMWPE/MWCNT nanocomposites was investigated in terms of parameters such as the onset temperature of degradation (T₁₀), the decomposition temperature at 50% wt loss (T₅₀), the degradation temperature of maximum rate of the weight loss (T_m), and the residual yields (W_R) from TGA. The degradation activation energies (E) of virgin UHMWPE and its nanocomposites were estimated using the Friedman, the Ozawa, Flynn, and Wall (OFW), and the Kissinger's methods. Results indicated that the degradation activation energy for the virgin UHMWPE was 281.3 kJ/mol. The activation energy increased with increasing nanotube loading up to 1.5 wt% indicating that MWCNTs had a stabilizing effect on the degradation of the matrix. However, loadings of 3.5 wt% of nanotube or more could slightly decrease the activation energy. The decrease in the activation energy for degradation of nanocomposites with higher MWCNT concentrations might be attributed to the catalytic effects of nanotubes and polymerization catalyst residues. The “model fitting” method indicated a mechanism of n ^th-order auto-catalysis from the form of the conversion curves for UHMWPE/MWCNTs nanocomposites prepared via in-situ polymerization.     

聚(4-乙烯基吡啶丁烷磺酸)硫酸氢盐:一个高效的多相聚(离子液体)固体酸催化剂用于无溶剂条件下一锅法合成1-酰氨基-2-萘酚和取代喹啉(英文)

Poly(4-vinylpyridinium butane sulfonic acid) hydrogen sulfate has been used as an efficient dual acidic catalyst for the one-pot preparation of 1-amidoalkyl-2-naphthols and substituted quinolines under solvent-free conditions.The catalyst was characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, and thermo-gravimetric analysis. The results revealed several advantages to our new catalyst system,including its reusability,facile work-up procedure, eco-friendly reaction conditions,short reaction time,and high product yields.     

EELS spectroscopy of iron fluorides and FeFx/C nanocomposite electrodes used in Li-ion batteries.

A new type of positive electrode for Li-ion batteries has been developed recently based on FeF3/C and FeF2/C nanocomposites. The microstructural and redox evolution during discharge and recharge processes was followed by electron energy loss spectroscopy (EELS) to determine the valence state of Fe by measuring the Fe L3 line energy shift and from Fe L3/L2 line intensity ratios. In addition, transition metal fluorides were found to be electron beam sensitive, and the effect of beam exposure on EELS spectra was also investigated. The EELS results indicate that for both FeF3/C and FeF2/C nanocomposite systems, a complete reduction of iron to FeO is observed upon discharge to 1.5 V with the formation of a finer FeO/LiF subnanocomposite ( approximately 7 nm). Upon complete recharging to 4.5 V, EELS data reveal a reoxidation process to a Fe2+ state with the formation of a carbon metal fluoride nanocomposite related to the FeF2 structure.     

Vitamin B1 as a metal-ion-free natural catalyst for sustainable quinoxaline ring condensation under sonochemical conditions

Abstract  

The role of vitamin B₁ as a catalyst is investigated for the quinoxaline ring condensation under various mild reaction conditions. The results revealed that the combination of vitamin B₁ and ultrasonic irradiation promotes the reaction more efficiently. The salient features of this environmentally benign method are fast conversions, excellent yields for a wide range of substrates, and the use of a low-cost, readily available, nontoxic, and metal-ion-free natural catalyst. The wide range of turnover frequency values (6–400 h⁻¹) shows that the reaction rate is highly dependent on the nature of the functional groups on the aromatic ring of substrates. Moreover, a plausible mechanism for the catalytic action of vitamin B₁ has been introduced.     

Mesophilic alcohol dehydrogenase behavior in imidazolium based ionic liquids

The use of ionic liquids to replace organic solvents in biocatalytic processes has recently gained much attention. Despite the wide applications of oxidoreductases, there are few reports of their catalyzed reaction in ionic liquid. We have investigated the influence of four water miscible ionic liquids on the activity, stability and structure of the mesophilic alcohol dehydrogenase from yeast. Upon changes in ionic liquids concentration, both activity and stability of the enzyme were affected. As the concentration of ionic liquids increased, K_m increased while k_cat decreased. Associated conformational changes caused by ILs (150 mM) were monitored using fluorescence technique. Finally, the effects of ILs cations and anions on the enzyme activity and stability in aqueous IL mixtures were discussed.     

ZnO microparticles,ZnO nanoparticles and Zn0.9Cu0.1O nanoparticles toward ethanol vapor sensing: A comparative study

ZnO and Zn_0.9Cu_0.1O nanoparticles were synthesized by the sonochemical method. Structural and morphological properties of the synthesized nanoparticles were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive analysis of X-ray (EDAX). The results revealed the formation of ZnO and Zn_0.9Cu_0.1O nanoparticles in wurtzite phase with average crystallite diameter of 30–40 nm calculated from Debye–Scherrer equation. Moreover, the ethanol vapor sensing properties of ZnO and Zn_0.9Cu_0.1O nanoparticles were investigated at different operating temperatures and they were compared with commercial ZnO microparticles. Comparative results demonstrated that Zn_0.9Cu_0.1O nanoparticles exhibit highest and fastest response to 250 ppm of ethanol at 300 °C. Results on response/recovery time, sensing mechanism, conductance variation and thermodynamics/kinetics of ethanol sensing is also studied and discussed.     

Nonparametric prediction intervals for progressive Type-II censored order statistics based on k-records

In this paper, we consider the prediction problem in two-sample case and study the non-parametric predicting future progressively Type-II censored order statistics based on observed $k$ -records from the same distribution. Also, prediction intervals for progressively Type-II censored spacings are obtained based on $k$ -record spacings. It is shown that the coverage probabilities of these intervals are exact and do not depend on the underlying distribution. Moreover, optimal prediction intervals are derived for each case. Finally, for illustrating the proposed procedure, we consider a real data set and numerical computations are given. The results of Ahmadi and Balakrishnan (Statistics 44:417–430, 2010) can be achieved as special cases of our results.