Combining engineering and chemistry for the selective continuous production of four different oxygenated compounds by photo-oxidation of cyclopentadiene using liquid and supercritical CO2 as solvents

A range of products is reported from the photo-oxidation of cyclopentadiene from photochemically generated singlet oxygen (¹O₂) using carbon dioxide (CO₂) as a solvent and 5,10,15,20-tetrakis-(pentafluorophenyl)porphyrin (TPFPP) as a CO₂-soluble photosensitizer. The endo-peroxide intermediate, generated from the reaction with singlet oxygen, is transformed into one of several different products in good yield depending on the conditions applied and by adding different reactors and reagents downstream of the photo-reactor, allowing the reaction products to be switched in one streamlined process. The addition of a thermal reactor facilitated the rearrangement of the endoperoxide to form Z-4,5-epoxy-2-pentanal. Quenching with thiourea yielded the syn-diol, (1R,3S)-cyclopent-4-ene-1,3-diol. Treatment with acid or base afforded furfuryl alcohol and 4-hydroxy-2-cyclopentenone respectively. High productivities for all products were obtained when compared to traditional batch reactions.     

Copper-catalyzed efficient synthesis of 5-arylindazolo[3,2-b]quinazolin-7(5H)-ones from 2-nitrobenzaldehydes

A novel and practical copper-catalyzed approach was developed for the preparation of 5-arylindazolo[3,2-b]quinazolin-7(5H)-ones. The 2-amino-N′-arylbenzohydrazideis easily prepared by a reaction of isatoic anhydride with arylhydrazine. Then, through a condensation/intramolecular cyclization reaction by 2-nitrobenzaldehydes in the present of CuI, the corresponding 5-arylindazolo[3,2-b]quinazolin-7(5H)-ones are produced in good yields.     

Magnetic dispersive solid phase extraction using modified magnetic multi-walled carbon nanotubes combined with electrothermal atomic absorption spectrometry for the determination of selenium

A novel magnetic dispersive solid phase extraction method using magnetic multi-walled carbon nanotubes modified with 5-mercapto-3-phenyl-1,3,4-thiadiazole-2-thione potassium salt (bismuthiol II) (MMWCNTs@Bis) as the sorbent was developed for the separation and preconcentration of inorganic selenium (IV) prior to its determination by electrothermal atomic absorption spectrometry. The prepared MMWCNTs@Bis sorbent was characterised by Fourier transform infrared spectroscopy, scanning electron microscopy, vibrating sample magnetometer and X-ray diffraction. Total selenium was determined after reduction of Se(VI) to Se(IV) by addition of hydrochloric acid and heating the mixture in a boiling water bath. Se(VI) concentration was determined from the difference between the amounts of total selenium and Se(IV). Under the optimised experimental conditions, an enhancement factor of 196 and a detection limit (based on 3S_b/m) of 0.003 µg L^?1 was obtained for aqueous samples. The relative standard deviation at 0.1 µg L^?1 concentration level of Se(IV) (n = 6) was found to be 5.2 and 7.7% for intra- and inter-day analysis, respectively. The method was successfully applied to the determination of inorganic selenium species in water and total selenium in food samples.     

A manganese Schiff base complex immobilized on copper–ferrite magnetic nanoparticles as an efficient and recyclable nanocatalyst for selective oxidation of alcohols

A magnetically recoverable nanocatalyst was synthesized by covalent binding of a Schiff base ligand, namely N,N′-bis(Salicylidene)-1,3-diaminopropane-2-ol (H₂salpn), onto the surface of silica-coated magnetic CuFe₂O₄ nanoparticles, followed by complexation with MnCl₂. The resulting core–shell nanoparticles were characterized by spectroscopic and microscopic methods, including FTIR, XRD, VSM, TGA elemental analysis, TEM, and SEM. The Mn content was determined by ICP analysis. The nanoparticles were investigated as a catalyst for the selective oxidation of alcohols to the corresponding carbonyl compounds with tertiary-butyl hydrogen peroxide. The catalyst can be magnetically separated for reuse, with no noticeable loss of activity in subsequent reaction cycles. FTIR, VSM, and leaching experiments after three successive cycles confirmed that the catalyst was strongly anchored to the magnetic nanoparticles. A suitable mechanism for the reaction is proposed.     

Calorimetric investigation of the structural relaxation and crystallization of amorphous Ge16Te84 alloys

Differential scanning calorimetric measurements have been performed on amorphous Ge₁₆Te₈₄ alloys; the study of the dependence of the cooling rate on the reciprocal fictive temperature yields the activation energy of the relaxation process; this value fits well that deduced from shear viscosity measurements. The enthalpy difference between the supercooled liquid and the crystal has been investigated by drop calorimetry on samples annealed at different temperatures below T_g, during different times. These results, combined with the former obtained by DSC lead to the enthalpy values of the metastable liquid system from 390 to 510 K.     

Riemannian Geometry on Hom-ρ-commutative Algebras*

Recently, some concepts such as Hom-algebras, Hom-Lie algebras, Hom-Lie admissible algebras, Hom-coalgebras are studied and some classical properties of algebras and some geometric objects are extended on them. In this paper by recalling the concept of Hom-ρ-commutative algebras, the authurs intend to develop some of the most classical results in Riemannian geometry such as metric, connection, torsion tensor, curvature tensor on it and also they discuss about differential operators and get some ...     

Inelastic effect of electron–phonon interactions in tunnelling magnetoresistance of a single metallofullerene

The effects of elastic and inelastic electron–phonon interactions on current–voltage characteristic and tunnelling magnetoresistance (TMR) of Li@C₅₉X (X = N, B) molecule that is coupled to two ferromagnetic electrodes was investigated using the non-equilibrium Green's function (NEGF) method. Our results by taking also into consideration spin degrees of freedom (excluding spin-mixing effects) indicate that the presence of inelastic electron–phonon interaction polaron formation increases current and shifts the TMR behaviour to higher values. Also, an increase of two orders of magnitude observed in current for Li@C₅₉B compared to C₆₀.     

Influence of Y2Cu2O5 nanoparticles doping on superconducting properties of YBa2Cu3O7-δ

ABSTRACT

The blue phase of YBa₂Cu₃O_{7- δ} (YBCO) family, Y₂Cu₂O₅ (Y202) nanoparticles were prepared and doped into (YBCO) superconductor and the effect of doping on critical current density and critical temperature was investigated. Y202 nanoparticles with particle sizes of 47, 107 and 206?nm were prepared by a sol–gel combustion method and added into the YBCO superconductor by 0.5–2?wt.%. XRD and scanning electron microscope measurements were used to characterize the samples. The measurement of critical current density at 77?K revealed that the doped superconductors had larger critical current density compared to the undoped superconductors. For a fixed dopant concentration, by increasing the size of nanoparticles, the J_c was increased. For the samples including 0.5?wt.% of nanoadditives, J_c was higher. The highest critical current density of 137?A/cm² was measured for the superconductors containing 0.5?wt.% of 206?nm Y202 nanoparticles. Also, by increasing the nanoparticles concentration, the T_c was reduced.     

Effects of Ag or Si on precipitation in the alloy Al-2.5 mass% Cu-1.5 mass% Mg

Calorimetric measurements and electron microscopy observations were performed on Al-2.5?mass% Cu-1.5?mass% Mg alloys containing also 0.4, 1 or 2% Ag or 0.5% Si, in order to improve understanding of the relationships between precipitation processes and age hardening. The analogous behaviour of calorimetric and hardness data confirms that the first hardening stage is initiated in all alloys by GPB zone formation which occurs via a nucleation and growth controlled mechanism. The vacancy-trapping effect of Mg is increased by Ag and Si additions and leads to slower precipitation kinetics. Consequently, refined GPB zones sizes are obtained leading to an increase in hardness with respect to the ternary alloy. During the second hardening stage, the formation of the more stable S′ phase increases the total amount of strengthening precipitates in the ternary alloy. Phases typical for binary Al–Cu alloys form additionally in the Si-containing alloy. In the Ag-bearing alloys, precipitation of the hardening X′ phase occurs the earlier the higher the Ag content; it is followed by S′ precipitation. During heating of the ternary alloy, the S′ phase forms after substantial dissolution of GPB zones and of the S′′ phase identified by high resolution electron microscopy; this contradicts the concept of a continuous precipitation sequence.