Dispersion and reactivity of copper catalysts supported on Al2O3-ZrO2

A series of CuO/Al(2)O(3)-ZrO(2) catalysts with Cu loadings varying from 1.0 to 20 wt % were prepared and characterized by X-ray diffraction (XRD), temperature-programmed reduction (TPR), temperature-programmed desorption (TPD) of CO(2) and NH(3), electron spin resonance (ESR), and Brunauer-Emmett-Teller surface area measurements. The dispersion and metal area of copper were determined by the N(2)O decomposition method. XRD results suggest that the copper oxide is present in a highly dispersed amorphous state at copper loadings < 10 wt % and as a crystalline CuO phase at higher Cu loadings. ESR results suggest the presence of two types of copper species on the Al(2)O(3)-ZrO(2) support. TPR results suggest well-dispersed copper oxide species at low Cu loadings and crystalline copper oxide species at high Cu loadings. Well-dispersed copper oxide species were reduced more easily than large copper oxide species by H(2). The results of CO(2) TPD suggest that the basicity of the catalysts was found to increase with an increase of copper loading up to 5.0 wt % and decreases with a further increase of copper loading. The results of NH(3) TPD suggest that the acidity of the catalysts was found to decrease with an increase of copper loading up to 5.0 wt % and increases with a further increase of copper loading. The catalytic properties were evaluated for the vapor-phase dehydrogenation of cyclohexanol to cyclohexanone and correlated with the results of CO(2) TPD measurements and the dispersion of Cu on the Al(2)O(3)-ZrO(2) support.     

Doping effect of Mn on the magnetic behavior in Ni-Zn ferrite nanoparticles prepared by sol-gel auto-combustion

The ferrite samples of a chemical formula Ni_0.5−xMn_xZn_0.5Fe₂O₄ (where x=0.0, 0.1, 0.2, 0.3, 0.4, and 0.5) were synthesized by sol-gel auto-combustion method. The synthesized samples were annealed at 600 °C for 4 h. An analysis of X-ray diffraction patterns reveals the formation of single phase cubic spinel structure. The lattice parameter increases linearly with increase in Mn content x. An initial increase followed by a subsequent decrease in saturation magnetization with increase in Mn content is observed showing inverse trend of coercivity (H_c). Curie temperature decreases with increase in Mn content x. The initial permeability is observed to increase with increase in Mn content up to x=0.3 followed by a decrease, the maximum value being 362. Possible explanation for the observed structural, magnetic, and changes of permeability behavior with various Mn content are discussed.     

Elastic,impedance spectroscopic and dielectric properties of TiO2 doped nanocrystalline NiCuZn spinel ferrites

ABSTRACT

Nanocrystalline Ni_0.4Cu_0.3Zn_0.3Fe₂O₄ ferrites doped with TiO₂ (0–10?wt %) were prepared by the sol-gel method. Elastic properties of synthesized samples were studied with the help of ultrasonic pulse transmission method. The elastic constants initially increase with an increase in TiO₂ up to 1?wt % and then decline. LCR-Q meter was used to study the dielectric properties within 50?Hz to 5?MHz range of the frequency. The dielectric constant (?′) and dielectric loss tangents were decreased continuously with increased frequency for all the selected samples at room temperature revealing normal dielectric behavior of ferrites. Also, the AC conductivity was increased with an increase in the frequency for all the selected samples. Cole-Cole plots were obtained for all investigated samples and showed single semicircle which indicates that the electrical conduction process appears only due to grain boundaries.     

Emission analysis of Dy and Pr:Bi2O3-ZnF2-B2O3-Li2O-Na2O glasses

In this paper, we present the spectral results of Dy³⁺ and Pr³⁺ (1.0 mol%) ions doped Bi₂O₃-ZnF₂-B₂O₃-Li₂O-Na₂O glasses. Measurements of X-ray diffraction (XRD), differential scanning calorimetry (DSC) profiles of these rare-earth ions doped glasses have been carried out. From the DSC thermograms, glass transition (T_g), crystallization (T_c) and melting (T_m) temperatures have been evaluated. The direct and indirect optical band gaps have been calculated based on the glasses UV absorption spectra. The emission spectrum of Dy³⁺:glass has shown two emission transitions ⁴F_7/2→⁶H_15/2 (482 nm) and ⁴F_7/2→⁶H_13/2 (576 nm) with an excitation at 390 nm wavelength and Pr³⁺:glass has shown a strong emission transition ¹D₂→³H₄ (610 nm) with an excitation at 445 nm. Upon exposure to UV radiation, Dy³⁺ and Pr³⁺ glasses have shown bright yellow and reddish colors, respectively, from their surfaces.     

One‐pot Synthesis of Fully Substituted Pyrimidines Using Amidine and Ketene Dithioacetals as Synthons and Their Antimicrobial Activity

A simple, convenient, and efficient one‐pot synthesis of fully substituted pyrimidines was developed by cyclocondensation of α‐oxo ketene dithioacetals with amidine in the presence of potassium carbonate in good yield. Structures of all the newly synthesized compounds were elucidated by elemental analysis and spectral analysis. All the newly synthesized compounds are tested toward different microorganisms.     

Alkali Metal–Promoted Facile Synthesis of Secondary Amines from Imines and Carbodiimides

We present here an efficient method for the hydroboration of aldimines (-C=N-) with pinacolborane (HBpin) using an alkali metal catalyst, potassium benzyl. The reaction was accomplished with unprecedented catalytic efficiency under mild and solvent-free conditions to afford the high yield of the corresponding N-boryl amines up to 97%. Various functionalities on aldimines were incorporated for hydroboration. The corresponding boryl amines were subjected to further hydrolysis to yield the corresponding secondary amines with good yields up to 89%. This protocol for the reaction demonstrates an atom-economic and green method with diverse imines that bears excellent functional group tolerance. Chemoselective reduction of imines was also attained, with good yields of 74–89%. We also propose the most plausible mechanism involving the formation of metal hydride as the active pre-catalyst.     

A General Approach Towards Triazole‐Linked Adenosine Diphosphate Ribosylated Peptides and Proteins

Current methods to prepare adenosine diphosphate ribosylated (ADPr) peptides are not generally applicable due to the labile nature of this post‐translational modification and its incompatibility with strong acidic conditions used in standard solid‐phase peptide synthesis. A general strategy is presented to prepare ADPr peptide analogues based on a copper‐catalyzed click reaction between an azide‐modified peptide and an alkyne‐modified ADPr counterpart. The scope of this approach was expanded to proteins by preparing two ubiquitin ADPr analogues carrying the biological relevant α‐glycosidic linkage. Biochemical validation using Legionella effector enzyme SdeA shows that clicked ubiquitin ADPr is well‐tolerated and highlights the potential of this strategy to prepare ADPr proteins.     

X-ray crystallographic and theoretical studies of substituted phenyl 3,5-di[N-methyl] carbamoyl-1,4-dihydropyridines: Targets for Ca2+ antagonist

A series of 4(x-substituted phenyl)-1,4-dihydropyridines (x=2—CF₃ (1), 2-CH₃ (2), 2-OCH₃ (3) and 2,4-Cl (4)) with a new substituent, the N-methylcarbamoyl (CONHCH₃) group at C3 and C5 are crystallographically characterized and a comparison has been made with important conformational parameters obtained theoretically. The dihydropyridine rings are in shallow boat conformation. The phenyl substituent orientation is synperiplanar. Both the carbonyl groups are oriented anticlinal in 1, 2 and 3; but in 4, one is synclinal and the other synperiplanar with the adjacent double bond. The presence of solvent molecules in 1 (CH₃OH), 2 (CH₃OH), and 3 (H₂O) has significantly changed the hydrogen bonding pattern. Theoretical studies at the semiempirical AM1 MO level reproduces the general features of the structures. The near planarity of the DHP ring and the orientation of the phenyl substituent make 1 and 2 encouraging targets for pharmacological, study. Crystallographic Data:1: a = 8.793(2), b = 29.962(5), c = 8.215(2) Å, = 115.28(2)°, Monoclinic, P2₁/c; 2: a = 8.799(2), b = 15.789(3), c = 14.074(2) Å, = 100.25(2)°, Monoclinic, P2₁/n; 3: a = 8.347(1), b = 8.986(1), c = 13.749(2) Å, = 97.50(1), = 94.78(1), = 101.38(1)° Triclinic, P1¯4: a = 12.928(3), b = 14.506(3), c = 9.740(2) Å, Orthorhombic, Pca2₁.     

An improved synthesis of pyrimidine- and pyrazole-based acyclo-C-nucleosides as carbohybrids

The synthesis of pyrimidine- and pyrazole-based acyclo-C-nucleosides as carbohybrids was optimized and developed. The synthesis of acyclic polyol-fused pyrimidines was achieved in good to excellent yield with high purity by the cyclocondensation of 2-C-formyl glycals and various amidines using K₂CO₃ as inorganic base in co-solvent system. In comparison, the syntheses of pyrazole-based acyclo-C-nucleosides were accomplished simply by the cyclocondensation of 2-C-formyl glycals with hydrazine hydrate at room temperature and with phenyl hydrazine at refluxing temperature in ethanol.     

LC–MS–MS Method for Simultaneous Analysis of Abacavir and Lamivudine in Human Plasma, and Its Application to a Bioequivalence Study

A rapid and sensitive LC–MS–MS method has been developed and validated for simultaneous analysis of abacavir (ABA) and lamivudine (LAM) in human plasma. The analytes were extracted from human plasma by SPE. Nelfinavir (NEL) and emtricitabine (EMT) were used as the internal standards for ABA and LAM, respectively. An RP18 column enabled chromatographic separation of the analytes. The method involves simple isocratic chromatography and MS detection in positive-ionization mode. Validation of the method showed response was a linear function of concentration in the ranges 100.0–7000.0 ng mL^?1 for ABA and 80.0–5000.0 ng mL^?1 for LAM. At the LOQ levels, inter-run and intra-run precision were within 5.80 and 3.51%, respectively, for ABA and within 4.68 and 3.16%, respectively, for LAM. Overall recovery for ABA and LAM was 59.32 and 105.18%, respectively. Total elution time was 2 min only, which enabled quantification of more than 200 plasma samples per day. This validated method was used successfully for analysis of plasma samples from a bioequivalence study.