Electron Paramagnetic Resonance Analysis of La(1-x)M(x)MnO(3+δ) (M = Ce, Sr) Perovskite-Like Nanostructured Catalysts

The physical-chemical properties of some nanostructured perovskite-like catalysts of general formula La(1-x)M(x)MnO(3+δ) (M = Ce, Sr) have been investigated, in particular by using the electron paramagnetic resonance (EPR) technique. We show that the interplay between the -O-Mn(3+)-O-Mn(4+)-O- electron double-exchange and the electron mobility is strictly dependent on the dopant nature and the annealing conditions in air. A relationship between the observed properties of these samples and their activity in the methane flameless catalytic combustion is proposed.     

Total Synthesis of (±) Kadsurenin M

KadsllreIlinM(7s.8s-.1.4.3'-tril1letllop'-7"oxo-n0r-8'.9'-7.0.4'.8.5'-neolignan)u'asisolatedfrollltlleaerialpart0fPiperKadsl1ra(Cl1ois}')0l1\viI'].aCllinesetraditiol1aldrugusedf0rtlletreatll1el1tofil1naI11l11ati0nundrl1eul1laticcol1diti0l1s.Aspartof0urresearcl1xt,0rkontlletotals}'lltllcsisofbe11z0fura11oidncolignans,l"ereportl1eret11efirstlotalsi'ntl1esisofkadsurenil1Masitsrecel11icfonn.Tllep-lltlleticro[1leisdepic1edi1ltl1ef0lloxt'il1gsclleme.3.4-Dilnetl1on'cil1nam}'lcllloride6.readil}'a\…     

Magnetization, Mössbauer and isothermal dilatometric behavior of oxidized YBa(Co,Fe)4O(7+δ)

M?ssbauer spectroscopy and magnetization studies of YBaCo(4-x)Fe(x)O(7+δ) (x = 0-0.8) oxidized at 0.21 and 100 atm O(2), indicate an increasing role of penta-coordinated Co(3+) states when the oxygen content approaches 8-8.5 atoms per formula unit. Strong magnetic correlations are observed in YBaCo(4-x)Fe(x)O(8.5) from 2 K up to 55-70 K, whilst the average magnetic moment of Co(3+) is lower than that for δ ≤ 0.2, in correlation with the lower (57)Fe(3+) isomer shifts determined from M?ssbauer spectra. The hypothesis on dominant five-fold coordination of cobalt cations was validated by molecular dynamics modeling of YBaCo(4)O(8.5). The iron solubility limit in YBaCo(4-x)Fe(x)O(7+δ) corresponds to approximately x ≈ 0.7. The oxygen intercalation processes in YBaCo(4)O(7+δ) at 470-700 K, analyzed by X-ray diffraction, thermogravimetry and controlled-atmosphere dilatometry, lead to unusual volume expansion opposing to the cobalt cation radius variations. This behavior is associated with increasing cobalt coordination numbers and with rising local distortions and disorder in the crystal lattice on oxidation, predicted by the computer simulations. When the oxygen partial pressure increases from 4 × 10(-5) to 1 atm, the linear strain in YBaCo(4)O(7+δ) ceramics at 598 K is as high as 0.33%.     

Tunability of the M(II)M(III)/M(II)(2) and M(III)(2)/M(II)M(III) (M=Mn, Co) couples in bis-μ-O,O'-carboxylato-μ-OR bridged complexes

A comparison of the electrochemical properties of a series of dinuclear complexes [M(2)(L)(RCO(2))(2)](+) with M = Mn or Co, L = 2,6-bis(N,N-bis-(2-pyridylmethyl)-sulfonamido)-4-methylphenolato (bpsmp(-)) or 2,6-bis(N,N-bis(2-pyridylmethyl)aminomethyl)-4-tert-butylphenolato (bpbp(-)) and R = H, CH(3), CF(3) or 3,4-dimethoxybenzoate demonstrates: (i) The electron-withdrawing sulfonyl groups in the backbone of bpsmp(-) stabilize the [M(2)(bpsmp)(RCO(2))(2)](+) complexes in their M(II)(2) oxidation state compared to their [M(2)(bpbp)(RCO(2))(2)](+) analogues. Manganese complexes are stabilised by approximately 550 mV and cobalt complexes by 650 mV. (ii) The auxiliary bridging carboxylato ligands further attenuate the metal-based redox chemistry. Substitution of two acetato for two trifluoroacetato ligands shifts redox couples by 300-400 mV. Within the working potential window, reversible or quasi-reversible M(II)M(III)? M(II)(2) processes range from 0.31 to 1.41 V for the [Co(2)(L)(RCO(2))(2)](+/2+) complexes and from 0.54 to 1.41 V for the [Mn(2)(L)(RCO(2))(2)](+/2+) complexes versus Ag/AgCl for E(M(II)M(III)/M(II)(2)). The extreme limits are defined by the complexes [M(2)(bpbp)(CH(3)CO(2))(2)](+) and [M(2)(bpsmp)(CF(3)CO(2))(2)](+) for both metal ions. Thus, tuning the ligand field in these dinuclear complexes makes possible a range of around 0.9 V and 1.49 V for the one-electron E(M(II)M(III)/M(II)(2)) couple of the Mn and Co complexes, respectively. The second one-electron process, M(II)M(III)? M(III)(2) was also observed in some cases. The lowest potential recorded for the E°(M(III)(2)/M(II)M(III)) couple was 0.63 V for [Co(2)(bpbp)(CH(3)CO(2))(2)](2+) and the highest measurable potential was 2.23 V versus Ag/AgCl for [Co(2)(bpsmp)(CF(3)CO(2))(2)](2+).     

Redox chemistry and magnetism of LaSrM(0.5)Ru(0.5)O(4±δ) (M = Co, Ni and Zn) Ruddlesden-Popper phases

The n = 1 Ruddlesden-Popper (RP) phases LaSrM(0.5)Ru(0.5)O(4±δ) (M = Co, Ni and Zn) have been prepared by solid state reactions and structurally characterized by powder X-ray and electron diffraction. All the samples adopt the tetragonal I4/mmm space group with random M and Ru cation occupation on the B-sites. The potential causes of no cation ordering are discussed. A combined analysis of the tolerance factors, the distortion of the octahedral coordination of M and Ru cations and the magnetic interactions between M and Ru cations provide a better understanding for forming a phase with 3D cation ordering on the B-sites in the n = 1 RP phases. The investigation of XPS spectra suggests that the transition element species exist as mixed ion pairs, Ru((4-δ)+)-Ru(4+)? Co(2+)-Co(3+) in LaSrCo(0.5)Ru(0.5)O(4), and Ru(4+)-Ru((4+δ)+)? Ni(+)-Ni(2+) in LaSrNi(0.5)Ru(0.5)O(4), which is consistent with cation disorder over the B sites. LaSrCo(0.5)Ru(0.5)O(4) shows a weakly ferromagnetic behaviour below 50 K; LaSrNi(0.5)Ru(0.5)O(4) is evidenced by the presence of long-range magnetic ordering at a Néel temperature of 125 K, and LaSrZn(0.5)Ru(0.5)O(4) exhibits a paramagnetic behaviour down to 5 K. Due to atomic disorder, Ru4d, O2p covalent coupling is weakened, strengthening the intraatomic spin-spin coupling among the π* electrons. Charge transfer between Ru and Co or Ru and Ni, as well as the increasing overlap of both nearest-neighbour and next-nearest-neighbour Ru 4d electrons due to atomic disorder, favour the formation of ferromagnetic interactions. Although antiferromagnetism is dominant, particularly in LaSrNi(0.5)Ru(0.5)O(4), ferromagnetic interactions are stronger in the title compounds than in the related La(2)MRuO(6) (M = Co, Ni) double perovskites where the B-site cations are ordered.     

New methods for the synthesis of phosphono-δ-lactones (microreview)

Chemistry of Heterocyclic Compounds - Phosphono-δ-lactones are widely used as bioactive compounds, flame retardants, and polymer building blocks. Over the past years, new methods to access...     

Raman analysis of mode softening in nanoparticle CeO(2-δ) and Au-CeO(2-δ) during CO oxidation

Oxygen vacancy levels are monitored during the oxidation of CO by CeO(2-δ) nanorods and Au-CeO(2-δ) nanorods, nanocubes, and nanopolyhedra by using Raman scattering. The first-order CeO(2) F(2g) peak near 460 cm(-1) decreases when this reaction is fast (fast reduction and relatively slow reoxidation of the surface), because of the lattice expansion that occurs when Ce(3+) replaces Ce(4+) during oxygen vacancy creation. This shift correlates with reactivity for CO oxidation. Increases in the oxygen deficit δ as large as ~0.04 are measured relative to conditions when the ceria is not reduced.     

Effect of dopant valence on the oxygen desorption and oxygen permeability of SrCo0.4Fe0.5M0.1O3-δ》(M=Ni, A1 and Zr) mixed-conducting oxides

The effect of dopant valence on oxygen desorption and oxygen permeability of SrCo0.4Fe<0.5>M0.1O3-δ(M=Ni, Al and Zr) mixed-conducting oxides were investigated in detail by O2-TPD and oxygen permeation measurement. The SrCo0.4Fe0.5M0.1O3-δ for M=Fe, Ni, AI and Zr were denoted as SCF, SCFN, SCFA and SCFZ, respectively. O2-TPD analysis revealed that the amount of α oxygen desorption decreased with increasing the valance of doped metal elements (SCFN>SCFA≈SCF>SCFZ). The oxygen permeation flux at the temperature higher than 1148 K decreased in the order of SCFN>SCF>SCFZ>SCFA. Single activation for oxygen permeation was observed for SCFZ oxide and the activation energies of SCF and SCFA change at around 1073K, while the change temperature of SCFN was about 1173K.     

Oxidation kinetics of nitrogen doped TiO(2-δ) thin films

The oxidation kinetics of nitrogen doped, oxygen deficient titanium dioxide thin films has been studied in atmospheres of pure oxygen or nitrogen at 500 °C, 550 °C, and 600 °C, respectively, by means of in situ optical spectroscopy. The thin films show high electronic absorbance in the visible and NIR region, accompanied by a red shift of the absorption edge of about 0.4 eV, e.g., from about 2.9 to 2.5 eV at 600 °C. The time dependent decrease of absorbance due to oxidation is found to follow a parabolic rate law. An activation energy of about 1.96 eV can be obtained from the temperature dependence of the parabolic oxidation rate constant. In the framework of a microscopic oxidation model, this energy barrier is attributed to the diffusion of titanium interstitials in the re-oxidized part of the thin films as a rate-determining process. In addition, an attempt is made to evaluate the kinetics of nitrogen release from the time dependent blue shift of the absorption edge during re-oxidation.     

Molecular characterization of protein kinase C delta (PKCδ)-Smac interactions

Background

Protein kinase C δ (PKCδ) is known to be an important regulator of apoptosis, having mainly pro- but also anti-apoptotic effects depending on context. In a previous study, we found that PKCδ interacts with the pro-apoptotic protein Smac. Smac facilitates apoptosis by suppressing inhibitor of apoptosis proteins (IAPs). We previously established that the PKCδ-Smac complex dissociates during induction of apoptosis indicating a functional importance. Because the knowledge on the molecular determinants of the interaction is limited, we aimed at characterizing the interactions between PKCδ and Smac.

Results

We found that PKCδ binds directly to Smac through its regulatory domain. The interaction is enhanced by the PKC activator TPA and seems to be independent of PKCδ catalytic activity since the PKC kinase inhibitor GF109203X did not inhibit the interaction. In addition, we found that C1 and C2 domains from several PKC isoforms have Smac-binding capacity.

Conclusions

Our data demonstrate that the Smac-PKCδ interaction is direct and that it is facilitated by an open conformation of PKCδ. The binding is mediated via the PKCδ regulatory domain and both the C1 and C2 domains have Smac-binding capacity. With this study we thereby provide molecular information on an interaction between two apoptosis-regulating proteins.

     

Synthesis and Some Transformations of Derivatives of Pyrido[3,2-b]indole (δ-Carboline)

The reactions of 2-dimethyliminomethyl-3-(p-nitrophenyl)aminoindole chloride with compounds with an active methylene center have been studied. A series of derivatives of -carboline have been synthesized. By the reaction of 3-ethoxycarbonyl-2-methyl-1-p-nitrophenylpyrido[3,2-b]indolinium chloride with the diethyl acetal of DMF the corresponding 2-dimethylaminovinyl derivative was synthesized which was converted into 5-p-nitrophenyl-1-oxo-1,10-dihydropyrano[3',4':5,6]pyrido[3,2-b]indol-5-ium chloride in the presence of acid.     

Theoretical studies of the reactions of M+ (M = Ta,W, Re) with CS2

Gas-phase CS₂ activation by M⁺ (M = Ta, W, Re) was studied by the B3LYP density functional method.The geometries for reactants, transition states, and products were completely optimized. CS₂ activation mediated by M⁺ (M = Ta, W, Re) were found to be a spin-forbidden process as a result of the crossing among the multistate energetic profiles. On the basis of the Hammond postulate, this was a typical two-state reactivity reaction. Among the different potential energy surfaces, the crossing points had been explored. The spin–orbit coupling (SOC) was also calculated between the electronic states of different multiplicities at the crossing point to estimate the intersystem crossing probability. For CP1, CP2, and CP4, the computed SOC constants were 80.28, 128.65, and 526.77 cm^?1, which obtained by using one-electron spin–orbit Hamiltonian in Gaussian 09.     

Syntheses, structures and magnetic properties of a family of one-dimensional M(Ⅱ)-lanthanide(Ⅲ) (M =Ni(Ⅱ) and Zn(Ⅱ)) coordination polymers

A series of 1D nickel(Ⅱ)/zinc(Ⅱ)-lanthanide(Ⅲ) coordination polymers, [M(μ-L)2Ln(NO3)3]n· solvents (HL =bis(2-pyridylcarbonyl)amine; M = Ni, Ln = Gd (1 · NiGd), Tb (2· NiTb), Dy (3· NiDy), Ho (4· NiHo), Y (5· NiY);M = Zn, Ln =Gd (6· ZnGd), Tb (7· ZnTb), Dy (8· ZnDy), Ho (9· ZnHo); solvents = H2O or H2O-ethanol), was synthesized and characterized. All of the complexes are isostructural at 293 K and crystallize in the orthorhombic space group Fddd. Magnetic measurements were performed on 1-9, where weak ferromagnetic interaction is found in 1 · NiGd, ferromagnetic interaction in 2·NiTb and 3·NiDy, and antiferromagnetic interaction in 4· NiHo. A remarkable dc magnetic field dependence of ac susceptibilities was found in this series of complexes.     

Mössbauer study of sodium ferrates(IV) and (VI)

Sodium ferrates(IV) and (VI) were synthesized by the reaction between Fe₂O₃ and Na₂O₂ in a dry oxygen stream. The Mössbauer data for the obtained samples are presented (for Na₂FeO₃–=0.18(2) mm/s; for Na₄FeO₅–=–0.54(2) mm/s). It was shown that pure K₂FeO₄ and Cs₂FeO₄ can be obtained by heating Fe₂O₃ with apropriate alkali metal peroxides.     

Syntheses, structures and magnetic properties of a family of one-dimensional M(Ⅱ)-lanthanide(Ⅲ) (M = Ni(Ⅱ) and Zn(Ⅱ)) coordination polymers

A series of 1D nickel(II)/zinc(II)-lanthanide(III) coordination polymers, [M(μ-L)2Ln(NO3)3]n·solvents (HL = bis(2-pyridylcarbonyl)amine; M = Ni, Ln = Gd (1·NiGd), Tb (2·NiTb), Dy (3·NiDy), Ho (4·NiHo), Y (5·NiY); M = Zn, Ln = Gd (6·ZnGd), Tb (7·ZnTb), Dy (8·ZnDy), Ho (9·ZnHo); solvents = H2O or H2O-ethanol), was synthesized and characterized. All of the complexes are isostructural at 293 K and crystallize in the orthorhombic space group Fddd. Magnetic measurements were performed on 1―9, where weak ferromagnetic interaction is found in 1·NiGd, ferromagnetic interaction in 2·NiTb and 3·NiDy, and antiferromagnetic interaction in 4·NiHo. A remarkable dc magnetic field dependence of ac susceptibilities was found in this series of complexes.     

Molten salt synthesis and supercapacitor properties of oxygen-vacancy LaMnO_(3-δ)

Due to the unique structure of perovskite materials,their capacitance can be improved by introducing oxygen vacancy.In this paper,the LaMnO_(3-δ) material containing oxygen vacancy was synthesized by molten salt method in KNO_3-NaNO_3-NaNO_2 melt.The La-Mn-O crystal grows gradually in molten salt with the increase of temperature.It was confirmed that LaMnO_(3-δ) with perovskite structure and incomplete oxygen content were synthesized by molten salt method and presented a three-dimensional shape.LaMnO_(3-δ) stores energy by redox reaction and adsorption of OH-in electrolyte simultaneously.In comparison with the stoichiometric LaMnO_3 prepared by the sol-gel method,LaMnO_(3-δ) prepared by molten salt method proffered higher capacitance and better performance.The galvanostatic charge-discharge curve showed specific capacitance of 973.5 F/g under current density of 1 A/g in 6 M KOH.The capacitance of LaMn0_(3-δ) was 82.7%under condition of 5 A/g compared with the capacitance at the current of 1A/g,and the specific capacitances of 648.0 and 310.0 F/g were obtained after 2000 and 5000 cycles of galvanostatic charging-discharging,respectively.Molten salt synthesis method is relatively simple and suitable for industrial scale,presenting a promising prospect in the synthesis of perovskite oxide materials.     

Interstitialcy diffusion of oxygen in tetragonal La2CoO(4+δ)

We report on the mechanism and energy barrier for oxygen diffusion in tetragonal La(2)CoO(4+δ). The first principles-based calculations in the Density Functional Theory (DFT) formalism were performed to precisely describe the dominant migration paths for the interstitial oxygen atom in La(2)CoO(4+δ). Atomistic simulations using molecular dynamics (MD) were performed to quantify the temperature dependent collective diffusivity, and to enable a comparison of the diffusion barriers found from the force field-based simulations to those obtained from the first principles-based calculations. Both techniques consistently predict that oxygen migrates dominantly via an interstitialcy mechanism. The single interstitialcy migration path involves the removal of an apical lattice oxygen atom out from the LaO-plane and placing it into the nearest available interstitial site, whilst the original interstitial replaces the displaced apical oxygen on the LaO-plane. The facile migration of the interstitial oxygen in this path is enabled by the cooperative titling-untilting of the CoO(6) octahedron. DFT calculations indicate that this process has an activation energy significantly lower than that of the direct interstitial site exchange mechanism. For 800-1000 K, the MD diffusivities are consistent with the available experimental data within one order of magnitude. The DFT- and the MD-predictions suggest that the diffusion barrier for the interstitialcy mechanism is within 0.31-0.80 eV. The identified migration path, activation energies and diffusivities, and the associated uncertainties are discussed in the context of the previous experimental and theoretical results from the related Ruddlesden-Popper structures.     

Stereoselective Synthesis of (E)-4-Cyano-γ,δ-Unsaturated Nitriles

(E)-4-Cyano-γ,δ-unsaturated nitriles were synthesized from the HMPA promoted sequential transformations of diethyl (cyanomethyl)phosphonate, potassium tert-butoxide, acrylonitrile and aldehydes in 71--83% yield.     

Thermodynamics of oxygen in CaMnO3 − δ

The experimental data for equilibrium oxygen content were used in order to extract increments of partial molar thermodynamic functions of oxygen with changes of oxygen stoichiometry in calcium manganite CaMnO_3???δ . It is shown that along with the oxygen exchange reaction, thermal excitation of Mn⁴⁺ cations plays an important role in equilibration of charged manganese species that appear in response to the loss of oxygen at heating. The interrelation of partial molar enthalpy and entropy of oxygen with electron and ion defect formation parameters is obtained in approximation of the point defect model. The nearly linear changes of oxygen partial molar enthalpy are shown to directly reflect thermally driven changes in concentration of Mn³⁺ cations.