Electrocatalytic activity of carbon-supported metallophthalocyanine catalysts toward oxygen reduction reaction in alkaline solution

Carbon-supported metallophthalocyanine catalysts, composed of a transition central metal M (M = Co, Mn, Ni, Fe) in the phthalocyanine ring, were synthesized in this work. As cathodic reaction in a fuel cell, the oxygen reduction reaction (ORR) was investigated in alkaline medium with linear scanning voltammetry at the surface of these electrocatalysts deposited onto a rotating disk electrode (RDE). It was found that the number of electrons transferred depended on the nature of the metallic cation in the catalyst. Evidences provided with Koutecky-Levich approach showed that iron phthalocyanine (FePc) exhibited the better electrocatalytic ability toward the ORR with four electrons exchanged and low activation overpotential. Among these different as-prepared materials, MnPc and FePc led to a four-electron pathway, while CoPc and NiPc proceeded by a two-electron route. The latter reaction process was also determined with a rotating ring-disk electrode (RRDE), which allowed the determination of hydrogen peroxide formed as O₂ reduction intermediate in a small amount, i.e., less than 1.2 %.     

In Vitro and In Vivo Trypanocidal Efficacy of Synthesized Nitrofurantoin Analogs

African trypanosomes cause diseases in humans and livestock. Human African trypanosomiasis is caused by Trypanosoma brucei rhodesiense and T. b. gambiense. Animal trypanosomoses have major effects on livestock production and the economy in developing countries, with disease management depending mainly on chemotherapy. Moreover, only few drugs are available and these have adverse effects on patients, are costly, show poor accessibility, and parasites develop drug resistance to them. Therefore, novel trypanocidal drugs are urgently needed. Here, the effects of synthesized nitrofurantoin analogs were evaluated against six species/strains of animal and human trypanosomes, and the treatment efficacy of the selected compounds was assessed in vivo. Analogs 11 and 12, containing 11- and 12-carbon aliphatic chains, respectively, showed the highest trypanocidal activity (IC₅₀ < 0.34 µM) and the lowest cytotoxicity (IC₅₀ > 246.02 µM) in vitro. Structure-activity relationship analysis suggested that the trypanocidal activity and cytotoxicity were related to the number of carbons in the aliphatic chain and electronegativity. In vivo experiments, involving oral treatment with nitrofurantoin, showed partial efficacy, whereas the selected analogs showed no treatment efficacy. These results indicate that nitrofurantoin analogs with high hydrophilicity are required for in vivo assessment to determine if they are promising leads for developing trypanocidal drugs.     

New Transition‐Metal Borides containing Trigonal‐Planar B4‐Units: Syntheses and Single‐Crystal Structure Analyses of Ti1.6Os2.4B2 and Ti1–xFexOs2RhB2 (0 < x < 0.5)

Single crystals of Ti_1.6Os_2.4B₂ and the solid solution Ti_1–xFe_xOs₂RhB₂ (0 < x < 0.5) were synthesized by arc‐melting the elements in a water‐cooled copper crucible under an argon atmosphere. The new silver‐like phases, structurally characterized by single‐crystal X‐ray and EDX analyses, crystallize in the hexagonal Ti_1.6Os_1.4RuB₂ structure type (space group (Nr. 189), Z = 3) and contain trigonal‐planar B₄‐units and one‐dimensional chains of titanium or mixed titanium/iron atoms, respectively.     

A Direct Calculation of First-Order Wave Function of Helium

We develop a simple analytic calculation for the first order wave function of helium in a model in which nuclear charge screening is caused by repulsive coulomb interaction. The perturbation term, first-order correlation energy, and first-order wave function are divided into two components, one componentassociated with the repulsive coulomb interaction and the other proportional to magnetic shielding. The resulting first-order wave functions are applied to calculate second-order energies within the model. We find that the second-order energies are independent of the nuclear charge screening constant in the unperturbed Hamiltonian with a central coulomb potential.     

Triangular Arrangement of Ferromagnetic Iron Chains in the High-TC Ferromagnet TiFe1−xOs2+xB2

Transition-metal borides (TMBs) containing B_n-fragment (n>3) have recently gained interest for their ability to enable exciting magnetic materials. Herein, we show that the B₄-containing TiFe_0.64(1)Os_2.36(1)B₂ is a new ferromagnetic TMB with a Curie temperature of 523(2) K and a Weiss constant of 554(3) K, originating from the chain of M₃-triangles (M=64 %Fe+36 %Os). The new phase was synthesized from the elements by arc-melting, and its structure was elucidated by single-crystal X-ray diffraction. It belongs to the Ti_1+xOs_2−xRuB₂-type structure (space group P 2 m, no. 189) and contains trigonal-planar B₄ boron fragments [B−B distance of 1.87(4) Å] interacting with M₃-triangles [M–M distances of 2.637(8) Å and 3.0199(2) Å]. The experimental results were supported by computational calculations based on the ideal TiFeOs₂B₂ composition, which revealed strong ferromagnetic interactions within and between the Fe₃-triangles. This discovery represents the first magnetically ordered Os-rich TMB, thus it will help expand our knowledge of the role of Os in low-dimensional magnetism of intermetallics and enable the design of such materials in the future.     

From 3D to 2D: Structural,Spectroscopic and Theoretical Investigations of the Dimensionality Reduction in the [PtAl2]δ− Polyanions of the Isotypic MPtAl2 Series (M=Ca–Ba,Eu)

Four new MPtAl₂ (M=Ca, Sr, Ba, Eu) compounds, adopting the orthorhombic MgCuAl₂-type structure, have been synthesized from the elements using tantalum ampoules. All compounds are obtained as platelet-shaped crystallites and exhibit an increasing moisture sensitivity with increasing size of the formal M cation. Structural investigations indicate a pronounced elongation of the crystallographic b-axis, which results in a significant distortion of the [PtAl₂]^δ− polyanion. Within the polyanion, layer-like arrangements can be found with bonding Pt−Al interactions within the slab; the increase of the b-axis can be attributed to increasing Al−Al distances and therefore decreasing interactions between the slabs, caused by the differently-sized formal M cations. While the alkaline earth (M=Ca, Sr) representatives exhibit Pauli paramagnetism, BaPtAl₂ shows diamagnetic behavior, finally EuPtAl₂ is ferromagnetic with T_C=54.0(5) K. The effective magnetic moment indicates that the Eu atoms are in a divalent oxidation state, which is confirmed by ¹⁵¹Eu Mössbauer spectroscopic investigations. Measurements below the Curie-temperature show a full magnetic hyperfine field splitting with B_hf=21.7(1) T. ²⁷Al and ¹⁹⁵Pt magic-angle spinning NMR spectroscopy corroborates the presence of single crystallographic sites for the Pt and Al atoms. The large ²⁷Al nuclear electric quadrupolar coupling constants confirm unusually strong electric field gradients, in agreement with the structural distortions and the respective theoretical calculations. X-ray photoelectron spectroscopy has been utilized to investigate the charge transfer within the polyanion. The Pt 4f binding energy decreases with decreasing electronegativity / ionization energy of the alkaline earth elements, suggesting an increasing electron density at the Pt atoms. Theoretical investigations underline the platinide character of the investigated compounds by Bader charge calculations. The analysis of the integrated crystal orbital Hamilton population (ICOHP) values, electron localization function (ELF) and isosurface analyses lead to a consistent structural picture, indicating stable layer-like arrangements of the [PtAl₂]^δ− polyanion.     

Unexpected Synergy between Magnetic Iron Chains and Stacked B6 Rings in Nb6Fe1−xIr6+xB8

The synergistic combination of experiment and density functional theory has led to the discovery of the first ferromagnetic material, Nb₆Fe_1?xIr_6+xB₈, containing in its crystal structure iron chains embedded in stacked B₆ rings. The strong ferromagnetic Fe–Fe interactions found in the iron chains induce an unexpected strengthening of the B–B interactions in the B₆ rings. Beside these strong B–B interactions, strong interlayer metal–boron bonds (Ir–B and Nb–B) ensure the overall structural stability of this phase, while the magnetic Fe–Fe interactions are mainly responsible for the observed ferromagnetic ordering below T_C=350 K.     

On singularities of solution of Maxwell's equations in axisymmetric domains with conical points

Boundary value problems (BVP) in three‐dimensional axisymmetric domains can be treated more efficiently by partial Fourier analysis. Partial Fourier analysis is applied to time‐harmonic Maxwell's equations in three‐dimensional axisymmetric domains with conical points on the rotation axis thereby reducing the three dimensional BVP to an infinite sequence of 2D BVPs on the plane meridian domain Ω_a?? of . The regularity of the solutions u _n (n∈?₀:={0, 1, 2,…}) of the two dimensional BVPs is investigated and it is proved that the asymptotic behaviour of the solutions u _n near an angular point on the rotation axis can be characterized by singularity functions related to the solutions of some associated Legendre equations. By means of numerical experiments, it is shown that the solutions u _n for n∈?₀\{1} belong to the Sobolev space H² irrespective of the size of the solid angle at the conical point. However, the regularity of the coefficient u ₁ depends on the size of the solid angle at the conical point. The singular solutions of the three dimensional BVP are obtained by Fourier synthesis. Copyright © 2006 John Wiley & Sons, Ltd.