Scaffolding, ladders, chains, and rare ferrimagnetism in intermetallic borides: electronic structure calculations and magnetic ordering

The electronic structures of "Ti(9-n)Fe(2+n)Ru(18)B(8)" (n=0, 0.5, 1, 2, 3), in connection to the recently synthesized Ti(9-n)Fe(2+n)Ru(18)B(8) (n=1, 2), have been investigated and analyzed using LSDA tight-binding calculations to elucidate the distribution of Fe and Ti, to determine the maximum Fe content, and to explore possible magnetic structures to interpret experimental magnetization results. Through a combination of calculations on specific models and using the rigid band approximation, which is validated by the DOS curves for "Ti(9-n)Fe(2+n)Ru(18)B(8)" (n=0, 0.5, 1, 2, 3), mixing of Fe and Ti is anticipated at both the 2b- and 4h-chain sites. The model "Ti(8.5)Fe(2.5)Ru(18)B(8)" (n=0.5) revealed that both Brewer-type Ti-Ru interactions as well as ligand field splitting of the Fe 3d orbitals regulated the observed valence electron counts between 220 and 228 electrons/formula unit. Finally, models of magnetic structures were created using "Ti(6)Fe(5)Ru(18)B(8)" (n=3). A rigid band analysis of the LSDA DOS curves concluded preferred ferromagnetic ordering at low Fe content (n≤0.75) and ferrimagnetic ordering at higher Fe content (n>0.75). Ferrimagnetism arises from antiferromagnetic exchange coupling in the scaffold of Fe1-ladder and 4h-chain sites.     

Poly-μ-2,5-dimethylpyrazine-μ-dithiocyanato-N, S,S-dicopper(I): a three-dimensional coordination polymer containing both molecular and anionic rod ligands

Reaction of CuSCN with 2,5-dimethylpyrazine (2,5-me₂pyz) yields a polymeric material, [Cu₂(SCN)₂(2,5-me₂pyz)], which has been crystallographically characterized. The compound crystallizes in the monoclinic space group P2₁/N with a = 5.6850(2) Å, b = 6.92877(3) Å, c = 14.3575(6) Å, = 93.435(1), and Z = 2. It contains [Cu(SCN)] sheets in which each thiocyanate ligand acts in a -N,S,S-bridging mode. The sheets are bridged by 2,5-dimethylpyrazine ligands to generate a three dimensional network. The compound has also been characterized by infrared spectroscopy and thermogravimetric analysis.     

Divergent photoreactivity in intramolecular cycloadditions amongst prop-2-enylcyclopentenones

Irradiation of the 1,4-diene(8) gave the corresponding geometrical isomer(10) whereas (5) produced the vinylcyclopropane(6), and (11a) and (11b) (in MeOH) led to the tricyclic adduct(14) and the isomeric cyclopentenone (15) respectively.     

Synthesis,spectroscopic characterization and fungicidal activity of triphenyltin derivatives of N,N-dimethylglycine: Crystal structure of [dimethyl(carboxylatomethyl)ammonium]-chlorotriphenylstannate

The new triorganotin complexes formulated as Me₂HNCH₂COO · Ph₃SnX, X = Cl, NCS were prepared and spectroscopically characterized, and their fungicidal properties against Ceratocystis ulmi were determined. An X-ray structure for [dimethyl(carboxylatomethyl)ammonium] chlorotriphenylstannate is also reported.     

Homogeneous saturation of the 6328 Å neon laser transition due to collisions in the weak collision model

Measurement of the collision broadened lineshapes of the 6328 Å Ne laser transition in absorbing ²⁰Ne and amplifying 7 : 1 ³He : ²⁰Ne discharges indicate that the transition saturates with a Doppler component as well as the Lorentzian holes expected of a Doppler broadened line. The homogeneous saturation, caused by elastic velocity-changing collisions, is much stronger in ²⁰Ne than in 7 : 1 ³He : ²⁰Ne. The results are in good agreement with a rate equation formulation in which the effect of velocity-changing collisions giving rise to cross-relaxation is introduced through the Fokker-Planck probability function.     

Orbites hétérocliniques au voisinage d'une bifurcation de Poincaré dégénérée pour les champs de vecteurs de ℝ2

We consider a ²-ordinary differential equation, where the fixed point (0, 0) presents a degenerate Poincaré-bifurcation of resonancek(=2k) and dominanced(=k–1). We prove the existence of a 2-dimensional linear manifoldV in the parameter space. , on which the perturbed dominant differential system (SD) possesses heteroclinic orbits between fixed points. The numerical continuation of the local stable or unstable manifolds of the saddle fixed points shows that for any neighborhood, in , of a point ofV corresponding to a saddle heteroclinic orbit, there exists only one stable (resp. unstable) periodic orbit close to the stable — in the Andronov sense [1]-(resp. unstable) heteroclinic orbit. Applications are given fork=4 andk=6.     

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.