Enhancing the superconducting transition temperature of the heavy fermion compound CeIrIn5 in the absence of spin correlations

We report on a pressure- (P-)induced evolution of superconductivity and spin correlations in CeIrIn(5) via the (115)In nuclear-spin-lattice-relaxation rate measurements. We find that applying pressure suppresses dramatically the antiferromagnetic fluctuations that are strong at ambient pressure. At P = 2.1 GPa, T(c) increases to T(c) = 0.8 K, which is twice T(c) (P = 0 GPa), in the background of Fermi-liquid state. This is in sharp contrast to the previous case in which a negative, chemical pressure (replacing Ir with Rh) enhances magnetic interaction and increases T(c). Our results suggest that multiple mechanisms work to produce superconductivity in the same compound CeIrIn(5).     

Electrical properties and defect structure of rutile slightly doped with Cr and Ta

The electrical conductivity of rutile doped with 0.3–3 at % Ta or 0.1–1 at % Cr is reported as a function of oxygen pressure in the temperature range 1273–1623 K. The results are discussed in terms of a point defect model, on assuming a charge compensation of foreign impurities by usual lattice point defects. In the case of Ta-doped materials, two kinds of charge compensation by an electronic or a lattice defect may occur, according to the oxygen pressure and temperature, the essential features of which are in good agreement with the theoretical analysis. While chromium is incorporated as a trivalent species under a reducing atmosphere, the lack of ionic conductivity due to compensating lattice defects prevents any definitive conclusion about the valence state of the foreign chromium cations under oxidizing conditions. Some additional information and some conclusions are drawn concerning the transport properties of pure or doped titanium dioxide at high temperature.     

Local and global gauge symmetries in temporal gauge

In the temporal gauge formalism, in order to make a distinction between the global limit of local gauge transformations and global ones a non-local operator, θ, is introduced. It is claimed that what kind of θ is used is equivalent to what kind of gauge-fixing schemes is chosen. Along this idea, in non-abelian theories the coulomb, axial and unitary gauges have been investigated. In the unitary gauge spontaneous breakdown of global gauge symmetry has been found to be reduced to a problem of the boundary condition for the Higgs field and the occurrence of symmetry breaking has been concluded.     

Formation and Isolation of a Four‐Electron‐Reduced Porphyrin Derivative by Reduction of a Stable 20π Isophlorin

The two‐electron reduction of a diprotonated dodecaphenylporphyrin derivative by Na₂S₂O₄ gave a corresponding isophlorin ( Iph ) selectively. Formation of Iph was confirmed by spectroscopic measurements and the isolation of tetramethylated Iph . Further reduction of Iph proceeded to form an unprecedented four‐electron‐reduced porphyrin ( IphH₂ ), which was fully characterized by spectroscopic and X‐ray crystallographic analysis. IphH₂ , with a unique conformation, could be oxidized to reproduce the starting porphyrin, resulting in a proton‐coupled four‐electron reversible redox system.     

Intramolecular construction of trifluoromethyl group by the palladium-catalyzed reaction of 2,3,3-trifluoroallylic carbonates with O-nucleophiles

The synthesis of the trifluoromethyl group containing enol ethers by the palladium-catalyzed intermolecular reaction of 2,3,3-trifluoroallylic carbonates with oxygen nucleophiles was accomplished. The reaction proceeds through the intermolecular attack of oxygen nucleophiles on the C-2 carbon atom of the allylic unit, and the intramolecular fluorine atom shift from the C-2 position to the C-3 position. The reactions with several types of alcohols and phenols proceeded smoothly, and afforded the corresponding trifluoromethyl group containing enol ethers in good to high yields.     

NMR characterization of α- and β-mannopyranurono-2,6-lactones

Determining the stereochemistry at the anomeric position of glycosides is imperative in chemical synthesis. As for 1,2-cis-β-glycosides such as β-mannosides, ¹³C-¹H coupling constants, ¹J_CHs, are conventionally used when glycosides are in an ordinary chair conformation. In this work, we searched for appropriate criteria to determine the stereochemistry of products in a recently developed glycosylation reaction using 2,6-lactones. As a result, we found that α-glycosides exhibited vicinal coupling constants of around 3.0?Hz?at the anomeric proton, as well as a long-range coupling between protons at C-1 and C-5, whereas β-glycosides had coupling constants of 1.2?Hz?at most. These figures are expected to be useful for future assignments. In addition, the observations obtained from this study revealed the conformation of glycosides with a 2,6-lactone moiety.     

Double amination of 2-fluoroallylic acetates by palladium catalysts

We accomplished the palladium-catalyzed double substitution of 2-haloallylic acetates with nitrogen nucleophiles. During the Pd₂(dba)₃/DPPE-catalyzed reaction of 2-fluoroallylic acetates with N-substituted-p-toluenesulfonamide, two equivalents of nitrogen nucleophiles were introduced to the allyl unit with a Z-selectivity through the carbon–fluorine bond cleavage. We further demonstrated the reaction of 2-chloroallylic acetates, and succeeded in obtaining the same doubly-substituted products in good yields with a high Z-selectivity.