Structural phase transition and structural properties in oxygenated La2CuO4+y; y ∼0.02

The crystal structure of the oxygenated La₂CuO_4+y; y ～0.02 has been studied by X-ray diffraction. It is found that the structural phase transition from tetragonal to orthorhombic symmetry occurring at about 450 K (Tc) is of second order and shows diffuse scattering above Tc. The diffuse scattering is related to static and/or dynamic short-range order of cooperative tilts of rigid-like elongated CuO₆ octahedra, which make two-dimensional networks stacked along the [001] axis. The structures at room temperature and 210K are determined using a 4-circle X-ray diffractometer and have the orthorhombic space group ¹⁰D_2h-Pccn. The structure is mainly characterized by anisotropic cooperative tilts of the CuO₄ octahedra around the [100]_p and [010]_p primitive axes in two-dimensional octahedron-networks, where suffix “p” means pseudo K₂NiF₄-type structure. The anisotropy of the tilting-angles results from pushing by excess oxygen atoms to apical oxygen atoms of the CuO₆ octahedra. It is also found by refinement of the structure that the excess oxygen atoms are randomly sited at the atomic coordinates (1/4,1/4,0.244) and/or (1/4, 1/4,0.279).     

Universality in heavy fermion systems with general degeneracy

We discuss the relation between the T2 coefficient of electrical resistivity A and the T-linear specific-heat coefficient gamma for heavy-fermion systems with general N, where N is the degeneracy of quasiparticles. A set of experimental data reveals that the Kadowaki-Woods relation, A/gamma2=1 x 10(-5) muOmega cm(K mol/mJ)2, collapses remarkably for large-N systems, although this relation has been regarded to be commonly applicable to the Fermi liquids. Instead, based on the Fermi-liquid theory we propose a new relation, A /gamma2=1 x 10(-5) with A =A/1/2N(N-1) and gamma =gamma/1/2N(N-1). This new relation exhibits an excellent agreement with the data for the whole range of degenerate heavy fermions.     

High ductility carbon nanoball

High compression strength and high ductility spherical nanoballs were produced by electric arc discharge with a carbon electrode containing silicon, oxygen, potassium, and sodium. Compression tests of the nanoballs were conducted by application of a load to nanoballs inserted between two polished sample stages with nanolevel surface roughness. Experimental estimation of the compression strength of nanomaterials was enabled by careful selection and polishing of the sample stage materials.     

Optical charge transfer absorption in proton injected tungsten oxide thin films analyzed with spectroscopic ellipsometry

Tungsten oxide thin films with protons injected during deposition (H_xWO₃) were prepared using reactive direct-current magnetron sputtering in a mixture of argon, oxygen, and hydrogen gases. The concentration of injected protons, given by the x-values in H_xWO₃, was evaluated by electrochemically ejecting protons from the films. The complex dielectric functions (? = ?₁ + i?₂) of the films were estimated by analyzing the experimental spectra of Ψ and Δ measured with spectroscopic ellipsometry using the model composed of a homogeneous tungsten bronze layer with an additional surface roughness layer. As a result of this analysis, the imaginary part of the dielectric function ?₂, which represents optical absorption, was composed of two Lorentz oscillator terms whose peak positions were about 1.0 eV (L₁) and 1.6 eV (L₂). The two terms with L₁ and L₂ are assumed using the modified site-saturation model to be due to optical charge transition between W⁶⁺ and W⁵⁺ sites, and between W⁶⁺ and W⁴⁺ sites, respectively.     

(2‐Aminoethanethiolato‐N,S)bis(ethylenediamine‐N,N′)cobalt(III) dinitrate

In the title compound, [Co(C₂H₆NS)(C₂H₈N₂)₂](NO₃)₂, the Co^III atom has a slightly distorted octahedral geometry, coordinated by one 2‐amino­ethane­thiol­ate and two ethyl­enedi­amine ligands. The three five‐membered chelate rings adopt a gauche conformation with the unfavoured (lel)₂(ob) form, which is ascribed to hydrogen bonds between the amine groups in the complex cation and the nitrate counter‐anions [N?O 2.900 (3)–3.378 (3) Å].     

Total Synthesis and Biological Evaluation of Heliolactone

Strigolactones are phytohormones, which affect diverse aspects of plant growth and development with potential application in modern agriculture. Recently, heliolactone has been isolated as a non‐canonical type of strigolactone from the root exudates of sunflower, and it could be involved in signaling in the rhizosphere as well as in planta. However, its biological activity is yet to be evaluated, due to its relative chemical instability and its low natural abundance. Herein, we describe the gram‐scale synthesis of heliolactone and its derivatives by using Stille cross‐coupling as the key bond‐forming reaction, and we disclose some of their biological activities (soil stability, binding ability to strigolactone receptor, corn germination, sunflower germination, Orobanche cumana germination and leaf senescence) in comparison with other canonical and non‐canonical strigolactones.     

An Engineered Aryl Acid Adenylation Domain with an Enlarged Substrate Binding Pocket

Adenylation (A) domains act as the gatekeepers of non‐ribosomal peptide synthetases (NRPSs), ensuring the activation and thioesterification of the correct amino acid/aryl acid building blocks. Aryl acid building blocks are most commonly observed in iron‐chelating siderophores, but are not limited to them. Very little is known about the reprogramming of aryl acid A‐domains. We show that a single asparagine‐to‐glycine mutation in an aryl acid A‐domain leads to an enzyme that tolerates a wide range of non‐native aryl acids. The engineered catalyst is capable of activating non‐native aryl acids functionalized with nitro, cyano, bromo, and iodo groups, even though no enzymatic activity of wild‐type enzyme was observed toward these substrates. Co‐crystal structures with non‐hydrolysable aryl‐AMP analogues revealed the origins of this expansion of substrate promiscuity, highlighting an enlargement of the substrate binding pocket of the enzyme. Our findings may be exploited to produce diversified aryl acid containing natural products and serve as a template for further directed evolution in combinatorial biosynthesis.