Mixed-Valent Trinuclear CoIII-CoII-CoIII Complex with 1,3-Bis(5-chlorosalicylideneamino)-2-propanol

A mixed-valent trinuclear complex with 1,3-bis(5-chlorosalicylideneamino)-2-propanol (H₃clsalpr) was synthesized, and the crystal structure was determined by the single-crystal X-ray diffraction method at 90 K. The molecule is a trinuclear Co^III-Co^II-Co^III complex with octahedral geometries, having a tetradentate chelate of the Schiff-base ligand, bridging acetate, monodentate acetate coordination to each terminal Co³⁺ ion and four bridging phenoxido-oxygen of two Schiff-base ligands, and two bridging acetate-oxygen atoms for the central Co²⁺ ion. The electronic spectral feature is consistent with the mixed valent Co^III-Co^II-Co^III. Variable-temperature magnetic susceptibility data could be analyzed by consideration of the axial distortion of the central Co²⁺ ion with the parameters Δ = –254 cm⁻¹, λ = –58 cm⁻¹, κ = 0.93, tip = 0.00436 cm³ mol⁻¹, θ = –0.469 K, g_z = 6.90, and g_x = 2.64, in accordance with a large anisotropy. The cyclic voltammogram showed an irreversible reduction wave at approximately −1.2 V·vs. Fc/Fc⁺, assignable to the reduction of the terminal Co³⁺ ions.     

A New Supramolecular Tetraruthenated Cobalt (II) Porphyrazine Displaying Outstanding Electrocatalytical Performance in Oxygen Evolution Reaction

A new supramolecular electrocatalyst for Oxygen Evolution Reaction (OER) was synthesized from a central multibridging cobalt tetrapyridylporphyrazine (CoTPyPz) species by attaching four [Ru(bpy)₂Cl]⁺ groups. Both CoTPyPz and the tetraruthenated cobalt porphyrazine species, TRuCoTPyPz, form very homogenous molecular films just by dropcasting their methanol solutions onto GCE electrodes. Such films exhibited low overpotentials for O₂ evolution, e.g., 560 e 340 mV, respectively, displaying high stability, typically exceeding 15 h. The kinetic parameters obtained from the Tafel plots showed that the peripheral complexes are very important for the electrocatalytic activity. Hyperspectral Raman images taken along the electrochemical process demonstrated that the cobalt center is the primary active catalyst site, but its performance is enhanced by the ruthenium complexes, which act as electron-donating groups, in the supramolecular system.     

Preparation of Ring and Chain Condensed Oligophosphates

Preparations of small-ring and short-chain condensed phosphates were made by dry and wet processes, respectively. The crystallization of tetra- hexa-, and octaphosphates from the phosphate solution was not easy, and metal salts of these oligophosphates were amorphous and unstable at normal temperature. Guanidine tetraphosphate and ammonium hexaphosphate were crystalline and stable at normal temperature.     

Polymeric Electron Carriers

Polymers containing 1,4-dihydronicotinamide (P-NAH) alloxan (P-A), and viologen (P-V²⁺) moieties were synthesized and characterized. P-NAH reduced various organic substances such as lipoic acid, alloxan, and viologens and also immobilized quinone mediated by alloxan. P-A was reduced to the polymer-bearing alloxan radical and the dialuric acid structure without crosslinks by one- and two-electron reduction, respectively, and P-A also mediated the redox reaction occurring between aqueous and organic (water-immiscible) layers. P-V²⁺ was converted to the stable viologen radical reversibly by one-electron reduction. Electric potentials and currents on photo-reduction of P-V²⁺ and catalytic behavior of P-V²⁺ in the reduction of carbonyl compounds were examined.     

Fast and quantitative analysis of branched-chain amino acids in biological samples using a pillar array column

In this study, a fast and quantitative determination method for branched-chain amino acids (BCAAs), namely leucine, isoleucine, and valine, was developed using a pillar array column. A pillar array column with low-dispersion turns was fabricated on a 20?×?20-mm² microchip using multistep ultraviolet photolithography and deep reactive ion etching. The BCAAs were fluorescently labeled with 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F), followed by reversed-phase separation on the pillar array column. The NBD derivatives of the three BCAAs and an internal standard (6-aminocaproic acid) were separated in 100 s. The calibration curves for the NBD-BCAAs had good linearity in the range of 0.4–20 μM, using an internal standard. The intra- and interday precisions were found to be in the ranges of 1.42–3.80 and 2.74–6.97 %, respectively. The accuracies for the NBD-BCAA were from 90.2 to 99.1 %. The method was used for the analysis of sports drink and human plasma samples. The concentrations of BCAAs determined by the developed method showed good agreements with those determined using a conventional high-performance liquid chromatography system. As BCAAs are important biomarkers of some diseases, these results showed that the developed method could be a potential diagnostic tool in clinical research.     

One‐Pot Synthesis of 2‐Arylthio‐2‐cyclohexenone Derivatives by the Diels–Alder Reaction of 4‐Arylthio‐3‐hydroxy‐2‐pyrones

The base‐catalyzed Diels–Alder reactions of 4‐arylthio‐3‐hydroxy‐2‐pyrones are reported. Treatment of 4‐arylthio‐3‐hydroxy‐2‐pyrones and dienophiles with triethylamine gave 2‐arylthio‐2‐cyclohexenone derivatives by the Diels–Alder reaction involving a decarboxylation in excellent to reasonable yields.     

Theoretical analysis of correlation between ionization threshold fluence in IR‐MALDI and IR absorption spectrum of matrix molecules

To investigate the correlation between the wavelength dependence of ionization threshold fluence of target molecule in matrix‐assisted laser desorption/ionization by infrared (IR) laser and the IR absorption spectrum of matrix molecule, we have analyzed the IR absorption spectra of four matrix molecules using density functional theory and correlated ab initio molecular orbital method. The calculated IR absorption spectra of the isolated molecules showed more qualitative correlation with the wavelength dependence of ionization threshold fluence than those of the solid state structures. We can consider that a portion of matrix molecules lost the ordered crystal structure and that the transition to the diluted or isolated state occurred at the early process of IR laser irradiation. © 2012 Wiley Periodicals, Inc.     

Additional cytotoxic substances isolated from the sponge-derived Gymnascella dankaliensis

A continuous investigation of secondary metabolites produced by the sponge-derived fungus, Gymnascella dankaliensis, has yielded a new polyketide tyrosine derivative, dankastatin C (3) and the known steroid, demethylincisterol A₃ (4), which was originally found from a Homaxinella marine sponge. The stereostructure of the new compound has been determined based on the analysis of 1D and 2D NMR data. Dankastatin C (3) showed potent cell growth inhibitory activity against the murine P388 cell line.     

Synthesis and properties of novel 1,1‐difluoropropoxy‐linked liquid crystalline compounds of negative dielectric anisotropy

A series of liquid crystalline compounds having the difluoropropyleneoxy moiety (–OCF₂C₂H₄–) as a linking group has been synthesized. The physical properties, i.e. dielectric anisotropy, birefringence, viscosity and phase transition temperatures, have been measured. This novel class of compounds shows a larger negative dielectric anisotropy than the corresponding compounds having a propyleneoxy (–OC₃H₆–) linking group. Their dielectric properties may be explained by the combined effect of fluorine atoms with large electron negativities and the electron donating feature of an oxygen atom substituted on the same carbon atom. The semi‐empirical quantum calculation method (AM1) also confirmed this dielectric behaviour of the difluoropropyleneoxy linkage group.