Mechanistic study of electrocatalytic oxidation of formic acid at platinum in acidic solution by time-resolved surface-enhanced infrared absorption spectroscopy

Surface-enhanced infrared absorption spectroscopy (SEIRAS) combined with cyclic voltammetry or chronoamperometry has been utilized to examine kinetic and mechanistic aspects of the electrocatalytic oxidation of formic acid on a polycrystalline Pt surface at the molecular scale. Formate is adsorbed on the electrode in a bridge configuration in parallel to the adsorption of linear and bridge CO produced by dehydration of formic acid. A solution-exchange experiment using isotope-labeled formic acids (H(12)COOH and H(13)COOH) reveals that formic acid is oxidized to CO(2) via adsorbed formate and the decomposition (oxidation) of formate to CO(2) is the rate-determining step of the reaction. The adsorption/oxidation of CO and the oxidation/reduction of the electrode surface strongly affect the formic acid oxidation by blocking active sites for formate adsorption and also by retarding the decomposition of adsorbed formate. The interplay of the involved processes also affects the kinetics and complicates the cyclic voltammograms of formic acid oxidation. The complex voltammetric behavior is comprehensively explained at the molecular scale by taking all these effects into account.     

Synthesis of spirocyclic C-arylribosides via cyclotrimerization

[reaction: see text] Spirocyclic C-arylribosides were synthesized from the known gamma-ribonolactone derivative. Lithium acetylide addition followed by glycosylation with 3-(trimethylsilyl)propargyl alcohol converted the ribonolactone to silylated diynes. After desilylation or iodination, subsequent ruthenium-catalyzed cycloaddition of resultant diynes with alkynes or chloroacetonitrile gave spirocyclic C-arylribosides.     

Determination of structures of cobalt(II)-chloro complexes in hydrochloric acid solutions by X-ray absorption spectroscopy at 298 K

The anion exchange reaction is fundamental to the adsorption and desorption of a specific species from a solution phase to an extracting phase, and it is widely used for separation and waste fluid treatment in industrial fields. However, the details of the anion exchange reaction are poorly understood. Quantitative thermodynamic analysis needs a precise solution condition before and after the exchange reaction. Identification of species adsorbed on the anion exchanger is also necessary because there are multiple species in the solution phase in general. Cobalt is a base metal that is widely used in modern society. One of the authors determined the distribution of cobalt-chloro complexes in hydrochloric acid solutions. It is necessary to know what species are adsorbed on anion exchangers for the thermodynamic analysis of the anion exchange reaction. The comparison in structures between the species in the solution phase and adsorbed on anion exchangers reveals what species are adsorbed. Therefore, the determination of the structures of cobalt-chloro complexes in the solution phase is the next step for quantitative analysis. X-ray absorption spectroscopy (XAS) was used for the structure analysis. Factor analysis can decompose extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) spectra consisting of multiple species into individual spectra of single species using the distribution determined using UV-Vis absorption spectra. Fitting EXAFS theoretical models to the decomposed individual spectra determined the structures of three cobalt-chloro complexes: an octahedron of [Co^II(H₂O)₆]²⁺, a distorted octahedron of [Co^II(H₂O)₅Cl]⁺, and a tetrahedron of [Co^IICl₄]^2?. The XANES spectra showed us that the Cl ligand in [Co^II(H₂O)₅Cl]⁺ was attracted to the center atom of Co^II by an electrostatic force, and the bonding system between Cl ligands and Co^II in [Co^IICl₄]^2? involved covalency.

     

Electron-boson coupling and oxygen-isotope effect in the optical conductivity of high-Tc superconductors

We have investigated electron-boson coupling in the optical conductivity of high-T_c superconductors through the optical self-energy. The real part of the self-energy (ReΣ^op(ω)) of YBa₂Cu₃O_y (YBCO) shows a characteristic doping dependence. In the optimally doped YBCO, ReΣ^op(ω) has a single peak around 65 meV, which corresponds to the kink structure of the band dispersion. On the other hand, in the under-doped YBCO, the peak structure of ReΣ^op(ω) splits into two parts. To evaluate contribution from the phonons in electron-boson coupling, we have measured oxygen-isotope effects by substituting ¹⁶O→¹⁸O for the optimally doped and under-doped YBCO.     

Performance of GPRML-AR system in perpendicular magnetic recording channel with thermal decay

The bit-error rate (BER) performance of the generalized partial response maximum likelihood with autoregressive (GPRML-AR) channel model system in perpendicular magnetic recording (PMR) channel with thermal decay is obtained. The 128/130(0,16/8) run-length-limited (RLL) code is used as a recording code. The GPR channel consists of the PR1 channel followed by the reduction circuit of predicted noise. The BER performance is evaluated by computer simulation using a thermal decay model. The model has been obtained by using an approximate equation that represents amplitude degradation of the reproducing waveform with elapsed time based on the experimental data for CoPtCr-SiO₂ PMR media. The Viterbi detector with an AR channel model is employed. Furthermore, long-term degradation of the required SNR to achieve a BER of 10⁻⁴ with elapsed time is obtained and the performance is compared with that of PR1ML system. The results show that the poorer the thermal stability of the medium becomes, the larger the SNR gain of the GPR1ML-AR system over the PR1ML system becomes. The SNR gain also increases with elapsed time.     

Photoluminescent properties and molecular structures of [NaphAu(PPh(3))] and [mu-Naph {Au(PPh(3))}(2)] ClO(4) (Naph = 2-naphthyl)

The complexes [NaphAu(PPh(3))], and [mu-Naph{Au(PPh(3))}(2)]ClO(4), having the Au-C (aromatic) bond have been synthesized and characterized. The unique structure of with two gold atoms bridged by a naphthyl group has been determined by X-ray crystallography. The intramolecular Au-Au separation in is 2.7731(4) A. Upon excitation at 266 nm, both complexes display intraligand phosphorescence at room temperature in solution and in solid state.     

Actinoperylone, a novel perylenequinone-type shunt product, from a deletion mutant of the actVA-ORF5 and ORF6 genes for actinorhodin biosynthesis in Streptomyces coelicolor A3(2)

A novel shunt product, actinoperylone, has been isolated from a deletion mutant of the actVA-ORF5 and ORF6 genes involved in the biosynthesis of a benzoisochromanequinone (BIQ) antibiotic actinorhodin (ACT) in Streptomyces coelicolor A3(2). Spectroscopic analysis revealed its perylenequinone-type skeleton with the four chiral centers, obviously derived from the dimerization of an ACT intermediate. The structure of actinoperylone indicates the essential role of ActVA-ORF5 in the oxygen introduction at C-6, which is common to the formation of BIQ chromophore. The present results also agree with the distribution of the actVA-ORF5 homologues in all known BIQ biosynthetic clusters in streptomycetes.