Spectrophotometric determination of cobalt in steel with 2-(2-thiazolylazo)-4-methyl-5-(sulfomethylamino) benzoic acid (TAMSMB)

Microchimica Acta - A method for the determination of cobalt in steel with 2-(2-thi-azolylazo)-4-methyl-5-(sulfomethylamino) benzoic acid (TAMSMB) is proposed. Iron and manganese were previously...     

Intermediate as catalyst: catalytic asymmetric conjugate addition of nitroalkanes to α,β-unsaturated thioamides

Catalytic asymmetric conjugate addition of nitroalkanes to α,β-unsaturated thioamides is promoted by a mesitylcopper/(R)-DTBM-Segphos precatalyst, affording γ-nitrothioamides in moderate to high syn-selectivity and excellent enantioselectivity. The intermediate Cu-thioamide enolate functions as a soft Lewis acid/hard Br?nsted base cooperative catalyst to drive the catalytic cycle efficiently under proton transfer conditions.     

A Designed Amide as an Aldol Donor in the Direct Catalytic Asymmetric Aldol Reaction

The direct catalytic asymmetric aldol reaction offers efficient access to β‐hydroxy carbonyl entities. Described is a robust direct catalytic asymmetric aldol reaction of α‐sulfanyl 7‐azaindolinylamide, thus affording both aromatic and aliphatic β‐hydroxy amides with high ee values. The design of this transformation features a cooperative interplay of a soft and a hard Lewis acid, which together facilitate the challenging chemoselective enolization by a hard Brønsted base.     

Water oxidation by a ruthenium complex with noninnocent quinone ligands: possible formation of an O-O bond at a low oxidation state of the metal

Tanaka and co-workers reported a novel dinuclear Ru complex, [Ru2(OH)2(3,6-Bu2Q)2(btpyan)](SbF6)2 (3,6-Bu2Q = 3,6-di tert-butyl-1,2-benzoquinone, btpyan = 1,8-bis(2,2':6',2'-terpyrid-4'-yl)anthracene), that contains redox active quinone ligands and has an excellent electrocatalytic activity for water oxidation when immobilized on an indium-tin-oxide electrode (Inorg. Chem., 2001, 40, 329-337). The novel features of the dinuclear and related mononuclear Ru species with quinone ligands, and comparison of their properties to those of the Ru analogues with the bpy ligand (bpy = 2,2'-bipyridine) replacing quinone, are summarized here together with new theoretical and experimental results that show striking features for both the dinuclear and mononuclear species. The identity and oxidation state of key mononuclear species, including the previously reported oxyl radical, have been reassigned. Our gas-phase theoretical calculations indicate that the Tanaka Ru-dinuclear catalyst seems to maintain predominantly Ru(II) centers while the quinone ligands and water moiety are involved in redox reactions throughout the entire catalytic cycle for water oxidation. Our theoretical study identifies [Ru2(O2(-))(Q(-1.5))2(btpyan)](0) as a key intermediate and the most reduced catalyst species that is formed by removal of all four protons before four-electron oxidation takes place. While our study toward understanding the complicated electronic and geometric structures of possible intermediates in the catalytic cycle is still in progress, the current status and new directions for kinetic and mechanistic investigations, and key issues and challenges in water oxidation with the Tanaka catalyst (and its analogues with Cl(-) or NO(2-)substituted quinones and a species with a xanthene bridge instead an antheracene) are discussed.     

Redox behavior of pyridinium salts and their polymers having radical stabilizing groups

The redox behavior of pyridinium salts having various substituents capable of stabilizing pyridinyl radicals at the 4-position was investigated by cyclic voltammetry in water with a platinum electrode, and their redox potentials were more positive in the order of 4-substituents of acetyl > cyano > carbomethoxy > carbamide groups. Sodium dithionite was found to be suitable for a chemical reducing agent of the pyridinium salts. Two types of homopolymers with pendant 4-carbamido-pyridinium groups were prepared and their redox potentials were more positive than the corresponding model compounds. The positive shift might be caused by charge repulsion between the neighboring pyridinium cations on the polymer main chain in the oxidized state.     

Electron transport analysis for improvement of solid-state dye-sensitized solar cells using poly(3,4-ethylenedioxythiophene) as hole conductors

Dye-sensitized solar cells (DSCs) using solid-state hole conductor, poly(3,4-ethylenedioxythiophene) (PEDOT), were fabricated using in-situ photoelectrochemical polymerization giving short-circuit photocurrent density of 3.20 mA cm-2, open-circuit voltage of 0.77 V, and fill factor of 0.50, and the resulting overall conversion efficiency of 1.25% on average under air mass 1.5 conditions. Furthermore, the electron transport properties of the DSCs based on PEDOT (PEDOT/DSCs) were analyzed using light intensity modulation induced photocurrent and photovoltage decay (SLIM-PCV) measurements and electrochemical impedance spectroscopy (EIS) measurements, and then compared to those of the DSCs based on organic liquid electrolyte containing I-/I3- as redox couple (liquid iodide/iodine electrolyte-DSCs, iodide/DSCs for short). The effective filling of PEDOT in the mesopores of dyed TiO2 layers is an important key to achieve the respectable conversion efficiency of PEDOT/DSCs that is comparable with iodide/DSCs.     

A novel lophine-based fluorescence probe and its binding to human serum albumin

The binding of a lophine-based fluorescence probe, 4-[4-(4-dimethylaminophenyl)-5-phenyl-1H-imidazol-2-yl]benzoic acid methyl ester (DAPIM) with human serum albumin (HSA) was investigated by fluorescence spectroscopy under physiological conditions. While DAPIM shows extreme low fluorescence in aqueous solution, DAPIM binding with HSA emits strong fluorescence at 510 nm. The binding constant and binding number determined by Scatchard plot was 3.65 × 10⁶ M⁻¹ and 1.07, respectively. Competitive binding between DAPIM and other ligands such as warfarin, valproic acid, diazepam and oleic acid, were also studied fluorometrically. The results indicated that the primary binding site of DAPIM to HSA is site II at subdomain IIIA. DAPIM can be a useful fluorescence probe for the characterization of drug-binding sites. In addition to the interaction study, because the fluorescence intensity of DAPIM increased in proportion to HSA concentration, its potential in HSA assay for serum sample was also evaluated.     

Inversion of spin photocurrent due to resonant transmission

We report on the inversion of spin-dependent photocurrent via interface localized states formed at the interface of an Fe/n-AlGaAs/GaAs quantum well heterostructure by means of an optical spin orientation technique. A careful adjustment of the excitation photon energy, which is determined by a separate analysis of electroluminescence spectra under a spin injection condition, enables us to explore the spin-dependent characteristics of photoelectron transmission from the quantum well into Fe. The bias dependence of the spin-dependent photocurrent shows clear spikelike features at the voltage which is compatible with the formation of the interface localized resonant states in the Schottky depletion layer.     

An Optochemical Oxygen Scavenger Enabling Spatiotemporal Control of Hypoxia

We present an optochemical O₂ scavenging system that enables precise spatiotemporal control of the level of hypoxia in living cells simply by adjusting the light intensity in the illuminated region. The system employs rhodamine containing a selenium or tellurium atom as an optochemical oxygen scavenger that rapidly consumes O₂ by photochemical reaction with glutathione as a coreductant upon visible light irradiation (560–590 nm) and has a rapid response time, within a few minutes. The glutathione-consuming quantum yields of the system were calculated as about 5 %. The spatiotemporal O₂ consuming in cultured cells was visualized with a hypoxia-responsive fluorescence probe, MAR. Phosphorescence lifetime imaging was applied to confirmed that different light intensities could generate different levels of hypoxia. To illustrate the potential utility of this system for hypoxia research, we show that it can spatiotemporally control calcium ion (Ca²⁺) influx into HEK293T cells expressing the hypoxia-responsive Ca²⁺ channel TRPA1.