Dihydrogen activation by sulfido-bridged dinuclear Ru/Ge complexes: insight into the [NiFe] hydrogenase unready state

A S/SH bridged hetero-dinuclear Ru/Ge complex cation reacted with H(2) to afford the μ-S/μ-H complex. The reaction was considerably slower compared to that of the μ-S/μ-OH complex. Thus, the μ-S/μ-SH and μ-S/μ-OH complexes might provide models for the unready and ready states, respectively, of [NiFe] hydrogenase.     

Disruption of reverse micelles and release of trapped ribonuclease A photochemically induced by Malachite Green leuconitrile derivative

Photoinduced disruption of a sodium bis(2-ethylhexyl) sulfosuccinate (AOT) reverse micelle is triggered by a Malachite Green leuconitrile derivative (MGL). UV irradiation of MGL solubilized in an AOT-water-chloroform mixture creates a cationic surfactant that interacts electrostatically with the anionic AOT. We investigated the disruption of the reverse micelle by using proton nuclear magnetic resonance spectroscopy and found that UV irradiation of MGL decreases the number of water molecules solubilized in the interior of the AOT reverse micelles. Furthermore, the photoinduced disruption of the reverse micelle is shown to release ribonuclease A, which is trapped in the water in the interior of the AOT reverse micelle. This photoinduced release may offer a desirable transport system of biopolymers.     

Noncovalent ligand-to-ligand interactions alter sense of optical chirality in luminescent tris(β-diketonate) lanthanide(III) complexes containing a chiral bis(oxazolinyl) pyridine ligand

Highly luminescent tris[β-diketonate (HFA, 1,1,1,5,5,5-hexafluoropentane-2,4-dione)] europium(III) complexes containing a chiral bis(oxazolinyl) pyridine (pybox) ligand--[(Eu(III)(R)-Ph-pybox)(HFA)(3)], [(Eu(III)(R)-i-Pr-pybox)(HFA)(3)], and [(Eu(III)(R)-Me-Ph-pybox)(HFA)(3)])--exhibit strong circularly polarized luminescence (CPL) at the magnetic-dipole ((5)D(0) → (7)F(1)) transition, where the [(Eu(III)(R)-Ph-pybox)(HFA)(3)] complexes show virtually opposite CPL spectra as compared to those with the same chirality of [(Eu(III)(R)-i-Pr-pybox)(HFA)(3)] and [(Eu(III)(R)-Me-Ph-pybox)(HFA)(3)]. Similarly, the [(Tb(III)(R)-Ph-pybox)(HFA)(3)] complexes were found to exhibit CPL signals almost opposite to those of [(Tb(III)(R)-i-Pr-pybox)(HFA)(3)] and [(Tb(III)(R)-Me-Ph-pybox)(HFA)(3)] complexes with the same pybox chirality. Single-crystal X-ray structural analysis revealed ligand-ligand interactions between the pybox ligand and the HFA ligand in each lanthanide(III) complex: π-π stacking interactions in the Eu(III) and Tb(III) complexes with the Ph-pybox ligand, CH/F interactions in those with the i-Pr-pybox ligand, and CH/π interactions in those with the Me-Ph-pybox ligand. The ligand-ligand interactions between the achiral HFA ligands and the chiral pybox results in an asymmetric arrangement of three HFA ligands around the metal center. The metal center geometry varies depending on the types of ligand-ligand interaction.     

Physically adsorbed chiral stationary phase of avidin on monolithic silica column for capillary electrochromatography and capillary liquid chromatography

The physical adsorption method proposed previously has been successfully applied to a monolithic silica column. By virtue of the physical adsorption, a chiral stationary phase of avidin was prepared onto the silica monolith. The phase ratio of resulting stationary phase was evaluated with frontal analysis. The method proved to be comparable in phase ratio to the chemical bonding methods used in high-performance liquid chromatography (HPLC). Enantiomer separations were carried out in capillary electrochromatography (CEC) and capillary liquid chromatography (CLC) modes. Due to its larger phase ratio, the resulting column showed more powerful separation capability as compared to open-tubular CEC (OTCEC). Twelve chiral compounds were baseline-resolved. The resulting column showed high separation efficiency, with average theoretical plate numbers of 66 000/m for CLC and 122 000/m for CEC. Good reproducibility was observed, with RSD value less than 1.3% for retention time, retention factor and separation factor, and less than 6.6% for plate counts and resolution (n = 40). Fast separations were achieved with a short column. The test enantiomers were baseline-resolved within 4 min under CLC and CEC modes. In addition, field-enhanced sample injection (FESI) was coupled to CLC as well as CEC to improve the detection sensitivity.     

Crystal Structure, Electric and Magnetic Properties of Layered Cobaltite β-NaxCoO2

The layered oxide thermoelectric material β-Na_0.67CoO₂ has been studied by powder neutron diffraction, electric and magnetic measurements. This compound includes an edge-sharing CoO₆ slab and a highly vacant Na⁺ sheet in a unit cell (space group symmetry C2/m, a=4.9023(4) Å, b=2.8280(2) Å, c=5.7198(6) Å and β=105.964(6)° at 300 K). The evaluated formal valence of cobalt ion, +3.33(1), is ascribed to the coexistence of Co³⁺ and Co⁴⁺ in the ratio 2:1. Polycrystalline β-Na_0.67CoO₂, a p-type thermoelectric material, exhibits metallic behavior of the electric resistivity below 300 K. The Curie-Weiss-type magnetic susceptibility indicates antiferromagnetic interactions between magnetic cobalt ions in the edge-sharing CoO₆ slab.     

Robust and simple interface for microchip electrophoresis-mass spectrometry

A robust and simple interface for microchip electrophoresis-mass spectrometry (MCE-MS) was developed using a spray nozzle connected to the exit of the separation channel of the microchip. The spray nozzle was attached to the microchip using a polyether ether ketone screw without adhesive, thus allowing easy replaced. Sample injection and electrophoretic separation was performed by control of the voltage only. The analysis of a few basic drugs was performed using the optimized MCE-MS system. The separation was improved by using a high-viscosity separation buffer and a spray nozzle with a small bore size. This system was also applied to the separation of peptides and protein-trypsin digests. Sample adsorption was minimized by adding acetonitrile to the separation buffer when using a quartz microchip.     

The unusual micelle micropolarity of partially fluorinated gemini surfactants sensed by pyrene fluorescence

New gemini surfactants having two fluorocarbon chains were prepared by refluxing partially fluorinated alkyl bromide with N,N,N',N'-tetramethyl-1,6-diaminohexane in acetonitrile. The partially fluorinated gemini surfactants containing a six-methylene spacer chain are easily soluble in water. The critical micelle concentrations (cmc's) were determined by various fluorescent probe methods. The hydrophobicity of a CF2 group was estimated to be 1.5 times that of a CH2 group according to the cmc values. The micelle micropolarity of a fluorocarbon gemini sensed by pyrene fluorescence was unusually high, suggesting an apparent iceberg-like environment in the location of pyrene. The significantly small micelle aggregation numbers of fluorinated gemini surfactants were ascertained by the pyrene fluorescence quenching method. The micelle ionization degree estimated by fluorescence quenching of 6-methoxy-N-(3-sulfopropyl)quinolinium (SPQ) gave tendencies similar to those of the corresponding hydrocarbon geminis.     

Cytotoxic diterpenoids from Vietnamese medicinal plant Croton tonkinensis GAGNEP

Six new ent-kaurane-type diterpenoids were isolated from the leaves of the endemic Vietnamese medicinal plant Croton tonkinensis GAGNEP. (Euphorbiaceae) together with three known ent-11alpha-acetoxy-7beta,14alpha-dihydroxykaur-16-en-15-one (1), ent-kaur-16-en-15-one 18-oic acid (5) and ent-18-hydroxykaur-16-ene (7). Their structures were determined by spectroscopic analyses to be ent-7beta-acetoxy-11alpha-hydroxykaur-16-en-15-one (2), ent-18-acetoxy-11alpha-hydroxykaur-16-en-15-one (3), ent-11alpha-acetoxykaur-16-en-18-oic acid (4), ent-15alpha,18-dihydroxykaur-16-ene (6), ent-11alpha,18-diacetoxy-7beta-hydroxykaur-16-en-15-one (8), and ent-(16S)-1alpha,14alpha-diacetoxy-7beta-hydroxy-17-methoxykauran-15-one (14). ent-Kaurane-type diterpenoids from Croton tonkinensis 2-4, 6, and 9-13, were tested for toxicity in the brine shrimp lethality assay. Compounds 9, 10, and 12 demonstrated significant activity, compounds 2, 3, 6, and 11 showed weak activity, and compounds 4 and 13 were inactive.     

Anion-selective properties of alkali metal-free lead phosphate glasses containing silver chloride and their application in an ion-selective electrode

Alkali-free lead phosphate glasses containing silver chloride have been developed for anion responsive sensors. From measurements of the final glass compositions by electron probe microanalysis, it became clear that some of chloride ions in the glass bulk were not volatilized during the glass melting process. Compared with phosphate glasses containing silver oxide, the new glass electrodes containing silver chloride could respond more rapidly, although the response behaviour for anionic species were similar. From the electrode potential vs. time curve for the anionic species, the potential rapidly reached equilibrium when these concentrations varied from 10^?5 to 10^?2 M. The response times, t₉₅, to thiocyanate of the new glass electrode and the phosphate glass electrode containing silver oxide were 30 and 110 s, respectively. Moreover, the response time required for an initial potential change with a concentration jump of thiocyanate with the new glass electrode was found to be independent of the membrane thickness within about 2 mm and of the measuring temperature between 15 and 40°C. It is concluded that the diffusion process of species such as silver ion in the glass bulk does not take part in the initial part of the response behaviour.     

Catalytic enantioselective cyclopropanation of allylic alcohols using recyclable fluorous disulfonamide ligand

Cyclopropanation of allylic alcohols with Et₂Zn and CH₂I₂ in the presence of a catalytic amount of fluorous disulfonamide 3 afforded the corresponding cyclopropylmethanols in 69-96% yield with 49-83% ee. The fluorous ligand 3 was readily recovered from the reaction mixture by the fluorous solid-phase extraction (FSPE) and could be reused without a significant loss of the catalytic activity and enantioselectivity.