Synthesis and structure of 1-metallacyclopent-3-yne complexes of group 4 metals

Five-membered metallacyclic alkyne complexes of titanium and hafnium, 1,1-bis(cyclopentadienyl)-1-titanacyclopent-3-yne (2) and trans-1,1-bis(cyclopentadienyl)-2,5-trimethylsilyl-1-hafnacyclopent-3-yne (6), were synthesized and structurally characterized. The structural analysis of titanium complex 2 implied a larger contribution of an η⁴-π,π-coordinated structure. The hafnium compound 6 has a similar structure to the corresponding zirconium analogue (1a), although slight differences in the bond lengths and angles were observed. A novel 1-zirconacyclopent-3-yne complex, 1,1-bis(methylcyclopentadienyl)-2,5-bis(trimethylsilyl)-1-zirconacyclopent-3-yne (5), was also prepared and the structure of the trans-isomer was determined.     

Fine synthetic nucleoside chemistry based on nucleoside natural products synthesis

Synthetic nucleoside chemistry based on nucleoside natural products synthesis were described. First, a samarium diiodide (SmI 2)-promoted aldol reaction with the use of alpha-phenylthioketone as an enolate was developed. The characteristics of this reaction are that the enolate can be regioselectively generated and the aldol reaction proceeds under near neutral condition. This reaction is proved to be a powerful reaction for the synthesis of complex nucleoside natural products, and herbicidin B and fully protected tunicaminyluracil, which were undecose nucleoside natural products, were synthesized. Next, the synthetic methodology of the caprazamycins, which are promising antibacterial nucleoside natural products, was also developed by the strategy including beta-selective ribosylation without using a neighboring group participation. Our synthetic route provided a range of key analogues with partial structures to define the pharmacophore. Simplification of the caprazamycins was further pursued to develop diketopiperazine analogs.     

Direct Monitoring of γ‐Glutamyl Transpeptidase Activity In Vivo Using a Hyperpolarized 13C‐Labeled Molecular Probe

The γ‐glutamyl transpeptidase (GGT) enzyme plays a central role in glutathione homeostasis. Direct detection of GGT activity could provide critical information for the diagnosis of several pathologies. We propose a new molecular probe, γ‐Glu‐[1‐¹³C]Gly, for monitoring GGT activity in vivo by hyperpolarized (HP) ¹³C magnetic resonance (MR). The properties of γ‐Glu‐[1‐¹³C]Gly are suitable for in vivo HP ¹³C metabolic analysis since the chemical shift between γ‐Glu‐[1‐¹³C]Gly and its metabolic product, [1‐¹³C]Gly, is large (4.3 ppm) and the T₁ of both compounds is relatively long (30 s and 45 s, respectively, in H₂O at 9.4 T). We also demonstrate that γ‐Glu‐[1‐¹³C]Gly is highly sensitive to in vivo modulation of GGT activity induced by the inhibitor acivicin.     

The separation of tellurium(IV) from water and sea water by flotation with hydrated iron(III) oxide

A flotation separation is described for sub-microgram levels of tellurium(IV) from 1-1 samples of water and sea water. Tellurium(IV) is coprecipitated with hydrated iron(III) oxide at pH 8–9. The precipitate is floated with the aid of surfactant solutions and small nitrogen bubbles, separated and dissolved in dilute hydrochloric acid. Tellurium is then converted to hydrogen telluride with sodium tetrahydroborate and measured by atomic absorption spectrometry. Recovery of added tellurium (0.4 and 0.8 μg l^?1) was about 83%. The time required for the preconcentration is 30 rain per sample, including 15 rain stirring.     

Laser-induced shape transformation of gold nanoparticles below the melting point: the effect of surface melting

Relatively large gold nanoparticles (mean diameter of major axis 38.2 nm, mean aspect ratio 1.29) in aqueous solution were found to undergo shape transformations from ellipsoids to spheres at ca. 940 degrees C, which is much lower than their melting point, ca. 1060 degrees C. The shape transformation of gold nanoparticles induced by a single pulse of a Nd:YAG laser (lambda = 355 nm, pulse width = 30 ps) was directly observed by a transmission electron microscope (TEM). Analysis of the experimental data showed that the threshold energy for photothermally induced shape transformation was on the order of 40 fJ for a particle, which is smaller than the energy, 67 fJ, required for its complete melting. Estimations based on the heat balance and surface melting model revealed that the temperature which particles reach after a single laser pulse was about 940 degrees C, with the thickness of the liquid layer on the surface of the solid core being 1.4 nm. We also examined thermally induced shape transformation of gold nanoparticles on Si substrates; above 950 degrees C they changed their shapes to spheres, which supported our estimation. Due to the surface melting of particles, their shape transformation occurs at a temperature much lower than their melting point.     

Zero-CO2 emission and low-crossover 'rechargeable' PEM fuel cells using cyclohexane as an organic hydrogen reservoir

High performance (open circuit voltage = 920 mV, maximum power density = 14-15 mW cm(-2)) of the PEM fuel cell was achieved by using cyclohexane as a fuel with zero-CO2 emission and lower-crossover through PEM than with a methanol-based fuel cell.     

Analysis of ″stepwise″ heterocoagulation process of small cationic polymer particles onto large anionic polymer particles using dynamic light scattering

In order to clarify in detail the process of the stepwise heterocoagulation of small polymer particles (SP) onto large polymer particles (LP), which we proposed to prepare anomalous polymer particles, the particle-size distribution in each step was estimated using dynamic light scattering.SP andLP have surface charges opposite to each other in emulsion states.SP were produced by emulsion copolymerization of styrene and methacryloyloxyethyltrimethylammonium chloride, andLP by emulsion terpolymerization of styrene, butyl acrylate, and methacrylic acid. Both emulsions in which nonionic emulsifier had been added were blended without coagulation and then the heterocoagulation was carried out by adjusting of the pH and heating.Part CXVII of the series Studies on Suspension and Emulsion.     

Laser-induced fluorescence spectroscopy of NC3S

In a discharged supersonic jet of acetonitrile and carbon disulfide, we have for the first time observed an electronic transition of the NC(3)S radical using laser-induced fluorescence (LIF) spectroscopy. A progression originating from the C-S stretching mode of the upper electronic state appears in the excitation spectrum. Each band of the progression has a polyad structure due to anharmonic resonances with even overtones of bending modes. Rotationally resolved spectra have been observed by high-resolution laser scans, and the electronic transition is assigned to A 2Pii-X 2Pii. For the vibronic origin band, the position and the effective rotational constant of the upper level have been determined to be 21 553.874(1) and 0.046 689(4) cm(-1), respectively. The dispersed fluorescence spectrum from the zero vibrational level of A 2Pi3/2 has also been observed; its vibrational structure is similar to that of the LIF excitation spectrum, showing a prominent C-S stretching progression with polyad structures. The vibrational frequencies of the C-S stretching mode in the ground and excited electronic states are determined to be 550 and 520 cm(-1), respectively. Fluorescence decay profiles have been measured for several vibronic levels of the A state.     

Oxidation of ascorbate and ascorbic acid at the aqueous|organic solution interface

An electron transfer reaction between ascorbate in an aqueous solution and oxidizing agents in an organic solution immiscible with water has been studied for the first time by polarography for charge transfer at the interface between two immiscible electrolyte solutions. A reversible electron transfer polarogram at the aqueous|organic solution interface could be observed when teterachlorobenzoquinone, dibromobenzoquinone and Meldola's Blue were used as oxidizing agents in the organic solution. The oxidation reaction of ascorbate at the aqueous|organic interface was discussed comparing with the reactions at the ordinary electrodes and in homogeneous solutions. The half-wave potentials of electron transfer polarograms at the aqueous|nitrobenzene interface were applied to evaluate the formal redox potential of ascorbate/ascorbate free radical.