Metal-insulator transition in VnO2n−1

Research on phase relationships and structure studies by electron diffraction confirm V_nO_2n?1 (n = 3–9) phases between V₂O₃ and VO₂. Metal-insulator phase transitions have been found in all phases but V₃O₅ and V₇O₁₃. Electrical, magnetic and thermodynamic properties associated with the transitions are reported for sintered samples or for single crystals prepared by a vapor-transport method. The results are collated and reviewed in summarized form.     

Ruthenium-catalyzed formation of aryl(diphenyl)phosphine oxides by reactions of propargylic alcohols with diphenylphosphine oxide

1,1-Diaryl-1-penten-4-yn-3-ols react with diphenylphosphine oxide in the presence of a thiolate-bridged diruthenium complex as a catalyst and give high yields of aryl(diphenyl)phosphine oxide products via an initial substitution followed by a cyclization at the produced allene intermediate. [reaction: see text]     

Novel Host Compounds, 1,1′-Binaphthyl-2,2′-Dihydroxy-5,5′- and 6,6′-Dicarboxylic Acid, which Trap Guest Molecules Tightly in their Inclusion Crystals

The host compounds 1,1’-binaphthyl-2,2′-dihydroxy-5,5′-dicarboxylic acid (1) and 1,1′-binaphthyl-2,2′-dihydroxy-6,6′-dicarboxylic acid (2) have been synthesized, and their inclusion properties have been studied. Inclusion complexes formed by 1 and 2 with volatile guests such as acetone and methanol release the guests only at much higher temperatures than their boiling points. The crystal structures of the inclusion complexes have been determined from single crystal X-ray diffraction data and show different host lattices.     

Cyclic dimer of a fused porphyrin zinc complex as a novel host with two pi-electronically coupled binding sites

Upon complexation with 4,4[prime or minute]-bipyridine, a cyclic dimer of a fused porphyrin zinc complex, having two pi-electronically coupled binding sites, shows a strong negative cooperativity in the second guest binding, to allow stepwise formation of 1 : 1 and 1 : 2 inclusion complexes.     

An atropisomeric M2L4 cage mixture displaying guest-induced convergence and strong guest emission in water

Introduction of atropisomeric axes into a bent bispyridine ligand leads to the quantitative formation of a complex mixture of atropisomeric M₂L₄ cages upon treatment with metal ions. Whereas the isomer ratio of the obtained cage mixture, consisting of up to 42 isomers, is insensitive to temperature and solvent, the quantitative convergence from the mixture to a single isomer is accomplished upon encapsulation of a large spherical guest, namely fullerene C₆₀. The observed isomerization with other guests depends largely on their size and shape (e.g., <10 and 82% convergence with planar triphenylene and bowl-shaped corannulene guests, respectively). Besides the unusual guest-induced convergence, the present cage mixture displays the strongest guest emission (Φ_F = 68%) among previously reported M_nL_m cages and capsules, upon encapsulation of a BODIPY dye in water.

A complex mixture of atropisomeric M₂L₄ cages is shown to undergo perfect convergence to a single isomer upon encapsulation of spherical C₆₀ in water. Moreover, the cage mixture displays very strong guest emission upon encapsulation of a BODIPY dye.     

Stabilization of the spark-discharge point on a sample surface by laser irradiation for steel analysis.

A combined technique with laser irradiation is suggested to control spark discharge for analytical use, having a unique feature that firing points of the spark discharge can be fixed by laser irradiation. Because the spark discharge easily initiates at particular surface sites, such as non-metallic inclusions, called selective discharge, the concentration of some elements sometimes deviates from their average one in spark discharge optical emission spectrometry. Therefore, stabilization of firing points on a sample surface could improve the analytical precision.     

Metal-metal d-d interaction through the discrete stacking of mononuclear M(II) complexes (M = Pt, Pd, and Cu) within an organic-pillared coordination cage

Two molecules of planar MII(acac)2 complexes (M = Pt, Pd, and, Cu; acac = acetylacetonato) are efficiently stacked within an organic-pillared coordination cage, exhibiting characteristic spectroscopies (for M = Pt and Pd) and electron spin-spin coupling (for M = Cu) attributable to metal-metal interaction.     

Evaluation of homogeneity of binary blends of poly(3-hydroxybutyrate) and poly(L-lactic acid) studied by near infrared chemical imaging (NIRCI).

The homogeneity of blends of poly((R)-3-hydroxybutyrate) (PHB) and poly(L-lactic acid) (PLLA) was evaluated by the near infrared chemical imaging (NIRCI) technique. NIRCI can nondestructively investigate a sample over a wide field of view within a few minutes to acquire a large number of spatially resolved NIR spectral data. NIRCI may be combined with multivariate analysis not only for qualitative analysis but also for statistically based quantitative analysis. The score images derived from the partial least squares regression (PLSR) analysis directly show that PHB/PLLA blends are highly homogeneous. The standard deviations (STD) of the histograms, indicating the distribution of the score values, show small values for the blends. These results qualitatively and quantitatively show the high level of homogeneity of PHB/PLLA blends. The predictions of the spatially averaged concentrations of the blend components obtained from PLSR results show values similar to the actual contents for the blends. The small errors of the predictions are also explained by STD values.     

Formation and stabilization model of the 42-mer Abeta radical: implications for the long-lasting oxidative stress in Alzheimer's disease

Amyloid fibrils mainly consist of 40-mer and 42-mer peptides (Abeta40, Abeta42). Abeta42 is believed to play a crucial role in the pathogenesis of Alzheimer's disease because its aggregative ability and neurotoxicity are considerably greater than those of Abeta40. The neurotoxicity of Abeta peptides involving the generation of free radicals is closely related to the S-oxidized radical cation of Met-35. However, the cation's origin and mechanism of stabilization remain unclear. Recently, structural models of fibrillar Abeta42 and Abeta40 based on systematic proline replacement have been proposed by our group [Morimoto, A.; et al. J. Biol. Chem. 2004, 279, 52781] and Wetzel's group [Williams, A. D.; et al. J. Mol. Biol. 2004, 335, 833], respectively. A major difference between these models is that our model of Abeta42 has a C-terminal beta-sheet region. Our biophysical study on Abeta42 using electron spin resonance (ESR) suggests that the S-oxidized radical cation of Met-35 could be generated by the reduction of the tyrosyl radical at Tyr-10 through a turn structure at positions 22 and 23, and stabilized by a C-terminal carboxylate anion through an intramolecular beta-sheet at positions 35-37 and 40-42 to form a C-terminal core that would lead to aggregation. A time-course analysis of the generation of radicals using ESR suggests that stabilization of the radicals by aggregation might be a main reason for the long-lasting oxidative stress of Abeta42. In contrast, the S-oxidized radical cation of Abeta40 is too short-lived to induce potent neurotoxicity because no such stabilization of radicals occurs in Abeta40.     

Slurry sampling techniques for the determination of lead in Bangladeshi fish samples by electrothermal atomic absorption spectrometry with a metal tube atomizer

Ultrasonic slurry sampling electrothermal atomic absorption spectrometry with a metal tube atomizer has been applied to the determination of lead in Bangladeshi fish samples. The slurry sampling conditions, such as slurry stabilizing agent, slurry concentration, pyrolysis temperature for the slurried fish samples, particle size and ultrasonic agitation time, were optimized for electrothermal atomic absorption spectrometry with the Mo tube atomizer. Thiourea was used as the chemical modifier for the interference of matrix elements. The detection limit was 53 fg (3S/N). The determined amount of lead in Bangladeshi fish samples was consistent with those measured in the dissolved acid-digested samples. The advantages of the proposed methods are easy calibration, simplicity, low cost and rapid analysis.