Photoinduced charge separation in titania nanotubes

The photocatalytic one-electron oxidation reaction of an aromatic compound during UV light irradiation of titania nanotubes and nanoparticles was investigated using time-resolved diffuse reflectance spectroscopy. Remarkably long-lived radical cations of the aromatic compound and trapped electrons were observed for the nanotubes when compared to those for nanoparticles. The influences of the morphology on the one-electron oxidation process of an aromatic compound adsorbed on the surface were discussed in terms of the charge recombination dynamics between the radical cation and electrons in TiO2.     

Catalytic [4+1] cycloaddition of alpha,beta-unsaturated carbonyl compounds with isocyanides

The GaCl(3)-catalyzed [4+1] cycloaddition reactions of alpha,beta-unsaturated ketones with isocyanides leading to lactone derivatives are described. While some other Lewis acids also show catalytic activity, GaCl(3) was the most efficient catalyst. The reaction is significantly affected by the structure of both the isocyanides and the alpha,beta-unsaturated ketones. Aromatic isocyanides, especially sterically demanding ones and those bearing an electron-withdrawing group, can be used, but aliphatic isocyanides cannot. The bulkiness of substituents at the beta-position of acyclic alpha,beta-unsaturated ketones is an important factor for the reaction to proceed efficiently. Generally, the more the bulky substituent, the higher is the yield. The reaction of alpha,beta-unsaturated ketones bearing geminal substituents at the beta-position gave the corresponding products in high yields. In monosubstituted derivatives, the yields are relatively low. However, substrates having a bulky substituent, such as a tert-Bu group, at the beta-position give high yields. Bulkiness is also required in cyclic alpha,beta-unsaturated ketones, but the effect is small. In alkyl vinyl ketones, the reactivity decreased with the steric bulk of the alkyl group. In aryl vinyl ketones, the presence of an electron-donating group on the aromatic ring decreases the reactivity. The success of the catalysis can be attributed to the low affinity of GaCl(3) toward heteroatoms, compared with usual Lewis acids.     

Regioselective electrophilic cyclization of o-ethynylbenzyl phenyl selenides to (Z)-1-methylidene-2-phenyl-1,3-dihydro-1H-benzo[c]selenophenium salts

o-Ethynylbenzyl phenyl selenides regioselectively reacted with trifluoromethanesulfonic acid to afford the (Z)-1-methylidene-2-phenyl-1,3-dihydro-1H-benzo[c]selenophenium salts as the major products during the 5-exo-dig mode cyclization in good yields together with minor E isomers. The structure of the major (Z)-selenophenium salt was established by the single crystal X-ray crystallographic analysis using a tert-butyl derivative.     

Light Scattering Changes in Isolated Brain Mitochondria during Anoxia - Magnesium Effect on Morphological Changes and Respiration -

Under pathological conditions, morphological changes of the cells and tissues may differ from those of normal conditions, which can be reflected by changes in light scattering (LS). Consequently, LS has been recognized as a potential non-invasive tool for optical diagnosis of living tissue. This paper aimed to identify the basic properties of LS of isolated brain mitochondria in vitro under normoxic and anoxic conditions in the presence and absence of Mg²⁺. An increase in LS was observed during anoxia in both the presence and absence of Mg²⁺. In both cases, the changes in LS initiated by anoxia and reoxygenation started concomitantly with the reduction of heme aa₃. The rates of LS changes were slower than those of heme aa₃, particularly in the presence of Mg²⁺. Mg²⁺ inhibited the morphological responses of mitochondria caused by the addition of ADP and ATP, and significantly reduced the oxygen consumption rate in state 4. These results are due to modulation of the K⁺/H⁺ antiporter affected by Mg²⁺. In addition, the mitochondria were well coupled, although the basal level of LS fell after addition of Mg²⁺. Therefore, the observed responses of mitochondria at anoxia were physiological and independent of the presence or absence of Mg²⁺. The relationship between LS and redox state of cytochrome c oxidase, an anoxic indicator, provides a basis to assess the tissue conditions in vivo.     

Path chromatic numbers of graphs

Let the finite, simple, undirected graph G = (V(G), E(G)) be vertex-colored. Denote the distinct colors by 1,2,…,c. Let V_i be the set of all vertices colored j and let <V_i be the subgraph of G induced by V_i. The k-path chromatic number of G, denoted by χ(G; P_k), is the least number c of distinct colors with which V(G) can be colored such that each connected component of V_i is a path of order at most k, 1 ? i ? c. We obtain upper bounds for χ(G; P_k) and χ(G; P_∞) for regular, planar, and outerplanar graphs.     

The effects of the homogeneity of non-crystalline Pb---Ti---O gels on the complex thermal processes leading to PbTiO3 formation

The effects of the homogeneity of precursor non-crystalline Pb---Ti---O gels on their transformation to crystalline PbTiO₃ were studied. Hydrous gels were prepared via two different routes, i.e., (i) mixing two unitary sols (MS), and (ii) co-precipitation (CP). Mechanical pretreatment was also carried out, primarily for the purpose of homogenization. The local homogeneity was evaluated by elementary microanalysis using a transmission electron microscope. The process of ball-milling the MS gel for 3 h improved its homogeneity only slightly. However, the homogeneity of the ball-milled MS gel suddenly increased to that of the CP gel on subsequent heating to a temperature as low as 483 K. This type of thermal homogenization was not observed for the unground MS gel. The evaporation of lead monoxide on further heating to 1023 K was also suppressed by preliminary ball-milling. All these results suggest that the ionic migration and the formation of Pb---O---Ti bonds in the gels take place during the mechanical activation with the aid of OH groups.     

Nickel-catalyzed reductive cleavage of aryl alkyl ethers to arenes in absence of external reductant

The reductive cleavage of the C–O bonds of aryl ethers has great potential in organic synthesis. Although several catalysts that can promote the reductive cleavage of aryl ethers have been reported, all such systems require the use of an external reductant, e.g., hydrosilane or hydrogen. Here, we report the development of a new nickel-based catalytic system that can cleave the C–O bonds of ethers in the absence of an external reductant. The hydrogen atom required in this new reductive cleavage reaction is provided by the alkoxy group of the substrate, which serves as an internal reductant. The absence of an external reductant enables the unique chemoselectivity, i.e., the selective reduction of an alkoxy group over alkenes and ketones.