Reaction of triarylphosphine radical cations generated from photoinduced electron transfer in the presence of oxygen

[reaction: see text] The 9,10-dicyanoanthracene (DCA)-sensitized photoreaction of triarylphosphines (1) was carried out in acetonitrile under aerobic conditions. Phosphine 1 was oxidized to the corresponding phosphine oxide with no appreciable side reactions. Product analysis and laser flash photolysis experiments suggest that the radical cation of 1 formed by the electron transfer from 1 to DCA in the singlet excited state ((1)DCA) reacts with O(2) to eventually afford the phosphine oxide.     

Dramatic effect of N-substituents in viologens on single electron transfer from tributylphosphine

A single electron transfer (SET) takes place from tributylphosphine (1a) to 1-alkyl-1'-methylviologens in acetonitrile containing a large amount of methanol under an argon atmosphere. In contrast, no SET takes place from 1a to viologens whose alkyl groups on the nitrogens are larger than the methyl group under the same conditions, 1a instead nucleophilically attacking the viologen to form a covalent adduct. This dramatic substituent effect is discussed in terms of SET occurring within a tight encounter complex formed between the phosphine and the viologen.     

On Spin(7) holonomy metric based on SU(3)/U(1): II

We continue the investigation of Spin(7) holonomy metric of cohomogeneity one with the principal orbit SU(3)/U(1). A special choice of U(1) embedding in SU(3) allows more general metric ansatz with five metric functions. There are two possible singular orbits in the first-order system of Spin(7) instanton equation. One is the flag manifold SU(3)/T² also known as the twistor space of CP(2) and the other is CP(2) itself. Imposing a set of algebraic constraints, we find a two-parameter family of exact solutions which have SU(4) holonomy and are asymptotically conical. There are two types of asymptotically locally conical (ALC) metrics in our model, which are distinguished by the choice of S¹ circle whose radius stabilizes at infinity. We show that this choice of M theory circle selects one of the possible singular orbits mentioned above. Numerical analyses of solutions near the singular orbit and in the asymptotic region support the existence of two families of ALC Spin(7) metrics: one family consists of deformations of the Calabi hyper-Kähler metric, the other is a new family of metrics on a line bundle over the twistor space of CP(2).     

Diffraction study of Li2O·SiO2 glass with computer simulation

The structure of Li₂O·SiO₂ glass has been determined by the pair-function analysis of the radial distribution function (RDF) obtained by X-ray and neutron diffraction measurements. The structure models were constructed by the molecular dynamics method (MD). The calculated RDFs, the summation of the pair-functions of the model, were compared with the observed RDFs while varying the MD parameters. Taking advantage of the negative scattering length of Li for neutron diffraction, the glass structure was investigated in detail, and it was found that the chains of SiO₄ tetrahedra bend at 20 °, which is a little less than for the crystal (23.48 °). It is known that the larger the size of the alkali ions (Na⁺ → K⁺ → Cs⁺), the smaller the bending angle of the chains. It was found that this rule also applies to Li⁺.     

Tensile strength of boric oxide glass in vacuum and at very low humidities

The tensile strength of a glass fiber of pure boric oxide was measured at low humidities and in vacuum. The strength increased from 60 kg/mm² in a relative humidity (RH) range of 7% to 120 kg/mm² at 0.4% RH, levelling off to 0.02% RH which was the lower limit of humidity in this experiment. At relative humidities higher than 0.4% weathering and stress corrosion were observed, while at relative humidities lower than 0.4%, weathering was not observed but the decrease of the strength with a dynamic loading duration was observed, although the behavior was somewhat different from the typical stress corrosion. The strength measured in vacuum was almost equal to that measured at relative humidities lower than 0.4%, although the data were more scattered. The strength of boric oxide glass was much lower than that of silica glass, even when weathering and stress corrosion were depressed to the extreme. This weakness of boric oxide glass may be attributed to its layer structure.     

Optical resolution of asymmetric triacylglycerols by chiral-phase high-performance liquid chromatography

A simple method for direct optical resolution of some asymmetric triacylglycerols (TGs) has been established. The method employs chiral-phase high-performance liquid chromatography (HPLC). An enantiomeric pair of TGs comprising 1-eicosapentaenoyl-2,3-dicapryroyl-sn-glycerol (ECC) and 1,2-dicapryroyl-3-eicosapentaenoyl-sn-glycerol (CCE) was resolved on a CHIRALCEL OF or on a CHIRALCEL OD column. The separation of another pair of asymmetric TGs, 1-docosahexaenoyl-2,3-dicapryroyl-sn-glycerol (DCC) and 1,2-dicapryroyl-3-docosahexaenoyl-sn-glycerol (CCD), was achieved with the CHIRALCEL OD column. The chiral-phase HPLC method in combination with silver-ion HPLC and high-temperature gas chromatography was used for monitoring two interesterification reactions, whose products were chiral TGs. Interesterification of tricapryloylglycerol with ethyleicosapentaenoate or with ethyldocosahexaenoate was performed using Rhizomucor miehei lipase as the catalyst. The products targeted were the asymmetric pair of TGs, ECC and CCE or DCC and CCD. The amounts of sn-1-substituted products (ECC or DCC) were greater than their sn-3-substituted counterparts (CCE or CCD) throughout the reaction period, suggesting that R. miehei lipase had a stereopreference towards the sn-1 position over the sn-3 position.     

Cobalt- and rhodium-catalyzed cross-coupling reaction of allylic ethers and halides with organometallic reagents

Reactions of 2-alkenyl methyl ether with phenyl, trimethylsilylmethyl, and allyl Grignard reagents in the presence of cobalt(II) complexes are discussed. The success of the reactions heavily depends on the combination of the substrate, ligand, and Grignard reagent. In the reaction of cinnamyl methyl ether, the formation of the linear coupling products predominates over that of the relevant branched products. In the cobalt-catalyzed allylation of allylic ethers, addition of a diphosphine ligand can change the regioselectivity, mainly providing the corresponding branched products. Rhodium complexes catalyze the reactions of allylic ethers and halides with allylmagnesium chloride and allylzinc bromide, respectively, in which the branched coupling product is the major product.     

Bubble motions confined in a microspace observed with stroboscopic technique

Dynamic motions of gas bubble confined in a microspace, i.e., in a channel of a microreactor, were observed with a video microscope and stroboscopic technique using a light emitting diode operated in a pulsed mode. There are many important phenomena related to the bubble dynamics synchronized with ultrasonic wave and continued for more than a few minutes. With the stroboscopic technique, the time-expanded bubble motions synchronized with ultrasound wave and the real time background images can be simultaneously observed. A number of interesting phenomena resulting from the dynamic motions of a microbubble in a microspace were observed; nonspherical bubble oscillation, rectified diffusion, emergence of cavitation, and microstreaming of different patterns depending on the input power of ultrasound. The observation technique described in this investigation could be a convenient tool for taming the bubble under a microscope to investigate the bubble dynamics in detail.     

Ultrasound induced formation of paraffin emulsion droplets as template for the preparation of porous zirconia

The paraffin particles were prepared by quenching process after sonicating the solution of paraffin and water at 80 °C. The resultant paraffin particles were then used as template for the preparation of macroporous zirconia materials. For this, zirconium normal butoxide (ZNB) modified with triethanolamine (TEA) was first hydrolyzed by water containing the dispersed paraffin particles with the surfactant, Sodium di(2-ethylhexyl) sulfosuccinate. This resulted in the formation of a slurry consisting of hydrolyzed sol and paraffin particles. After centrifugation, a cake packed with hydrated sol and paraffin particles were obtained which was then subjected to heat treatment. The sample obtained after heat treatment contained finely dispersed pores in the size range from 40 nm to 2 μm. Moreover, using the present approach it has also been observed that, change in pore size of zirconia wall is possible with a change in size of the paraffin particles. Thus, the present approach is a novel way of producing porous materials as the particle size of the template could be changed and templates become hard when they were molded as compared to the conventional methods in which there is no change in phase for the templates under 100 °C.