Unsteady and chaotic characteristics of natural convection field in vertical slots at large Prandtl number

In this study we examined the unsteady and chaotic characteristics of the natural convection field in vertical slots at large Prandtl number. In the computation, temperature dependence of viscosity was partially taken into consideration. As a result we discovered that the spatial region where a significant temperature fluctuation is detected corresponds to the spatial region where the secondary cells exist. The largest Lyapunov exponents calculated from the temperature on the center line have a local maximum at the lower region of the enclosure when the viscosity change was considered. These characteristics agree well with the experimental ones that have been observed by authors (Ishida, Kure and Kimoto 2001).     

Pentamethylcyclopentadienide in organic synthesis: nucleophilic addition of lithium pentamethylcyclopentadienide to aromatic aldehydes and carbon-carbon bond cleavage of the adducts affording the parent aldehydes

Treatment of aromatic aldehyde with lithium pentamethylcyclopentadienide provided the corresponding carbinol in excellent yield. The carbinol returns to the parent aldehyde and pentamethylcyclopentadiene upon exposure to an acid or due to heating. The combination of the two reactions can represent a protection of aromatic aldehyde.     

Oxysulfide Sm(2)Ti(2)S(2)O(5) as a stable photocatalyst for water oxidation and reduction under visible light irradiation (lambda < or = 650 nm)

A Ti-based oxysulfide, Sm(2)Ti(2)S(2)O(5), was studied as a visible light-driven photocatalyst. Under visible light (440 nm < or = lambda < or = 650 nm) irradiation, Sm(2)Ti(2)S(2)O(5) with a band gap of approximately 2 eV evolved H(2) or O(2) from aqueous solutions containing a sacrificial electron donor (Na(2)S-Na(2)SO(3) or methanol) or acceptor (Ag(+)) without any noticeable degradation. This oxysulfide is, therefore, a stable photocatalyst with strong reduction and oxidation abilities under visible-light irradiation. The electronic band structure of Sm(2)Ti(2)S(2)O(5) was calculated using the plane-wave-based density functional theory (DFT) program. It was elucidated that the S3p orbitals constitute the upper part of the valence band and these orbitals make an essential contribution to the small band gap energy. The conduction and valence bands' positions of Sm(2)Ti(2)S(2)O(5) were also determined by electrochemical measurements. It indicated that conduction and valence bands were found to have satisfactory potentials for the reduction of H(+) to H(2) and the oxidation of H(2)O to O(2) at pH = 8. This is consistent with the results of the photocatalytic reactions.     

A Novel Production of γ-Butyrolactone Catalyzed by Homogeneous Ruthenium Complexes

γ-Butyrolactone (hereafter abbreviated GBL) is produced by the two-stage hydrogenation of maleic anhydride(MAH) in the liquid phase: the hydrogenation of MAH to succinic anhydride(SAH) in the first stage and the subsequent hydrogenation of SAH to GBL in the second stage. A novel ruthenium catalyst system consisting of Ru salts, trialkylphosphine and p-toluene sulfonic acid (p-TsOH) was found very effective for the hydrogenation of SAH affording GBL, which exhibited excellent catalyst performance, exceeding 97% selectivity for GBL and high activity.     

Intramolecular tandem Michael-type addition/aldol cyclization induced by TiCl(4)-R(4)NX combinations

[reaction: see text] Treatment of formyl alpha,beta-enones with a TiCl(4)-R(4)NX combination induces an intramolecular aldol cyclization to furnish 2-acyl-3-halocyclohexanol with three controlled consecutive stereogenic centers. The reaction of bis-alpha,beta-enones with the combination provides cyclic diketones with high stereoselectivity via an intramolecular Michael addition reaction.     

Midgap levels of photoexcited conductive polymers. I. A simple description of the midgap levels based on molecular orbital interaction

We studied the midgap levels appearing in the photoexcited conductive polymers such as trans- and cis-polyacetylenes, poly(p-phenylene), polypyrrole, and polyacene based on the molecular orbital analysis. The midgap levels are constructed from the transformation of the highest occupied molecular orbital and the lowest unoccupied molecular orbital of the ground state. As the result of the localization of the wave functions associated with these midgap levels, large polarization is induced between adjacent carbon atoms. Based on the examination of the energy gap between the two midgap levels, the polymers with a nondegenerate ground state such as cis-polyacetylene, poly(p-phenylene), and polypyrrole would show no sizable photoconductivities.     

Cationic ring-opening polymerization of 1,4-anhydro-2,3-di-O-benzyl-α-L-arabinopyranose and synthesis of L-arabinofuranan

1,4-Anhydro-2,3-di-O-benzyl-α-L -arabinopyranose (=1,5-anhydro-2,3-di-O-benzyl-β-L -arabinofuranose) (ABAP) was synthesized and underwent cationic ring-opening polymerization with several kinds of Lewis acids. All the polylmers prepared by Lewis acids as catalyst were found to consist of two different structural units, α-furanosidic and β-furanosidic units, and the structure of the polymers greatly depended on the polymerization conditions. Polymerization of ABAP with antimony pentachloride catalyst at 0°C for 42 h gave a polymer with the highest α content of 93%, and that at ?20°C for 3 h gave a polymer with the lowest (25%) α content. The other catalysts such as phosphorus pentafluoride, boron trifluoride etherate, niobium pentafluoride, and tantalum pentafluoride also afforded polymers with mixed structure of α-and β-furanosides. After debenzylation of poly(ABAP), a new polysaccharide, L -arabinofuranan was obtained.     

Biodegradable Phosphorylcholine Polymer Hydrogels Cross‐Linked with Vinyl‐Functionalized Polyphosphate

A vinyl‐functionalized polyphosphate (PIOP) was synthesized by ring‐opening polymerization of 2‐isopropyl‐2‐oxo‐1,3,2‐dioxaphospholane and 2‐(2‐oxo‐1,3,2‐dioxaphosphoroyloxyethyl methacrylate) with triisobutylaluminum as an initiator. The number‐averaged molecular weight of the PIOP was 1.2 × 10⁴. The average number of vinyl groups in the PIOP is 2.20. Transparent hydrogels were prepared by the radical polymerization of 2‐methacryroyloxyethyl phosphorylcholine with PIOP as a cross‐linking reagent. These hydrogels may have many applications in the biomedical field because of their biodegradability and biocompatibility.

Synthetic route of PIOP.     

Tuning the Reactivity of a Substrate for SNAP-Tag Expands Its Application for Recognition-Driven DNA-Protein Conjugation

Recognition-driven modification has been emerging as a novel approach to modifying biomolecular targets of interest site-specifically and efficiently. To this end, protein modular adaptors (MAs) are the ideal reaction model for recognition-driven modification of DNA as they consist of both a sequence-specific DNA-binding domain (DBD) and a self-ligating protein-tag. Coupling DNA recognition by DBD and the chemoselective reaction of the protein tag could provide a highly efficient sequence-specific reaction. However, combining an MA consisting of a reactive protein-tag and its substrate, for example, SNAP-tag and benzyl guanine (BG), revealed rather nonselective reaction with DNA. Therefore new substrates of SNAP-tag have been designed to realize sequence-selective rapid crosslinking reactions of MAs with SNAP-tag. The reactions of substrates with SNAP-tag were verified by kinetic analyses to enable the sequence-selective crosslinking reaction of MA. The new substrate enables the distinctive orthogonality of SNAP-tag against CLIP-tag to achieve orthogonal DNA-protein crosslinking by six unique MAs.