Optical and magnetic studies on the phosphorescent state of phthalazine in polar and non-polar hosts

The ground state potential energy curve for the beryllium dimer is calculated using non-degenerate many-body perturbation theory and the multi-configuration self-consistent-field/configuration interaction method. Quasi-degeneracy in this system makes it useful in exploring the limitation of the applicability of the non-degenerate formulation of diagrammatic many-body perturbation theory. Both methods are applied within the algebraic approximation defined by a contracted gaussian basis set of triple zeta quality. It is shown that non-degenerate perturbation theory can lead to a potential energy curve which is in close agreement with the configuration interaction curve when taken to third order in the energy and [2/1] Padé approximants constructed.     

White and Taylor Type Guest Host Displays Without Scattering Effects Using the Tilted Boundary Conditions

White and Taylor type guest host displays using the tilted boundary condition have been reported. The parallel or the perpendicular boundary condition is usually used for these displays and both conditions cause scattering phemomena after the electric field removal. The present paper reports the relaxation processes of samples with the tilted boundary after the field removal. Using the tilted boundary, two types of nonscattering conditions depending on the thickness of the liquid crystal layer (d), the natural pitch (Po) and the boundary condition (φ) exist. Both types of conditions are discussed in detail.     

Orientation of polymer molecules during melt spinning. II. Orientation of crystals in as-spun polyolefin fibers

Three different polyolefins, a linear polyethylene, an isotactic polypropylene, and an isotactic polybutene-1, were melt-spun into filaments. The degree of orientation of the filaments was measured by polarized-light microscopy, x-ray diffraction, and a retraction technique, and the results were then related to the melt-draw ratio. The increase in the elastic deformation ratio of polymer chains by spin-stretching, estimated by thermal retraction at a temperature above T_m, was monotonic with respect to the melt-draw ratio. On the other hand, as-spun filaments of polyethylene and polypropylene were characterized by a plateau in birefringence over the range of melt-draw ratios from 8 to 80. The change in orientation functions for crystals in these filaments was similar to the change of birefringence. On the other hand, the birefringence and the crystalline orientation functions for polybutene-1 increased smoothly with increasing melt-draw ratio. The most highly melt-drawn filaments of these polymers had a strongly oriented structure, corresponding to that in highly cold-drawn specimens.     

Nitrile anion cyclization with epoxysilanes followed by Brook rearrangement/ring-opening of cyclopropane nitriles/alkylation

[reactions: see text] The reaction of delta-silyl-gamma,delta-epoxypentanenitrile derivatives 9-12 with a base and an alkylating agent affords (Z)-delta-siloxy-gamma,delta-unsaturated pentanenitrile derivatives via a tandem process that involves the formation of a cyclopropane derivative by epoxy nitrile cyclization followed by Brook rearrangement and an anion-induced cleavage of the cyclopropane ring. Exclusive formation of a (Z)-derivative from trans-epoxides is explained by the reaction pathway that involves a backside displacement of the epoxide by the alpha-nitrile carbanion and the O-Si bond formation followed by concerted processes involving Brook rearrangement and the anti-mode of eliminative ring fission of the cyclopropane from the rotamer 19. The fact that (E)-isomers are exclusively obtained from cis-epoxides and alpha-cyclopropyl-alpha-silylcarbinol derivative 26 provides experimental support for the proposed pathway.     

The Bacterial [Fe]‐Hydrogenase Paralog HmdII Uses Tetrahydrofolate Derivatives as Substrates

[Fe]‐hydrogenase (Hmd) catalyzes the reversible hydrogenation of methenyl‐tetrahydromethanopterin (methenyl‐H₄MPT⁺) with H₂. H₄MPT is a C1‐carrier of methanogenic archaea. One bacterial genus, Desulfurobacterium, contains putative genes for the Hmd paralog, termed HmdII, and the HcgA–G proteins. The latter are required for the biosynthesis of the prosthetic group of Hmd, the iron–guanylylpyridinol (FeGP) cofactor. This finding is intriguing because Hmd and HmdII strictly use H₄MPT derivatives that are absent in most bacteria. We identified the presence of the FeGP cofactor in D. thermolithotrophum. The bacterial HmdII reconstituted with the FeGP cofactor catalyzed the hydrogenation of derivatives of tetrahydrofolate, the bacterial C1‐carrier, albeit with low enzymatic activities. The crystal structures show how Hmd recognizes tetrahydrofolate derivatives. These findings have an impact on future biotechnology by identifying a bacterial Hmd paralog.     

Control of dark current in photoelectrochemical (TiO2/I--I3-)) and dye-sensitized solar cells

The ruthenium complex bis-tetrabutylammonium cis-dithiocyanato-N,N'-bis-2,2'-bipyridine-4-carboxylic acid, 4'-carboxylate ruthenium(II), N-719, was found to block the dark current of dye sensitized solar cells (DSC), based on mesoporous TiO2 films deposited on a F-doped tin oxide electrode and the effect was compared to surface treatment by TiCl4 and the introduction of a compact TiO2 blocking layer.     

Fibers from polyblends containing nylon 6 as basic component. I. Melt spinning and physical properties of blend fibers

Five series of two-component blend filaments, comprising nylon 6 (N6) and nylon 66 (N66), nylon 610 (N610), nylon 11 (N11), nylon 12 (N12), or poly(ethylene terephthalate) (PET), were prepared by using a research spinning machine and a conventional drawing machine. The microstructure and the physical properties of the resultant filaments were evaluated with a tensile tester, a optical microscope, a density-gradient column, and a DTA instrument. When both components were mixed homogeneously so that they would form a three-dimensional network, the tensile properties of the blend filament were at least equivalent to the values predicted from those of both components. On the other hand, as in the cases of 30/70 and 70/30 N6–PET, when the minor component was discretely distributed as short fibrils in the matrix of the major component, the blend filament had an extremely weak tenacity. A supertenacity filament was obtained from 50/50 N6–N610. The marked increase of the tensil strength and the initial modulus of 50/50 N6–N610, about 12 g/den and 520 kg/mm², respectively, may be due to a significant increase in the crystallinity and the orientation of the blend.