Cooperation of σ–π and σ*–π* Conjugation in the UV/Vis and Fluorescence Spectra of 9,10-Disilylanthracene

In 1996, we reported that silyl groups of 9,10-disilylanthracenes significantly affect the UV/Vis and fluorescence spectra. Although the results indicate that the silyl groups have strong electronic effects on anthracene, the details of the mechanisms responsible for this have not yet been clarified. This article describes the analysis of the UV/Vis and fluorescence spectra of 9,10-bis(diisopropylsilyl)anthracene by theoretical calculations. This study reveals that π conjugation of anthracene is extended by cooperation of σ–π and σ*–π* conjugation between the silyl groups and anthracene. This effect increases the transition moment of the π–π* transition of anthracene. As a result, the molecular extinction coefficient of the ¹L_a band and the fluorescence quantum yield are increased.     

O2/n2-separation by polymer-bound cobalt complexes

Facilitated or complexation-mediated transport of oxygen in the solid membrane containing a fixed carrier was described, by using the polymer-bound cobalt Schiff's base chelate (CoS) and cobaltporphyrin (CoP). α³ β-Substituted cobaltporphyrin derivatives were synthesized: The oxygen-binding reaction to cobalt was affected by the cavity structure on porphyrin, i.e., unbulky amido-substituted groups such as acetylamido- and acrylamido-substituents enhanced oxygen-binding and -dissociation rate constant or provided an oxygen-binding pathway. Oxygen transport through the membranes of these polymer-bound CoP derivatives was selectively augmented due to the rapid and reversible oxygen-binding. Diffusion constants via the fixed CoPs correlated to the characteristics of oxygen-binding reaction.     

Presence of β-Turn Structure in Recombinant Spider Silk Dissolved in Formic Acid Revealed with NMR

Spider dragline silk is a biopolymer with excellent mechanical properties. The development of recombinant spider silk protein (RSP)-based materials with these properties is desirable. Formic acid (FA) is a spinning solvent for regenerated Bombyx mori silk fiber with excellent mechanical properties. To use FA as a spinning solvent for RSP with the sequence of major ampullate spider silk protein from Araneus diadematus, we determined the conformation of RSP in FA using solution NMR to determine the role of FA as a spinning solvent. We assigned ¹H, ¹³C, and ¹⁵N chemical shifts to 32-residue repetitive sequences, including polyAla and Gly-rich regions of RSP. Chemical shift evaluation revealed that RSP is in mainly random coil conformation with partially type II β-turn structure in the Gly-Pro-Gly-X motifs of the Gly-rich region in FA, which was confirmed by the ¹⁵N NOE data. In addition, formylation at the Ser OH groups occurred in FA. Furthermore, we evaluated the conformation of the as-cast film of RSP dissolved in FA using solid-state NMR and found that β-sheet structure was predominantly formed.     

Preparation of palladium clusters protected by silica-supported,crosslinking, partially phosphorylated poly(vinyl alcohol) and their catalytic activity

The palladium cluster protected by silica-supported, crosslinking, partially phosphorylated poly(vinyl alcohol) (P-PVA) was prepared from a crosslinking P-PVA–Pd(II) complex by reduction in alcohol. The P-PVA–Pd complex and the palladium cluster protected by P-PVA were analyzed by electron spectroscopy, X-ray photoelectron spectrometry and transmission electron microscopy. The complex formation between the Pd(II) ion and phosphoric acid groups in P-PVA was important in the formation of a fine palladium cluster. Palladium clusters protected by silica-supported crosslinking P-PVA were used as catalysts for the hydrogenation of nitrobenzene or acrylic acid at 30°C under atmospheric pressure. The palladium cluster protected by crosslinking P-PVA supported on silica was the most active catalyst, was stable and had no by-products, compared with the palladium cluster protected by silica-supported noncrosslinking P-PVA or PVA.