Electronic state observation of inner organic thin films beneath electrodes: Fluorescence-yield X-ray absorption spectra of pentacene derivative films

The electronic states of inner organic thin films have been investigated by X-ray absorption spectroscopy (XAS) in a bulk-sensitive fluorescence-yield (FY) mode with theoretical analysis. The thin films of the synthesized pentacene derivative, i.e., 6,13-dihydrodiazapentacence (C₂₀N₂H₁₄), on SiO₂-covered Si substrates were fabricated and their morphology and crystallinity were characterized by atomic force microscopy (AFM) and X-ray diffraction (XRD) analysis, respectively. The observed N K-edge FY-XAS spectra were different from the surface-sensitive XAS spectra measured in a partial-electron-yield (PEY) mode. The peaks on the FY-XAS spectra were well reproduced by the theoretical calculation of the unoccupied states of an HAPn molecule. In addition, the incident angle dependence of the FY-XAS spectra was consistent with the expected molecular orientation in the thin films. As a result, we successfully obtained the N and C K-edge FY-XAS spectra of the inner HAPn thin films even beneath Au electrodes.     

Characterization of a Water-Dispersed Biodegradable Polyurethane-Silk Composite Sponge Using 13C Solid-State Nuclear Magnetic Resonance as Coating Material for Silk Vascular Grafts with Small Diameters

Recently, Bombyx mori silk fibroin (SF) has been shown to be a suitable material for vascular prostheses for small arteries. In this study, we developed a softer SF graft by coating water-dispersed biodegradable polyurethane (PU) based on polycaprolactone and an SF composite sponge on the knitted SF vascular graft. Three kinds of ¹³C solid-state nuclear magnetic resonance (NMR), namely carbon-13 (¹³C) cross-polarization/magic angle spinning (MAS), ¹³C dipolar decoupled MAS, and ¹³C refocused insensitive nuclei enhanced by polarization transfer (r-INEPT) NMR, were used to characterize the PU-SF coating sponge. Especially the ¹³C r-INEPT NMR spectrum of water-dispersed biodegradable PU showed that both main components of the non-crystalline domain of PU and amorphous domain of SF were highly mobile in the hydrated state. Then, the small-diameter SF artificial vascular grafts coated with this sponge were evaluated through implantation experiments with rats. The implanted PU-SF-coated SF grafts showed a high patency rate. It was confirmed that the inside of the SF grafts was covered with vascular endothelial cells 4 weeks after implantation. These results showed that the water-dispersed biodegradable PU-SF-coated SF graft created in this study could be a strong candidate for small-diameter artificial vascular graft.     

Optical spectroscopy study of modifications induced in cerium dioxide by electron and ion irradiations

UV-visible absorption spectroscopy and Raman spectroscopy were used to study damage production in cerium dioxide epitaxial films and polycrystalline sintered samples after irradiation with electrons for three energies to span the threshold displacement energies of cerium and oxygen atoms, and 2.4-MeV Cu ions. Neither amorphization nor specific colour-centre bands were detected. Evolutions of the refractive index were derived from the interference fringes in the optical transmission spectra of epilayers after irradiation. No significant change of the refractive index occurred for the 1.0-MeV electron irradiation, whereas a maximum decrease by 28?±?8% was deduced for the 1.4-MeV and 2.5-MeV energies. These modifications are consistent with ballistic damage on the cerium sublattice for high electron energies producing Ce³⁺ ions. However, no significant change of refractive index was found for the Cu ion irradiation. This likely stems from the high rate of Frenkel pair recombination in the collision cascades induced by more energetic recoils than for the electron irradiations, combined with electronic excitations and hole capture on Ce³⁺ ions. This study reveals modifications of the electronic structure upon irradiation that could take place in other non-amorphizable oxide systems.     

Studies on the Antisense Oligonucleotide Conjugate

Four oligonucleotides (15 mer) 13–16 and their conjugates 17–20 in which psoralen was covalently linked to 5′ end were synthesized. Compounds 16 and 20 contain the sequence which is complementary to the sense strand covering the first four codons and the upstream sequence close to the ribosome binding site of c-Ha-ras mRNA. It was found that compounds 16 and 20 inhibited the growth of cells that had been transformed by the c-Ha- ras plasmid activated c-Ha- ras oncogene. Compound 20 that carried psoralen was more efficient in inhibiting the growth of transformed cells than compound 16 without psoralen, suggesting that the psoralen might have increased permeability of oligodeoxynucleotides. A model experiment of duplex formation was pertinent to the idea that the inhibitory effect was caused by RNase H activity.     

Pionic decays of Λ-hypernuclei and nucleon occupation probabilities

It is argued that pionic decays of Λ hypernuclei can be probe to see real occupation probabilities of nucleon hole orbits. Pionic decay rates are evaluated by taking into account correlation probability effects and are found to show a saturation property in heavy hypernuclei, which is necessary to be compatible with experimental indications.     

Aggregation and solvation of 9-propylfluorenyllithium and of α,ω-BIS(9-fluorenyllithium)polymethylenes in toluene

Bolaform salts of the type Li⁺,Fl^?(CH₂)_n Fl^?,Li⁺ (Fl^? = 9-fluorenyl, n = 2,4 or 6), when dissolved in toluene, were shown to be present as intramolecular aggregates (λ_m 370 nm) which can be broken up on addition of tetrahydrofuran (THF) or tetrahydropyran (THP) to form solvated tight ion pairs (λ_m 361 nm) and loose ion pairs (λ_m 386 nm). For n = 6 the ratio K₁/K₂ of the loose ion pair formation constants for the two terminal ion pairs is close to the statistical factor 4, but for n = 2 the ratio is only 0.3. This is attributed to a higher stability of the intramolecular aggregate for this compound. The data for the bolaform salts were compared with those obtained for the one ended salt 9-(n-propyl)-fluorenyllithium. For the latter compound, an equilibrium between the monomeric ion pair (λ_m 353 nm) and the dimeric ion pair aggregate (λ_m 370 nm) was found, the dissociation constant K_d being 2.9 X 10^?6M. Addition of THP produces the THP solvated tight ion pair (λ_m 361 nm) and the loose ion pair (λ_m 386 nm).     

Resonance energy transfer from dibucaine to acriflavine in polystyrene latex dispersions

Resonance energy transfer from dibucaine (DC) to acriflavine (AF) has been investigated both in homogeneous aqueous solutions and in polystyrene latex dispersions. The energy transfer reaction is observed by monitoring fluorescence quenching of DC as well as sensitized emission of AF. It is found that the energy transfer from DC to AF is remarkably enhanced on going from the aqueous homogeneous solution to the latex dispersion. This is mainly attributed to the fact that both the donor and acceptor are effectively adsorbed onto the latex particles, as evidenced by the measurement of adsorption isotherms. From the adsorption experiments, it is also elucidated that electrostatic interaction is significant at low DC concentration, while hydrophobic interaction dominates at the higher concentration especially at higher pH.     

Stereocontrol in organic synthesis using silicon-containing compounds. Studies directed towards the synthesis of ebelactone A

Several approaches to the synthesis of ebelactone A 2 are described, culminating in the synthesis of the benzenesulfonate of 2-epi-ebelactone A 161. All the approaches were based on three fragments A, B and C, originally defined in general terms in, but eventually used as the aldehyde 72, the allenylsilane 3 and the aldehyde 139, respectively. They were joined, first B with C, and then B+C with A. In the main routes to fragments A and C, the relative stereochemistry was controlled by highly stereoselective enolate methylations 67-->67, 68-->69, and 135-->136, in each case anti to an adjacent silyl group, and by a highly stereoselective hydroboration of an allylsilane 137-->138, also anti to the silyl group. The hydroxyl groups destined to be on C-3 and C-11 were unmasked by silyl-to-hydroxy conversions 69-->70 and 138-->139 with retention of configuration. The stereochemistry created in the coupling of fragment B to C was controlled by the stereospecifically anti S(E)2' reaction between the enantiomerically enriched allenylsilane 3 and the aldehyde 139. The double bond geometry was controlled by syn stereospecific silylcupration 148-->151, and preserved by iododesilylation 151-->152 of the vinylsilane with retention of configuration, and Nozaki-Hiyama-Kishi coupling with the aldehyde 72 gave the whole carbon skeleton 153 of ebelactone A with the correct relative configuration, all of which had been controlled by organosilicon chemistry. In the steps to remove the superfluous allylic hydroxyl, an intermediate allyllithium species 156 abstracted the proton on C-2, and its reprotonation inverted the configuration at that atom. Other routes to the fragments A and C were also explored, both successful and unsuccessful, both silicon-based and conventional, and a number of unexpected side reactions were investigated.