Excited-state structure and dynamics of 1,3,5-tris(phenylethynyl)benzene as studied by Raman and time-resolved fluorescence spectroscopy

Excited-state structure and dynamics of 1,3,5-tris(phenylethynyl)benzene (TPB) have been studied in n-hexane and n-heptane solutions. Time-resolved fluorescence spectra, fluorescence anisotropy, and lifetime of TPB were recorded with femtosecond to nanosecond time resolution. Raman depolarization ratio was also measured to elucidate a nonplanar structure of the ground state. Two fluorescence components, the short-lived component with 150 fs lifetime and the long-lived component with 10 ns lifetime, were observed. The analysis of the fluorescence anisotropy values combined with the Raman depolarization data has led to a conclusion that TPB is primarily excited to a short-lived excited singlet state with a nonplanar structure, and then it relaxes to a long-lived excited singlet state with a 3-fold axis. A rapid structural change from a nonplanar to a planar structure is suggested to take place in the process of relaxation.     

Syntheses, crystal and solution structures, ligand-exchange, and ligand-coupling reactions of mixed pentaarylantimony compounds

All possible combinations of mixed pentaarylantimony compounds bearing p-methylphenyl and p-trifluoromethylphenyl groups were synthesized; ArnTol5-nSb (n=0-5: Ar=p-CF3C6H4, Tol=p-CH3C6H4): Tol5Sb (1), ArTol4Sb (2), Ar2Tol3Sb (3), Ar3Tol2Sb (4), Ar4TolSb (5), and Ar5Sb (6). Compounds 2-5 are the first well-characterized examples of mixed acyclic pentaarylantimony species. The structures of 2-6 were determined by X-ray crystallography to feature trigonal-bipyramidal (TBP) geometry with the more electronegative p-trifluoromethylphenyl substituents selectively occupying the apical positions. Consideration of the chemical shifts of the ipso carbons of the aryl and tolyl groups suggested that the solution structures of 1-6 were also TBP, although their pseudorotation could not be frozen even at -80 degrees C. Ligand-exchange reactions (LERs) took place between 1 and 6 at approximately 60 degrees C in [D6]benzene and all six species 1-6 were found in the equilibrium mixture. The relative stabilities of 1-6 were determined quantitatively by comparison of the observed molar ratios of 1-6 in equilibrium with calculated statistical molar ratios, and Ar2Tol3Sb (3) was found to be the most stable. The ligand-coupling reactions (LCRs) of 2-5 in solution were greatly accelerated by adding Cu(acac)2 or Li+TFPB- (TFPB: [3,5-(CF3)2 C6H3]4 B), whereby the rate becomes comparable to the LER. The use of flash vacuum thermolysis (FVT) allowed the LCR to occur with very little ligand-exchange; the exception ArTol4Sb had very fast ligand-exchange. The selectivities of the LCRs were calculated from the yield of the biaryls synthesized by using FVT. These results were highly consistent with reactions catalyzed in solution, in which bitolyl was not obtained at all. The experimental results suggested that the LCR of pentaarylantimony compounds proceeds in the manner of apical-apical coupling.     

Metachromins R--T, new sesquiterpenoids from marine sponge Spongia sp

Three new sesquiterpenoids, metachromins R--T (1--3), have been isolated from an Okinawan marine sponge Spongia sp. The structures and stereochemistry of 1--3 were elucidated on the basis of the spectroscopic data. Metachromins S (2) and T (3) showed modest cytotoxicity.     

Electric quadrupole model on the formation of molecular chirality dependent domain shapes of lipid monolayers at the air-water interface

Shapes and orientational deformation of a lipid monolayer domain have been analyzed taking into account the surface pressure, line tension, and electrostatic energy due to the spontaneous polarization and electric quadrupole density generated from the domain. The electrostatic energy due to the generation of spontaneous polarization and electric quadrupole density contributes to the formation of orientational deformation as the Frank elastic energy and spontaneous splay, respectively. Since the orientational configuration of the electric quadrupole density and in-plane spontaneous polarization is dependent on the molecular chirality, and the positive splay deformation of electric quadrupole density is induced by the spontaneous splay, the bending direction of in-plane spontaneous polarization depends on the chirality of constituent lipids. The electrostatic energy due to the in-plane spontaneous polarization is dependent on the orientational deformation of in-plane spontaneous polarization, and bends the domain shape towards the bending direction of the in-plane spontaneous polarization. It has been demonstrated that the chiral dependence of the domain shapes of lipid monolayers originated from the chiral dependence of orientational structure due to the electric quadrupole density.     

Reaction of electron-deficient N=N, N=O double bonds, singlet oxygen, and CC triple bonds with acyloxyketenes or mesoionic 1,3-dioxolium-4-olates: generation of unstable mesoionic 1,3-dioxolium-4-olates from acyloxyketenes

Reactions of azodicarboxylates and nitrosobenzene derivatives with acyloxyketenes generated from dehydrochlorination of alpha-acyloxyarylacetyl chlorides were carried out to give triacylbenzamidine and N-arylimide derivatives, respectively, in good yields. The same compounds were obtained from the reaction with mesoionic 1,3-dioxolium-4-olates generated by Rh2(OAc)4-catalyzed decomposition of aryldiazoacetic anhydride derivatives. Formation of the same compounds from the different starting materials indicates that their reactions involve the same intermediates. The formation of triacylbenzamidine and N-arylimide derivatives is explained by 1,3-dipolar cycloaddition between electron-deficient N=N or N=O bonds and mesoionic 1,3-dioxolium-4-olates following by decarboxylation, ring opening of the resultant carbonyl ylides, and subsequent Mumm rearrangement of the corresponding imidates. The reaction with singlet oxygen composed of more electronegative atoms than N=N and N=O bonds also gave products arising from the singlet oxygen adducts with 1,3-dioxolium-4-olates. The generation of less stable mesoionic 1,3-dioxolium-4-olates from acyloxyketenes was also confirmed by isolation of furandicarboxylates on generation of acyloxyketenes from alpha-acyloxyarylacetyl chlorides in the presence of reactive dipolarophile dimethyl acetylenedicarboxylate.     

In Vitro Analyses of Spinach-Derived Opioid Peptides,Rubiscolins: Receptor Selectivity and Intracellular Activities through G Protein- and β-Arrestin-Mediated Pathways

Activated opioid receptors transmit internal signals through two major pathways: the G-protein-mediated pathway, which exerts analgesia, and the β-arrestin-mediated pathway, which leads to unfavorable side effects. Hence, G-protein-biased opioid agonists are preferable as opioid analgesics. Rubiscolins, the spinach-derived naturally occurring opioid peptides, are selective δ opioid receptor agonists, and their p.o. administration exhibits antinociceptive effects. Although the potency and effect of rubiscolins as G-protein-biased molecules are partially confirmed, their in vitro profiles remain unclear. We, therefore, evaluated the properties of rubiscolins, in detail, through several analyses, including the CellKey^TM assay, cADDis^® cAMP assay, and PathHunter^® β-arrestin recruitment assay, using cells stably expressing µ, δ, κ, or µ/δ heteromer opioid receptors. In the CellKey^TM assay, rubiscolins showed selective agonistic effects for δ opioid receptor and little agonistic or antagonistic effects for µ and κ opioid receptors. Furthermore, rubiscolins were found to be G-protein-biased δ opioid receptor agonists based on the results obtained in cADDis^® cAMP and PathHunter^® β-arrestin recruitment assays. Finally, we found, for the first time, that they are also partially agonistic for the µ/δ dimers. In conclusion, rubiscolins could serve as attractive seeds, as δ opioid receptor-specific agonists, for the development of novel opioid analgesics with reduced side effects.     

Ion–ion interactions of LiPF6 and LiBF4 in propylene carbonate solutions

Self-diffusion coefficients of Li⁺ D_Li⁺, PF₆⁻ D_PF6⁻ and solvent propylene carbonate (PC) D_PC in LiPF₆−PC solutions were determined at 298 K by the pulse gradient spin echo (PGSE) NMR technique over the salt concentration range of 0.1–3.0 M (M = mol dm^– 3). The order of the diffusion coefficients was found to be D_Li⁺ < D_PF6⁻ < D_PC over the concentration range examined, and they were monotonically decreased with increasing the salt concentration. Haven ratio Λ/Λ_NMR, where Λ and Λ_NMR represent the ionic conductivity measured electrochemically and that estimated via the Nernst-Einstein equation using the diffusion coefficient, respectively, was evaluated as the measure of the ion–ion interaction in the LiPF₆–PC solutions. Though Λ/Λ_NMR values for LiPF₆-solutions decrease with increasing the salt concentration, they were greater than those for LiBF₄–PC solutions over the whole concentration range examined, which indicates that the ion pair formation ability of PF₆^– ion is weaker than that of the BF₄^– ion. The smaller value of the ionic conductivity for the highly concentrated LiPF₆–PC solution (above 2.0 M) than that of the LiBF₄-solutions can be attributed to the more rapidly increased viscosity relative to the LiBF₄-solution. Classic molecular dynamics (MD) simulations for the respective LiPF₆ and LiBF₄-solution of 0.5 and 1.0 M were also carried out based on the effective pair potentials. Diffusion coefficients, ionic conductivity and Haven ratio for these solutions were calculated from MD trajectories, and they qualitatively agree with those evaluated by experiments. Pair correlation functions g_LiO(r) (for Li⁺–O (PC) pair) and g_LiPF6(r) (for Li⁺–PF₆^– pair) or g_LiBF4(r) (for Li⁺–BF₄^– pair) revealed that the lithium ion weakly forms the contact ion pairs with PF₆^–, whilst strongly with BF₄^–, which supports the present experimental results. Moreover, the simulation results show that both anions in the contact ion pairs predominantly take the monodentate form, which is in contrast to the multidentate coordination predicted by ab initio calculation in gas phase.     

Purcell effect of GaAs quantum dots by photonic crystal microcavities

We fabricate photonic crystal slab microcavities embedded with GaAs quantum dots by electron beam lithography and droplet epitaxy. The Purcell effect of exciton emission of the quantum dots is confirmed by the micro photoluminescence measurement. The resonance wavelengths, widths, and polarization are consistent with numerical simulation results.     

Adaptive exponential approximation of optical density ratio using third-order regression equations for depth profiling of a blood inclusion in a skin tissue model

We propose the use of the third-order multiple regression equations in approximating an optical density ratio with an adaptive exponential function for measuring depth and thickness of a blood inclusion embedded in a skin tissue model. To ensure accuracy of the exponential approximation, we investigated numerically various relations of optical density ratios versus depth and thickness, on the basis of Monte Carlo simulations for a layered skin tissue model. The third-order multiple regression analysis based on the relations above was used to derive regression equations for the determination of depth and thickness. Experiments with skin tissue phantoms were used to assess this approach.     

Proton conductivity and microstructures of the core-shell type solid electrolytes in the MO2-In2O3-P2O5 (MTi,Sn, Zr) systems

The proton conducting 0.9MO₂·0.05In₂O₃·1.3P₂O₅ (MTi, Sn, Zr) electrolytes based on a core-shell structure were synthesized by a ball milling method. The core-shell type electrolytes showed the proton conductivities ranging from a higher value than those of Nafion membranes to 10^? 5 Scm^? 1 at intermediate temperatures of 150–200 °C, depending on the heat-treatment conditions. The samples with high conductivity were proved to adopt a core-shell structure by SEM observation, powder XRD analysis and ³¹P MAS-NMR measurements.