Electronic structures of the highest occupied molecular orbital bands of a pentacene ultrathin film

We report the energy dispersions of the highest occupied molecular orbitals (HOMO)-derived bands of a pentacene (Pn) thin film, whose in-plane structure resembles closely that of the ab plane of a low-density bulk Pn phase. Our present photoemission result indicates that the overlap of the pi-orbitals of adjacent Pn molecules is larger than what was expected from theoretical calculations. Further, of the two HOMO-derived bands, the large dispersion width of the band with higher binding energy suggests that this one mainly contributes to the bandlike charge transport in a Pn crystal.     

Coupled whispering gallery modes in a multilayer-coated microsphere

Whispering gallery modes in a microsphere coated with three layers of high, low, and high refractive indices (RIs) are considered. Coastal modes and inland modes, centered on the outer and inner high-RI layers, exist as different radial modes. At right values of RI and thickness of the three layers, an inland mode and a coastal mode couple to produce a radial distribution of the photonic field that resembles bonding and antibonding orbitals. The coupling occurs across a layer of the middle low-RI layer, much thicker than the wavelength of light. The coupling is analyzed in a quantum-mechanical analog of a one-dimensional particle in a double-well potential.     

Improving Data Quality in Traditional Low-Dose Scanning Transmission Electron Microscopy Imaging

It has become very important to study and find optimal conditions for imaging electron-beam (e-beam) sensitive materials in scanning transmission electron microscopy under low electron-dose with high signal-to-noise ratio (SNR). Convergence and collection angles and electron-probe current are essential parameters. However, these parameters have rarely been discussed in a systematic way. In this paper, the illumination and collection conditions are optimized according to the resolution requirement of different materials by adjusting the condenser and intermediate lenses in a commercial transmission electron microscope. To demonstrate the significance of optimizing these parameters, two examples, zeolite MFI and metal–organic framework (MOF) MIL-101, are taken among the sensitive materials, with the most important electron incidences along the [010] and <110> directions, respectively. High SNR atomic resolution images of MFI are obtained with e-beam current as low as 0.50 pA, reaching information transfer for reflection up to 18 0 2 corresponding to d-spacing of 0.11 nm, close to the resolution limit of 0.098 nm from resolvable diffraction limit. MOF MIL-101 is characterized under an even lower e-beam 0.2 pA to avoid severe beam damage. High-quality annular dark and bright field images are obtained, which proves the wide applicability of this method on more e-beam sensitive materials.     

Experimental study of the Kolmogorov refined similarity variable

Recently Thoroddsen and Van Atta (1992, Phys. Fluids A4, 2592) showed that Kolmogorov's refined similarity hypothesis (1962, J. Fluid Mech. 13, 77; 82) is supported by experimental data from a wind-tunnel study of a cylinder wake, at Re_λ of 550. We show here that the probability density of the Kolmogorov similarity variable approaches a Gaussian distribution. The data also suggest that it may obey an even more demanding conditional similarity, which leads to important conclusions regarding the scaling exponents.     

Acid-induced conformational alteration of cis-preferential aromatic amides bearing N-methyl-N-(2-pyridyl) moiety

A series of cis-preferential aromatic N-methyl amides was designed and synthesized, and acid-induced conformational alteration of these compounds was investigated by means of NMR measurements in solution and X-ray crystal structure analysis. Compounds with a terminal N-methyl-N-(2-pyridyl) amide unit showed acid-induced conformational change from cis to trans, while those with a terminal N-methyl-2-pyridinecarboxamide unit showed a change of the carbonyl orientation from anti to syn with retention of cis conformation.     

The first total synthesis and structural determination of antibiotics K1115 B1s (alnumycins)

K1115 B₁, isolated from the broth of Streptomyces species, was found to be a mixture of stereoisomers. Authors synthesized all stereoisomers of K1115 B₁ by convergent synthesis coupling a rhamnose derivative, an isobenzofuranone, and a chiral tetraol. Comparison of ¹H NMR spectra and optical rotations made it clear that the absolute structures of K1115 B_1α (the major isomer) and K1115 B_1β (the minor isomer) were (1R, 17S)- and (1R, 17R)-configurations, respectively. The optical rotations of the stereoisomers revealed that alnumycin, reported as the identical structure with K1115 B₁, might be another mixture of stereoisomers.     

Synthesis of the proposed structure of phaeosphaeride A

The first total synthesis of the proposed structure of phaeosphaeride A has been achieved via six-membered-ring formation by means of an intramolecular vinyl-anion aldol reaction as the key step. This synthesis suggests a revised configurational assignment for phaeosphaeride A.     

Stabilization mechanism of clarithromycin tablets under gastric pH conditions

It has been reported that tablets of clarithromycin (CAM), a 14-membered macrolide antibiotic, are especially stable under low pH conditions such as in gastric fluid, and showed excellent antibacterial efficiency even though CAM molecules themselves are rapidly decomposed. Therefore, we aimed to clarify the stabilization mechanism of CAM tablets under low pH conditions. From the results of stability and dissolution tests, the optimal decomposition rate constant (K(dec)) and dissolution rate constant (K(dis)) at various pH values were calculated by curve-fitting to consecutive reactions. Consequently, log(K(dec)) increased as pH decreased. On the other hand, log(K(dis)) increased as pH decreased from 3.0 to 1.5, but decreased as pH decreased from 1.5 to 1.0. In addition, the disintegration time of commercially available tablets at pH 1.0 and 1.2 was found to be delayed, resulting in a decrease of K(dis). Furthermore, from powder X-ray diffraction, HPLC and elemental analysis, the delay in disintegration time might be attributable to the formation of a transparent gel, formed by the reaction between CAM molecule and hydrochloric acid under low pH conditions, on the surface of CAM tablet. On the basis of these results, this report can be considered the first case where a transparent gel prevents gastric fluid from penetrating the tablet, resulting in reduced decomposition of CAM following oral administrating.     

Formal enantioselective total synthesis of schulzeines A-C via Pd-catalyzed intramolecular asymmetric allylic amination

Formal enantioselective total synthesis of schulzeines A-C was accomplished, featuring highly efficient Pd-catalyzed asymmetric allylic amination using novel diphosphonite ligands (BOPs) to provide 1-vinyltetrahydroisoquinoline key intermediates, as well as Ru-catalyzed ring-closing metathesis reaction to construct the key tricyclic cores in enantiopure form with correct absolute configurations.     

Electric field dependent photocurrent generation in a thin-film organic photovoltaic device with a [70]fullerene-benzodifuranone dyad

A [70]fullerene-benzodifuranone acceptor dyad synthesized by a Ag?-mediated coupling reaction was used to construct a thin-film organic solar cell. The fullerene and the benzodifuranone dye in the dyad have close-lying LUMO levels in the range of 3.7-3.9 eV, so that energy transfer from the dye to the fullerene can take place. A p-n heterojunction photovoltaic device consisting of a tetrabenzoporphyrin and a [70]fullerene-benzodifuranone dyad showed a weak but discernible contribution from light absorption of the dyad to the photocurrent under both a positive and a negative effective bias. These results indicate that the benzodifuranone moiety attached to the acceptor contributes to light-harvesting by energy transfer.