Self-assembled submicron-height terrace structures of pentacene single crystals formed in liquid crystal cells

A flat-surface single crystal structure of pentacene organic semiconductor was formed, with a submicron-height terrace structure, in liquid crystal solvent cells; the formation mechanism is discussed. By cooling the pentacene solution in a heated cell until supersaturated, a variety of segregated crystal morphology was observed, including dendrite, lozenge and needle-like crystals. Segregation of lozenge crystals was promoted by the appropriate pentacene concentration combined with the rubbing process of polyimide alignment layers, and the crystal morphology was examined in detailed. As a result, based on terrace-structural growth, low-profile flat-surface crystal morphology was found in addition to conventional pyramidal morphology. The molecular alignment of the flat pentacene crystal was confirmed by anisotropy of the microscopic Raman scattering intensity of the polarized incident light used for excitation. The self-assembly of flat thin single crystal plates, whose maximum size reach 150 µm approximately, may be applicable to practical electronic devices such as organic transistors.     

Measurement of solubility of organic solvents in polyisobutylene using the piezoelectric-quartz sorption method

The solubilites of five organic solvents (benzene, cyclohexane, n-hexane, toluene and ethylbenzene) in polyisobutylene have been measured using the piezoelectric-quartz sorption method at 25, 40 and 65°C and under low pressures. The consistency of the method is confirmed by a comparison of literature and experimental data. The effect of coating thickness was also investigated, and the results show that the experimental results are independent of thickness in the range ～ 0.2-1.6 μm. Two different polymers (weight-average molecular weights of 50000 and 100000) were tested to investigate the effect of polymer molecular weight. The results did not differ appreciably. The experimental data are compared with the predictions of the modified UNIFAC method due to Oishi and Prausnitz.     

Double-armed and tetra-armed cyclen-based cryptands

Double-armed and tetra-armed cyclen-based cryptands (1a–1d and 2) that bridge two aromatic rings by diethyleneoxy and triethyleneoxy units were prepared. The CSI-MS of 1:1 mixtures ([Ag⁺]/[ligand]) indicated that these new cryptands form 1:1 complexes with Ag⁺. The log K values for the interaction between Ag⁺ and 2 was greater than those of 1a–1d, double-armed cyclens (3a–3c and 4), and tetra-armed cyclen (5). The Ag⁺-ion-induced ¹H NMR spectral changes suggest that the Ag⁺–π interactions of the Ag⁺ complexes with the cryptands (1a–1d and 2) are stronger than those in Ag⁺/double-armed and tetra-armed cyclens. To visualise the Ag⁺?π interactions, the isosurfaces of the LUMO and HOMOs of the Ag⁺ complexes were calculated at the B3LYP/3–21G(*) theoretical level. The LUMO of the Ag⁺ ion is distorted by interaction with the HOMOs of the aromatic side arms. The calculations reveal Ag⁺?π interactions between the Ag⁺ ion and the aromatic side arms, and these are shown graphically.     

Total syntheses of (+)-spiculoic acid A and (+)-zyggomphic acid, new marine natural products of polyketide origin

The total syntheses of both natural (+)-spiculoic acid A and (+)-zyggomphic acid, new cytotoxic marine natural products of polyketide origin, have been accomplished for the first time. These syntheses were achieved by the highly stereoselective and high-yielding intramolecular Diels-Alder reaction of a functionalized (E,E,E)-2,7,9-dodecanal derivative to construct the core tetrahydroindan-2-one skeleton. A stereocongener of (+)-spiculoic acid A, i.e., the (2R,5S,6R)-isomer, was also synthesized. The details of these total syntheses are described.     

Chiral ruthenabicyclic complexes: precatalysts for rapid, enantioselective, and wide-scope hydrogenation of ketones

A novel ruthenabicyclic complex with base shows excellent catalytic activity in the asymmetric hydrogenation of ketones. The turnover frequency of the hydrogenation of acetophenone reaches about 35,000 min(-1) in the best case, affording 1-phenylethanol in >99% ee. Several aliphatic and base-labile ketones are smoothly converted to the corresponding alcohols in high enantioselectivity. The catalytic cycle for this hydrogenation, in which the ruthenabicyclic structure of the catalyst is maintained, is proposed on the basis of the deuteration experiment and spectroscopic analysis data.     

Discovery of orally available 8-aza-5-thiaProstaglandin E1 analogs as highly selective EP4 agonists

Analogs 8-aza-16-aryl prostaglandin E(1) (PGE(1)) and 8-aza-5-thia-16-arylPGE(1) were synthesized and evaluated with respect to their subtype receptor affinity and EP4 agonist activity for the purposes of identifying subtype-selective EP4 agonists that demonstrate oral efficacy. Using an inhibition assay of lipopolysaccharide (LPS)-induced tumor necrosis factor (TNF)-α production in rats, representative compounds were evaluated for their pharmacokinetic profiles and in vivo efficacy. Structure-activity relationships (SARs) were characterized and presented. Of the compounds tested, several demonstrated better oral exposure and/or in vivo efficacy compared with the previously reported analog 2a.     

Comparison of pulsed-excitation and phase-modulation methods for estimating fluorescence lifetime values using a convolved-autoregressive model and a high-gain photomultiplier tube

A comparative study between pulsed excitation (PE) and phase modulation (PM) methods has been carried out numerically and experimentally to estimate fluorescence lifetime values in the combined use of the following two measurement techniques: (i) To enhance the sensitivity in light detection, we have connected a load resistor with a large value at the output of a photomultiplier tube (PMT), which also brings about improvement in the signal-to-noise ratio (SNR) in measurements. (ii) The application of a convolved-autoregressive (C-AR) model to time-series data obtained from such a high-gain PMT enabled us to precisely estimate the fluorescence lifetime values in a nanosecond region. Although dependent on various measurement parameters, we have found that the PM method has potential in the field of biology or biochemistry for screening fluorescent samples.     

Thermal phase transition behaviour of liquid crystals in submicron pores formed with stretched polymer fibrils

This paper discusses thermal phase transitions in a nematic liquid crystal material, filling a highly strained porous polyolefin film. Ruptured and aligned polymer fibrils, whose minimum diameter reaches several tens of nm, formed polymer networks in the porous film. From observations of temperature-controlled composite films using a polarizing microscope, it was noted that the isotropic-to-nematic phase transition temperatures of submicron liquid crystal domains, located in or near molecularly aligned streak-like polymer areas, were significantly higher than those located at some distance from these areas. It was assumed that the highly aligned polymer chains in the fine fibrils promote the nematic phase of the liquid crystal. The stretched porous polymer, exhibiting spatial ordering on a submicron scale, is thus suitable for the control of thermal phase transitions in a liquid crystal.