Ordered State and Superfluidity of Quasi-Two-Dimensional Excitons in Type-II Quantum Wells

One of the best ways to obtain unambiguous experimental evidence for the superfluidity of excitons is to observe phenomena that are directly related to the phase of the condensed excitons. As an advantageous candidate for this purpose, we propose a quasi-two-dimensional exciton system in type-II quantum wells (QWs). We consider the condensed excitons in the type-II QW irradiated by a weak laser light and show that under the control of an external current J ex , the system takes the ordered state with (without) net superflow of excitons at T = 0 K when J ex is larger (smaller) than a certain critical value. Introducing probable mechanisms of phase transitions, we calculate the transition temperatures and construct the phase diagram.     

Laser Spectroscopy and Lifetime Measurements of the S1 State of Tetracyanoquinodimethane (TCNQ) in a Cold Gas-Phase Free-Jet

The S₁ electronic state of 7,7,8,8-Tetracyanoquinodimethane (TCNQ) has been investigated by laser induced fluorescence (LIF), dispersed fluorescence (DF) spectroscopy, and lifetime measurements under jet-cooled conditions in the gas-phase. The LIF spectrum showed a weak origin band at 412.13 nm (24262 cm⁻¹) with prominent progression and combination bands involving vibrations of 327, 1098, and 2430 cm⁻¹. In addition, very strong bands appeared at ∼363.6 nm (3300 cm⁻¹ above the origin). Both the LIF and DF spectra indicate considerable geometric change in the S₁ state. The fluorescence lifetime of S₁ at zero-point level was obtained to be 220 ns. This lifetime is 40 times longer than the radiative lifetime estimated from the S₁−S₀ oscillator strength. Furthermore, the lifetimes of the vibronic bands exhibited drastic energy dependence, indicating a strong mixing with the triplet (T₁) or intramolecular charge-transfer (CT) state. This study is thought to disclose intrinsic nature of TCNQ, which has been well known as a component of organic semiconductors and a versatile p-type dopant.     

Biphenyl ether and biphenyl quinolizidine lactone alkaloids from Heimia salicifolia

Three new biphenyl ether quinolizidine lactone alkaloids (1–3) and 13 new biphenyl quinolizidine lactone alkaloids (4–16) were isolated from Heimia salicifolia (Lythraceae) together with seven known alkaloids. Their structures were determined by spectroscopic analyses and chemical conversions.     

Electrical conduction mechanisms in amorphous GeTe thin films

A measurement of potential distribution was carried out on amorphous GeTe thin films at various applied voltages. The potential falls steeply near the anode. The results were consistently explained with the hypothesis that the free carriers which flow away from the regions near the cathode and the anode into the inner part of the sample are not replenished by injected carriers. An estimate was made of the density of space-charge and of the free carrier concentration as a function of position. The fact that the distributions of both the potential and the free carrier concentration are nonuniform indicate that the diffusion current cannot be neglected. In the steady state, the observed current density as a function of applied field agrees well with the predictions of a theoretical model that includes both diffusion and drift currents.     

Total synthesis of mycestericin A

The first total synthesis of mycestericin A (1) starting from tartrates is described. The Overman rearrangement of an allylic trichloroacetimidate generated a tetra-substituted carbon with nitrogen, and subsequent stereoselective transformations afforded the highly functionalized vinyl iodide. The cross-coupling of the vinyl iodide with a chiral organozinc species under Negishi conditions, followed by deprotection, completed the total synthesis of 1.     

Production of 67Cu via the 68Zn(p,2p)67Cu reaction and recovery of 68Zn target

The radionuclide ⁶⁷Cu was produced via the ⁶⁸Zn(p,2p)⁶⁷Cu reaction by irradiating enriched ⁶⁸Zn targets with 70 MeV proton beam. Copper-67 was chemically separated from the zinc target by ion-exchange chromatography using Chelex-100 chelating ion-exchange resin. Procedure for recovery of the enriched ⁶⁸Zn was developed. The target recovery yield of this method was evaluated to be more than 97%.     

C−F Transformations of Benzotrifluorides by the Activation of Ortho-Hydrosilyl Group

Single C−F transformations of aromatic trifluoromethyl compounds are challenging issues due to the strong C−F bond. We have recently developed selective methods for single C−F transformations such as allylation of o-hydrosilyl-substituted benzotrifluorides through the hydride abstraction with trityl cations. Single C−F thiolation and azidation of o-(hydrosilyl)benzotrifluorides were achieved using trityl sulfides and trityl azide catalyzed by Yb(OTf)₃. Treatment of o-(hydrosilyl)benzotrifluorides with trityl chloride resulted in single C−F chlorination. The resulting fluorosilyl group served in further transformations including protonation, halogenation, and Hiyama cross-coupling with C−Si cleavage. We also synthesized benzyl fluorides by LiAlH₄-reduction of the resulting fluorosilanes and further C−F transformations. These methods enabled us to prepare a broad range of organofluorines from simple benzotrifluorides through C−F and C−Si transformations.     

Global analysis of dynamic changes in lipid raft proteins during T-cell activation

Lipid rafts are considered as specialized microdomains within the plasma membrane with unique lipid compositions different from surrounding membranes. Following T-cell receptor (TCR) stimulation, lipid rafts assemble in T-cell/antigen-presenting cell (APC) contact site known as the immunological synapse, inner leaflets of which serve as activation or docking sites for downstream signaling components. To understand the signaling events occurring in lipid rafts, we globally analyzed dynamic changes in lipid raft proteins during TCR/CD28 costimulation using 2-D fluorescence difference gel electrophoresis. We detected multiple spots whose intensities were enhanced after costimulation, and identified proteins in these spots by PMF. Identified proteins include Src family tyrosine kinases, tyrosine phosphatase, phosphatidylinositol 3-kinase (PI3-kinase), actin-binding proteins, and regulators for small GTPases. Of particular interest, a number of pleckstrin homology (PH) domain-containing proteins were identified. Biochemical and histochemical analyses confirmed the translocation of these proteins from cytosol to lipid rafts. We also demonstrated that these proteins assembled at the T-cell/APC interface. These results indicate the efficacy of our system to systematically analyze dynamics of lipid raft proteins during extracellular stimulation.     

Controlled polymerization of an AB2 monomer using a chloromethylarene as comonomer: branched polymers from activated methylene compounds

Hyperbranched and branched polymers were synthesized by one-pot reaction of the AB₂ monomer 4-(4′-chloromethylbenzyloxy)phenylacetonitrile (1 ). The polymerization of 1 was controlled by adding a chloromethylarene (A₁ comonomer) such as methoxybenzyl chloride and by adding TBAC (tetrabutylammonium chloride). Copolymerization of 1 with A₂ comonomers, bis(chloromethyl)arenes, gives the corresponding copolymers.