Xenon-plasma light ultrahigh-resolution ARPES study of low-energy single-particle excitation gap in (Bi,Pb)2Sr2CuO6

We have performed ultrahigh-resolution angle-resolved photoemission spectroscopy of (Bi,Pb)₂Sr₂CuO₆ by using a newly developed xenon-plasma light source to clarify the origin of the pseudogap (PG). We determined the comprehensive momentum and temperature dependences of the superconducting (SC) gap and the PG, and revealed a smooth evolution of the PG from the SC gap. We also found a linear scaling behavior of the characteristic PG temperature with the SC gap size regardless of the momentum location. These experimental results strongly suggest that the observed PG is caused by the precursor pairing.     

Simultaneous magneto-optical trapping of lithium and ytterbium atoms towards production of ultracold polar molecules

We have successfully implemented the first simultaneous magneto-optical trapping (MOT) of lithium (⁶Li) and ytterbium (¹⁷⁴Yb) atoms towards production of ultracold polar molecules of LiYb. For this purpose, we developed the dual atomic oven which contains both atomic species as an atom source and successfully observed the spectra of the Li and Yb atoms in the atomic beams from the dual atomic oven. We constructed the vacuum chamber including the glass cell with the windows made of zinc selenium (ZnSe) for the CO₂ lasers, which are the useful light sources of optical trapping for evaporative and sympathetic cooling. Typical atom numbers and temperatures in the compressed MOT are 7×10³ atoms, 640 μK for ⁶Li, 7×10⁴ atoms, and 60 μK for ¹⁷⁴Yb, respectively.     

Synthesis,spectral and thermal studies on dicarboxylate-bridged palladium(II) coordination polymers. Part II

The synthesis and thermal behavior of the new [Pd(fum)(bipy)] _n ·2nH₂O (1), [Pd(fum)(bpe)] _n ·nH₂O (2) and [Pd(fum)(pz)] _n ·3nH₂O (3) {bipy = 4,4′-bipyridine, bpe = 1,2-bis(4-pyridyl)ethene and pz = pyrazine} fumarate complexes are described in this work as well their characterization by IR and ¹³C CPMAS NMR spectroscopies. TG curves showed that the compounds released organic ligands and lattice water molecules in the temperature range of 46–491 °C. In all the cases, metallic palladium was identified as the final residue.     

Complex Allylation by the Direct Cross‐Coupling of Imines with Unactivated Allylic Alcohols

Regioselective, stereoselective : The convergent coupling of allylic alcohols with imines to deliver stereodefined homoallylic amines is described (see scheme). The process proceeds with net allylic transposition without the intermediacy of allylic organometallic reagents. Two stereodefined centers and a geometrically defined di‐ or trisubstituted alkene are forged with high selectivity.

     

Effect of Head Size in Head‐Tail‐Type Polycations on their in vitro Performances as Nonviral Gene Vectors

Three kinds of head‐tail‐type block copolymers composed of polyamidoamine (PAMAM) dendron heads and poly(L ‐lysine) (PLL) tail blocks (PAMAM dendron‐PLL), having PAMAM dendrons with different generations (G2.5‐PLL, G3.5‐PLL and G4.5‐PLL) were synthesized. Some of the dendron heads were located at polyplex surface, and G2.5‐PLL and G3.5‐PLL could form small polyplexes (less than 150 nm in size). G2.5‐PLL and G3.5‐PLL polyplexes were taken up into the cells more effectively. PAMAM dendron‐PLL that had a larger dendron head could show a more‐effective buffering effect. The in vitro performance of the PAMAM dendron‐PLL polyplexes was controlled by the balance of cellular uptake and endosomal escape by a buffering effect.

     

Effect of phenyl substitution on the lifetime and product distribution of cyclobutylidene: preference change in the rearrangements via 1,2-carbon shift and 1,2-hydrogen shift

Steady state and laser flash photolytic experiments with precursors 6 and 11 revealed that diphenyl substitution affects the lifetime and reaction mode of cyclobutylidene. 2,2-Diphenylcyclobutylidene 3 (τ <0.1 ns) produces methylenecyclopropane 1 via 1,2-carbon in significant preference to the positional isomer 2 or cyclobutene 4. On the other hand, 3,3-diphenylcyclobutylidene 5 (τ = ca. 4 ns) gives 1,2-hydrogen shift product 4 more favorably than 1,2-carbon shift product 2 together with formal carbene dimer 14. MRMP2//MP2 calculations afford useful results to understand the interrelationship among substitution, structure, and reactivity.     

Molecular-shape imprinting and immobilization of biomolecules on a polymer containing azo dye

We demonstrate a novel technique for molecular imprinting and immobilization on a surface of a polymer containing azo dyes (azopolymer). The azopolymer was found to be capable of immobilizing micrometer- and nanometer-scale macromolecules (e.g., lambda-DNA, immunoglobulin G (IgG), bacterial protease, and 1-mum polystyrene particles) through photoirradiation with blue-wavelength light. Fluorescence and atomic force microscopy studies revealed that the azopolymer surface deformed along with the shape of the macromolecules, holding them in place after photoirradiation. The desorption of the immobilized macromolecules from the azopolymer surface in an aqueous medium was observed to be very slow, on the time scale of 10 min to weeks, depending on the photoirradiation time. Immunological and enzymatic studies showed that IgG and bacterial protease immobilized on the azopolymer surface retained their original functionality. These results suggest that the azopolymer physically, not chemically, binds the macromolecules because of the increase in contact area between the macromolecules and the azopolymer surface after photoirradiation.     

Topographic, electrochemical, and optical images captured using standing approach mode scanning electrochemical/optical microscopy

We developed a high-resolution scanning electrochemical microscope (SECM) for the characterization of various biological materials. Electrode probes were fabricated by Ti/Pt sputtering followed by parylene C-vapor deposition polymerization on the pulled optical fiber or glass capillary. The effective electrode radius estimated from the cyclic voltammogram of ferrocyanide was found to be 35 nm. The optical aperture size was less than 170 nm, which was confirmed from the cross section of the near-field scanning optical microscope (NSOM) image of the quantum dot (QD) particles with diameters in the range of 10-15 nm. The feedback mechanism controlling the probe-sample distance was improved by vertically moving the probe by 0.1-3 microm to reduce the damage to the samples. This feedback mode, defined as "standing approach (STA) mode" (Yamada, H.; Fukumoto, H.; Yokoyama, T.; Koike, T. Anal. Chem. 2005, 77, 1785-1790), has allowed the simultaneous electrochemical and topographic imaging of the axons and cell body of a single PC12 cell under physiological conditions for the first time. STA-mode feedback imaging functions better than tip-sample regulation by the conventionally available AFM. For example, polystyrene beads (diameter approximately 6 microm) was imaged using the STA-mode SECM, whereas imaging was not possible using a conventional AFM instrument.     

Electron-transfer fluorescence quenching of aromatic hydrocarbons by europium and ytterbium ions in acetonitrile

To make the effects of molecular size on photoinduced electron-transfer (ET) reactions clear, the ET fluorescence quenching of aromatic hydrocarbons by trivalent lanthanide ions M3+ (europium ion Eu3+ and ytterbium ion Yb3+) and the following ET reactions such as the geminate and free radical recombination were studied in acetonitrile. The rate constant k(q) of fluorescence quenching, the yields of free radical (phi(R)) and fluorescer triplet (phi(T)) in fluorescence quenching, and the rate constant k(rec) of free radical recombination were measured. Upon analysis of the free energy dependence of k(q), phi(R), phi(T), and k(rec), it was found that the switchover of the fluorescence quenching mechanism occurs at deltaG(fet) = -1.4 to -1.6 eV: When deltaG(fet) < -1.6 eV, the fluorescence quenching by M3+ is induced by a long-distance ET yielding the geminate radical ion pairs. When deltaG(fet) > -1.4 eV, it is induced by an exciplex formation. The exciplex dissociates rapidly to yield either the fluorescer triplet or the geminate radical ion pairs. The large shift of switchover deltaG(fet) from -0.5 eV for aromatic quenchers to -1.4 to -1.6 eV for lanthanide ions is almost attributed to the difference in the molecular size of the quenchers. Furthermore, it was substantiated that the free energy dependence of ET rates for the geminate and free radical recombination is satisfactorily interpreted within the limits of the Marcus theory.