Influence of exchange coupling on current-driven domain wall motion in a nanowire

In this study, the effect of exchange stiffness constant on current-driven domain wall motion in nanowires with in-plane magnetic anisotropy (IMA) and perpendicular magnetic anisotropy (PMA) has been investigated using micromagnetic simulation. The critical current density in a nanowire with IMA decreases as the exchange stiffness constant decreases because the domain wall width at the upper edge of the nanowire narrows according to the decrease of the exchange stiffness constant. On the other hand, the critical current density in a nanowire with PMA slightly decreases contrary to that of IMA although the domain wall width reasonably decreases as the exchange stiffness constant decreases. The slight reduction rate of the critical current density is due to the increase of the effective hard-axis anisotropy of PMA nanowire.     

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.     

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.

     

Convergent synthesis of the common FGHI-ring part of ciguatoxins

Convergent synthesis of the common FGHI-ring part (54) of ciguatoxins was achieved via the following key steps: (i) the Nozaki-Hiyama-Kishi reaction connecting the F-ring part (6) with the I-ring part (7); (ii) regio- and stereoselective epoxidation; (iii) the 6-exo-epoxide opening reaction forming simultaneously the H-ring and the quaternary asymmetric center at C30; (iv) inversion of the C29 stereocenter by a two-step oxidation/reduction process, where the successful inversion depended on proper management of the steric environment of the substrate; and (v) final reductive cyclization constructing the G-ring.     

Determination of antihyperglycemic biguanides in serum and urine using an ion-pair solid-phase extraction technique followed by HPLC-UV on a pentafluorophenylpropyl column and on an octadecyl column

An HPLC-UV method was established for the determination of metformin and buformin in biological fluids. Metformin was not retained on particles packed in conventional solid-phase extraction cartridges; in contrast, buformin was retained too firmly and not eluted with a solvent for recovery. However, both drugs were retained on particles that had been treated with an ion-pair reagent of heptanesulfonate or dodecylsulfate and recovered almost completely. The recovered fraction was subjected to HPLC on a pentafluorophenylpropyl column which was suitable for the determination of both biguanides in serum and in urine. Limits of quantitation were low enough for clinical use, and reproducibility was high with an RSD of 0.9-2.3%. HPLC on a conventional octadecyl column was suitable only for the determination of buformin in serum since interfering peaks appeared on the chromatograms of urine samples. The method was applied to analysis of some clinical specimens.     

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.     

A simple picture for the rotational enhancement of the rate for the F + HCl --> HF + Cl reaction: a dynamical study using a new ab initio potential energy surface

Quantum scattering calculations for the reaction F + HCl --> HF + Cl are performed on a new ground-state ab initio potential energy surface. The reagent rotation is found to have a dramatic effect on the reaction probability. Furthermore, the exit channel rotational thresholds leave a strong imprint on the reaction probabilities and even on the cumulative reaction probability. A very simple vibrationally adiabatic model is shown to account for most aspects of the reaction dynamics. In this model, the fast vibrational motion is adiabatically eliminated leaving the key reaction dynamics represented by a reduced atom + rotor collision. The shape of the adiabatic potential surface immediately yields to a simple and intuitive interpretation for the rotational enhancement of the rate. The rotational enhancement is shown to be an effect of the entrance channel dynamics of the atom-rotor problem.