Preparation of48V source for measurements of lineshapes of annihilation radiations and positron lifetimes

The preparation of the⁴⁸V positron source induced in a 1 μm thick Ti foil by (³He, pxn) reaction with a cyclotron is described. This source is very convenient for measurements of lineshapes of annihilation radiations and positron lifetimes at low or high temperatures, in a vacuum or for liquid metals. The absence of the mixing of long lifetime components is also convenient for the study of defects.     

Formation of gold nanoparticles in microreactor composed of helical peptide assembly in water

A novel microreactor was prepared by self-assembly of an amphiphilic block copolymer composed of a hydrophobic helical peptide unit with a naphthyl group at the C terminal and a hydrophilic poly(ethylene glycol) unit. The copolymer formed a self-assembly in water, taking a vesicular structure. Noticeably, when the copolymer was dispersed in an Au(3+) aqueous solution, gold nanoparticles were formed without addition of any reducing reagent. The naphthyl groups, which are located at the inner surface of the vesicular assembly, promoted the reduction of Au(3+) ions with accompanying pH decrease.     

Thin film coating of photocatalytics on ultra light ceramic tile by use of supercritical fluid

Abstract

Although sol-gel method is an easy procedure to form a thin film, it's extremely difficult to coat on the surface of small size particles, fibers, and fiber ceramics, because concentration occurs by capillary phenomena and causes peeling or breakage of film.

In order to solve this problem, we use supercritical CO₂ rapid expansion from supercritical solution (RESS), nano-sized particles of TiO₂ with high intensity can be sprayed out of a nozzle, then collected on the surface of substrates, but can be absorbed into fibers or porous materials, being not interfered by viscosity of a solution.

TiO₂ sol made by hydrolysis process is set in a pressure cell and mixed together with super-critical CO₂. Controlling the pressure and the temperature, we could obtain TiO₂ sol and super critical fluid mixture, and then discharge to the substrate. At this point, Titania sol viscosity is so low that a surface wettability of the substrate becomes negligible.

By the use of the characteristics of the supercritical fluid, without constraint condition of viscosity or capillarity, this sol can penetrate into the interstices of the substance's structure.

Thus, clearing obstruction of capillary phenomena, supercritical fluid coating method shows its capability to penetrate deep into inside of entangled fiber of the three-dimensional structure so as considered to be a heat resistant filter with 95% porosity.     

Effect of doping and thermal vacancies on positron annihilation in semiconductors

The effect of lattice defects on positron annihilation in semiconductors was studied. In silicon, any detectable doping effect could not be found. In germanium, the thermal equilibrium measurements of annihilation lineshapes showed no vacancy effect. From these experimental facts, the interaction of positrons with lattice defects was discussed.     

Effects of monolayer structures on long-range electron transfer in helical peptide monolayer

Self-assembled monolayers of alpha-helical peptides were prepared on gold, and the effects of the monolayer structures (kind of constituent amino acid, molecular orientation, and molecular packing) on long-range electron transfer through the helical peptides were studied. The helical peptides were 16mer peptides having a thiophenyl linker at the N-terminal for immobilization on gold and a redox active ferrocene moiety at the C-terminal as an electron-transfer probe. The peptides were immobilized on gold by a gold-sulfur linkage and the electron transfer from the ferrocene moiety to gold was studied by electrochemical methods. When two types of the peptides, one with the repeating unit of Leu-Aib (Aib represents 2-aminoisobutyric acid) and the other with that of Ala-Aib, were compared, the electron transfer was found one order slower in the Leu-Aib peptide monolayer than that in the Ala-Aib peptide monolayer. The self-assembled monolayers of the Ala-Aib peptide with mixing of three different lengths of the peptides, 8mer, 12mer, and 16mer without a ferrocene moiety, were also prepared. The monolayer regularity in terms of molecular orientation and packing was higher roughly in the order of the monolayers mixed with 16mer > 12mer > no additive > 8mer, but the electron transfer became faster in the opposite order. The logarithms of the standard rate constants showed a nearly linear relationship with the direct distances between the ferrocene moiety and gold (beta = 0.32 A (-1)). Some data deviated from this linear relationship, but the deviations could be explained from the difference in the molecular packing, which was evaluated from the monolayer capacitance. It is thus concluded that an electron is transferred along a few molecules along the surface normal so that the vertical orientation or the increase of the interchain backbone separation slows down the electron transfer. Further, it is demonstrated that a tightly packed monolayer, where vibrational mode is restricted, suppresses the electron transfer. Three models are proposed to account for the observed molecular dynamics effects on the basis of either electron-transfer mechanism of electron tunneling or sequential hopping.     

Asymmetric total synthesis of (-)-Linderol A

The first asymmetric total synthesis of (-)-Linderol A, a potent inhibitor of melanin biosynthesis of cultured B-16 melanoma cells, has been achieved via two key reactions: a diastereoselective [2+2] photocycloaddition of a coumarin-3-carboxylate bearing a chiral auxiliary with 3-methyl-1-butene and a subsequent stereoconvergent transformation of the photoadducts with use of dimethylsulfoxonium methylide to afford a tetrahydrodibenzofuran derivative.     

Suppression of HOMO-LUMO transition in a twist form of oligo(phenyleneethynylene) clamped by a right-handed helical peptide

A donor-π-acceptor (D-π-A) system of oligo(phenyleneethynylene) (OPE) was twisted by clamping both ends of the OPE with a right-handed helical peptide (SSA8=OPE). The induced twist in OPE was in a right-handed way. SSA8=OPE showed a weaker HOMO-LUMO band in the absorption spectrum than that of a reference compound AcOPE without the helix bridge. The fluorescence quantum yield of SSA8=OPE was extremely low (0.0045-0.0165), which was in contrast to AcOPE with a moderate quantum yield of 0.355. The fluorescence life times of SSA8=OPE and AcOPE were nearly the same. Time-dependent density functional theory calculations (b3lyp/6-31G(d,p) level) on a twisted conformation of the D-π-A system qualitatively reproduced CD spectra and UV spectra of a weak oscillator strength of the HOMO-LUMO transition. Upon twisting the D-π-A system, the oscillator strength of the HOMO-LUMO transition is thus reduced.     

Preparation of fibrous cellulose by enzymatic polymerization using cross-linked mutant endoglucanase II

A cross-linked mutant endoglucanase II was prepared for enzymatic polymerization to cellulose. The cross-linked enzyme is composed of three mutant enzymes showing polymerization activity. A characteristic feature of the polymerization with this cross-linked enzyme is formation of cellulose fibrils in contrast to plate-like crystals obtained by using a free enzyme.     

Nitric oxide adsorbed on zeolites: EPR studies

CW-EPR studies of NO adsorbed on sodium ion-exchanged zeolites were focused on the geometrical structure of NO monoradical and (NO)2 biradical formed on zeolites. The EPR spectrum of NO monoradical adsorbed on zeolite can be characterized by the three different g-tensor components and the resolved y-component hyperfine coupling with the 14N nucleus. Among the g-tensor components, the value of g(zz) is very sensitive to the local environment of zeolite and becomes a measure of the electrostatic field in zeolite. The temperature dependence of the g-tensor demonstrated the presence of two states of the Na-NO adduct, in rigid and rotational states. The EPR spectra of NO adsorbed on alkaline metal ion-exchanged zeolite and their temperature dependency are essentially the same as that on sodium ion-exchanged zeolite. On the other hand, for NO adsorbed on copper ion-exchanged zeolite it is known that the magnetic interaction between NO molecule and paramagnetic copper ion are observable in the spectra recorded at low temperature. The signals assigned to (NO)2 biradical were detected for EPR spectrum of NO adsorbed on Na-LTA. CW-EPR spectra as well as their theoretical calculation suggested that the two NO molecules are aligned along their N-O bond axes. A new procedure for automatical EPR simulation is described which makes it possible to analyze EPR spectrum easily. In the last part of this paper, some instances when other nitrogen oxides were used as a probe molecule to characterize the zeolite structure, chemical properties of zeolites, and dynamics of small molecules were described on the basis of selected literature data reported recently.