Diffusion of hydrogen in metals

The present status of our understanding of the diffusion of hydrogen in metals, both experimental and theoretical, is reviewed. Discussions are focused on the mechanism of diffusion of hydrogen isotopes H, D and T in f.c.c. and b.c.c. metals; the positive muon (μ ⁺) is referred to where appropriate. An up-to-date compilation of diffusion data as a function of temperature and isotope mass has been made, and a clear distinction in general diffusion behaviour in f.c.c. and b.c.c. metals is noted. Subsequently, the results obtained from the Gorsky effect, nuclear magnetic resonance and quasi-elastic neutron scattering that provide information on elementary jump processes are discussed.

A conceptual framework of the quantum diffusion of light interstitials in metals is given, including the recent Kondo theory that emphasizes the crucial importance of particle-conduction electron interactions in the diffusion process, especially at low temperatures. It is shown with the help of recent estimates of the tunneling matrix element that the overall feature of diffusion of hydrogen isotopes in b.c.c. metals as well as μ ⁺ in f.c.c. metals can be explained consistently within the frame presented here.

Finally, recent advances in the diffusion studies on hydrogen in b.c.c. metals are described. They include a re-analysis of quench-recovery experiments that manifested nearly athermal diffusion of H, D and T in Ta at low temperatures, and an enormous enhancement of the diffusivity under stress (superdiffusion) observed for H and D in V.     

Stereoselective Syntheses of all the Possible Stereoisomers of Coronafacic Acid

An efficient and stereoselective syntheses of all the possible stereoisomers of coronafacic acid (CFA) has been developed. The stereochemistries of C3a and C7a were controlled in a diastereoselective Diels-Alder type cycloaddition using a chiral auxiliary. CFA and 6-epi-CFA were synthesized by hydrogenation of a common intermediate. During the synthesis of 6-epi-CFA, we established that its cis-fused configuration is important for the introduction of C4-C5 double bond by dehydration. This report is the first practical synthesis of both 6-epi-CFA, and its enantiomer.     

Evaluation and comparison of three novel microbubbles: Enhancement of ultrasound-induced cell death and free radicals production

Three novel lipid-shell-type microbubbles (MBs), AS-0100, BG6356A and BG6356B, have been evaluated for their impact on ultrasound (US)-induced cell death and free radicals production. Previously studied and well-characterized US exposure conditions were employed in which human myelomonocytic lymphoma U937 cells were exposed to 1 MHz pulsed US beam (0.3 W/cm², 10% duty factor) for 1 min with or without MBs. Three different concentrations of each MB were used. Apoptosis and cell lysis were assessed by examining phosphatidylserine externalization and by counting viable cells, respectively, 6 h post-exposure. Free radicals production and scavenging activities were evaluated using electron paramagnetic resonance (EPR)-spin trapping. The results showed that only AS-0100 and BG6356A were able to enhance the US-induced apoptosis, mainly by increasing the secondary necrosis. Apoptosis and cell lysis seemed to depend more on mechanical forces exerted by oscillating MBs while free radicals played a trivial role. BG series MBs exhibited pronounced scavenging activities. Generally, despite the need for further optimization, AS-0100 and BG6356A appear to be promising as adjuncts in cases where US-induced cell death is required.     

Preparation of Starch Succinate WITH INTERMEDIATE DS BY AQUEOUS SLURRY REACTION

Modification of starch by chemical derivatization has been widely studied since early 1950s. The formation of starch ester such as acetate and propionate imparts starch water resistance. In contrast, the introduction of carboxylates onto starch increases the hydrophilicity of starch. One example is carboxymethyl starch (CMC), which has been widely used in several industry areas. Succinic anhydride reacts with starch to form starch succinates. Since starch succinates are polyanions, they off…     

Mechanism of Oxygen Adsorption on Partially K Exchanged Na-A Type Zeolite

Accordingly, the observation of oxygen selectivity on Na-K-A would indicate that nitrogen has a greater steric hindrance at the window than does oxygen. Using single crystal X-ray diffraction (SCXD), it was confirmed that K at 8-member rings was relocated to 6-member rings and that the location of Na at 8-member rings became uncertain with calcination. It was also observed that Na-K-A was thermally more stable than Na-A. Using magic angle spin nuclear magnetic resonance (MAS-NMR), it was confirmed that Na at 8-member rings irreversibly changed location from a symmetric position to an asymmetric position with calcination.Using the atomic positions determined by SCXD, the mean square displacements (MSD) of oxygen and nitrogen inside the crystal of Na-A and Na-K-A were estimated by means of molecular dynamic simulation (MD). When temperature was decreased, the MSD of nitrogen was reduced to a greater extent than that of oxygen and the MSD of nitrogen inside Na-K-A was reduced by a greater margin than that inside Na-A.     

Cytotoxicity of asymmetric platinum complexes against L-1210 cells. Effect of bulky substituents

The asymmetric platinum complexes cis-Pt(LL')Cl2 (L = NH3, L' = CH3NH2, (CH3)2NH, C2H5NH2 and (C2H5)2NH and LL' = N,N-dimethylethylenediamine),--one of the NH3 groups of cis-Pt(NH3)2Cl2 was substituted by alkylamine--, were synthesized and their cytotoxic effects have been measured using L-1210 cells. The IC50 values of the asymmetric platinum complexes,--being obtained after 24 h exposure of L-1210 cells to the platinum complexes--, are almost comparable to the corresponding value of cis-Pt(NH3)2Cl2. In 2 h exposure, however, the IC50 values of the platinum complexes were dramatically changed, i.e., a marked difference was observed between those of L' = RNH2 and L' = R2NH. On the other hand, the amounts of platinum taken into the L-1210 cells is little affected by the alkylamino substitution. The results suggest that the bifunctional platinum binding to the target molecule may be responsible for the cytotoxicity.     

Suppression of particle generation in a plasma process using a sine-wave modulated rf plasma

Sine-wave modulated rf plasma has been used to control particle generation and growth in a plasma-enhanced chemical vapor deposition of silicon dioxide thin films using TEOS/O₂. The density and the size of particles generated in the plasma are greatly reduced when the plasma is modulated with sine-wave modulation at low modulation frequency (<1000 Hz). In addition, particle contamination on the films is significantly reduced also for nanoparticles, and the film growth rates at the range of modulation frequencies where particle generation are greatly reduced do not decrease appreciably. Compared to its counterpart pulse-wave modulation plasma, the sine-wave modulation plasma has demonstrated a better performance in terms of reduction of particle generation and film contamination, and of film growth rate. Thus, the sine-wave modulation plasma has shown as a promising method to be applied in the production of thin film with a high deposition rate and a low particle contamination.     

Antibacterial thymol derivatives isolated from Centipeda minima

Two new monoterpenoids, 8,10-dihydroxy-9(2)-methylbutyryloxythymol (1) and 10-hydroxy-8,9-dioxyisopropylidene-thymol (2), together with five known thymol derivatives: 8,9,10-trihydroxythymol (3), thymol-beta-glucopyranoside (4), 9-hydroxythymol (5), 8,10-dihydroxy-9-isobutyryloxythymol (6), and 8-hydroxy-9,10-diisobutyryloxythymol (7), were isolated from Centipeda minima. Their structures were identified by means of spectroscopic analyses. Interestingly, compound 2 is not an extraction artifact according to a close HPLC examination of material after extraction by analytical MeOH at ambient temperature. The antibacterial activities of compounds 1-7 were evaluated against eight microbial strains by the agar dilution method.     

Superionic Conduction in Co‐Vacant P2‐NaxCoO2 Created by Hydrogen Reductive Elimination

The layered P2‐Na_xMO₂ (M: transition metal) system has been widely recognized as electronic or mixed conductor. Here, we demonstrate that Co vacancies in P2‐Na_xCoO₂ created by hydrogen reductive elimination lead to an ionic conductivity of 0.045 S cm^?1 at 25 °C. Using in situ synchrotron X‐ray powder diffraction and Raman spectroscopy, the composition of the superionic conduction phase is evaluated to be Na_0.61(H₃O)_0.18Co_0.93O₂. Electromotive force measurements as well as molecular dynamics simulations indicate that the ion conducting species is proton rather than hydroxide ion. The fact that the Co‐stoichiometric compound Na_x(H₃O)_yCoO₂ does not exhibit any significant ionic conductivity proves that Co vacancies are essential for the occurrence of superionic conductivity.