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91.
Jun‐ichi Kadokawa Shima Inomata Yasuhiro Iwasaki Hideyuki Tagaya Koji Chiba 《Macromolecular rapid communications》2000,21(17):1253-1256
This communication reports the group‐transfer polymerization of a cyclic trimethylsilyl dienolate, 2‐(trimethylsilyloxy)furan ( 1 ), initiated with benzaldehyde. The polymerization proceeded in the presence of a tetrabutylammonium salt as the catalyst in THF solvent at 0–50°C. The product was isolated as an ethyl acetate insoluble fraction after acidic work‐up. The structure of the product polymer was determined by means of 1H NMR, 13C NMR, and IR spectroscopy to be polylactone 3 . The mechanism of the polymerization can be explained by a Michael‐type addition of 1 onto the propagating end. 相似文献
92.
Sebastian Schaupp Francisco J. Arriaza-Gallardo Dr. Nicole Paczia Kenichi Ataka Dr. Seigo Shima 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2024,136(6):e202316478
[Fe]-hydrogenase harbors the iron-guanylylpyridinol (FeGP) cofactor, in which the Fe(II) complex contains acyl-carbon, pyridinol-nitrogen, cysteine-thiolate and two CO as ligands. Irradiation with UV-A/blue light decomposes the FeGP cofactor to a 6-carboxymethyl-4-guanylyl-2-pyridone (GP) and other components. Previous in vitro biosynthesis experiments indicated that the acyl- and CO-ligands in the FeGP cofactor can scramble, but whether scrambling occurred during biosynthesis or photolysis was unclear. Here, we demonstrate that the [18O1-carboxy]-group of GP is incorporated into the FeGP cofactor by in vitro biosynthesis. MS/MS analysis of the 18O-labeled FeGP cofactor revealed that the produced [18O1]-acyl group is not exchanged with a CO ligand of the cofactor, indicating that the acyl and CO ligands are scrambled during photolysis rather than biosynthesis, which ruled out any biosynthesis mechanisms allowing acyl/CO ligands scrambling. Time-resolved infrared spectroscopy indicated that an acyl-Fe(CO)3 intermediate is formed during photolysis, in which scrambling of the CO and acyl ligands can occur. This finding also suggests that the light-excited FeGP cofactor has a higher affinity for external CO. These results contribute to our understanding of the biosynthesis and photosensitive properties of this unique H2-activating natural complex. 相似文献
93.
94.
Crystal growth and the magnetic properties of bismuth substituted yttrium iron garnet (Bi-YIG) nanoparticles were studied with particular focus on the bismuth composition dependence of the magnetic properties of the particles and the effects of annealing on the garnet phase formation. The Bi-YIG nanoparticles of 47–67 nm in size can be chemically synthesized when they are annealed at 650–850 °C. Both the lattice constant and the magnetization of the garnet nanoparticles linearly increase when the bismuth composition in the Bi-YIG particles increases. We have found that chemically synthesized nanoparticles transform from the amorphous to the garnet phase when annealed at temperatures below 650 °C, while the onset of magnetic moment of iron in the garnet nanoparticles is observed slightly above 650 °C. According to Mössbauer effect measurements, the hyperfine fields of 57Fe at the tetrahedral and octahedral sites in the garnet are 39 and 48 T, respectively. 相似文献
95.
Irradiation-induced magnetism in carbon nanostructures 总被引:1,自引:0,他引:1
Talapatra S Ganesan PG Kim T Vajtai R Huang M Shima M Ramanath G Srivastava D Deevi SC Ajayan PM 《Physical review letters》2005,95(9):097201
Nitrogen (15N) and carbon (12C) ion implantations with implant energy of 100 keV for different doses were performed on nanosized diamond (ND) particles. Magnetic measurements on the doped ND show ferromagnetic hysteresis behavior at room temperature. The saturation magnetization (M(s)) in the case of 15N implanted samples was found to be higher compared to the 12C implanted samples for dose sizes greater than 10(14) cm(-2). The role of structural modification or defects along with the carbon-nitrogen (C-N) bonding states for the observed enhanced ferromagnetic ordering in 15N doped samples is explained on the basis of x-ray photoelectron spectroscopy measurements. 相似文献
96.
The first successful solution of the BKLT equations for reactive scattering for a realistic potential and three finite mass atoms is reported. These equations are completely general, as is also our non-propagative method of solution and provide a new framework for treating arbitrary reactive scattering problems. 相似文献
97.
Self-consistent non-empirical band structures of third and fourth stage graphite intercalation compounds have been calculated by using the numerical-basis-set LCAO method within the local density functional formalism. The calculations are carried out for a thin film model consisting of n contiguous graphite layers bounded by two partially ionized intercalant layers. The calculated band structures show that most of electrons transferred from the intercalant layers occupy the states in the lowest two conduction π bands mainly localized on the bounding graphite layers. The low-energy optical transitions of higher stage GICs are discussed in terms of the obtained band structures. 相似文献
98.
99.
Lyon EJ Shima S Boecher R Thauer RK Grevels FW Bill E Roseboom W Albracht SP 《Journal of the American Chemical Society》2004,126(43):14239-14248
The iron-sulfur-cluster-free hydrogenase Hmd (H(2)-forming methylenetetrahydromethanopterin dehydrogenase) from methanogenic archaea has recently been found to contain one iron associated tightly with an extractable cofactor of yet unknown structure. We report here that Hmd contains intrinsic CO bound to the Fe. Chemical analysis of Hmd revealed the presence of 2.4 +/- 0.2 mol of CO/mol of iron. Fourier transform infrared spectra of the native enzyme showed two bands of almost equal intensity at 2011 and 1944 cm(-)(1), interpreted as the stretching frequencies of two CO molecules bound to the same iron in an angle of 90 degrees . We also report on the effect of extrinsic (12)CO, (13)CO, (12)CN(-), and (13)CN(-) on the IR spectrum of Hmd. 相似文献
100.
The second harmonic of a Rayleigh wave passing through a minute surface crack has been numerically analyzed by semi-explicit FEM including special elements which account for a nonlinear stress-strain relation at crack surfaces. Minute cracks perpendicular to a free, flat surface close under compressive stress when width of the crack opening is less than the longitudinal amplitude of the Rayleigh wave. Thereafter, compressive and shear stresses are partially transmitted through the closed cracks, whereas tensile and shear stresses are not transmitted through cracks that remain open. This leads to marked nonlinear ultrasonic response. Calculation was performed for an aluminum block having a surface crack. The transverse component of the Rayleigh wave propagating through the cracks shows distorted waveforms, making the second harmonic amplitude clearly noticeable. In an experiment, the second harmonic component of the leaky Rayleigh wave was detected for a simple crack model consisting of two aluminum blocks, by use of a PVDF line-focused transducer. The results of the experiment show that the second harmonic amplitude is a second-order function of the fundamental wave amplitude, and is more pronounced for low compressive stress applied to close the crack surfaces. 相似文献