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991.
992.
Ukena T Satake M Usami M Oshima Y Fujita T Naoki H Yasumoto T 《Rapid communications in mass spectrometry : RCM》2002,16(24):2387-2393
Negative-ion fast-atom bombardment collision-induced dissociation tandem mass spectrometric (FAB-CID-MS/MS) methodology was successfully applied to verify the highly complex structure of ostreocin-D (MW 2633), a new palytoxin analog isolated from the marine dinoflagellate Ostreopsis siamensis and proposed to be 42-hydroxy-3,26-didemethyl-19,44-dideoxypalytoxin based on NMR data. The charge-remote fragmentations were facilitated by a negative charge introduced to a terminal amino group or to a hydroxyl group at the other terminus by a reaction with 2-sulfobenzoic acid cyclic anhydride. Product ions generated from the [M - H](-) ions provided information on the structural details of ostreocin-D. Comparisons between the spectral data for ostreocin-D and palytoxin also provided a rational basis for the assignments of product ions. 相似文献
993.
Kazuo Matsuyama Takeshi Komai Katsukiyo Ito 《Journal of polymer science. Part A, Polymer chemistry》1986,24(10):2425-2432
T-butylperoxy phenylcarbonate (BPPC) was prepared. Its decomposition rate constant in cumene is given by kd = 2.39 × 1015 exp(?17,300/T), where T is the absolute temperature. When BPPC decomposes to polymerize styrene at 100°C, it produces 12% phenoxy radical to total primary radicals. The phenoxy radical hardly adds to styrene and reacts the other primary radicals and polymer radical. Thus it retards the rate of polymerization. 相似文献
994.
We have investigated the binding of noble-gas (Ng) atoms (Ng=Ar,Kr,Xe) with Pt atom by the ab initio coupled-cluster CCSD(T) method, taking into account the relativistic effects. It is shown that two Ng atoms can bind with Pt atom in linear geometry in the singlet lowest state where the second Ng atom attaches to Pt with the larger binding energy than the first Ng atom. The binding energy is evaluated as 8.2, 17.9, and 33.4 kcal/mol for Ar-Pt-Ar, Kr-Pt-Kr, and Xe-Pt-Xe, respectively, relative to the triplet ground state of the dissociation limit Pt ((3)D)+2Ng. The present results indicate that these Ng-Pt-Ng compounds are possible new gas-phase or matrix species. 相似文献
995.
Tayagaki T Galet A Molnar G Muñoz MC Zwick A Tanaka K Real JA Bousseksou A 《The journal of physical chemistry. B》2005,109(31):14859-14867
The 1A1 left arrow over right arrow 5T2 spin transition has been investigated in the solid solutions of Fe(x)M(1-x)(pyrazine)[Pt(CN)4] (M = Ni or Co, 0 < or = x < or = 1) having a three-dimensional polynuclear structure. Both Ni and Co dilutions tend to decrease the hysteresis width and smooth the transition curves. The enthalpy (entropy) change associated with the spin transition was found to decrease from 26 kJ mol(-1) (84 J K(-1) mol(-1)) for x = 1 to 12 kJ mol(-1) (47 J K(-1) mol(-1)) for 47% Co dilution and to 15 kJ mol(-1) (54 J K(-1) mol(-1)) for 59% Ni dilution. Raman spectroscopy revealed a mixed one- and two-mode behavior in the solid solutions. For the first time, a correlation between vibrational frequencies exhibiting one-mode behavior and the entropy change, which drives the spin crossover, is established. 相似文献
996.
Takebayashi Y Yoda S Sugeta T Otake K Sako T Nakahara M 《The Journal of chemical physics》2004,120(13):6100-6110
The (13)C-NMR chemical shift of acetone delta((13)C[Double Bond]O) was measured in aqueous solution at high temperatures up to 400 degrees C and water densities of 0.10-0.60 g/cm(3) for the study of hydration structure in the supercritical conditions. The average number N(HB) of hydrogen bonds (HBs) between an acetone and solvent waters and the energy change DeltaE upon the HB formation were evaluated from the delta and its temperature dependence, respectively. At 400 degrees C, N(HB) is an increasing function of the water density, the increase being slower at higher water densities. The acetone-water HB formation is exothermic in supercritical water with larger negative DeltaE at lower water densities (-3.3 kcal/mol at 0.10 g/cm(3) and -0.3 kcal/mol at 0.60 g/cm(3)), in contrast to the positive DeltaE in ambient water (+0.078 kcal/mol at 4 degrees C). The corresponding Monte Carlo simulations were performed to calculate the radial and orientational distribution functions of waters around the acetone molecule. The density dependence of N(HB) calculated at 400 degrees C is in a qualitative agreement with the experimental results. In the supercritical conditions, the HB angle in a neighboring acetone-water pair is weakly influenced by the water density, because of the absence of collective HB structure. This is in sharp contrast to the hydration structure in ambient water, where the acetone-water HB formation is orientationally disturbed by the tetrahedral HB network formation among the surrounding waters. 相似文献
997.
Takeshi HiroseHiroyuki Imai Toshio NaitoTamotsu Inabe 《Journal of solid state chemistry》2002,168(2):535-546
Three kinds of the 1:1 Ni(dmit)2 salts with 4-(4-pyridyl)pyridinium (PP), 4-[2-(4-pyridyl)ethenyl]pyridinium (P=P), and 4-[2-(4-pyridyl)ethyl]pyridinium (P-P) cations have been prepared and structurally characterized. All of these crystals are composed of a multi-dimensional network of the Ni(dmit)2 anions and the hydrogen-bonding one-dimensional cation chains. Compared with tight hydrogen bonds in the P=P and P-P chains, that in the PP chain is rather loose. The P=P and P-P salts show semiconducting behavior with high resistivity and large activation energy, while the PP salt shows the op-posite temperature dependence with low resistivity at high temperature. The thermoelectric power indicates that the PP salt is an n-doped semiconductor. The proton defects may occur in the loosely bound PP chain which results in the carrier doping in the conduction band formed by the π-π interaction of the Ni(dmit)2 anion radicals. 相似文献
998.
Mizuno K Hata K Saito T Ohshima S Yumura M Iijima S 《The journal of physical chemistry. B》2005,109(7):2632-2637
We have studied the compatibility of various catalysts for ethylene and ethanol chemical vapor deposition (CVD) syntheses of single-walled carbon nanotubes (SWNTs) on Si substrates. A strong selectivity between the catalyst elemental species and carbon source was found; SWNT yield for Fe (Co) catalysts was much higher for ethylene (ethanol) CVD than for ethanol (ethylene) CVD. This strong and completely opposite selectivity implies significantly different SWNT growth mechanisms for ethanol and ethylene CVD on Si substrates. 相似文献
999.
Morikawa MA Yoshihara M Endo T Kimizuka N 《Journal of the American Chemical Society》2005,127(5):1358-1359
Supramolecular nanowires are specifically self-assembled from adenosine 5'-triphosphate (ATP) and dichloro-substituted thiacarbocyanine dyes. Spectral blue-shift and induced circular dichroism with exciton coupling are observed upon mixing the dye and ATP molecules in water. These observations indicate the formation of chiral 1/ATP supramolecular assemblies with excitation energy delocalized in the parallel-oriented (H-aggregated) chromophores. Interestingly, formation of H-aggregates is facilitated most in the presence of ATP and not by other nucleotides (ADP or AMP). In electron microscopy, aqueous 1/ATP mixture gives developed nanowires with a minimum width of ca. 10 nm and lengths of several micrometers. The ATP-directed nanowires exhibit reversible thermal self-assembly accompanied by supramolecular thermochromism. This is the first example of ATP-based supramolecular nanoassemblies, and the use of small biomolecules as building blocks for functional supermolecules provides a new perspective in the design of bio-nanomaterials. 相似文献
1000.
In this paper, multi-walled carbon nanotubes (MWCNTs) were successfully immobilized on the surface of a glassy carbon electrode by mixing with horse-radish peroxidase (HRP). The electrochemical behavior of H2O2 was also studied with the MWCNTs-HRP modified electrode as a working electrode. The MWCNTs-HRP modified electrode showed excellent response of reduction current for the determination of H2O2 at the potential of -300 mV (vs. Ag/AgCl). We assembled the MWCNTs-HRP modified electrode in a thin-layer flow cell and the H2O2 solution was continuously introduced into the cell with a syringe pump. We optimized the sensitivity of the H2O2 sensor by adjusting the working potential and the pH of the buffer solution. The peak current increased linearly with the concentration of H2O2 in the range 3.0 x 10(-7) to approximately 2.0 x 10(-4) mol L(-1). The detection limit is 1.0 x 10(-7) mol L(-1) (S/N = 3). The interferences from ascorbic acid, uric acid and other electroactive substances can be greatly excluded since the sensor can be operated at -300 mV. Stability and reproducibility of the MWCNTs-HRP chemically modified electrode were also studied in this paper. Fabricated with glucose and lactate oxidase, the MWCNTs-HRP electrode was also applied to prepare the on-line glucose and lactate biosensors because of the high sensitivity for the determination of H2O2. 相似文献