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151.
Ming Zhao Yuji Wang Caixia Huo Chunyu Li Xiaoyi Zhang Li Peng Shiqi Peng 《Tetrahedron: Asymmetry》2009,20(2):247-258
In lead detoxification, the α-anomer of N-glycocyl-l-amino acid is more potent than its β-anomer. Here a six-step-reaction route for stereoselectively preparing N-(α-l-arabinose-1-yl)-l-amino acids is reported. Treating l-arabinose with acetic anhydride and sodium acetate provided 1,2,3,5-tetra-O-acetyl-l-arabinofuranose in 90% yield. After removing the 1-acetyl group, the thus formed 2,3,5-tri-O-acetyl-l-arabinofuranose and N-(2-nitrophenylsulfonyl)-l-amino acid t-butylesters were treated with triphenylphosphine to perform Mitsunobu dehydration and form 2,3,5-tri-O-acetyl-l-arabinofuranosyl-l-[N-(2-nitrophenylsulfonyl)]amino acid t-butylesters 2a–f, and the ratios of their α- to β-anomer ranged from 8/1 to 9/1. Chromatographic separation provided epimerically pure 2a–f-α and 2a–f-β. In the presence of CF3CO2H, 2a–f-α and 2a–f-β were converted to α- and β-anomers of N-(2,3,5-tri-O-acetyl-l-arabinofuranosyl)-N-(2-nitrobenzenesulfonyl)-l-amino acids, 3a–f-α and 3a–f-β, in 87–92% yields. While in the presence of NaOCH3, 3a–f-α and 3a–f-β were converted to α- and β-anomers of N-(l-arabinofuranosyl)-N-(2-nitrobenzenesulfonyl)-l-amino acids, 4a–f-α and 4a–f-β, in 90–96% yields. Treating 4a–f-α and 4a–f-β with N-ethyldiisopropylamine (DIPEA) and thiophenol, their 2-nitrophenylsulfonyl groups were removed, and the α- and β-anomers of N-(l-arabinose-1-yl)-l-amino acids were formed in 70–79% yields. The bioassay confirmed that the lead detoxification activity of the α-anomer was significantly higher than that of the β-anomer. 相似文献
152.
Takuya Hasegawa Tomonari Umemura Akira Koide Koichi Chiba Yuji Ueki Kin-ichi Tsunoda Hiroki Haraguchi 《Analytical sciences》2005,21(8):913-916
An octadecylsilica (ODS) column modified with zwitterionic/nonionic mixed surfactants was evaluated for the direct injection determination of inorganic anions in biological fluids by ion chromatography. A zwitterionic surfactant (sulfobetaine-type) and a nonionic surfactant (polyoxyethylene-type) were used for a stationary-phase modification. When aqueous electrolyte solutions with concentrations of sub-mM to several mM were used as a mobile phase, the zwitterionic surfactant coated on the ODS surface exhibited unique separation selectivity for ionic species, while the nonionic surfactant coated on the ODS might have formed a hydrophilic network over the ODS surface and restricted matrix proteins from adsorbing on the stationary phase. Consequently, the mixed surfactant-modified column system allowed an efficient ion chromatographic separation of inorganic anions as well as a size-exclusive removal of column-fouling proteins. This separation system was applied to the direct injection determination of UV-absorbing anions in human saliva. The detection limits for nitrite, nitrate, iodide and thiocyanate were 3.1, 2.7, 4.5 and 25 microM, respectively, with UV detection at 210 nm (injection volume; 20 microl), and their relative standard deviations for 5 replicate measurements of saliva samples spiked with 100 microM each of those anions were 1.4, 0.9, 2.2 and 5.5%, respectively. 相似文献
153.
Yong Fan Junqi Guo Minhyeok Lee Norihiko Iki Yuji Suzuki 《Proceedings of the Combustion Institute》2021,38(2):2361-2370
A premixed H2/air flame with N2 dilution (Uin = 533 cm/s, ? = 1) was formed in a quartz micro flow reactor with/without a 100-nm thick Inconel coating for the investigation of wall chemical effect of the metal surface. Two-dimensional distributions of OH radical, O atom and H atom in the hydrogen flame were measured via the planar laser induced fluorescence (PLIF) and two-photon absorption laser induced fluorescence (TALIF), respectively. It is found that the distributions of all these three main species in the hydrogen flame are significantly affected by the wall chemical effect. OH, O and H shift downstream in the Inconel-coated channel, and also their concentration becomes lower than those in the less-reactive quartz channel. Based on the measured distributions of OH, O and H over the Inconel surface, the initial sticking coefficients (S0) of the radical quenching model are optimized. It is found that S0 for Inconel are 0.4–0.5, 0.1–0.2 and < 0.05 for OH, O and H, respectively, showing different sticking coefficients for different species for the first time. 相似文献
154.
N-Aryl-protecting groups were introduced in glucosamines to achieve β-selective glycosylation. Various N-aryl aminosugars were synthesized via Buchwald–Hartwig reaction. Glycosylation using glycosyl trichloroacetimidates of N-aryl aminosugars smoothly proceeded in the presence of trimethylsilyl trifluoromethanesulfonate. Use of a glycosyl donor comprising an electron-donating 2,4-dimethoxyphenyl (DMP) group led to the glycosylation proceeding with high β selectivity. This stereoselectivity seemed to be derived from the formation of an aziridine intermediate. The DMP-protecting group can be removed immediately by using ammonium hexanitratocerate (IV). 相似文献
155.
从虚功原理出发,证明了薄板小挠度弯曲问题的功的互等定理,并由此推出了求解矩形薄板自然频率的公式.算例表明,该公式计算简便,精度较高. 相似文献
156.
Bis(trifluoromethanesulfonyl)amide (TFSA), hexafluorophosphate (PF(6)(-)), and iodide salts of 1-ferrocenyl-3-alkylimidazolium were prepared and their thermal and physical properties, including the dependence on alkyl chain length (methyl-hexadecyl), were investigated. The TFSA salts were highly viscous ionic liquids with melting points around room temperature. 1-Ferrocenyl-4-methyltriazolium salts were also prepared for comparison. The ferrocenylimidazolium and ferrocenyltriazolium cations showed redox waves for both the ferrocenyl moiety and the azolium moiety and exhibited corresponding charge-transfer bands at around 330 nm, which were analyzed using the Marcus-Hush model. Crystal structure determinations at low temperature revealed that the PF(6) and iodide salts form layerlike structures composed of ionic layers of the charged moieties. The TFSA salt exhibited short hydrogen-bond-like intermolecular contacts between the hydrogen atoms of the cation and oxygen atoms of the anion. 相似文献
157.
Yuji Suzaki 《Journal of organometallic chemistry》2010,695(23):2512-213
Cyclization reactions of Fe{C5H4OCH2(CH2OCH2)nCH2OTs}2 (n = 1, 2) with C6H4-1,2-(OH)2, C6H4-1,3-(OH)2, and Fe(C5H4OAc)2 under basic conditions yield the corresponding macrocyclic 1,1′-ferrocenophanes. The ferrocenophane having a pyrido-crown ether structure was also synthesized. These ferrocenophanes were characterized by X-ray crystallography and NMR spectroscopy. Cyclic voltammograms of the ferrocenophanes exhibited reversible redox peaks assigned to the oxidation and reduction of the ferrocene unit. The macrocyclic pyrido-containing ferrocenophane forms pseudorotaxane with [NH2{(CH2)9Me}2]BARF (BARF = B{C6H3-3,5-(CF3)2}4) in CDCl3. 相似文献
158.
Katsumi Katoh Shunsuke Ito Yuji Ogata Jun-ichi Kasamatsu Hiroshi Miya Masaaki Yamamoto Yuji Wada 《Journal of Thermal Analysis and Calorimetry》2010,99(1):159-164
In order to prevent the spontaneous ignition of nitrocellulose (NC), NC is stabilized by washing with industrial water in
its synthesis process. However, there is a possibility that the components in industrial water contribute to the thermal stability
of NC. In this way, the purpose of this study is to clarify the effect of industrial water components on the thermal stability
of NC. In experiments, a heat flux calorimeter was used to observe the thermal behavior of NC with the residue of vaporized
industrial water. The induction period of heat release of NC with 2-mass% residues was approximately 2–5 h shorter than that
of NC alone whose induction period was observed at 7 h. Those results indicate that the residue destabilized NC. On the other
hand, when the additive amount of the residue was increased, the induction period gradually increased as well. Based upon
these results, we assume that inorganic salts contributing to stabilization and destabilization competitively coexist in the
industrial water components. The same thermal analysis was performed on NC with CaCO3, CaSO4, CaCl, ZnSO4, NaCl, and CuCl. Those salts are predicted to exist in the industrial water. In the results, the induction period of NC with
2-mass% CaCO3 was approximately 15-h longer than that of NC alone, while the induction period with the inorganic salts CaSO4, CaCl, ZnSO4, NaCl, and CuCl was 4–5-h shorter. Therefore, when the industrial water components accumulate in NC, the destabilization
by inorganic salts such as CaSO4, CaCl, ZnSO4, NaCl, and CuCl and the stabilization by compounds such as CaCO3 are thought to countervail against each other. 相似文献
159.
Eiji Hashimoto Yuichi Seshimo Keita Sasanuma Yuichiro Aoki Hitoshi Kanazawa Yuji Ike Seiji Kojima 《Journal of Thermal Analysis and Calorimetry》2010,99(1):45-50
The fragility of ethylene glycol and glucose aqueous solution systems has been investigated by temperature-modulated differential
scanning calorimetry (TMDSC). The frequency and temperature dependences of complex specific heat have been observed in the
vicinity of a glass-transition temperature T
g
. It is shown that the value of the fragility index m can be determined from the temperature dependence of the α-relaxation times observed by TMDSC. We have also studied the elastic
properties of these aqueous solutions by micro-Brillouin scattering, and determined these relaxation times of elastic properties
in the gigahertz range. 相似文献
160.