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排序方式: 共有243条查询结果,搜索用时 15 毫秒
71.
Chamakura V. N. S. Varaprasad Kanda S. Ramasamy Zhi Hong 《Journal of heterocyclic chemistry》2006,43(2):325-336
1,2,3,5‐Tetra‐O‐acetyl‐4‐deoxy‐4‐(acetamido)‐β‐D‐ribofuranose 5 was prepared from L‐lyxose, which on condensation with silylated nucleoside bases gave the corresponding protected 4′‐azanucleosides. The protecting groups were removed using methanolic ammonia to afford the N‐acetyl‐4′‐azanucleosides, wherein the sugar ring oxygen is replaced with a substituted nitrogen atom, in good yields. Further, the 1‐(4‐deoxy‐4‐acetamido‐β‐D‐ribofuranosyl)thymine 16 was transformed to the corresponding 2′‐deoxy, 2′,3′‐dideoxy derivatives. The stereochemical assignments of the synthesized nucleosides were established based on NMR and X‐ray studies. 相似文献
72.
Yabushita A Kanda D Kawanaka N Kawasaki M Ashfold MN 《The Journal of chemical physics》2006,125(13):133406
The photodissociation dynamics of amorphous solid water (ASW) films and polycrystalline ice (PCI) films at a substrate temperature of 100 K have been investigated by analyzing the time-of-flight (TOF) mass spectra of photofragment hydrogen atoms at 157 and 193 nm. For PCI films, the TOF spectrum recorded at 157 nm could be characterized by a combination of three different (fast, medium, and slow) Maxwell-Boltzmann energy distributions, while that measured at 193 nm can be fitted in terms of solely a fast component. For ASW films, the TOF spectra measured at 157 and 193 nm were both dominated by the slow component, indicating that the photofragment H atoms are accommodated to the substrate temperature by collisions. H atom formation at 193 nm is attributed to the photodissociation of water species on the ice surface, while at 157 nm it is ascribable to a mixture of surface and bulk photodissociations. Atmospheric implications in the high latitude mesopause region of the Earth are discussed. 相似文献
73.
We consider the problem of determining , the smallest possible length for which an code of minimum distance over the field of order 4 exists. We prove the nonexistence of codes for and the nonexistence of a code for using the geometric method through projective geometries, where . This yields to determine the exact values of for these values of . We also give the updated table for for all except some known cases. 相似文献
74.
Muranaka A Yoshida K Shoji T Moriichi N Masumoto S Kanda T Ohtake Y Kobayashi N 《Organic letters》2006,8(12):2447-2450
A series of supramolecular complexes formed between oxotitanium(IV) phthalocyanine and apple procyanidins have exhibited characteristic bisignate CD signals in the Q region (ca. 700 nm). The helicity of the oligomeric procyanidins is proposed to be left-handed on the basis of the CD analyses. [structure: see text] 相似文献
75.
Time-of-flight (TOF) spectra of photofragment H atoms from the photodissociation of water ice films at 193 nm were measured for amorphous and polycrystalline water ice films with and without dosing of hydrogen chloride at 100-145 K. The TOF spectrum is sensitive to the surface morphology of the water ice film because the origin of the H atom is the photodissociation of dimerlike water molecules attached to the ice film surfaces. Adsorption of HCl on a polycrystalline ice film was found to induce formation of disorder regions on the ice film surface at 100-140 K, while the microstructure of the ice surface stayed of polycrystalline at 145 K with adsorption of HCl. The TOF spectra of photofragment Cl atoms from the 157 nm photodissociation of neutral HCl adsorbed on water ice films at 100-140 K were measured. These results suggest partial dissolution of HCl on the ice film surface at 100-140 K. 相似文献
76.
High-energy protons and neutrons produce various radionuclides in the air, mainly through the nuclear spallation of atmospheric
elements. Air samples were collected from the EP-2 tunnel of the KEK 12 GeV proton synchrotron facility with a filter pack,
which consisted of a membrane filter for aerosols, a Na2CO3-impregnated filter for acidic gases, and an activated carbon fiber filter for non-acidic gases. Sulfur-38 was found on the
membrane and Na2CO3-impregnated filters, 38Cl and 39Cl were on the membrane, Na2CO3-impregnated, and ACF filters, and 82Br was only on the ACF filter. The results on the relative abundances of aerosol and gaseous acidic components have indicated
that 38Cl produced by thermal neutron capture, which is the main reaction for 38Cl production in the EP-2 tunnel air, are likely not to be present as aerosol or acidic gas. This was similar to the case
of 82Br produced by thermal neutron capture. 相似文献
77.
Y. Kanda Y. Oki A. Endo M. Numajiri K. Kondo 《Journal of Radioanalytical and Nuclear Chemistry》2001,247(1):25-31
The irradiation of atmospheric air with high-energy protons has been performed at the 12 GeV proton synchrotron. The specific activity of 13N, one of the principal airborne radioactivities, was measured as a function of the irradiation time at a dose rate of about 6·1016 eV/g/s, and compared with the calculated values. The predominant chemical species of 13N produced were found to be 13N2and 13NO2. Their proportions were approximately 55% for 13N2 and 45% for13NO2, being almost independent of the irradiation time. Smaller quantities of 13NO and H13NO2 were also observed. Measurements of radiolytic products showed that ozone is a main product and that NO2predominates among the products of nitrogen compounds, including HNO2 and HNO3. The G-value for ozone formation in air was estimated from the experimental data as 6.4 molecules/100 eV. 相似文献
78.
Midori Kanda Ko Urushibara Soyoung Park Shinya Fujii Hyuma Masu Kosuke Katagiri Isao Azumaya Hiroyuki Kagechika Aya Tanatani 《Tetrahedron》2019,75(19):2771-2777
N,N′-Bis(ortho-substituted phenyl)squaramides afforded chiral crystals, in which squaramide molecules are arranged in one-handed helical networks, upon simple recrystallization. Three types of crystals with different helices were obtained, depending on the substituents or recrystallization solvent. Folded-type intermolecular hydrogen-bonding interactions of squaramides play a key role in forming the helical networks. 相似文献
79.
A method is described for fast dual-column separation of pesticides by use of dual low thermal mass gas chromatography–mass spectrometry (dual LTM-GC–MS) with different temperature programming. The method can provide two total ion chromatograms with different separation on DB-5 and DB-17 in a single run, which allows improved identification capability, even with short analysis time (<17 min). Also simultaneous detection with MS and elemental selective detector, e.g. pulsed flame photometric detection (PFPD) was evaluated for fast dual-column separation of 82 pesticide mixtures including 27 phosphorus pesticides. Dual LTM-GC–MS/PFPD was applied to analysis of pesticides in a brewed green tea sample with dual stir bar sorptive extraction method (dual SBSE). 相似文献
80.
Harada T Hiraoka Y Kusukawa T Marutani Y Matsui S Nakatsugawa M Kanda K 《Organic letters》2003,5(26):5059-5062
Bis-BINOLs 7a-c in which two BINOL units are tethered by phenylenebis(ethynyl) groups react with titanium tetraisopropoxide (2 equiv) to form intramolecular dimeric titanium(IV) aggregates 2a-c. Of these, 2a,b with an o-phenylenebis(ethynyl) tether are stable in the presence of excess titanium tetraisopropoxide. Complex 2a exhibits a relatively high enantioselectivity in asymmetric addition of diethylzinc to an aldehyde. [structure: see text] 相似文献