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991.
George R. Pettit Peter Brown James J. Einck Kiyoshi Yamauchi Richard M. Blazer 《合成通讯》2013,43(7):449-456
Prominent molecular ions are generally observed in the field ionization (FI) mass spectra of unprotected nucleosides.2 In the one exception so far observed, that of guanosine, we found the simple methyl derivative, N2,N2-dimethylguanosine, to afford an easily detectible molecular ion. The electron impact (EI) mass spectrum of N2,N2-dimethylguanosine also displayed a molecular ion and suggested that nucleoside methyl derivatives might be more easily studied by EI methods. For this purpose and the more important objective of developing methods for sequencing small nucleic acid units by computer assisted3 FI-EI mass spectrometry, a program was initiated (1967) to explore permethylation of nucleosides. We believe protection by permethylation to be superior to pertrimethylsilylation and acetylation principally for reasons involving molecular weight and stability. Concurrently it was anticipated that such nucleoside methylation studies would afford routes to partially mathylated nucleosides of value in characterizing such components of virus and cellular DNA and RNA4. Subsequently, using variations of the methanol-DCCI,5 diazomethane with various Lewis acids,6 methyl iodide in, for example, dimethylsulfoxide,7 methyl iodide-sodium hydride in dimethylformamide,8 methyl iodide-silver oxides9 and methyl iodidemethylsulfinyl carbanion in dimethylsulfoxide,10 techniques were evaluated but none was found to provide permethyl nucleosides in high yield.11 The latter two methods have, however, been applied to methylating nucleosides for EI mass spectral investigations.12 相似文献
992.
Since the discovery of a potent antiviral activity of 3-amino-4-homoisotwistane (tricyclo [5.3.1.0]undecane, VIII) our efforts have been directed to find out better methods of synthesizing the parent hydrocarbons. In this communication is reported synthesis of a new precursor to 4-homoisotwistane (VIII), endo-tricyclo [5.2.1.0]dec-8-exo-ylcarbinol (IIIx), via hydroformylation of endo-dicyclo-pentadiene (endo-tricyclo [5.2.1.0]deca-3,8-diene) (I) in the presence of rhodium complex catalysts. 相似文献
993.
Aniline–terephthalaldehyde resin p-toluenesulfonic acid (ATRT) salt was easily prepared by the reaction of aniline with 1.25 equiv of terephthalaldehyde in the presence of 1.0 equiv of p-toluenesulfonic acid at 75 °C for 24 h in EtOH. ATRT efficiently catalyzed the tetrahydropyranylation of alcohols and deprotection of tetrahydropyranyl (THP), triethylsilyl (TES), and tert-butyldimethylsilyl (TBDMS) ethers. Deprotection of dodecyl THP ether and dodecyl TBDMS ether catalyzed by ATRT proceeded faster than those by pyridinium p-toluenesulfonate (PPTS). ATRT was reused without significant loss of activities. 相似文献
994.
995.
Zenjiro Osawa Mitsue Suzuki Yoshitaka Ogiwara Isao Sugaya Kiyoshi Hirama Takao Kasuga 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(2):275-285
Polymeric ultraviolet absorbers were prepared from 2-hydroxy-4-acryloyloxybenzophenone and 2-hydroxy-4-methacryloyloxybenzophenone and their inhibitive effect for photodegradation of polyethylene were examined by measuring mechanical strength, melt index, carbonyl group, and color difference. The polymeric ultraviolet absorbers were superior to the same type of ultraviolet absorber with low molecular weight in many properties, but inferior to Tinuvin, a commercial reagent, which has a different molecular structure. Therefore, within the ultraviolet absorbers examined, molecular structure seems to be a more important factor than molecular weight. 相似文献
996.
Kiyoshi Matsumoto Mitsuo Toda Naoto Hayashi Jong Chul Kim Akikazu Kakehic 《Supramolecular chemistry》2013,25(1):79-92
Abstract X-ray analyses of the 2,2′-dialkoxybenzpinacols have established that the previously tentative assignment of configuration is incorrect. For example, the dl-and meso-isomer of 2,2′-dimethoxy-, 2,2′-diethoxy-, and 2,2′-dibutoxybenzpinacols proved to have a rigid conformation (1aα, 1bα, 1eα) and (1aβ, 1bβ, 1cα) where hydroxy groups are always in an anti fashion, in the solid state, respectively. MM2 and semi-empirical molecular orbital calculations for possible conformations were performed, suggesting that the conformational stability of the present pinacols is controlled by repulsive gauche interactions between aryl groups associated with intramolecular hydrogen bondings. 相似文献
997.
Mohamed H. Gabr Nguyen T. Phong Mohammad Ali Abdelkareem Kazuya Okubo Kiyoshi Uzawa Isao Kimpara Toru Fujii 《Cellulose (London, England)》2013,20(2):819-826
In this research, fully environment-friendly, sustainable and biodegradable ‘green’ composites were fabricated. A novel material comprised of microfibrillated cellulose and laponite clay with different inorganic/organic ratios (m/m) was prepared. The composites were characterized by tensile, bending and water absorption tests as well as dynamic mechanical analysis. The morphologies of these nanocomposites were evaluated through scanning electron microscopy. Results showed considerable improvement of mechanical properties; specifically in elastic modulus, tensile strength and flexural modulus with the addition of nanoclay up to 7.5 wt% nano-clay. The modulus of elasticity increased significantly by about 26 % at 5 wt% nanocaly. The flexural modulus increased by about 90 % at 7.5 wt% nanoclay. However, with an increased load of clay in the nanocomposite, the mechanical properties decreased due to the agglomeration of excessive nanoclay. The storage modulus was significantly increased at high temperature with increasing the load of nanoclay. 相似文献
998.
Thin films of copper oxides can be synthesized on substrates by using approaches that are inspired by microbial mineralization processes. In nature, precipitates of manganese and iron oxides with controlled oxidation states and crystal phases are produced through biomineralization by microorganisms. We have previously reported microbial‐mineralization‐inspired approaches that are comprised of direct and intermediate routes for the controlled syntheses of transition‐metal oxides. Herein, these approaches are applied to the thin‐film formation and coating of copper oxides and a related compound with controlled crystal phases and morphologies. Thin films of CuO, Cu2O, and Cu2(OH)3Cl were selectively synthesized by using direct or intermediate routes. Notably, CuO mesocrystal nanosheets formed a thin film over the whole of the substrate. The resultant CuO mesocrystal nanosheets showed enhanced properties for the electrochemical detection of dopamine. This study shows the potential applicability of microbial‐mineralization‐inspired approaches to thin‐film coatings. 相似文献
999.
1000.
Methodology and Computing in Applied Probability - In this article, we consider random occupancy models and the related problems based on the methods of generating functions. The waiting time... 相似文献