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221.
N. Oshima E. Hamada T. Suzuki K. Kondo I. Kanazawa Y. Ito 《Journal of Radioanalytical and Nuclear Chemistry》1999,239(2):329-333
Pulsed slow positrons were produced using a time-varying moderator bias with an interval of 82 ns; 97% of the positrons were
compressed within 2 ns width at the target position. Both the positron annihilation lifetime and Doppler broadening of the
positron annihilation radiation (DBPR) of polytetrafluoroethylene (PTFE) were measured as a function of the incident energy
of slow positrons. It was shown that the lifetime and intensity of the long-lived component of positron annihilation are independent
of the positron incident energy above 1.2 keV. However, the width of the Doppler-broadened annihilation γ-ray increased in
the energy region below 1.2 keV. 相似文献
222.
The Raman, infrared and 1H-NMR spectra of (CH3)3 -X-Si (CH3)3 (X=O,S,Se,Te) were measured, and the assignment was carried out by comparison with those of the structurally related compounds, (CH3)3 SiCl and (CH3)3 Si-Si (CH3)3. The vibrational spectra of (CH3)3 Si-X-Si (CH3)3 can be interpreted in terms of a non-rigid D3d symmetry with internal rotations, because those of skeletones of the molecules indicate the lack of coincidence between Raman and infrared frequencies. The 1H-NMR spectra also support a non-rigid D3d model, because only one band for CH3 group appears. 相似文献
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226.
The effect of alpha-tocopherol and its acetate on the membrane structure of egg yolk phosphatidylcholine (egg PC) dispersions was investigated using phosphate-31 nuclear magnetic resonance (31P-NMR) and small-angle X-ray diffraction. The incorporation of alpha-tocopherol into egg PC dispersions induced a change in the 31P-NMR spectrum from a multilamellar bilayer line shape to a hexagonal HII one. The phase transition by alpha-tocopherol was also confirmed by small-angle X-ray diffraction analysis. The amount of hexagonal HII phase increased with increase in concentration of alpha-tocopherol. Egg PC dispersions containing a molar ratio of 0.8 of alpha-tocopherol gave a 31P-NMR spectrum of an approximately hexagonal HII type at 37 degrees C. The amount of hexagonal HII phase increased with increasing temperature, indicating that the alpha-tocopherol-induced phase transition is thermotropic and that the transition temperature of egg PC membranes from the lamellar to the hexagonal HII phase is lowered by alpha-tocopherol. The incorporation of alpha-tocopherol acetate did not induce any phase transition. This fact indicates that the hydroxyl group of alpha-tocopherol may play an important role in the hexagonal HII phase formation of egg PC dispersions. 相似文献
227.
Catalytic asymmetric aldol reactions in aqueous media using chiral bis-pyridino-18-crown-6-rare earth metal triflate complexes 总被引:1,自引:0,他引:1
Hamada T Manabe K Ishikawa S Nagayama S Shiro M Kobayashi S 《Journal of the American Chemical Society》2003,125(10):2989-2996
Catalytic asymmetric aldol reactions in aqueous media have been developed using Pr(OTf)(3) and chiral bis-pyridino-18-crown-6 1. In the asymmetric aldol reaction using rare earth metal triflates (RE(OTf)(3)) and 1, slight changes in the ionic diameters of the metal cations greatly affected the diastereo- and enantioselectivities of the products. The substituents (MeO, Br) at the 4-position of the pyridine rings of the crown ether did not significantly affect the selectivities in the asymmetric aldol reaction, although they affected the binding ability of the crown ether with RE cations and the catalytic activity of Pr(OTf)(3)-crown ether complexes. From X-ray structures of RE(NO(3))(3)-crown ether complexes, it was found that they had similar structures regardless of the RE cations and the crown ethers used. Accordingly, the binding ability of the crown ether with the RE cation and the catalytic activity of the complex are important for attaining high selectivity in the asymmetric aldol reaction. Various aromatic and alpha,beta-unsaturated aldehydes and silyl enol ethers derived from ketones and a thioester can be employed in the catalytic asymmetric aldol reactions using Pr(OTf)(3) and 1, to provide the aldol adducts in good to high yields and stereoselectivities. In the case using the silyl enol ether derived from the thioester, 2,6-di-tert-butylpyridine significantly improved the yields of the aldol adducts. 相似文献
228.
Tatsuro Ouchi Hidetake Miyazaki Hidetoshi Arimura Fumitaka Tasaka Atsushi Hamada Yuichi Ohya 《Journal of polymer science. Part A, Polymer chemistry》2002,40(9):1218-1225
The syntheses of amphiphilic AB‐type diblock copolymers composed of hydrophobic polylactide segment and hydrophilic polydepsipeptide segment with amino or carboxyl groups were performed. The protected cyclodepsipeptides cyclo[Glc‐Lys(Z)] and cyclo[Glc‐Asp(OBzl)] (where Glc is glycolic acid, Lys is lysine, Asp is aspartic acid, Z is benzyloxycarbonyl, and OBzl is benzyl) were first polymerized in tetrahydrofuran (THF) with potassium ethoxide as an initiator to obtain the corresponding protected polydepsipeptides. After the terminal hydroxyl groups of the protected polydepsipeptides were converted into the potassium alcoholates with K/naphthalene, L ‐lactide was polymerized in the presence of the corresponding polymeric alcoholates as macroinitiators in THF to obtain poly[Glc‐Lys(Z)]‐block‐poly(L ‐lactide) and poly[Glc‐Asp(OBzl)]‐block‐poly(L ‐lactide). Subsequent deprotection of Z and OBzl groups gave the objective amphiphiles poly(Glc‐Lys)‐block‐poly(L ‐lactide) and poly(Glc‐Asp)‐block‐poly(L ‐lactide), respectively. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1218–1225, 2002 相似文献
229.
Platinum intercalated into a hydrotalcite-like solid, Mg0.74Al0.26(OH)2(NO3)0.26, was found to catalytically reduce interlayer nitrate (NO3-) to N2/N2O so as to give rise to a large surface area micro/mesoporous structure at lower temperature of ca. 300 degrees C, compared to 500 degrees C required for the decomposition of the pristine hydrotalcite phase. 相似文献
230.
The influence of the host lattice on the antigenicity of glycophorin in membranes was confirmed by complement-dependent immune lysis of liposomes with two rabbit antisera, which were prepared by immunization with either human red blood cells or isolated glycophorin A. The immune lysis by either antiserum depended on the kind of phospholipid in the liposomes. Anti-glycophorin antiserum more strongly recognized glycophorin in egg-lecithin membranes than in dipalmitoyl-lecithin membranes, as did anti-red blood cell antiserum. Cholesterol in the liposomal membranes influenced the antigenicity of glycophorin. The relationship between the state of glycophorin in membranes and recognition by antibody is discussed. 相似文献