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41.
Yoshiki Chujo Kenji Kohno Noriyuki Usami Yuya Yamashita 《Journal of polymer science. Part A, Polymer chemistry》1989,27(6):1883-1890
Amphiphilic block copolymers, i.e., poly(methyl methacrylate)-b-poly(2-dimethylethylammoniumethyl methacrylate), were synthesized by the reaction between two prepolymers. Carboxyl-terminated poly(methyl methacrylate) and hydroxyl-terminated poly(2-dimethylaminoethyl methacrylate) were prepared by radical polymerization of the corresponding monomers in the presence of thioglycolic acid and 2-mercaptoethanol as a chain transfer agent, respectively. Two condensation methods, i.e., DCC and the acid chloride method, were used for the reactions of these prepolymers. The subsequent quarternization produced the amphiphilic block copolymers. Surface property of poly(methyl methacrylate) films containing this amphiphilic block copolymer was examined by measuring contact angles for water. The addition of only 0.5 wt% of the block copolymer was sufficient to make poly(methyl methacrylate) surfaces hydrophilic. The block copolymer formed a polymeric micelle in acetone–water mixed solvent. 相似文献
42.
To investigate the helical conformation of oligo(m-phenylene ethynylene)s, a pair of TEMPO spin labels were appended to the backbone. The two TEMPO radicals were separated by the four, five, and six repeating units. ESR spectra of the labeled oligomers were measured in chloroform and in ethyl acetate solvents in which the oligomers are disordered and folded, respectively. The measurement and analysis of ESR spectra revealed that six repeating units make one helical turn. 相似文献
43.
By the self-immolative asymmetric synthesis, optically pure key intermediate β-piperonyl-γ-lactone (R)-(+)- was found to be prepared in reasonable yield from the easily available chiral γ-lactone synthon () which had been also reported to give an antipode (S)-(-)-. The optically pure (R)-(+)- was shown to be converted successfully into several optically pure natural lignan lactones. 相似文献
44.
A flow-injection system is described for the simultaneous determination of calcium and magnesium with simultaneous injection of two sample plugs and a masking agent plug and with a single detector. The system utilizes the simultaneous injection of an ethylene glycol-bis(2-aminoethylether)-N,N,N',N'-tetra-acetic acid plug and two small sample plugs into the same carrier stream and which are merged downstream with 3,3'-bis[N,N-bis(carboxymethyl)aminomethyl)]-o-cresolphthalein solution for spectrophotometric determination of calcium and magnesium. The results for the analysis of natural waters by the proposed method correspond well with those obtained by the conventional titration method with ethylenediaminetetra-acetic acid, and showed good reproducibility. The rate of analysis is about 15 samples/hr. 相似文献
45.
Hoteling AJ Kawaoka K Goodberlet MC Yu WM Owens KG 《Rapid communications in mass spectrometry : RCM》2003,17(14):1671-1676
Details of the optimization of the collision-induced dissociation (CID) process, using a collision cell on a matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) mass spectrometer, are described using poly(ethylene glycol) 1000 (PEG 1000) as a model analyte. The effects of collision gas identity (helium, air, and argon), as well as collision gas pressure, on the resulting MS/MS data were investigated. With PEG 1000, helium was found to give the best results with respect to signal-to-noise (S/N) ratio. The optimum pressure for each gas was found to be in the range where the precursor ion signal was attenuated to approximately 30-50% for helium and 40-60% for argon. The effect of cation choice (Li, Na, and K) on the CID of PEG was also studied. CID spectra were produced for each, but PEG cationized with lithium was found to produce the spectra with the highest S/N ratio. The MALDI-TOF CID spectra that were generated for PEG were compared with the high-energy and low-energy MS/MS spectra obtained from a sector mass spectrometer and from a triple quadrupole mass spectrometer, respectively. The results observed for PEG confirm that CID on a MALDI-TOF mass spectrometer is a high-energy MS/MS technique. 相似文献
46.
(+)-Steganacin was synthesized in a new and highly specific asymmetric pathway based on the novel application of chiral γ-lactone as a chiral synthon. By this synthesis the absolute stereochemistry of natural (?)-steganacin could be determined in unequivocal way. 相似文献
47.
Yoshinori Kadoma Takashi Toida Kenji Takeda Keikichi Uno Yoshio Iwakura 《Journal of polymer science. Part A, Polymer chemistry》1975,13(3):707-716
The polymerization of picryl (PMA), 2,4-dinitrophenyl (2,4-DNMA),2,6-dinitrophenyl (2,6-DNMA), 2-methyl-4,6-dinitrophenyl (MDNMA), and 2,6-dimethylphenyl methacrylates (DMMA) was carried out in benzene at 60°C. PMA, 2,6-DNMA, and MDNMA did not undergo radical homopolymerization, while 2,4-DNMA and DMMA did. The results suggest that the growing radical readily attacks the oxygen atom of the nitro group at the 2 position of the terminal phenyl group due to the steric effect of the substituent at the 6 position, resulting in chain termination. PMA formed a charge-transfer complex with 2-naphthyl methacrylate (NMA). The stoichiometric composition of this complex was shown to be 1:1 molar complex. PMA was readily copolymerized with NMA. The amount of solvent affected the composition of the copolymer obtained at a given same mole fraction in feed. The results suggest that charge-transfer interaction between the ester groups affects the copolymerization mechanism. 相似文献
48.
Introduction of atropisomeric axes into a bent bispyridine ligand leads to the quantitative formation of a complex mixture of atropisomeric M2L4 cages upon treatment with metal ions. Whereas the isomer ratio of the obtained cage mixture, consisting of up to 42 isomers, is insensitive to temperature and solvent, the quantitative convergence from the mixture to a single isomer is accomplished upon encapsulation of a large spherical guest, namely fullerene C60. The observed isomerization with other guests depends largely on their size and shape (e.g., <10 and 82% convergence with planar triphenylene and bowl-shaped corannulene guests, respectively). Besides the unusual guest-induced convergence, the present cage mixture displays the strongest guest emission (ΦF = 68%) among previously reported MnLm cages and capsules, upon encapsulation of a BODIPY dye in water.A complex mixture of atropisomeric M2L4 cages is shown to undergo perfect convergence to a single isomer upon encapsulation of spherical C60 in water. Moreover, the cage mixture displays very strong guest emission upon encapsulation of a BODIPY dye. 相似文献
49.
Heterogeneous structure of silk fibers from Bombyx mori resolved by 13C solid-state NMR spectroscopy
Asakura T Yao J Yamane T Umemura K Ulrich AS 《Journal of the American Chemical Society》2002,124(30):8794-8795
The molecular conformation of silk fibrion is characterized by solid-state 13C NMR before spinning (silk I structure) and after spinning (silk II structure). We compare native silk fibers with the quasi-crystalline Cp-fraction and a synthetic model peptide (Ala-Gly)15, both of which can be converted either into silk I by dialysis from 9 M LiBr or into silk II by treatment with formic acid. Our results demonstrate that silk II fibers are intrinsically heterogeneous, consisting of beta-sheets, distorted beta-turns, and distorted beta-sheets. This higher-order heterogeneity is revealed by the 13C-NMR Cbeta-peak of Ala, indicating that the Ala side chains are stacked partially in parallel and partially face-to-face, at a ratio of 1:2. 相似文献
50.