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排序方式: 共有507条查询结果,搜索用时 31 毫秒
501.
Yosuke Demizu Nanako Yamagata Saori NagoyaYukiko Sato Mitsunobu DoiMasakazu Tanaka Kazuo NagasawaHaruhiro Okuda Masaaki Kurihara 《Tetrahedron》2011,67(34):6155-6165
Stapled helical l-leucine-based heptapeptides were synthesized and used as catalysts for the enantioselective epoxidation of α,β-unsaturated ketones. All N-terminal free stapled peptides were successfully used as chiral catalysts. Among them, the use of H-hS3,7hS-10 gave epoxide products with high enantioselectivities of up to 99% ee. Furthermore, the dominant conformations of the N-terminal protected stapled peptides R3,7R-10 and hS3,7hS-10 were investigated by 1H NMR, IR, CD spectra, and X-ray crystallographic analysis. The peptide R3,7R-10 formed a right-handed (P) α-helix in solution and in the crystalline state, while hS3,7hS-10 formed a right-handed (P) 310-helix in solution. 相似文献
502.
503.
Miyashita M Hanai Y Awane H Yoshikawa T Miyagawa H 《Rapid communications in mass spectrometry : RCM》2011,25(9):1130-1140
An improved method of de novo peptide sequencing based on mass spectrometry using novel N-terminal derivatization reagents with high proton affinity has been developed. The introduction of a positively charged group into the N-terminal amino group of a peptide is known to enhance the relative intensity of b-ions in product ion spectra, allowing the easy interpretation of the spectra. However, the physicochemical properties of charge derivatization reagents required for efficient fragmentation remain unclear. In this study, we prepared several derivatization reagents with high proton affinity, which are thought to be appropriate for peptide fragmentation under low-energy collision-induced dissociation (CID) conditions, and examined their usefulness in de novo peptide sequencing. Comparison of the effects on fragmentation among three derivatization reagents having a guanidino or an amidino moiety, which differ in proton affinity, clearly indicated that there was an optimal proton affinity for efficient fragmentation of peptides. Among reagents tested in this study, derivatization with 4-amidinobenzoic acid brought about the most effective fragmentation. This derivatization approach will offer a novel de novo peptide sequencing method under low-energy CID conditions. 相似文献
504.
Takuya Maeyama Shinichi Yamashita Mitsumasa Taguchi Gérard Baldacchino Lembit Sihver Takeshi Murakami Yosuke Katsumura 《Radiation Physics and Chemistry》2011,80(12):1352-1357
The G(OH) values in aqueous coumarin-3-carboxylic-acid (3-CCA) solutions irradiated with 12C6+ beams having the energies of 135, 290 and 400 MeV/u were measured by a fluorescent method around the Bragg peak, with 0.6 mm intervals, and quartz cells of 1 cm optical lengths, at the Heavy Ion Medical Accelerator in Chiba, National Institute of Radiological Sciences (NIRS). For each ion, the G(OH) has been calculated as a function of dose average LET and position. The calculated results have been compared to measurements, and the results, reproducibility and reliability of the calculations are discussed in the paper. 相似文献
505.
By measuring the emission spectra and the fluorescence lifetime of the 4 I 13 /2 state of Er 3+ ions in Gd 2 SiO 5 crystal at different temperatures,the effects of temperature on the spectra and the lifetime of the 4 I 13 /2 state are investigated. When the temperature increases,the emission line width for the 4 I 13 /2 → 4 I 15 /2 transition is broadened,and the main emission lines at 1 596,1 609,and 1 644 nm shifte toward shorter wavelengths. The measured lifetime of the 4 I 13 /2 state decreases from 13.2 to 8.4 ms with temperature increase from 13 to 300 K,which is mainly due to the temperature dependence of multiphonon relaxation between the 4 I 13 /2 and 4 I 15 /2 states and the changing population distribution among the Stark levels within the 4 I 13 /2 state. The experimental results imply that low temperature condition is better for the ~1.6-μm laser output. 相似文献
506.
507.
Dr. Yosuke Akae Prof. Dr. Toshikazu Takata 《European journal of organic chemistry》2023,26(12):e202300171
The acylation of a cyclodextrin-based [3]rotaxane was implemented with anhydride reagents following a facile procedure. Methacrylic anhydride facilitated the introduction of a vinyl-group into the rotaxane structure toward achieving a crosslinker. Interestingly, only a few methacrylic units were attached to the cyclodextrin at reaction temperatures of up to 60 °C even with an excess amount of the reagent, probably due to steric hindrance. Therefore, the number of vinyl groups on the [3]rotaxane framework was easily controlled to be approximately two units via a simple random acylation, which worked effectively as a facile synthesis route for the rotaxane crosslinker. The acylation behavior was investigated in detail by NMR and MALDI-TOF-MS analyses. Such a proposed approach will help overcome the trade-off between convenience and utility associated with the mono-modification of cyclodextrins. 相似文献