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排序方式: 共有316条查询结果,搜索用时 15 毫秒
1.
Nabeshima T Yoshihira Y Saiki T Akine S Horn E 《Journal of the American Chemical Society》2003,125(1):28-29
In supramolecular chemistry, a great deal of attention has focused on regulating guest binding via an external stimulus. To utilize the same effector for both highly guest-selective positive and negative allosteric effects, however, stricter and more precise regulation of the host structure is required. A novel allosteric host 1 binds Fe(II) to afford the pseudocryptand, 1.Fe(II), which bears a cavity that is surrounded by three polyether chains in a helical fashion. The binding selectivity of 1 (Na+ > K+ > Rb+ > Cs+) is the opposite of 1.Fe(II) (Cs+ > Rb+ > K+ > Na+). Single-ion transport through a liquid membrane shows ion selectivity similar to the equilibrium constants. To the best of our knowledge, this is the first example of an allosteric recognition system, in which the same effector, that is, Fe(II), exhibits both large positive and negative allosteric effects on equilibrium and dynamic recognition events. The X-ray analysis and 1H NMR examination indicate that the combination of the macrobicyclic effect and the intramolecular interchain interactions (CH-pi interaction and steric hindrance) finely controls the positive and negative allosteric effects, which depend on the size of the guest. The helical framework opens a new general method for constructing more sophisticated, controllable receptors for helical biomolecules, for example, DNA and proteins, and helical molecular devices such as a molecular coil or spring responding to a stimulus. 相似文献
2.
Chisuzu Tokoh Keiji Takabe Minoru Fujita Hiroshi Saiki 《Cellulose (London, England)》1998,5(4):249-261
Acetobacter xylinum was cultured in Hestrin-Schramm medium (control medium) and Hestrin-Schramm medium containing acetyl glucomannan (mannan medium). Loose bundles of the cellulose microfibrils are formed in the mannan medium in contrast to the normal ribbons being produced in the control medium. Rapid-freeze and substitution method followed by metal-shadowing revealed the droplet-like structures around the microfibril synthesized in the mannan medium. The cellulose synthesized in the mannan medium was stained heavily by the periodic acid-thiocarbohydrazide-silver proteinate (PATAg) method, while the cellulose synthesized in the control medium was not stained. X-ray diffractometry and FT-IR spectroscopy indicated that the addition of mannan induced a change in the crystal structure from the algal-bacterial type to the cotton-ramie type. Thus the presence of acetyl glucomannan in the medium prevents the assembly of cellulose microfibrils and changes the crystal structure of cellulose. 相似文献
3.
A. M. G. Figueiredo A. L. Alcalá R. B. Ticianelli M. Domingos M. Saiki 《Journal of Radioanalytical and Nuclear Chemistry》2004,259(1):59-63
Epiphytic bromeliadTillandsia usneoides was used as a biomonitor of metal atmospheric pollution in the city of São Paulo, Brazil. The samples were collected from an unpolluted area and were exposed for 8 weeks in 10 sites of the city and in a control site. The data obtained showed that the control site presented lower concentration for most elements analyzed and the highest concentrations of Na, Cl, Br, K. The highest concentrations of Zn, Cu and V were observed in stations submitted to industrial and vehicular sources. The results obtained for rare earth elements, Al, Fe, Mg, Mn, Rb and Sc indicate mineral dust origin. The elements Ba, As and Sb presented higher values in stations near streets with heavy traffic. 相似文献
4.
Nabeshima T Saiki T Iwabuchi J Akine S 《Journal of the American Chemical Society》2005,127(15):5507-5511
Synthesis and binding behavior of a novel multi-responsive host 1, in which two esters, two polyether moieties, two urea sites, and two bipyridine units as ion binding sites are arranged on the calix[4]arene skeleton, is reported. 1 recognizes Na(+) and Ag(+) simultaneously and quantitatively and captures an anionic guest. The ability of 1 to recognize anions, including CF(3)SO(3)(-) and BF(4)(-), remarkably increases in a stepwise manner using Na(+) and Ag(+) as effectors. The enhancement of the K(a) eventually reaches factors of 1500 and 2000 for NO(3)(-) and CF(3)SO(3)(-), respectively, in the presence of both Na(+) and Ag(+), compared to the free 1. The regulation of binding of multiple ligands may be applicable to multistep cascade systems for the amplification of molecular events, and further studies in this field could provide insight applicable to more advanced molecular devices. 相似文献
5.
Gel was prepared from 6-O-carboxymethyl-chitin (CM-chitin) by the addition of iron(III) chloride under mild conditions without any organic solvent. The optimal conditions for the gel formation were 15 to 30 mM iron(III) chloride and 0.5 to 0.8 degree of substitution in CM-chitin. The amounts of bovine serum albumin (BSA) and the anticancer drug doxorubicin (DOX) incorporated into CM-chitin gels were more than 80% and 30%, respectively under the conditions described above. The release of BSA or DOX from the gels was observed to be increased by lysozyme digestion in a time-dependent manner. This result indicates that CM-chitin might prove useful as a carrier gel for the sustained release of drugs and cytokines, including vaccines. 相似文献
6.
Ikuo Ashikawa Mariko Kito Kimiyuki Satoh Hiroyuki Koike Yorinao Inoue Kayoko Saiki Kiyoshi Tsukida Yasushi Koyama 《Photochemistry and photobiology》1987,46(2):269-275
All- trans β-carotene-5,6-epoxide has been found in the thylakoid membranes of spinach and of the cyanobacterium Synechococcus vulcanus Copeland. The epoxide was extracted from the thylakoid membranes with acetone, and was isolated by high-performance liquid chromatography (HPLC). The structure of the epoxide was identified by means of mass, Raman, and electronic absorption spectroscopy. Changes in the amount of the epoxide, as a result of epoxidation and (apparent) de-epoxidation reactions in the membranes, were traced by analysis of extracts on HPLC. In isolated thylakoid membranes, only the epoxidation reaction took place. The reaction was caused by irradiation or by the addition of ferricyanide, suggesting that electron transport reactions in the membranes are involved in the epoxidation. In intact spinach leaves, however, both epoxidation and de-epoxidation took place; the extent of epoxidation correlated with the intensity of light incident on the leaves. The epoxidation and de-epoxidation of all- trans β-carotene are contrasted with those of xanthophylls (in the violaxanthin cycle). 相似文献
7.
Prof. Dr. Junfeng Yang Yuto Mori Prof. Masahiro Yamanaka Prof. Naohiko Yoshikai 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(37):8302-8307
A simple cobalt-diphosphine catalyst has been found to efficiently promote intramolecular cyclization of ortho-cyclopropylvinyl- and cyclopropylidenemethyl-substituted benzaldehydes into benzocyclooctadienone and benzocycloheptadienone derivatives, respectively. This ring-opening hydroacylation likely involves aldehyde C−H oxidative addition, olefin insertion, cyclopropane cleavage by β-carbon elimination, and C−C bond-forming reductive elimination, as was supported by mechanistic experiments and DFT calculations. 相似文献
8.
Yasuhiro Igarashi Daisuke Asano Kazuo Furihata Naoya Oku Satoshi Miyanaga Hiroaki Sakurai Ikuo Saiki 《Tetrahedron letters》2012,53(6):654-656
During the course of screening natural products for the inhibitors of tumor cell invasion, pterocidin, a linear polyketide with a δ-lactone terminus, was rediscovered from a Streptomyces strain of a marine sediment-origin. A series of J-based configuration analyses and NOESY analysis, coupled with chemical derivatization and chiral anisotropy analysis, established the absolute stereochemistry of five asymmetric centers in this compound. 相似文献
9.
10.
Fluorescence correlation spectroscopy (FCS) of colloidal nanoparticles using a near-field fiber probe was numerically simulated.
The near-wall dynamics was simulated by accounting for the anisotropic mobility of nanoparticles owing to hydrodynamic interaction
with a wall (Stokes viscous force). By comparing the simulation results with theoretical model calculations, we found that
the influence of anisotropic diffusion is insignificant in near-field FCS autocorrelation analysis. 相似文献