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991.
C5–C10 Directly Bonded Tetrodotoxin Analogues: Possible Biosynthetic Precursors of Tetrodotoxin From Newts 下载免费PDF全文
Yuta Kudo Yoko Yamashita Prof. Dr. Dietrich Mebs Dr. Yuko Cho Prof. Dr. Keiichi Konoki Prof. Dr. Takeshi Yasumoto Prof. Dr. Mari Yotsu‐Yamashita 《Angewandte Chemie (International ed. in English)》2014,53(52):14546-14549
The identification of novel tetrodotoxin (TTX, 1 ) analogues would significantly contribute to the elucidation of its biosynthetic pathway. In this study, the first C5–C10 directly bonded TTX analogues, 4,9‐anhydro‐10‐hemiketal‐5‐deoxyTTX ( 2 ) and 4,9‐anhydro‐8‐epi‐10‐hemiketal‐5,6,11‐trideoxyTTX ( 3 ), were found in the newt Cynops ensicauda popei by using a screening method involving HILIC‐LC–MS/MS focused on the fragment ions of TTX analogues, and their structures were elucidated by spectroscopic methods. Compound 2 was detected in a wide range of newt species, and the 2 and TTX contents of 22 newt specimens were correlated (rs=0.88). Based on these results and its structural features, 2 was predicted to serve as a precursor of TTX that would be directly converted into 4,9‐anhydroTTX ( 4 ) by Baeyer–Villiger‐like oxidation or via 4,9‐anhydro‐5‐deoxyTTX formed by cleavage of the C5–C10 bond. The bicyclic carbon skeletons of 2 and 3 suggested a possible monoterpene origin for TTX. 相似文献
992.
Ryoya Hiraoki Hayaka Fukuzumi Yuko Ono Tsuguyuki Saito Akira Isogai 《Cellulose (London, England)》2014,21(1):167-176
Two cellouronic acids [sodium (1 → 4)-β-polyglucuronates, CUAs] and one 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-oxidized wood cellulose (TOC) became soluble in 8 % lithium chloride/N,N-dimethylacetamide (LiCl/DMAc) after the methylation of C6 carboxyl groups in these samples using trimethylsilyldiazomethane (TMSD). The obtained solutions were diluted to 1 % LiCl/DMAc and subjected to size-exclusion chromatography combined with multi-angle laser-light scattering (SEC-MALLS). Neither depolymerization nor side reactions took place during methylation; this was confirmed by SEC-MALLS and nuclear magnetic resonance analyses, using CUAs as models. The SEC-MALLS analysis of the original wood cellulose and the carboxyl-methylated TOC prepared from it, using 1 % LiCl/N,N-dimethyl-2-imidazolidinone and 1 % LiCl/DMAc, respectively, as eluents, showed that the weight-average degree of polymerization of the original wood cellulose decreased from 3,100 to 2,210 through TEMPO-mediated oxidation. The molecular-mass distributions of the original wood cellulose and the TOC both consisted of one large peak with a small shoulder, indicating that some of the oxidized hemicelluloses remained in the TOC. The combination of methylation of carboxyl groups in polysaccharides using TMSD and subsequent SEC-MALLS analysis using 1 % LiCl/DMAc as an eluent may be applicable not only to TOCs, but also to other polysaccharides with carboxyl groups, for evaluation of their molecular-mass parameters. 相似文献
993.
In this study, both α-chitin powders and nanofibers were successfully dissolved in 20 wt% NaOH solutions at low temperatures. Elemental analysis confirmed that this NaOH-freezing treatment did not cause deacetylation of chitin. After heating and neutralizing with water, chitin hydrogels could be prepared. X-ray diffraction and field emission scanning electron microscope data demonstrated that these two hydrogels formed typical regenerated microporous structures with low crystallinity, which was caused by the dissolution process. Based on this result, cold ethanol was used for α-chitin nanofibers during the initial stages of neutralization, which effectively prevented the dissolution and decrease in crystallinity and was even able to preserve the continuous network structure of original nanofiber. This gelation behavior seems to be attributed to interdigitation and aggregation between neighboring nanofibers in cold alkali solution leading to the shrinkage of the hydrogel. In general, by avoiding the dissolution process, highly crystalline hydrogel based on α-chitin nanofibers was prepared by a simple NaOH treatment without use of any other chemical solvents or cross-linking agents. We expect this new type of hydrogel could be promoted to wide applications and research studies as novel green nanomaterials. 相似文献
994.
Unsteady compressible boundary layer flow in the stagnation region of a sphere with a magnetic field
H. S. Takhar K. Yano S. Nakamura G. Nath 《Archive of Applied Mechanics (Ingenieur Archiv)》1997,67(7):478-486
Summary An analysis is performed to study the unsteady compressible laminar boundary layer flow in the forward stagnation-point region
of a sphere with a magnetic field applied normal to the surface. We have considered the case where there is an initial steady
state that is perturbed by the step change in the total enthalpy at the wall. The nonlinear coupled parabolic partial differential
equations governing the flow and heat transfer have been solved numerically using a finite-difference scheme. The numerical
results are presented, which show the temporal development of the boundary layer. The magnetic field in the presence of variable
electrical conductivity causes an overshoot in the velocity profile. Also, when the total enthalpy at the wall is suddenly
increased, there is a change in the direction of transfer of heat in a small interval of time.
Received 15 January 1996; accepted for publication 21 November 1996 相似文献
995.
Nishi Teppei Suzuki Noritomo Takahashi Naoko Yano Kazuhisa 《Journal of nanoparticle research》2013,15(4):1-7
Strontium titanate (SrTiO3) has attracted a lot of attention because of its possible applications in new microelectronic devices. It is a material with a high dielectric constant, low leakage current, and some of its properties can be changed by adding or modifying the concentration of a dopant, which can be used for a wide range of functional purposes, from simple capacitors to complicated microwave devices. Therefore, in this work, we report the development of a new route to synthesize SrTiO3 nanoparticles based on the solvothermal method by employing two precursor solutions: strontium chloride and titanium(IV) butoxide. Our route allows the production of cubic SrTiO3 nanoparticles with a narrow size distribution. The particle sizes range between 8 and 24 nm, forming agglomerates of SrTiO3 in the range of 128–229 nm. It was demonstrated that the Ti/Sr molar ratio employed into the precursor solution has an important effect onto the chemical composition of the resulting SrTiO3 nanoparticles: when using Ti/Sr < 1, the formation and incorporation of the SrCO3 compound into the nanoparticles was observed while with Ti/Sr ≥ 1 nanoparticles are free of contaminants. The as-prepared nanoparticles were characterized by energy-dispersive X-ray spectroscopy, X-ray diffraction, transmission electron microscopy, high-resolution TEM, selected area electron diffraction, scanning electron microscopy, and dynamic light scattering. 相似文献
996.
Kouji Yano 《Journal of Theoretical Probability》2013,26(1):259-283
A necessary and sufficient condition for a random walk in a finite directed graph subject to a road coloring to be measurable with respect to the driving process is proved to be that the road coloring is synchronizing. The key to the proof is to find a hidden symmetry in the non-synchronizing case. 相似文献
997.
We introduce a Petrov–Galerkin regularized saddle approximation which incorporates a “model” (partial differential equation) and “data” (M experimental observations) to yield estimates for both state and model bias. We provide an a priori theory that identifies two distinct contributions to the reduction in the error in state as a function of the number of observations, M: the stability constant increases with M; the model-bias best-fit error decreases with M. We present results for a synthetic Helmholtz problem and an actual acoustics system. 相似文献
998.
Yuko Suzuki Prof. Dr. Takahiro Sasamori Dr. Jing‐Dong Guo Prof. Dr. Shigeru Nagase Prof. Dr. Norihiro Tokitoh 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(39):13784-13788
Treatment of 2,5‐di(3,5‐tert‐butylphenyl)‐1‐lithioferrocene with GeCl2?dioxane afforded the corresponding chlorogermylenoid that exhibited an ambident reactivity in different solvents; it displayed a behavior characteristic for a dichlorogermylene anion in THF, while it exhibited the typical reactivity of a chlorogermylene in toluene. X‐Ray diffraction analysis of a single crystal of this chlorogermylenoid, obtained from recrystallization in THF, revealed a separated‐ion‐pair structure in the solid state. 相似文献
999.
Junki Yano Kazuhiko Ishihara Shin‐ichi Yusa 《Journal of polymer science. Part A, Polymer chemistry》2017,55(15):2432-2439
A diblock copolymer (P98N100) composed of a biocompatible water‐soluble block (PMPC) and a lower critical solution temperature (LCST) type thermo‐responsive block (PNIPAM) was prepared via controlled radical polymerization. To dissolve fullerene (C60) in water, the C60/P98N100 complex was prepared by mixing C60 and P98N100 powders. The maximum solubilized C60 concentration in water was 1.39 g/L, as estimated from UV–vis adsorption, when the polymer concentration was 5.0 g/L. The percent transmittance of the aqueous solution of the C60/P98N100 complex decreased above 36 °C due to inter‐complex association above the LCST for the PNIPAM block. While the hydrodynamic radius of C60/P98N100 complex was 135 nm at 20 °C, it increased to 161 nm at 50 °C. Despite the observation of 1H NMR signals from PMPC and PNIPAM blocks for the C60/P98N100 complex in D2O at room temperature, the signals from PNIPAM disappeared above 35 °C due to restricted motion of PNIPAM. Generation of singlet oxygen (1O2) from the C60/P98N100 complex by photo‐irradiation was confirmed using 9,10‐anthracene dipropionic acid (ADPA). The absorbance of ADPA decreased with increasing irradiation time due to oxidation of ADPA by 1O2. It is expected that the C60/P98N100 complex can be applied as a thermo‐responsive carrier for photodynamic therapy. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2432–2439 相似文献
1000.
Micro‐pulverized extraction pretreatment for highly sensitive analysis of 11‐nor‐9‐carboxy‐Δ9‐tetrahydrocannabinol in hair by liquid chromatography/tandem mass spectrometry 下载免费PDF全文