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281.
The optically active cobalt(III) complex with chiral cyclen, (2S,5S,8S,11S)-2,5,8,11-tetraethyl-1,4,7,10-tetraazacyclododecane, preferentially binds to D-phenylglycine (D-Phg) or D-t-leucine (D-t-Leu) rather than L-Phg or L-t-Leu, respectively, with 20% de in dimethyl sulfoxide at 293 K. Comparative studies on the crystal structures of cobalt(III) complexes with d-Phg and l-Phg revealed that the diastereoselectivity is due to the difference in the steric hindrance that should occur between the amino group of Phg and the ethyl group of cyclen. 相似文献
282.
Yamaguchi T Ishii N Tashiro K Aida T 《Journal of the American Chemical Society》2003,125(46):13934-13935
An acyclic dimer of a dendritic zinc porphyrin bearing six carboxylic acid functionalities (1acid) interacts with fullerenes, such as C60 and C70, to form "supramolecular peapods", composed of a hydrogen-bonded zinc porphyrin nanotube and fullerenes (3). According to TEM, the peapods are very long (>1 mum) and have a uniform diameter of 15 nm. Without fullerenes, the zinc porphyrin dimer forms only a heavily entangled, irregular assembly. In contrast with 1acid, an ester version of the acyclic dimer without hydrogen-bonding capability (1ester) hardly interacts with fullerenes. 相似文献
283.
Ryu Tashiro Hiroaki Taguchi Kumi Hidaka Masayuki Endo Hiroshi Sugiyama 《化学:亚洲杂志》2019,14(23):4140-4145
Understanding the mechanism responsible for the progression of amyloid deposition is important for developing methods to suppress this process in the treatment of Alzheimer's disease. The effects of physical damage during the transition phase of amyloid β fibril formation are unclear. In this study, we used high‐speed atomic force microscopy to investigate the effects of damage to the intermediates of amyloid β in real time. Physical damage to intermediates did not suppress, but instead promoted fibrillization. This progression was accompanied by morphological changes from globular oligomers to protofibrils. These results suggest that the properties of the intermediates, such as structural fragility and stability, are highly related to the rate of fibrillization. 相似文献
284.
Microscopically-viewed structural changes in solvent-induced phase transitions of synthetic polymers
Structural changes occurring in the solvent-induced phase transition have been investigated by carrying out the time-resolved measurements of X-ray diffraction, infrared spectra and Raman spectra. First example is about the solvent-induced crystallization of syndiotactic polystyrene glass. By comparing the time evolution of the various infrared and Raman bands and the X-ray reflections, the process of nucleation, growth, and aggregation of regular helical sequences in the crystalline lattice could be traced concretely. It was also found experimentally that the amorphous chain segments started an active motion immediately after absorbing solvent molecules and became a trigger to induce the local regularization of random coils into regular helical segments. The second example is the reversible solid-state phase transition of poly(ethylene imine) between the anhydrate of doubly-stranded helices and the hydrates of planar zigzag chains. By carrying out the time-resolved infrared spectral measurements in water vapor atmosphere (H2O or D2O), the characteristic bands could be identified for these crystalline phases and the structural transformation in the hydration process could be clarified in detail. 相似文献
285.
Masao Shiozaki Takuya Tashiro Hiroyuki Koshino Tomokuni Shigeura Hiroshi Watarai Masaru Taniguchi Kenji Mori 《Tetrahedron》2013
RCAI-80 is one of the ester analogs of KRN7000 (α-galactosylceramide). This compound released mainly T helper 2 (Th2) cytokines, such as IL-4 rather than T helper 1 (Th1) cytokines, such as IFNγ from the invariant natural killer T (iNKT) cells. In addition, it has been known that some of the hydroxylated derivatives of KRN7000 make the cytokine secretion bias to Th2 by decreasing the IFNγ production to almost zero. This time, the three compounds having these two characteristic properties, namely an ester group and also some extra hydroxy groups existing on the ester side chain and/or on the 2-acyloxy-3,4-dihydroxyoctadecyl main chain of RCAI-80, were synthesized to examine the biological activities. As a result, it was found that these compounds made the cytokine secretion skew to Th2. Therefore, their effectiveness for experimental autoimmune encephalomyelitis (EAE) was examined. It was recognized that one of them showed moderate suppression of EAE symptom. 相似文献
286.
Pimsai Tanphibal Kohji Tashiro Suwabun Chirachanchai 《Macromolecular rapid communications》2016,37(8):685-690
Diarylbutadiyne derivatives are ideal monomers for providing the π‐electron‐conjugated system of polydiacetylenes (PDAs). The geometrical parameters for diacetylene topochemical polymerization are known. However, control of the molecules under these parameters is yet to be addressed. This work shows that by simply tailoring diarylbutadiyne with amide side‐chain substituents, the arrangement of the substituents and the resulting hydrogen bond framework allows formation of π‐electron‐conjugated PDA.
287.
288.
The new families of aluminate glasses obtained by the present authors from their melts in the systems K2O–Ta2O5–Al2O3, Na2O–K2O–Ta2O5–Al2O3, K2O –Cs2O– Ta2O5–Al2O3, K2O–Nb2O5–Al2O3, Na2Oz.sbnd;K2O–TiO2–Al2O3, BaO–TiO2–Al2O3, BaO–ZrO2–TiO2–Al2O3 and Na2O–K2O–BaO–ZrO2–Ta2O5–TiO2 –Al2O3 showed high transmissions of visible and infrared (IR) radiation ranging from 0.4 to about 6 μm, as well as high refractive indices up to 2.0. Their physical and chemical properties such as glass-forming ability, softening temperature, hardness and hygroscopicity were comparable to conventional silicate glasses. These properties are useful for IR applications. The cause of the high IR transmission of the aluminate glasses was interpreted in terms of the masses of the constituent cations and the single bond strengths of the cations with oxygen ions. 相似文献
289.
Nylon-11 was crystallized into different crystalline phases by appropriate methods. The α phase was obtained by precipitating nylon-11 in 1,4-butanediol. The melt crystallized sample at 175 °C gave pseudohexagonal phase. The γ phase was obtained by casting nylon-11 in trifluroacetic acid (TFA). The change in the structure was monitored in situ by high temperature wide-angle X-ray scattering (HTWAXS) and high temperature Fourier transform infrared spectroscopy (HTFTIR). The studies have shown that nylon-11 is one of the few nylons that exhibit extensive degree of polymorphism. HTFTIR studies revealed, apart from the conformational differences between various phases of nylon-11, some information on the formation of γ phase. 相似文献
290.
Natural enzymes control the intrinsic reactivity of chemical reactions in the natural environment, giving only the necessary products. In recent years, challenging research on the reactivity control of terpenes with structural diversity using artificial host compounds that mimic such enzymatic reactions has been actively pursued. A typical example is the acid-catalyzed olefin isomerization of (+)-limonene, which generally gives a complex mixture due to over-isomerization to thermodynamically favored isomers. Herein we report a highly controlled conversion of (+)-limonene by kinetic suppression of over-isomerization in a confined space of a porous metal–macrocycle framework (MMF) equipped with a Brønsted acid catalyst. The terminal double bond of (+)-limonene migrated to one neighbor, preferentially producing terpinolene. This reaction selectivity was in stark contrast to the homogeneous acid-catalyzed reaction in bulk solution and to previously reported catalytic reactions. X-ray structural analysis and examination of the reaction with adsorption inhibitors suggest that the reactive substrates may bind non-covalently to specific positions in the confined space of the MMF, thereby inhibiting the over-isomerization reaction. The nanospaces of the MMF with substrate binding ability are expected to enable highly selective synthesis of a variety of terpene compounds.A porous metal–macrocycle framework (MMF) equipped with a Brønsted acid catalyst in nanochannels enables highly selective isomerization of limonene to terpinolene by kinetically suppressing over-isomerization at confined acid sites. 相似文献