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排序方式: 共有4741条查询结果,搜索用时 15 毫秒
1.
Gary W. Breton Lauren A. Hahn Kenneth L. Martin 《Acta Crystallographica. Section C, Structural Chemistry》2019,75(9):1208-1212
Tetrahydrotetrazoles are five‐membered‐ring heterocycles containing four contiguous saturated nitrogen atoms. Very few examples of such compounds have been reported in the literature. Our previous attempt at the synthesis of a member of this class of compound suggested that the N—N bonds may be more labile than expected. This finding raised the question as to whether the structures of any of the previously reported tetrahydrotetrazoles had been properly assigned. We have reproduced the synthesis of a reported tetrahydrotetrazole, namely 1,2‐di‐tert‐butyl 3‐phenyl‐1H,2H,3H,10bH‐[1,2,3,4]tetrazolo[5,1‐a]isoquinoline‐1,2‐dicarboxylate, C25H30N4O4, and have now confidently confirmed its structure via X‐ray crystallography. However, while sufficiently stable in the crystal phase, we discovered that it remains very labile in solution (having a half‐life of only 15 min at 20 °C in CDCl3). A tentative reaction pathway for its dissociation based on 1H NMR spectral evidence is provided. 相似文献
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Sung Hwan Koo Dong Jun Li Taeyeong Yun Dong Sung Choi Kyung Eun Lee Gil Yong Lee Youngtak Oh Joonwon Lim Suchithra Padmajan Sasikala Ho Jin Lee In Ho Kim Hong Ju Jung Rishabh Jain Sang Ouk Kim 《Particle & Particle Systems Characterization》2019,36(7)
Efficient water electrolysis catalyst is highly demanded for the production of hydrogen as a sustainable energy fuel. It is reported that cobalt derived nanoparticle (CoS2, CoP, CoS|P) decorated reduced graphene oxide (rGO) composite aerogel catalysts for highly active and reliable hydrogen evolution reaction electrocatalysts. 7 nm level cobalt derived nanoparticles are synthesized over graphene aerogel surfaces with excellent surface coverage and maximal expose of active sites. CoS|P/rGO hybrid aerogel composites show an excellent catalytic activity with overpotential of ≈169 mV at a current density of ≈10 mA cm?2. Accordingly, efficient charge transfer is attained with Tafel slope of ≈52 mV dec?1 and a charge transfer resistance (Rct) of ≈12 Ω. This work suggests a viable route toward ultrasmall, uniform nanoparticles decorated graphene surfaces with well‐controlled chemical compositions, which can be generally useful for various applications commonly requiring large exposure of active surface area as well as robust interparticle charger transfer. 相似文献
4.
Sajeesh Kumar Madhurakkat Perikamana Sang Min Lee Jinkyu Lee Taufiq Ahmad Min Suk Lee Hee Seok Yang Heungsoo Shin 《Macromolecular bioscience》2019,19(4)
Plant derived flavonoids have not been well explored in tissue engineering applications due to difficulties in efficient formulations with biomaterials for controlled presentation. Here, the authors report that surface coating of epigallocatechin gallate (EGCG) on polymeric substrates including poly (L‐lactic acid) (PLLA) nanofibers can be performed via oxidative polymerization of EGCG in the presence of cations, enabling regulation of biological functions of multiple cell types implicated in bone regeneration. EGCG coating on the PLLA nanofiber promotes osteogenic differentiation of adipose‐derived stem cells (ADSCs) and is potent to suppress adipogenesis of ADSCs while significantly reduces osteoclastic maturation of murine macrophages. Moreover, EGCG coating serves as a protective layer for ADSCs against oxidative stress caused by hydrogen peroxide. Finally, the in vivo implantation of EGCG‐coated nanofibers into a mouse calvarial defect model significantly promotes the bone regeneration (61.52 ± 28.10%) as compared to defect (17.48 ± 11.07%). Collectively, the results suggest that EGCG coating is a simple bioinspired surface modification of polymeric biomaterials and importantly can thus serve as a promising interface for tuning activities of multiple cell types associated with bone fracture healing. 相似文献
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The European Physical Journal E - The isothermal gas adsorption of two hexane isomers (n-hexane and cyclohexane) in the mesopores of MCM-41 silica have been investigated by small angle neutron... 相似文献
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In this paper, the special construction of a parallel robot, called spatial servopneumatic multi-axis test facility, will be discussed. The investigations include the following aspects: (i) the laboratory set-up of the robot, (ii) various results obtained in laboratory experiments, taking into account quite different control algorithms and command-input signals, (iii) a comparison of the laboratory experiments with the computer simulations of Part I of this paper, and ({vi}) a quality check of the results compared with the cost of the different controller realizations. The results of both the computer simulations and the laboratory experiments show: (i) The dynamic behavior of the parallel structure can be tremendously improved by using sophisticated nonlinear control algorithms. (ii) This improvement has to be paid by a drastically increased amount of work for deriving the model equations and control algorithms, and by augmented hardware cost of the sensing elements and controller electronics. (iii) Carefully developed model equations and identified model parameters provide theoretical models of the complex parallel structure that are very close to reality. This enables the design engineer to systematically investigate constructive alternatives of the design parameters, sensor and actuator concepts, and control strategies of the MAP prior to their hardware realization.This work has been supported by the German Science Foundation (DFG) under Contract No. Ha 1666/6-3. 相似文献
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Dong Il Han Hoe Jin Hah Hong-Woo Park Sang Man Koo 《Journal of Sol-Gel Science and Technology》2004,32(1-3):47-51
Composite silica particles were synthesized by a two-step (acid-base) process in an aqueous solution with a mixture of organoalkoxysilane monomers. The two-step process separates the hydrolysis and condensation procedures to easily control condensation rate. In this study, the silane monomers used were phenyltrimethoxysilane (PTMS), vinyltrimethoxysilane (VTMS), methyltrimethoxysilane (MTMS), and tetraethyl-orthosilicate (TEOS). The physical properties of the resultant composite particles were investigated with the change in the molar ratio of monomers. The size of the particles increased with increasing the molar ratio of RaSi(OR)3/RbSi(OR)3 or RaSi(OR)3/TEOS (Ra: phenyl; Rb: vinyl, methyl). 相似文献
10.
Sang‐Uk Kim Choonkeun Lee Saimani Sundar Wonbong Jang Seung‐Jin Yang Haksoo Han 《Journal of Polymer Science.Polymer Physics》2004,42(23):4303-4312
A series of polyimides were synthesized from 2,2‐Bis(3,4‐dicarboxyphenyl)hexafluoropropane, 2,2‐bis(3‐amino‐4‐hydroxyphenyl)‐hexafluoropropane, and 4,4′‐oxydianiline by chemical imidization. The effects of the diamine ratios on the properties of the films were evaluated through the study of their thermal, electrical, and morphological properties. All the polymers exhibited better solubility in most of the organic solvents and hence were easily processable. Polyimides with more 2,2‐bis(3‐amino‐4‐hydroxyphenyl)‐hexafluoropropane exhibited better solubility and a low refractive index, which is highly desired for microelectronic applications. The dielectric constant and birefringence were strongly dependent on the fluorine content. With an increase in the fluorine substitution, both the dielectric constant and birefringence decreased. All the polymers exhibited high thermal stability (>400 °C). The absence of crystalline melting in differential scanning calorimetry and broad wide‐angle X‐ray diffraction patterns revealed the amorphous nature of the polymers, which was due to the presence of bulky CF3 groups and hinged ether linkages of the diamine component. The residual stress values decreased with an increase in the 4,4′‐oxydianiline content, and the results were in agreement with the dielectric constant. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4303–4312, 2004 相似文献