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951.
Min Cheng Daoyuan Kang Xiaoli Zhang Huawei Yin Yuhong Wang 《Crystal Research and Technology》2015,50(4):331-337
Comparing with the traditional concentric rotation method (rotation radius is 0 cm), the effects of different rotation radii on the growth rate of KDP crystals were studied by experimental methods. It was found that with the increase of rotation radius from 0 cm, the growth rate of each direction of crystals first increased and then decreased in a size‐unchanged vessel. The smaller the distance between the crystal and vessel wall, the less the growth rate. This phenomenon was named the “wall collision effect”. Also, the value of growth rate reached a maximum when the rotation radius was about half of its allowable largest value in the size‐unchanged vessel. In addition, an increase of the rotation radius could improve the crystal growth rate under the same linear velocity of crystal movement. Finally, the uniformity of crystal growth has also been analyzed compared with the concentric rotation radius. It was found that the uniformity of crystal growth was best when the rotation radius was half of its allowable maximum value, and it was more conducive to the actual application of KDP crystals. 相似文献
952.
Hongfei Cheng Kuo Li Qinfu Liu Shuai Zhang Xiaoguang Li Ray L. Frost 《Journal of Thermal Analysis and Calorimetry》2014,117(3):1231-1239
The thermal decomposition process of kaolinite–potassium acetate intercalation complex has been studied using simultaneous thermogravimetry coupled with Fourier-transform infrared spectroscopy and mass spectrometry (TG-FTIR-MS). The results showed that the thermal decomposition of the complex took place in four temperature ranges, namely 50–100, 260–320, 320–550, and 650–780 °C. The maximal mass losses rate for the thermal decomposition of the kaolinite–potassium acetate intercalation complex was observed at 81, 296, 378, 411, 486, and 733 °C, which was attributed to (a) loss of the adsorbed water, (b) thermal decomposition of surface-adsorbed potassium acetate (KAc), (c) the loss of the water coordinated to potassium acetate in the intercalated kaolinite, (d) the thermal decomposition of intercalated KAc in the interlayer of kaolinite and the removal of inner surface hydroxyls, (e) the loss of the inner hydroxyls, and (f) the thermal decomposition of carbonate derived from the decomposition of KAc. The thermal decomposition of intercalated potassium acetate started in the range 320–550 °C accompanied by the release of water, acetone, carbon dioxide, and acetic acid. The identification of pyrolysis fragment ions provided insight into the thermal decomposition mechanism. The results showed that the main decomposition fragment ions of the kaolinite–KAc intercalation complex were water, acetone, carbon dioxide, and acetic acid. TG-FTIR-MS was demonstrated to be a powerful tool for the investigation of kaolinite intercalation complexes. It delivers a detailed insight into the thermal decomposition processes of the kaolinite intercalation complexes characterized by mass loss and the evolved gases. 相似文献
953.
Jialin Liu Jingrui Li Mengjin Fan Junying Zhang Jue Cheng 《Journal of Thermal Analysis and Calorimetry》2014,117(2):603-610
Aromatic amine curing agent with flexible unit in backbone, 1,4-bis (4-diaminobenzene-1-oxygen) n-butane (DDBE), was synthesized, and the structure was confirmed by FT-IR and 1H NMR. The curing kinetics of tetraglycidyl methylene dianiline (TGDDM, or AG80) using DDBE and 4,4′-bis-(diaminodiphenyl) methane (DDM) as curing agents, respectively, were comparatively studied by non-isothermal DSC with a model-fitting Málek approach and a model-free advanced isoconversional method of Vyazovkin. The dynamic mechanical properties and thermal stabilities of the cured materials were investigated by DMTA and TG, respectively. The results showed that the activation energy of AG80/DDBE system was slightly higher than that of AG80/DDM system. ?esták-Berggren model can generally simulate well the reaction rates of these two systems. DMTA measurements showed that the storage modulus of cured AG80/DDBE is similar to that of cured AG80/DDM at the temperature below glass transition temperature (T g) and lower than that of cured AG80/DDM at the temperature above glass transition temperature, while T g of cured AG80/DDBE is lower than that of cured AG80/DDM. TG showed that the thermal stabilities of these two cured systems are similar. 相似文献
954.
Biosynthesis of Streptolidine Involved Two Unexpected Intermediates Produced by a Dihydroxylase and a Cyclase through Unusual Mechanisms
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Dr. Chin‐Yuan Chang Syue‐Yi Lyu Dr. Yu‐Chen Liu Ning‐Shian Hsu Dr. Chih‐Chung Wu Dr. Cheng‐Fong Tang Kuan‐Hung Lin Dr. Jin‐Yuan Ho Dr. Chang‐Jer Wu Dr. Ming‐Daw Tsai Dr. Tsung‐Lin Li 《Angewandte Chemie (International ed. in English)》2014,53(7):1943-1948
Streptothricin‐F (STT‐F), one of the early‐discovered antibiotics, consists of three components, a β‐lysine homopolymer, an aminosugar D ‐gulosamine, and an unusual bicyclic streptolidine. The biosynthesis of streptolidine is a long‐lasting but unresolved puzzle. Herein, a combination of genetic/biochemical/structural approaches was used to unravel this problem. The STT gene cluster was first sequenced from a Streptomyces variant BCRC 12163, wherein two gene products OrfP and OrfR were characterized in vitro to be a dihydroxylase and a cyclase, respectively. Thirteen high‐resolution crystal structures for both enzymes in different reaction intermediate states were snapshotted to help elucidate their catalytic mechanisms. OrfP catalyzes an FeII‐dependent double hydroxylation reaction converting L ‐Arg into (3R,4R)‐(OH)2‐L ‐Arg via (3S)‐OH‐L ‐Arg, while OrfR catalyzes an unusual PLP‐dependent elimination/addition reaction cyclizing (3R,4R)‐(OH)2‐L ‐Arg to the six‐membered (4R)‐OH‐capreomycidine. The biosynthetic mystery finally comes to light as the latter product was incorporation into STT‐F by a feeding experiment. 相似文献
955.
Hexanuclear Gold(I) Phosphide Complexes as Platforms for Multiple Redox‐Active Ferrocenyl Units
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Dr. Terence Kwok‐Ming Lee Dr. Eddie Chung‐Chin Cheng Dr. Nianyong Zhu Prof. Dr. Vivian Wing‐Wah Yam 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(1):304-310
The synthesis, X‐ray crystal structures, electrochemical, and spectroscopic studies of a series of hexanuclear gold(I) μ3‐ferrocenylmethylphosphido complexes stabilized by bridging phosphine ligands, [Au6(P?P)n(Fc‐CH2‐P)2][PF6]2 (n=3, P?P=dppm (bis(diphenylphosphino)methane) ( 1 ), dppe (1,2‐bis(diphenylphosphino)ethane) ( 2 ), dppp (1,3‐bis(diphenylphosphino)propane) ( 3 ), Ph2PN(C3H7)‐PPh2 ( 4 ), Ph2PN(Ph‐CH3‐p)PPh2 ( 5 ), dppf (1,1′‐bis(diphenylphosphino)ferrocene) ( 6 ); n=2, P?P=dpepp (bis(2‐diphenylphosphinoethyl)phenylphosphine) ( 7 )), as platforms for multiple redox‐active ferrocenyl units, are reported. The investigation of the structural changes of the clusters has been probed by introducing different bridging phosphine ligands. This class of gold(I) μ3‐ferrocenylmethylphosphido complexes has been found to exhibit one reversible oxidation couple, suggestive of the absence of electronic communication between the ferrocene units through the Au6P2 cluster core, providing an understanding of the electronic properties of the hexanuclear AuI cluster linkage. The present complexes also serve as an ideal system for the design of multi‐electron reservoir and molecular battery systems. 相似文献
956.
Phenylene‐Coated Magnetic Nanoparticles that Boost Aqueous Asymmetric Transfer Hydrogenation Reactions
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Dr. Xiaoshuang Gao Rui Liu Dacheng Zhang Meng Wu Tanyu Cheng Prof. Guohua Liu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(6):1515-1519
Phenylene‐coated organorhodium‐functionalized magnetic nanoparticles are developed through co‐condensation of chiral 4‐(trimethoxysilyl)ethyl)phenylsulfonyl‐1,2‐diphenylethylene‐diamine and 1,4‐bis(triethyoxysilyl)benzene onto Fe3O4 followed complexation with [{Cp*RhCl2}2]. This magnetic catalyst exhibits excellent catalytic activity and high enantioselectivity in asymmetric transfer hydrogenation in aqueous medium. Such activity is attributed to the high hydrophobicity and the confined nature of the chiral organorhodium catalyst. The magnetic catalyst can be easily recovered by using a small external magnet and it can be reused for at least 10 times without loss of its catalytic activity. This characteristic makes it an attractive catalyst for environmentally friendly organic syntheses. 相似文献
957.
Conformational Control of Oligo(p‐phenyleneethynylene)s with Intrinsic Substituent Electronic Effects: Origin of the Twist in Pentiptycene‐Containing Systems
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Che‐Jen Lin Dr. Sandip Kumar Kundu Dr. Cheng‐Kai Lin Prof. Jye‐Shane Yang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(45):14826-14833
Dependence of the backbone planarity of oligo(p‐phenyleneethynylene)s (OPEs) on the intrinsic electronic character of substituents and on the nature of the solvent has been experimentally demonstrated with a series of center‐symmetrical five‐ring systems, pentiptycene‐pentiptycene‐arene‐pentiptycene‐pentiptycene, differing in the substituents on the central arene. In frozen 2‐methyltetrahydrofuran (MTHF), the adjacent pentiptycene units prefer to be in a mutually twisted orientation when the substituents are electron‐withdrawing (F and amido), resulting in a TPPT or TTTT conformation, whereas a planarized PPPP backbone is favored in the case of electron‐donating substituents (alkyl and alkoxy). The propensity to adopt the PPPP form is generally enhanced by replacing MTHF with either methylcyclohexane or mixed ethanol/methanol as solvent. These observations reveal that the twist between adjacent pentiptycene units in OPEs is a consequence of the electronic rather than steric effects of iptycenyl substituents. The electronic effect of iptycenyl substituents is manifested in decreased phenylene π polarizability as the net effect of both electron‐donating hyperconjugation and an electron‐withdrawing inductive effect. Variable‐temperature electronic absorption and emission spectroscopies are the critical tools for this work. Our findings provide important guidelines for conformational and electronic engineering of OPEs and for the design of novel iptycene‐based organic electronic materials. 相似文献
958.
Direct X‐ray Observation of Trapped CO2 in a Predesigned Porphyrinic Metal–Organic Framework
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Jacob A. Johnson Dr. Shuang Chen Tyler C. Reeson Dr. Yu‐Sheng Chen Prof. Xiao Cheng Zeng Prof. Jian Zhang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(25):7632-7637
Metal–organic frameworks (MOFs) are emerging microporous materials that are promising for capture and sequestration of CO2 due to their tailorable binding properties. However, it remains a grand challenge to pre‐design a MOF with a precise, multivalent binding environment at the molecular level to enhance CO2 capture. Here, we report the design, synthesis, and direct X‐ray crystallographic observation of a porphyrinic MOF, UNLPF‐2, that contains CO2‐specific single molecular traps. Assembled from an octatopic porphyrin ligand with [Co2(COO)4] paddlewheel clusters, UNLPF‐2 provides an appropriate distance between the coordinatively unsaturated metal centers, which serve as the ideal binding sites for in situ generated CO2. The coordination of CoII in the porphyrin macrocycle is crucial and responsible for the formation of the required topology to trap CO2. By repeatedly releasing and recapturing CO2, UNLPL‐2 also exhibits recyclability. 相似文献
959.
Magnetically Encoded Luminescent Composite Nanoparticles through Layer‐by‐Layer Self‐Assembly
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Prof. Dr. Erqun Song Weiye Han Hongyan Xu Yunfei Jiang Dan Cheng Prof. Dr. Yang Song Prof. Dr. Mark T. Swihart 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(45):14642-14649
Sensitive and rapid detection of multiple analytes and the collection of components from complex samples are important in fields ranging from bioassays/chemical assays, clinical diagnosis, to environmental monitoring. A convenient strategy for creating magnetically encoded luminescent CdTe@SiO2@n Fe3O4 composite nanoparticles, by using a layer‐by‐layer self‐assembly approach based on electrostatic interactions, is described. Silica‐coated CdTe quantum dots (CdTe@SiO2) serve as core templates for the deposition of alternating layers of Fe3O4 magnetic nanoparticles and poly(dimethyldiallyl ammonium chloride), to construct CdTe@SiO2@n Fe3O4 (n=1, 2, 3, …?) composite nanoparticles with a defined number (n) of Fe3O4 layers. Composite nanoparticles were characterized by zeta‐potential analysis, fluorescence spectroscopy, vibrating sample magnetometry, and transmission electron microscopy, which showed that the CdTe@SiO2@n Fe3O4 composite nanoparticles exhibited excellent luminescence properties coupled with well‐defined magnetic responses. To demonstrate the utility of these magnetically encoded nanoparticles for near‐simultaneous detection and separation of multiple components from complex samples, three different fluorescently labeled IgG proteins, as model targets, were identified and collected from a mixture by using the CdTe@SiO2@n Fe3O4 nanoparticles. 相似文献
960.
Cerium‐Based M4L4 Tetrahedra as Molecular Flasks for Selective Reaction Prompting and Luminescent Reaction Tracing
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Yang Jiao Dr. Jian Wang Dr. Pengyan Wu Liang Zhao Dr. Cheng He Jing Zhang Prof. Chunying Duan 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(8):2224-2231
The application of metal–organic polyhedra as “molecular flasks” has precipitated a surge of interest in the reactivity and property of molecules within well‐defined spaces. Inspired by the structures of the natural enzymatic pockets, three metal–organic neutral molecular tetrahedral, Ce‐TTS, Ce‐TNS and Ce‐TBS (H6TTS: N′,N′′,N′′′‐nitrilotris‐4,4′,4′′‐(2‐hydroxybenzylidene)‐benzohydrazide; H6TNS: N′,N′′,N′′′‐nitrilotris‐6,6′,6′′‐(2‐hydroxybenzylidene)‐2‐naphthohydrazide; H6TBS: 1,3,5‐ phenyltris ‐4,4′,4′′‐(2‐hydroxybenzylidene)benzohydrazide), which exhibit different size of the edges and cavities, were achieved through self‐assembly by incorporating robust amide‐containing tridentate chelating sites into the fragments of the ligands. They acted as molecular flasks to prompt the cyanosilylation of aldehydes with excellent selectivity towards the substrates size. The amide groups worked as trigger sites and catalytic driven forces to achieve efficient guest interactions, enforcing the substrates proximity within the cavity. Experiments on catalysts with the different cavity radii and substrates with the different molecular size demonstrated that the catalytic performance exhibited enzymatical catalytic mechanism and occurred in the molecular flask. These amides were also able to amplify guest‐bonding events into the measurable outputs for the detection of concentration variations of the substrates, providing the possibility for metal–organic hosts to work as smart molecular flasks for the luminescent tracing of catalytic reactions. 相似文献