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111.
Li BS Kang SZ Cheuk KK Wan L Ling L Bai C Tang BZ 《Langmuir : the ACS journal of surfaces and colloids》2004,20(18):7598-7603
In the present work, we investigated self-assembling of a poly(phenylacetylene) carrying L-valine pendants (PPA-Val) in a water/methanol solution, upon evaporation of the solution on mica, and on the water surface. With intercalation of a fluorescence probe of Ru(phen)2(dppx)2+ (phen = 1,10-phenanthroline, dppx=7,8-dimethyldipyridophenazine) into the hydrophobic cavities associated by the PPA-Val chains, their helical structures were directly detected in solution with an in situ fluorescence microscope. Helical aggregates were observed with AFM upon evaporation of the solvents, suggesting that the helical structures in the solution are the building blocks of the helical aggregates. Self-assembling structures of PPA-Val on the water surface were, however, very different from that formed upon evaporation of its THF solution on the mica surface. The polymer chains associated into a monolayer of extended fibers on the water surface, whereas superhelical fibers formed on the mica surface. Water molecules play a critical role in inducing the polymer to form diverse morphological structures in its bulk solution and on its surface. In solution, the isotropic hydrophobic effect drove the polymer chains to form superhelical aggregates, while on the water surface, the hydrophobic effect concentrated mainly on the lateral part of the polymer, thus giving a monolayer of extended fibers. 相似文献
112.
Yu Liu Yong Chen Shi-Zhao Kang Li Li Chun-Hua Diao Heng-Yi Zhang 《Journal of inclusion phenomena and macrocyclic chemistry》2003,47(1-2):91-95
Two novel benzo-15-crown-5 tethered β-cyclodextrins 1 and 2have been synthesized by coupling substituted benzo-15-crown-5 with correspondingβ-cyclodextrin derivatives. Their inclusion complexation behavior withrepresentative guests, such as cyclohexanol, cyclohexane carboxylic acid, cyclohexaneacetic acid, sodium cyclohexane carboxylate, and potassium cyclohexane carboxylate,was investigated in aqueous solution by means of fluorescence spectrometry. As compared with parent β-cyclodextrin, benzo-15-crown-5 tethered β-cyclodextrins 1–2 display significantly enhanced molecular binding abilities and selectivities towards model substrates, especially towards substrates containing alkali-metal cations. These results indicate that, bearing two recognition sites in a single molecule, these supramolecular architectures can strongly enhance the molecular binding ability of parent β-cyclodextrin by the cooperative binding of the β-cyclodextrin cavity and the crown ether moiety. Possessing a shorter linker, crown ether-β-cyclodextrin 2 shows much higher binding affinity with guest molecules than crown ether-β-cyclodextrin 1, which may be attributed to the binding size and molecular multiple recognition behavior between host and guest. 相似文献
113.
Jeong Hyun Kim Seung-Hyun Kang Il Nam Jung Kwan Mook Kim Bok Ryul Yoo Myong Euy Lee 《Journal of Sol-Gel Science and Technology》2004,32(1-3):31-35
Reaction of (triphenylmethyl)silanetriol (1) with cyclopentadienyltitanium trichloride (CpTiCl3) in the presence of triethylamine as a HCl scavenger gave both compounds of a partial open-cage type {[Ph3CSiO(OH)]3(Ph3CSiO3/2)(CpTiO3/2)4} (2) and cube type (Ph3CSiO3/2CpTiO3/2)4 (3). The 1:1 reaction of 1 and CpTiCl3 in toluene solvent at reflux temperature for 3 d afforded compounds 2 (22%) and 3 (36%). When 1 is reacted with a 1.5 fold excess of CpTiCl3 under the same conditions, compound 3 was obtained in high yield (81%) along with 2 in trace quantities. Compounds 2 and 3 were fully characterized by the analyses of 1H, 13C, 29Si NMR, IR, and FAB MS data. The solid-state structure of 3 was determined by a single crystal X-ray diffraction study. Compound 3 had shown to have catalytic activity for the oxidation of alkenes such as 1-octene, cyclooctene, and norbornene with t-butyl hydrogen peroxide. The effect of solvent was observed in this epoxidation reaction. The order of reactivity were decreased as follows: CHCl3 > hexane THF. 相似文献
114.
115.
The anodic reaction of Ni in an alkaline solution was studied by the tip–substrate voltammetry mode of scanning electrochemical microscopy (SECM) and cyclic voltammetry (CV). A platinum microdisc electrode was selected as the tip electrode, which functioned as a pH sensor with transient response capability. The pH value of the solution near the Ni electrode surface varied while the Ni substrate oxidation reaction occurred, and the pH variation could be detected by the tip faradic current. The cyclic voltammogram results showed that two types of hydroxides: i.e. α‐Ni(OH)2 and β‐Ni(OH)2 were formed during Ni oxidation in the lower potential region. In the proceedings of α‐Ni(OH)2 → γ‐NiOOH and β‐Ni(OH)2 → β‐NiOOH, the process of OH? concentration decrease in the solution was ahead and behind of electron transfer in the solid phase, respectively. These results indicate that the OH? adsorption process occurs as an elementary step in the former reaction and the H+ diffusion process from the inner to the outer layer of the solid phase occurs as a subsequent step in the latter reaction. The results also revealed that the oxide film on the Ni surface has a two‐layer structure. The real potential of the oxygen evolution reaction (OER) on the Ni surface with different cycles is also analyzed in the paper. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
116.
A one-step chromatographic method capable of separating all isomers of polyethylene glycol (PEG)-growth hormone-releasing factor (GRF) (1-29) conjugates was developed. The unmodified GRF (1-29) and seven different isomers of PEG-GRF (1-29) conjugates were separated by using a simple reversed-phase HPLC method depending on the differences of hydrophobicity due to the number and site of PEG attachment. The PEGylation sites of all isomers of PEG-GRF (1-29) conjugates were identified by determining the molecular masses of the Lys-C digested fragments with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. This study is a first report for the separation of all PEG-conjugate isomers and would be useful for further studies to find the promising conjugate by evaluating biological activity and stability of each isomer. 相似文献
117.
H. Moon S. W. Kim J. Lee S. K. Rhee E. S. Choi H. A. Kang I. H. Kim S. I. Hong 《Applied biochemistry and biotechnology》2003,111(2):65-79
As a novel feeding strategy for aptomizing human epidermal growth factor (hEGF) production with a recombinant Hansenula polymorpha DL-1 using the methanol oxidase (MOX) promoter in H. polymorpha DL-1, independent exponential feeding of two substrates was used. A simple kinetic model considering the cell growth on two
substrates was established and used to calculate the respective feeding rates of glycerol and methanol. In the fedbatch culture
with methanol-only feeding, the optimal set point of specific growth rate on methanol was found to be 0.10 h−1. When the fed-batch cultures were conducted by the independent feeding of glycerol and methanol, the actual specific growth
rate on glycerol and methanol was slightly lower than the set point of specific growth rate. By the uncoupled feeding of glycerol
and methanol the volumetric productivity of hEGF increased from 6.4 to 8.0 mg/(L·h), compared with methanol-only feeding. 相似文献
118.
原油乳状液破乳的动态法研究 总被引:5,自引:0,他引:5
The stability of different crude oil emulsions from ASP flooding production well is studied by the method of a stirred tank. The demulsifying of crude-oil emulsion by different demulsifying agents is discussed. The breakage of the crude oil emulsions from the well PO11 by the different types and concentrations of the emulsifying agents is also discussed. The breaking mechanism of the demulsifying agent is described microscopically. 相似文献
119.
Kang De Yao Tao Peng Han Bao Feng Yu Ying He 《Journal of polymer science. Part A, Polymer chemistry》1994,32(7):1213-1223
The aqueous swelling kinetics of a series of crosslinked chitosan (cr-CS) with glutaraldehyde (GA) interpenetrating polyether hydrogels have been studied as functions of pH, the N-deacetylation degree of chitosan, the amount of crosslinking agent, the electrolyte composition in solution, temperature, and gel composition. Based on these results, the swelling mechanism of the hydrogels was discussed. The release profiles of chlorhexidini acetas from the semi-IPN were also investigated. © 1994 John Wiley & Sons, Inc. 相似文献
120.
Sungzong Kang 《Journal of Molecular Structure》1973,17(1):127-142
The energy calculations using the INDO molecular orbital method and classical potential function show that the syn conformation of pyrimidine nucleosides having the C(2')-endo or C(2')-endo-C(3')-endo sugar ring puckering is as stable as the corresponding anti form.The O(2')-O(2') base-ribose hydrogen bonding significantly alters the ΦCN conformation by confining the allowed ΦCN ranges to about 150–210°. 相似文献