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71.
Jong Bum Lee Soong Ho Um Jeong-Woo Choi Kee-Kahb Koo 《Colloids and surfaces. B, Biointerfaces》2003,30(4):307-314
The self-assembled ferredoxin monolayer onto the (100) surface of the silicon substrate was prepared and the nonspecifically adsorbed aggregates of ferredoxin on the substrate were successfully eliminated by using a zwitterionic surfactant, 3-[(3-cholamidopropyl) dimethylammonio]-1-propanesulfonate (CHAPS). The AFM image of the self-assembled ferredoxin monolayer on the silicon substrate treated with CHAPS clearly shows that the size of ferredoxin clusters is about 20–30 nm, which is on the order of an aggregate of about five ferredoxin molecules, whereas the size of ferredoxin aggregates on the substrate without CHAPS treatment was measured to be about 100–200 nm. Those results offer a useful method for the elimination of the nonspecific adsorption of proteins onto inorganic substrates, which has been a long-term problem in the fabrication of biomolecular electronic devices by the self-assembly technique. 相似文献
72.
Dendritic chelating agents. 1. Cu(II) binding to ethylene diamine core poly(amidoamine) dendrimers in aqueous solutions 总被引:2,自引:0,他引:2
Diallo MS Christie S Swaminathan P Balogh L Shi X Um W Papelis C Goddard WA Johnson JH 《Langmuir : the ACS journal of surfaces and colloids》2004,20(7):2640-2651
This paper describes an investigation of the uptake of Cu(II) by poly(amidoamine) (PAMAM) dendrimers with an ethylenediamine (EDA) core in aqueous solutions. We use bench scale measurements of proton and metal ion binding to assess the effects of (i) metal ion-dendrimer loading, (ii) dendrimer generation/terminal group chemistry, and (iii) solution pH on the extent of binding of Cu(II) in aqueous solutions of EDA core PAMAM dendrimers with primary amine, succinamic acid, glycidol, and acetamide terminal groups. We employ extended X-ray absorption fine structure (EXAFS) spectroscopy to probe the structures of Cu(II) complexes with Gx-NH2 EDA core PAMAM dendrimers in aqueous solutions at pH 7.0. The overall results of the proton and metal ion binding measurements suggest that the uptake of Cu(II) by EDA core PAMAM dendrimers involves both the dendrimer tertiary amine and terminal groups. However, the extents of protonation of these groups control the ability of the dendrimers to bind Cu(II). Analysis of the EXAFS spectra suggests that Cu(II) forms octahedral complexes involving the tertiary amine groups of Gx-NH2 EDA core PAMAM dendrimers at pH 7.0. The central Cu(II) metal ion of each of these complexes appears to be coordinated to 2-4 dendrimer tertiary amine groups located in the equatorial plane and 2 axial water molecules. Finally, we combine the results of our experiments with literature data to formulate and evaluate a phenomenological model of Cu(II) uptake by Gx-NH2 PAMAM dendrimers in aqueous solutions. At low metal ion-dendrimer loadings, the model provides a good fit of the measured extent of binding of Cu(II) in aqueous solutions of G4-NH2 and G5-NH2 PAMAM dendrimers at pH 7.0. 相似文献
73.
The use of hyphenated LC-NMR and LC-MS techniques for the purpose of directly identifying the major constituents of Belamcanda chinensis was investigated. Reversed-phase isocratic chromatography was performed using an acetonitrile-water solvent system on a C18 column. The NMR spectrum yielded five main peaks, whose analysis revealed them to be 5, 6, 7, 3'-tetrahydroxy-4'-methoxyisoflavone (1), tectorigenin (2), iristectorigenin A (3), irigenin (4), and irisflorentine (5). The identification of these constituents was confirmed by performing LC-ESI-MS experiment. This study shows that hyphenated LC-NMR and LC-MS can be used for the rapid (70 min) identification of the isoflavonoids. 相似文献
74.
Chen D Albuquerque IF Baublis VV Bondar NF Carrigan RA Cooper PS Lisheng D Denisov AS Dobrovolsky AV Dubbs T Endler AM Escobar CO Foucher M Golovtsov VL Goritchev PA Gottschalk H Gouffon P Grachev VT Khanzadeev AV Kubantsev MA Kuropatkin NP Lach J Lang Pengfei Lebedenko VN Li Chengze Li Yunshan Mahon JR McCliment E Morelos A Newsom C Pommot Maia MC Samsonov VM Schegelsky VA Shi Huanzhang Smith VJ Sun CR Tang Fukun Terentyev NK Timm S Tkatch II Uvarov LN Vorobyov AA Yan Jie Zhao Wenheng 《Physical review letters》1992,69(23):3286-3289
75.
Foucher M Albuquerque IF Bondar NF Carrigan R Chen D Li Chengze Cooper PS Denisov AS Dobrovolsky AV Dubbs T Endler AM Escobar CO Tang Fukun Golovtsov VL Goritchev PA Gottschalk H Gouffon P Grachev VT Shi Huanzhang Yan Jie Khanzadeev AV Kubantsev MA Kuropatkin NP Lach J Luksys M Lebedenko VN Dai Lisheng Mahon JR McCliment E Morelos A Newsom C Lang Pengfei Pommot Maia MC Samsonov VM Zheng Shuchen Smith VJ Terentyev NK Timm S Tkatch II Uvarov LN Vorobyov AA Zhao Wenheng Zhong Yuanyuan 《Physical review letters》1992,68(20):3004-3007
76.
77.
Robert M. Adlington Jack E. Baldwin William MC Coull Gareth J. Pritchard Christopher J. Schofield Nicholas J. Westwood 《合成通讯》2013,43(21):3803-3813
N-Arylsulfonylation of 2-azetidinones can lead to the diastereoselective formation of oligomerization products. However, a simple increase of arylsulfonyl chloride concentration minimized oligomerization and allowed preparation of 1-arylsulfonyl-2-azetidinones in good yield. 相似文献
78.
Kyung Jae Kim Bara Kim Ji Won Um Jung Je Son Bong Dae Choi 《Annals of Operations Research》2008,162(1):85-107
Extended real time polling service (ErtPS) is added to IEEE 802.16e-2005 standards in order for VoIP service to use uplink
resources efficiently by considering on/off characteristic of voice source. Recently average queueing delay of ErtPS algorithm
for VoIP service was investigated, and it was shown that ErtPS allows to admit more users than UGS algorithm. But we need
the probability distribution of queueing delay rather than average queueing delay in order to provide a necessary information
for QoS. In this paper we obtain the probability distribution of queueing delay of ErtPS for VoIP service by using the matrix
analytic method for the GI/M/1 type and the M/G/1 type matrices in cases of the service time being exponential and deterministic respectively. By applying the results on
deterministic service time we find the maximum allowable number of VoIP users with the required constraint on queueing delay.
This research was supported by the MIC (Ministry of Information and Communication), Korea, under the ITRC (Information Technology
Research Center) support program supervised by the IITA (Institute of Information Technology Assessment). 相似文献
79.
A kinetic study is reported for aminolysis of 4-pyridyl X-substituted-benzoates 5a-i. Plots of pseudo-first-order rate constants (k(obsd)) vs [amine] curve upward for the reactions of substrates possessing a strong electron-withdrawing group in the benzoyl moiety (5a-d) but are linear for the reactions of those bearing an electron-donating group (5e-i), indicating that the electronic nature of substituent X governs the reaction mechanism. The k(1)k(2)/k(-1) and k(1)k(3)/k(-1) values were calculated from the intercept and slope of the linear plots of k(obsd)/[amine] vs [amine], respectively. The Hammett plot for k(1)k(2)/k(-1) consists of two intersecting straight lines, while the Yukawa-Tsuno plot exhibits an excellent linear correlation with ρ(X) = 0.41 and r = 1.58, implying that the nonlinear Hammett plot is not due to a change in rate-determining step but is caused by stabilization of substrates possessing an electron-donating group through resonance interactions. The small ρ(X) suggests that the k(2)/k(-1) ratio is little influenced by the nature of substituent X. The Br?nsted-type plots for aminolysis of 4-pyridyl 3,5-dinitrobenzoate 5a are linear with β(nuc) = 0.98 and 0.79 for k(1)k(2)/k(-1) and k(1)k(3)/k(-1), respectively. The effect of amine basicity on the microscopic rate constants is also discussed. 相似文献
80.
The concept of reaction severity, which combines residence time and temperature, is often used in the pulp and paper and biorefining industries. The influence of corn stover pretreatment severity on yield of sugar and major degradation products and subsequent effects on enzymatic cellulose hydrolysis was investigated. The pretreatment residence time and temperature, combined into the severity factor (Log R o), were varied with constant acid concentration. With increasing severity, increasing concentrations of furfural and 5-hydroxymethylfurfural (5-HMF) coincided with decreasing yields of oligosaccharides. With further increase in severity factor, the concentrations of furans decreased, while the formation of formic acid and lactic acid increased. For example, from severity 3.87 to 4.32, xylose decreased from 6.39 to 5.26?mg/mL, while furfural increased from 1.04 to 1.33?mg/mL; as the severity was further increased to 4.42, furfural diminished to 1.23?mg/mL as formate rose from 0.62 to 1.83?mg/mL. The effects of dilute acid hydrolyzate, acetic acid, and lignin, in particular, on enzymatic hydrolysis were investigated with a rapid microassay method. The microplate method gave considerable time and cost savings compared to the traditional assay protocol, and it is applicable to a broad range of lignocellulosic substrates. 相似文献