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排序方式: 共有6139条查询结果,搜索用时 15 毫秒
71.
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73.
Huang XJ Im HS Yarimaga O Kim JH Lee DH Kim HS Choi YK 《The journal of physical chemistry. B》2006,110(43):21850-21856
Carboxylated single-walled carbon nanotubes (SWCNT) chemically assembled on gold substrate was employed as netlike electrode to investigate the charge-transfer process and electrode process kinetics using uric acid as an example. The electrochemical behavior of uric acid in carboxylated SWCNT system was investigated using cyclic voltammetry, chronoamperometry, and single potential time-based techniques. The properties of raw SWCNT electrode were also studied for comparison purpose. Uric acid has better electrochemical behavior whereas ascorbic acid has no effective reaction on the carboxylated SWCNT electrode. Cyclic voltammograms indicate that the assembled carboxylated SWCNT increases more active sites on electrode surface and slows down the electron transfer between the gold electrode and uric acid in solution. The charge-transfer coefficient (alpha) for uric acid and the rate constant (k) for the catalytic reaction were calculated as 0.52 and 0.43 s(-1), respectively. The diffusion coefficient of 0.5 mM uric acid was 7.5 x 10(-6) cm2 x s(-1). The results indicate that electrode process in the carboxylated SWCNT electrode system is governed by the surface adsorption-controlled electrochemical process. 相似文献
74.
Choi JC Kohno K Masuda D Yasuda H Sakakura T 《Chemical communications (Cambridge, England)》2008,(6):777-779
Iron triflate, in situ-formed from FeCl3 and triflic acid, or FeCl3 and silver triflate efficiently catalyse the intermolecular addition of carboxylic acids to various alkenes to yield carboxylic esters; the reaction is applicable to the synthesis of unstable esters, such as acrylates. 相似文献
75.
Yoon SH Moon JH Choi KM Kim MS 《Rapid communications in mass spectrometry : RCM》2006,20(14):2201-2208
A deflection system consisting of four deflectors was designed and used to reduce the interference from post-source decay (PSD) product ions in photodissociation (PD) tandem time-of-flight (TOF) mass spectrometry. For simple protonated peptides generated by matrix-assisted laser desorption/ionization, the presence of PSD product ions at the laser irradiation spot was found to noticeably alter the minor peaks in the PD spectra even though the major ones were hardly affected. Other benefits from the use of the deflection system such as the improvement in the resolving power in PSD tandem mass spectra are discussed. 相似文献
76.
TiO(2) sensitized by derivatized ruthenium bipyridyl complexes has been intensively investigated as a tool to utilize visible light. This article describes an alternative approach to attaching ruthenium complex sensitizers at the TiO(2)/H(2)O interface, which is a much simpler and more efficient way to produce hydrogen. The surface of TiO(2) particles are simply coated with perfluorosulfonate polymer (cation-exchange resin: Nafion), and then Ru(bpy)(3)(2+) (as a cationic form), whose bipyridyl ligands are not functionalized with carboxylic acid groups, are bound within the Nafion layer through electrostatic attraction. The visible-light-induced production of H(2) on Nf/TiO(2) using simple Ru(bpy)(3)(2+) as a sensitizer is far more efficient than that on Ru(dcbpy)(3)-TiO(2), upon which many sensitized photoelectrochemical conversion systems are based. Effects of various experimental parameters such as pH, concentration of Ru(bpy)(3)(2+), Nafion loading, and the kind of TiO(2) were investigated. Under optimized conditions, the H(2) production rate was about 80 mumol/h, which corresponds to an apparent photonic efficiency of 2.6%. The roles of the Nafion layer on TiO(2) in the sensitized H(2) production are proposed to be twofold: to provide binding sites for cationic sensitizers and to enhance the local activity of protons in the surface region. 相似文献
77.
S.-Y. Jeon M.-B. Choi J.-H. Hwang E. D. Wachsman Sun-Ju Song 《Journal of Solid State Electrochemistry》2012,16(2):785-793
The oxygen excess nonstoichiometry of La2NiO4 + δ
is measured as a function of temperature and oxygen partial pressure (pO2) by coulometric titration method. A positive deviation from the ideal dilution solution behavior is exhibited, and the partial
molar thermodynamic quantities of La2NiO4 + δ
are calculated from the Gibbs–Helmholtz equation for regular solution by introducing the activity coefficient of the charge
carriers. The activity coefficient of holes is successfully calculated by using the Joyce–Dixon approximation of the Fermi–Dirac
integral. The effective mass of holes (
m\texth* m_{\text{h}}^{{*}} ) is 1.27–1.29 times the rest mass (m
h), which indicate the action of band-like conduction and allow the effect of the small degree of polaron hopping to be ignored.
The activity coefficient of holes calculated against the oxygen nonstoichiometry clearly illustrates the early positive deviation
of the activity coefficient of holes from unit, leading to
g\texth · \gamma_{{{\text{h}}^{ \bullet }}} ≈ 14 at δ ≈ 0.08, which is quite close to the literature value of
g\texth · \gamma_{{{\text{h}}^{ \bullet }}} ≈ 10 at δ ≈ 0.08. All the evaluated thermodynamic quantities are in good agreement with the experimental literature values. 相似文献
78.
Ju Yong Lee Hye Kyeong Min Donghoon Choi Myeong Hee Moon 《Journal of chromatography. A》2010,1217(10):1660-1666
This study describes a coupled analytical method to carry out the systematic profiling of phospholipids (PLs) in high-density lipoproteins (HDL) and low-density lipoproteins (LDL) from human blood plasma. HDL and LDL of healthy human plasma samples were separated by size and collected on a semi-preparative scale using multiplexed hollow fiber flow field-flow fractionation (MxHF5). Phospholipid mixtures contained in the resulting HDL and LDL fractions were analyzed by shotgun nanoflow liquid chromatography–tandem mass spectrometry (nLC–ESI-MS–MS). We utilized a dual scan method for the separation and simultaneous characterization of complicated PL mixtures by nLC–ESI-MS–MS, such that phosphatidylcholine (PC) and phosphatidylethanolamine (PE) molecules were detected in positive ion mode in a first LC run. In a second LC run, phosphatidylinositol (PI), phosphatidylglycerol (PG), and phosphatidic acid (PA) were detected in negative ion mode. In this study, a total of 56 PLs from HDL and 52 PLs from LDL particles were characterized by their molecular structures from data dependent collision-induced dissociation (CID) experiments, and their relative abundances were compared. 相似文献
79.
80.
Giseop Kwak Hong‐Qing Wang Kyu‐Han Choi Kyu‐Ho Song Soon‐Hak Kim Hyeok‐Soo Kim Sam‐Jong Lee Ho‐Young Cho Eon‐Ju Yu Hyo‐Jeong Lee Eun‐Jung Park Lee‐Soon Park 《Macromolecular rapid communications》2007,28(12):1317-1324
New poly(diphenylacetylene)s with alkoxy and fluoroalkyl groups as electron‐donating and electron‐withdrawing groups, respectively, were synthesized by using a WCl6‐n‐Ph4Sn catalyst. The polymer solutions emitted strong, bluish‐green lights when photo‐excited. The polymers that contained the electron‐donating alkoxy groups showed longer fluorescence‐maximum peaks when compared to the polymers that contained the electron‐withdrawing fluoroalkyl groups. However, such an effect of the substituent on the absorption property was not clearly seen. The emission bands of the solid films did not show any significant red shift, relative to that of the dilute solution.