排序方式: 共有31条查询结果,搜索用时 15 毫秒
1.
2.
制备了甘氨酸-壳聚糖复合膜修饰玻碳电极(Gly-CTS/GCE),研究了抗坏血酸(AA)和尿酸(UA)在该修饰电极上的电化学行为。结果表明在pH=5.59的磷酸盐缓冲溶液中,AA、UA在Gly-CTS/GCE上均产生灵敏的不可逆氧化峰,其峰电流与浓度在一定范围内呈良好的线性关系。对AA和UA混合溶液平行测定7次,相对标准偏差分别为4.6%、2.9%,表明该电极重现性和稳定性良好。AA、UA在Gly-CTS/GCE电极上的氧化峰峰电位相差340mV,据此可实现对二者的同时检测,并可应用于实际样品测定。 相似文献
3.
C70X2(X=H,F, Cl)的稳定性和电子光谱 总被引:1,自引:0,他引:1
用INDO方法研究C70H2四种异构体的稳定性, 表明其最稳定异构体为1, 9-C70H2和7, 8-C70H2, 两者能量差为16.3KJ.mol^-^1, 与实验值及ab initio计算值接近; 光谱计算表明, 其特征吸收峰与实验值一致。在此基础上预测C70F2和C70Cl2的稳定性和电子光谱, 表明C70F2四种异构体的稳定性顺序与C70H2一致, 而C70Cl2则以21, 42-异构体最为稳定。二者的电子光谱与C70H2极其相似只是在500nm以上有细微差别。 相似文献
4.
5.
Devaraj NK Dinolfo PH Chidsey CE Collman JP 《Journal of the American Chemical Society》2006,128(6):1794-1795
We demonstrate selective functionalization of independently addressed microelectrodes by electrochemical activation and deactivation of a coupling catalyst. 1,2,3-Triazole formation between terminal acetylenes and organic azides is efficiently catalyzed by copper(I) complexes (a Sharpless "click" reaction), while the oxidized copper(II) complexes are inactive. By electrochemically activating or deactivating the catalyst by switching its redox state, we demonstrate control over triazole formation between surface-immobilized azides and ethynylferrocene. The reaction proceeds on the time scale of minutes using submicromolar concentration of reactants and catalyst, requires mild potentials for catalyst activation and deactivation, and works in aqueous and mixed aqueous-organic solvents. By appropriate biasing of each electrode, we selectively modify one of two chemically identical 10-mum-wide electrodes separated by 10 mum in an interdigitated array. The ability to switch on or off the reaction by electrical addressing together with the chemoselectivity of this reaction makes Cu(I)-catalyzed triazole formation an ideal method for the chemical modification of multielectrode arrays. 相似文献
6.
James A. Shymansky Sandra Enger Jennifer L. Chidsey Larry D. Yore Margaret Jorgensen Laura Henriques Edward W. Wolfe 《School science and mathematics》1997,97(4):172-183
The Iowa Assessment Project was funded by the National Science Foundation to explore the feasibility of combining the expertise of science teachers, science educators, and test developers to build innovative performance assessments that complement traditional, norm-referenced, multiple-choice science tests. The science teachers, graduate students, and science educators designed and tested performance assessment tasks to enhance the picture of science understanding in students through multiple points of evidence. This paper describes the design of four science performance tasks for Grade 9 students and the relationship between their performance on these tasks and multiple-choice items in the Iowa Tests of Educational Development. Students and schools used to develop the tasks were not included in the verification sample. 相似文献
7.
Smalley JF Finklea HO Chidsey CE Linford MR Creager SE Ferraris JP Chalfant K Zawodzinsk T Feldberg SW Newton MD 《Journal of the American Chemical Society》2003,125(7):2004-2013
The standard heterogeneous electron-transfer rate constants between substrate gold electrodes and either ferrocene or pentaaminepyridine ruthenium redox couples attached to the electrode surface by various lengths of an alkanethiol bridge as a constituent of a mixed self-assembled monolayer were measured as a function of temperature. The ferrocene was either directly attached to the alkanethiol bridge or attached through an ester (CO(2)) linkage. For long bridge lengths (containing more than 11 methylene groups) the rate constants were measured using either chronoamperometry or cyclic voltammetry; for the shorter bridges, the indirect laser induced temperature jump technique was employed to measure the rate constants. Analysis of the distance (bridge length) dependence of the preexponential factors obtained from an Arrhenius analysis of the rate constant versus temperature data demonstrates a clear limiting behavior at a surprisingly small value of this preexponential factor (much lower than would be expected on the basis of aqueous solvent dynamics). This limit is independent of both the identity of the redox couple and the nature of the linkage of the couple to the bridge, and it is definitely different (smaller) from the limit derived from an equivalent analysis of the rate constant (versus temperature) data for the interfacial electron-transfer reaction through oligophenylenevinylene bridges between gold electrodes and ferrocene. There are a number of possible explanations for this behavior including, for example, the possible effects of bridge conformational flexibility upon the electron-transfer kinetics. Nevertheless, conventional ideas regarding electronic coupling through alkane bridges and solvent dynamics are insufficient to explain the results reported here. 相似文献
8.
Devaraj NK Miller GP Ebina W Kakaradov B Collman JP Kool ET Chidsey CE 《Journal of the American Chemical Society》2005,127(24):8600-8601
A chemoselective route to routinely and rapidly attach oligonucleotide probes to well-defined surfaces is presented. Cu(I) tris(benzyltriazolylmethyl)amine-catalyzed coupling of terminal acetylenes to azides on a self-assembled monolayer is used instead of traditional nucleophilic-electrophilic coupling reactions. The reaction proceeds well even in the presence of purposely introduced nucleophilic and electrophilic impurities. The density of oligonucleotide probes can be controlled by controlling the amount of azide functionality. Although most of our work was done on gold surfaces, this technique should be readily applicable to any surface on which an azide-containing monolayer can be assembled as we have preliminarily demonstrated by derivatizing azidotrimethoxysilane-modified glass slides with fluorescein-containing oligonucleotides. 相似文献
9.
McCrory CC Devadoss A Ottenwaelder X Lowe RD Stack TD Chidsey CE 《Journal of the American Chemical Society》2011,133(11):3696-3699
A Cu(I) complex of 3-ethynyl-phenanthroline covalently immobilized onto an azide-modified glassy carbon surface is an active electrocatalyst for the four-electron (4-e) reduction of O(2) to H(2)O. The rate of O(2) reduction is second-order in Cu coverage at moderate overpotential, suggesting that two Cu(I) species are necessary for efficient 4-e reduction of O(2). Mechanisms for O(2) reduction are proposed that are consistent with the observations for this covalently immobilized system and previously reported results for a similar physisorbed Cu(I) system. 相似文献
10.
McCrory CC Ottenwaelder X Stack TD Chidsey CE 《The journal of physical chemistry. A》2007,111(49):12641-12650
Mononuclear Cu complexes with a 1,10-phenanthroline-based ligand adsorbed onto an edge-plane graphite electrode act as electrocatalysts for the 4-electron reduction of O2 to H2O. A mechanism is proposed for the electrocatalytic O2 reduction that accounts for the observed redox and kinetic dependences on coordinating anions and proton donors in the buffer. Systematic increases of ligand electron-withdrawing properties and/or the steric demands near the Cu center increase the E0 of the Cu catalysts but decrease the rate of O2 reduction. The kinetic rate of O2 reduction at E0, reported as kinetic current divided by catalyst redox charge, decreases as E0 increases: from 16 s(-1) measured at E0 in air-saturated solutions for adsorbed Cu(phen) to 0.4 s(-1) for Cu(2,9-Et2-phen). The maximum value of E for which catalytic activity can be attained is estimated to be +350 mV vs NHE. Near E0, the kinetic current deviates from that expected if O2 binding were the sole rate-limiting step. This indicates that one or more of the electrochemical reduction steps are rate limiting at potentials near E0. 相似文献