High-throughput electrochemistry (HTP): a new approach to the rapid development of modified carbon electrodes

The major aim of this project was development of novel covalently modified glassy carbon electrodes for application in NADH-dependent biosensors using combinatorial and high-throughput methods. Studies on transition metal complexes containing redox active 1,1-phenanthroline-5,6-dione (phendione) ligand(s) showed they are effective electrocatalysts for oxidation of NADH. In order to covalently tether the metal complexes at the GC surface, the design of GC electrodes modified with novel metal complexes bearing phendione ligand(s) was proposed based on sequential electrochemical and solid-phase synthesis methods. Initial work involved optimisation of the process for modification of individual GC electrodes. Firstly, following earlier work, the GC electrodes were electrochemically functionalised by primary amines or a diazonium salt bearing Boc-protected amine groups, which allowed introduction of chelating ligands at the GC surface under solid-phase coupling conditions. The final step involved coordination of the bidentate ligand at the GC surface to the metal centre and formation of novel metal complexes under solid-phase coupling conditions. The successfully modified individual electrodes were applied in the design of a library of GC electrodes modified with different linkers, ligands and metal complexes and prepared in a combinatorial and parallel way. The library was electrochemically screened in a high-throughput way using a multichannel potentiostat, which allowed instant comparison of electrochemical and electrocatalytic properties between different members of the library. The experimental data extracted from HTP screening of the library were used for evaluation of a) the surface coverage obtained for different library members; b) the catalytic activity towards NADH oxidation and c) the kinetics parameters kcat and KM for the electrocatalytic oxidation of NADH for all members of the library

Synthesis of a rotaxane CuI Triazolide under aqueous conditions

We describe the serendipitous isolation of a stable, neutral, monomeric mechanically interlocked CuI triazolide under aqueous conditions. This “trapped” intermediate of the CuAAC catalytic cycle is sterically protected from reprotonation by the rotaxane architecture, which renders the CuI–C bond stable toward moisture and air—even carboxylic acids protonate the CuI–C bond only slowly. The isolation of this remarkably stable CuI organometallic points toward potential applications of mechanical bonding in the study of reactive intermediates

Electrografting of Mono-N-Boc-Ethylenediamine from an Acetonitrile/Aqueous NaHCO3 Mixture

碳电极表面的伯胺电嫁接被广泛地应用于电极表面改性. 本文通过比较发现，在比例为4:1的乙腈和0.1 mol•L-1 碳酸氢钠溶液混合物中，玻碳电极表面嫁接上叔丁氧羟基-乙二胺的效率比在单纯的乙腈中显著提高. 有碳氢酸钠存在时，循环伏安测得电极的初始电流增大，表明电极表面胺嫁接层的形成更快速，从而使得电极表面更容易钝化，导致乙二胺-叔丁氧羟基膜层更严重地阻碍[Fe(CN)6]3-. 的反应. 通过去除叔丁氧羟基保护层，在蒽醌-2-羧酸上接自由胺，可获得较高的蒽醌表面覆盖度. 采用简单动力学模型模拟了电嫁接反应，结果表明，模拟得到的循环伏安曲线与实验测得的循环伏安曲线相一致. 对比在单纯乙腈和乙腈/碳酸氢钠溶液混合物中模型拟合得到的参数值可知，胺自由基与碳表面的反应和在均相溶液中的反应相互竞争，更有利于乙腈与碳氢酸钠的表面反应.The electrografting of primary amines to carbon electrodes is now widely employed for electrode modification. Using a mixture of acetonitrile and 0.1 mol•L-1 aqueous sodium hydrogen carborate (NaHCO3) in the ratio of 4:1, the efficiency for coupling of mono-N-Boc-ethylenediamine (EDA-Boc) on the surface of glassy carbon was significantly improved as compared with that obtained using acetonitrile alone. In the presence of NaHCO3 the initial current determined in the cyclic voltammogram became higher, and the layer of attached amine was formed more rapidly, accordingly, the electrode was passivated more rapidly. The resulting film of EDA-Boc was shown to be more severely blocking toward the electrochemical reaction of [Fe(CN)6]3-. Following removal of the Boc protecting group and coupling of the free amine to anthraquinone-2-carboxylic acid, a higher surface coverage of the anthraquinone was obtained. Modelling for the electrograftng reaction using a simple kinetic scheme, it was demonstrated that the simulated voltammograms agreed well with the experimentally measured voltammograms . Comparison between the model fitting parameters obtained from the acetonitrile alone and the acetonitrile/NaHCO3 mixture showed that the competition between reaction of the amine radicals with the carbon surface and reaction in the homogeneous solution became more favourable for the surface reaction in the acetonitrile/NaHCO3 mixture.H. Hamzah would like to thank the Majlis Amanah Rakyat Malaysia (MARA) for the PhD scholarship. P. Bartlett gratefully acknowledges receipt of a Wolfson Research Merit award.H. Hamzah would like to thank the Majlis Amanah Rakyat Malaysia (MARA) for the PhD scholarship. P. Bartlett gratefully acknowledges receipt of a Wolfson Research Merit award.作者联系地址：1. 南安普顿大学化学系，英国南安普顿，SO17 1AL；2. 伦敦大学玛丽女王学院，生物与化学科学学院，英国伦敦，E1 4NS；3. 阿伯丁大学国王学院，英国阿伯丁，AB24 3FXAuthor's Address: 1. Chemistry, University of Southampton, Southampton, SO171AL, UK; 2. School of Biological and Chemical Sciences Queen Mary University of London, Mile End Road, London, E1 4NS, UK; 3. King’s College, The University of Aberdeen, Aberdeen, AB24 3FX, UK通讯作者E-mail：[email protected]

Synthesis of a Rotaxane Cu^I Triazolide under Aqueous Conditions

We describe the serendipitous isolation of a stable, neutral, monomeric mechanically interlocked Cu^I triazolide under aqueous conditions. This “trapped” intermediate of the CuAAC catalytic cycle is sterically protected from reprotonation by the rotaxane architecture, which renders the Cu^I–C bond stable toward moisture and aireven carboxylic acids protonate the Cu^I–C bond only slowly. The isolation of this remarkably stable Cu^I organometallic points toward potential applications of mechanical bonding in the study of reactive intermediates

Synthesis of a Rotaxane Cu^I Triazolide under Aqueous Conditions

We describe the serendipitous isolation of a stable, neutral, monomeric mechanically interlocked Cu^I triazolide under aqueous conditions. This “trapped” intermediate of the CuAAC catalytic cycle is sterically protected from reprotonation by the rotaxane architecture, which renders the Cu^I–C bond stable toward moisture and aireven carboxylic acids protonate the Cu^I–C bond only slowly. The isolation of this remarkably stable Cu^I organometallic points toward potential applications of mechanical bonding in the study of reactive intermediates

Covalent modification of glassy carbon surface with organic redox probes through diamine linkers using electrochemical and solid-phase synthesis methodologies

Various mono-Boc-protected diamines have been covalently grafted to glassy carbon electrodes by electrochemical oxidation of the free amine. After deprotection of the Boc group, anthraquinone and nitrobenzene probes were coupled to the linkers using solid-phase coupling reactions. X-Ray photoelectron spectroscopy and cyclic voltammetry were used to monitor the coupling efficiency, effect of linker length on the surface coverage and electron transfer between the attached redox probes and electrode. The anthraquinone surface coverage was found to decrease as the chain length of alkyl diamine linker increased and the electron transfer kinetics were found to be faster for the lower coverages and the longer, more flexible linkers. In the case of nitrobenzene, there was only a slightly change in coverage with increasing linker length. This electrochemical attachment of protected diamine linkers followed by solid-phase coupling provides a very versatile methodology for attaching a wide range of molecular architectures onto glassy carbon surfaces

High-Throughput Synthesis and Electrochemical Screening of a Library of Modified Electrodes for NADH Oxidation

We report the combinatorial preparation and high-throughput screening of a library of modified electrodes designed to catalyze the oxidation of NADH. Sixty glassy carbon electrodes were covalently modified with ruthenium­(II) or zinc­(II) complexes bearing the redox active 1,10-phenanthroline-5,6-dione (phendione) ligand by electrochemical functionalization using one of four different linkers, followed by attachment of one of five different phendione metal complexes using combinatorial solid-phase synthesis methodology. This gave a library with three replicates of each of 20 different electrode modifications. This library was electrochemically screened in high-throughput (HTP) mode using cyclic voltammetry. The members of the library were evaluated with regard to the surface coverage, midpeak potential, and voltammetric peak separation for the phendione ligand, and their catalytic activity toward NADH oxidation. The surface coverage was found to depend on the length and flexibility of the linker and the geometry of the metal complex. The choices of linker and metal complex were also found to have significant impact on the kinetics of the reaction between the 1,10-phenanthroline-5,6-dione ligand and NADH. The rate constants for the reaction were obtained by analyzing the catalytic currents as a function of NADH concentration and scan rate, and the influence of the surface molecular architecture on the kinetics was evaluated