- Self-assembled monolayers of isocyanides on nickel electrodes
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(Figure Presented) Alligator clip on a nickel electrode: Monolayers of ferrocenyl-terminated isocyanides are strongly chemisorbed on nickel surfaces (see picture). The nickel-isocyanide interaction has a parallel binding mode, and the monolayers have higher thermal stability in boiling ethanol than thiol monolayers on gold. The nickel-isocyanide monolayers could be useful in molecular electronics.
- Lee, Youngu,Morales, Gustavo M.,Yu, Luping
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- Anion-induced adsorption of ferrocenated nanoparticles
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Au nanoparticles fully coated with ω-ferrocenyl hexanethiolate ligands, with average composition Au225(ω-ferrocenyl hexanethiolate)43, exhibit a unique combination of adsorption properties on Pt electrodes. The adsorbed layer is so robust that electrodes bearing submonolayer, monolayer, and multilayer quantities of these nanoparticles can be transferred to fresh electrolyte solutions and there exhibit stable ferrocene voltammetry over long periods of time. The kinetics of forming the robustly adsorbed layer are slow; monolayer and submonolayer deposition can be described by a rate law that is first order in nanoparticle concentration and in available electrode surface. The adsorption mechanism is proposed to involve entropically enhanced (multiple) ion-pair bridges between oxidized (ferrocenium) sites and certain specifically adsorbed electrolyte anions on the electrode. Adsorption is promoted by scanning to positive potentials (through the ferrocene wave) and by high concentrations of Bu 4N+X- electrolyte (X- = ClO 4-, PF6-) in the CH 2Cl2 solvent; there is no adsorption if X- = p-toluenesulfonate or if the electrode is coated with an alkanethiolate monolayer. The electrode double layer capacity is not appreciably diminished by the adsorbed ferrocenated nanoparticles, which are gradually desorbed by scanning to potentials more negative than the electrode's potential of zero charge. At very slow scan rates, voltammetric current peaks are symmetrical and nearly reversible, but exhibit Efwhm considerably narrower (typically 35 mV) than ideally expected (90.6 mV, at 298 K) for a one-electron transfer or for reactions of multiple, independent redox centers with identical formal potentials. The peak narrowing is qualitatively explicable by a surface-activity effect invoking large, attractive lateral interactions between nanoparticles and, or alternatively, by a model in which ferrocene sites react serially at formal potentials that become successively altered as ion-pair bridges are formed. At faster scan rates, both ΔEpeak and Efwhm increase in a manner consistent with a combination of uncompensated ohmic resistance of the electrolyte solution and of the adsorbed film, as distinct from behavior produced by slow electron transfer.
- Stiles, Rebecca L.,Balasubramanian, Ramjee,Feldberg, Stephen W.,Murray, Royce W.
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- Derivatisation of microcystin with a redox-active label for high-performance liquid chromatography/electrochemical detection
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Microcystins are a group of low molecular weight, cyclic peptide hepatotoxins. The most common detection and quantitation methods for these toxins are liquid chromatography with UV or mass spectrometric detections, phosphatase inhibition assays and enzyme-linked immunosorbent assays. In addition, derivatisation of these toxins with organic fluorophores followed by CE/laser induced fluorescence detection and HPLC/chemiluminescence detection; and with luminescent lanthanide chelates for competition assays have also been reported. However, the use of an electrochemical-active unit as a tag for microcystins has never been explored. Since the sulfhydryl group of 6-ferrocenylhexanethiol (Fc-C6-SH) can undergo a facile addition reaction with the α,β-unsaturated carbonyl group, this compound has been used as a redox-active labelling agent for a derivative of microcystins, microcystin-LR (MC-LR). The conjugate, Fc-MC-LR, has been isolated by high-performance liquid chromatography with electrochemical detection. The peak height-concentration curve was linear in the test range 20-400 ng of MC-LR (r value for linear regression > 0.9987). The detection limit was determined to be ca. 18 ng MC-LR (S/N ≈ 3). Meanwhile, the conjugate Fc-MC-LR has also been characterised by positive-ion electrospray-ionisation mass spectrometry. Electrochemical studies show that the adduct displays a reversible ferrocenium/ferrocene couple at ca. -0.040 V vs. SCE (scan rate = 50 mV s-1) in 0.1 M aqueous ammonium acetate-acetonitrile (55:45 v/v).
- Lo, Kenneth Kam-Wing,Ng, Dominic Chun-Ming,Lau, Jason Shing-Yip,Wu, Rudolf Shiu-Sun,Lam, Paul Kwan-Sing
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p. 274 - 279
(2007/10/03)
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