Search

Abstract: We have recently revised the oft-cited model of cation insertion into electroreduced C60 film-modified electrodes in aqueous, basic electrolytes [L. Xiao, G.G. Wildgoose, A. Crossley, R.G. Compton, The electroreduction of “C60” films in aqueous electrolyte does not lead to alkali metal ion insertion—evidence for the involvement of adventitious poly-epoxidated C60 (C60O n ), submitted for publication]. Instead we have proposed that the observed reduction corresponds to adventitious polyepoxidated C60O n within the starting material [L. Xiao, G.G. Wildgoose, A. Crossley, R.G. Compton, The electroreduction of “C60” films in aqueous electrolyte does not lead to alkali metal ion insertion—evidence for the involvement of adventitious poly-epoxidated C60 (C60O n ), submitted for publication]. In this paper, we further show, using scanning electron microscopy and cyclic voltammetry of ascorbic acid, how our alternative model can be used to explain both the voltammetric behaviour observed during the reduction of “C60” films in aqueous electrolytes, and how the structure of these films can give rise to misleading claims of apparent “electrocatalytic” behaviour. The latter arises due to restructuring of the deposited C60 film giving rise to a porous, partially blocked electrode, coupled with possible thin-layer effects. We find no evidence that C60 itself is reduced within the potential window offered by aqueous electrolytes, nor that it is involved in any form of electron mediation or electrocatalysis. [Copyright &y& Elsevier]

Abstract: In this letter, we present experimental data which challenges the model proposed since the mid-1990s that the reduction of C60 films in aqueous electrolytes involves the formation of [M+ n C60 n−] where M+ represents a metal cation or proton. Instead we provide voltammetric, XPS and UV–vis evidence that the reduction of “C60” films in aqueous media is instead the reduction of adventitious poly-epoxidated C60O n with subsequent chemically irreversible loss of “O2 −” as water, and that C60 is not reduced within the potential windows of aqueous electrolytes. [Copyright &y& Elsevier]

Gold nanoparticles (∼30–60 nm in diameter) were deposited onto the surface of glassy carbon microspheres (10–20 μm) through electroless plating to produce bulk (i.e., gram) quantities of nanoparticle surface-modified microspheres. The gold nanoparticle-modified powder was then characterized by means of scanning electron microscopy and cyclic voltammetry. The voltammetric response of a macroelectrode consisting of a film of gold nanoparticle-modified glassy carbon microspheres, bound together and ‘wired-up’ using multiwalled carbon nanotubes (MWCNTs), was investigated. We demonstrate that by intelligently exploiting both nano- and microchemical architectures and wiring up the electroactive centers using MWCNTs in this way, we can obtain macroelectrode voltammetric behavior while only using ∼1% by mass of the expensive gold material that would be required to construct the equivalent gold film macrodisk electrode. The potential utility of electrodes constructed using chemical architectures such as this was demonstrated by applying them to the analytical determination of arsenic-(III) concentration. An optimized limit of detection of 2.5 ppb was obtained. [ABSTRACT FROM AUTHOR]

A simple pH probe is developed based upon the covalent chemical derivatisation of carbon particles with anthraquinone. The amperometric response of electrodes constructed from this material is examined and shown to produce a Nernstian linear response to pH from 1 to 9, over a range of temperatures from 20 to 70 °C, consistent with a two-electron, two-proton electrochemical process. [Copyright &y& Elsevier]

The bond energy of the unsupported Au–Au bond in the Au(ii) dimer [(C∧N∧C)Au]2 and the difference between AuIII–OH and AuIII–H bond enthalpies have been determined experimentally by electrochemical methods, with Au–OH and Au–H complexes showing unexpected differences in their reduction pathways, supported by DFT modelling. [ABSTRACT FROM AUTHOR]

Abstract: CuO nanorod agglomerates were synthesised via a simple hydrothermal method in the presence of polyethylene glycol (PEG; M w 20,000). The chemical composition, size and morphology of the prepared CuO material was investigated by X-ray powder diffraction, voltammetry and transmission electron microscopy. A basal plane pyrolytic graphite electrode (bppg) was modified with the CuO nanorods and used to study the direct oxidation of glucose, fructose and sucrose in an alkaline medium (0.1M NaOH). The CuO nanorod modified electrode was shown to have far larger analytical signals in the presence of carbohydrates than an electrode modified with CuO microparticles and gave a limit of detection for glucose of 1.2×10−6 M which is comparable with the literature. As such it is a non-selective, non-enzymatic, total carbohydrate sensor. The CuO nanorod modified bppg electrode was also used for the detection of H2O2, it was shown that in this case it is preferential to look at the oxidation of the analyte due to interference of oxygen in the reductive window. A limit of detection of 2.2×10−7 M was obtained for the sensing of hydrogen peroxide in an alkaline solution. [Copyright &y& Elsevier]

The synthesis of the bimetallic permethylpentalene complexes Pn*2M2 (M = V, Cr, Mn, Co, Ni; Pn* = C8Me6) has been accomplished, and all of the complexes have been structurally characterized in the solid state by single-crystal X-ray diffraction. Pn*2V2 (1) and Pn*2Mn2 (3) show very short intermetallic distances that are consistent with metal-metal bonding, while the cobalt centers in Pn*2Co2 (4) exhibit differential bonding to each side of the Pn ligand that is consistent with an η5:η³ formulation. The Pn* ligands in Pn*2Ni2 (5) are best described as η³:η³-bonded to the metal centers. ¹H NMR studies indicate that all of the Pn*2M2 species exhibit D2h molecular symmetry in the solution phase; the temperature variation of the chemical shifts for the resonances of Pn*2Cr2 (2) indicates that the molecule has an S = 0 ground state and a thermally populated S = 1 excited state and can be successfully modeled using a Boltzmann distribution (ΔH° = 14.9 kJ mol-1 and ΔS° = 26.5 J K-1 mol-1). The solid-state molar magnetic susceptibility of 3 obeys the Curie-Weiss law with μeff = 2.78μB and θ = -1.0 K; the complex is best described as having an S = 1 electronic ground state over the temperature range 4-300 K. Paradoxically, attempts to isolate the "double ferrocene" equivalent, Pn*2Fe2, led only to the isolation of the permethylpentalene dimer Pn*2 (6). Solution electrochemical studies were performed on all of the organometallic compounds; 2-5 exhibit multiple quasi-reversible redox processes. Density functional theory calculations were performed on this series of complexes in order to rationalize the observed structural and spectroscopic data and provide estimates of the M-M bond orders. [ABSTRACT FROM AUTHOR]

Abstract: The direct electrochemistry of a HRP–chi–[C4mim][BF4] film (where HRP = horseradish peroxidase, chi = chitosan, and [C4mim][BF4] = the room temperature ionic liquid (RTIL) 1-butyl-3-methylimidazolium tetrafluoroborate) has been studied by cyclic voltammetry on a glassy carbon electrode. The mechanism for the electrochemical reaction of HRP is suggested to be EC for the reduction, and CE for the following re-oxidation, as the oxidative peak potential remained approximately unchanged across the scan rate range. The half wave potential of HRP reduction was found to be pH dependent, suggesting that a concomitant proton and electron transfer is occurring. Using theoretical simulations of the experimentally obtained peak positions, the standard electron transfer rate constant, k 0, was found to be 98 (±16) s−1 at 295 K in pH 7 phosphate buffer solution, which is very close to the value reported in the absence of ionic liquid. This suggests that the ionic liquid used here in the HRP–chi–[C4mim][BF4]/GC electrode does not enhance the rate of electron transfer. k 0 was found to increase systematically with increasing temperature and followed a linear Arrhenius relation, giving an activation energy of 14.20 kJ mol−1. The electrode kinetics and activation energies obtained are identical to those reported for HRP films in aqueous media. This leads us to question if the use of RTIL films provide any unique benefits for enzyme/protein voltammetry. Rather the films may likely contain aqueous zones in which the enzymes are located and undergo electron transfer. [Copyright &y& Elsevier]

Abstract: We report the first construction of a random array of boron doped diamond (BDD) nano-disc electrodes (RAN BDD), formed by a simple three-step method. First molybdenum(IV) dioxide nanoparticles are electrodeposited onto a BDD substrate. Second the electrode surface is covered in an insulating polymer film by the electropolymerization of a 4-nitrophenyldiazonium salt. Third the molybdenum dioxide nanoparticles are dissolved from the BDD surface (removing the polymer layer directly above them only) using dilute hydrochloric acid to expose nano-discs of BDD, ca. 20±10nm in diameter surrounded by a polymer insulating the remainder of the BDD. This method produces up to 650±25million BDD nano-disc electrodes per cm2. Various RAN BDD electrodes were produced using this method with a similar distribution of nano-disc size and number density, confirming that this is a reliable and reproducible method of manufacturing such nanoelectrode arrays. At modest scan rates the RAN BDD array was found to produce peak currents approaching that of the Randles–Ševčík limit for the equivalent geometric electrode area despite the fact that most of the surface was insulated by the polymer as shown by voltammetry and atomic force microscopy. The experimental results are compared with simulations of both ordered and random arrays of nano-disc electrodes, the results of which demonstrate that the maximum current obtainable at such arrays is that predicted by the Randles–Ševčík equation. The array of BDD nano-discs shows a significantly reduced capacitive background current compared to the bare BDD electrode, suggesting that such devices may offer improved signal resolution in electroanalytical measurements. [Copyright &y& Elsevier]

We herein explore whether tris(aryl)borane Lewis acids are capable of cleaving H2 outside of the usual Lewis acid/base chemistry described by the concept of frustrated Lewis pairs (FLPs). Instead of a Lewis base we use a chemical reductant to generate stable radical anions of two highly hindered boranes: tris(3,5‐dinitromesityl)borane and tris(mesityl)borane. NMR spectroscopic characterization reveals that the corresponding borane radical anions activate (cleave) dihydrogen, whilst EPR spectroscopic characterization, supported by computational analysis, reveals the intermediates along the hydrogen activation pathway. This radical‐based, redox pathway involves the homolytic cleavage of H2, in contrast to conventional models of FLP chemistry, which invoke a heterolytic cleavage pathway. This represents a new mode of chemical reactivity for hydrogen activation by borane Lewis acids. [ABSTRACT FROM AUTHOR]

We herein report the synthesis of novel "Janus" calix[4]arenes bearing four "molecular tethering" functional groups on either the upper or lower rims of the calixarene. These enable facile multipoint covalent attachment to electrode surfaces with monolayer coverage. The other rim of the calixarenes bear either four azide or four ethynyl functional groups, which are easily modified by the copper(I)-catalyzed azide-alkyne cycloaddition reaction (CuAAC), either pre- or postsurface modification, enabling these conical, nanocavity reactor sites to be decorated with a wide range of substrates to impart desired chemical properties. Redox active species decorating the peripheral rim are shown to be electrically connected by the calixarene to the electrode surface in either "up" or "down" orientations of the calixarene. [ABSTRACT FROM AUTHOR]

Three structural isomers of tris{bis(trifluoromethyl)phenyl}borane have been studied as the acidic component of frustrated Lewis pairs. While the 3,5-substituted isomer is already known to heterolytically cleave H2 to generate a bridging-hydride; ortho-substituents in the 2,4- and 2,5-isomers quench such reactivity through electron donation into the vacant boron pz orbital and steric blocking of the boron centre; as shown by electrochemical, structural and computational studies. Electrochemical studies of the corresponding borohydrides identify that the two-electron oxidation of terminal-hydrides occurs at more positive potentials than observed for [HB(C6F5)3]−, while the bridging-hydride oxidizes at a higher potential still, comparable to that of free H2. [ABSTRACT FROM AUTHOR]

Reaction of [Au(C6F5)(tht)] (tht = tetrahydrothiophene) with 2,2′:6′,2″-terpyridine (terpy) leads to complex [Au(C6F5)(η¹-terpy)] (1). The chemical oxidation of complex (1) with 2 equiv of [N(C6H4Br-4)3](PF6) or using electrosynthetic techniques affords the Au(III) complex [Au(C6F5)(η³-terpy)](PF6)2 (2). The X-ray diffraction study of complex 2 reveals that the terpyridine acts as tridentate chelate ligand, which leads to a slightly distorted square-planar geometry. Complex 1 displays fluorescence in the solid state at 77 K due to a metal (gold) to ligand (terpy) charge transfer transition, whereas complex 2 displays fluorescence in acetonitrile due to excimer or exciplex formation. Time-dependent density functional theory calculations match the experimental absorption spectra of the synthesized complexes. In order to further probe the frontier orbitals of both complexes and study their redox behavior, each compound was separately characterized using cyclic voltammetry. The bulk electrolysis of a solution of complex 1 was analyzed by spectroscopic methods confirming the electrochemical synthesis of complex 2. [ABSTRACT FROM AUTHOR]