Are nanoparticles spherical or quasi-spherical?

The geometry of quasi-spherical nanoparticles is investigated. The combination of SEM imaging and electrochemical nano-impact experiments is demonstrated to allow sizing and characterization of the geometry of single silver nanoparticles

Structural effects of the highly protective V127 polymorphism on human prion protein

Prion diseases, a group of incurable, lethal neurodegenerative disorders of mammals including humans, are caused by prions, assemblies of misfolded host prion protein (PrP). A single point mutation (G127V) in human PrP prevents prion disease, however the structural basis for its protective effect remains unknown. Here we show that the mutation alters and constrains the PrP backbone conformation preceding the PrP β-sheet, stabilising PrP dimer interactions by increasing intermolecular hydrogen bonding. It also markedly changes the solution dynamics of the β2-α2 loop, a region of PrP structure implicated in prion transmission and cross-species susceptibility. Both of these structural changes may affect access to protein conformers susceptible to prion formation and explain its profound effect on prion disease

Multi-electron transfer to and from organic molecules

Herein, the influence of protonation and adsorption upon the redox and electrocatalysis of quinone species - specifically anthraquinone derivatives – is investigated.Through the comparison of the measured rate constants of one-electron reductions of a family of quinones in acetonitrile at both graphite and gold electrodes, it was confirmed that the redox potential indirectly influences the rate of electron transfer in a manner consistent with the potential-dependence of the density of states. In aqueous media, the voltammetric response of both anthraquione-2-sulfonate (AQMS) and anthraquinone-2,6-disulfonate (AQDS) was measured over the full aqueous pH range. A model is provided which is able to describe not just the variation in the formal potential but also the peak height as a function of pH. Importantly, this model predicts that the formal potential for the first (Ef1) and second (Ef2) electron transfers are comparable in magnitude (E^θ _f2−E^_θf1 equals -15mV for AQMS and -36mV for AQDS). This quantitative model is then further extended to consider the situation in which the system is not fully buffered, giving insight into the change of pH at the electrode surface during experimentation.Adsorption to graphitic electrodes can impart a strong influence on the measured voltammetric response. It is demonstrated that through the pre-exposure of a newly prepared graphitic electrode to organic solvents, these adsorption processes can be predominantly blocked. Moreover, it is shown that the electroactivity of the electrode is not significantly altered. This thesis also highlights two cases in which adsorption of the electroactive species may be used to positive effect. First, the surface adsorption of anthraquinone-2-monosulfonate is studied on a graphite electrode, where it is demonstrated that the heterogeneity of the electrode surface may be probed through studying the electrochemical response of the adsorbed species. From this work it is concluded that the rate of electron transfer at the graphitic basal plane is 2-3 orders of magnitude lower than that observed on the edge plane sites. Second, the co-adsorption of DNA and anthraquinone-2-monosulfonate is used as an indirect method to measure the solution phase concentration of DNA (LOD = 8.8μM).The reduced form of anthraquinone is also known to readily reduce oxygen. Through the use of a boron-doped diamond electrode it was possible to directly study the anthraquinone mediated reduction mechanism. Significantly, the voltammetric response indicates the reduction of the oxygen via the semi-quinone intermediate (kf = 4.8 × 10⁹ mol⁻¹ dm³ s⁻¹) is over two orders of magnitude faster than the reaction involving the di-reduced form (kf = 1 × 10⁷ mol⁻¹ dm³ s⁻¹). More importantly, this work provides voltammetric evidence for the existence of the semi-quinone species. This work is subsequently extended through the investigation of the poorly soluble anthraquinone derivative quinizarin. Not only is it possible to detect voltammetrically this biologically relevant species to concentrations as low as 5nM (100ppt), but the methodology also allows the electrochemistry of the quinizarin species to be probed, something which was not previously possible.</p

Voltammetry of multi-electron electrode processes of organic species

Classically the analysis of the voltammetric response of multi-electron transfer processes is achieved through the use of the Randles- Ševčík equations based on analytical theory. In such it is assumed that the after the 'rate determining step' all electron transfers are highly driven. Conversely, it is commonly found experimentally that the formal potentials for different electrochemical steps (1, 2, 3 ...) are found to be at comparable potentials (i.e. Ef,1θ∼Ef,2θ∼Ef,3θ); this leads to significant deviations from the Randles-Ševčík analysis. This article highlights various 'simple' electrochemical mechanisms (EE, EC, EEC) and discusses how the voltammetric peak height resulting from linear sweep voltammetry is expected to vary with scan rate and other parameters, with the aim of providing a general theoretical basis upon which analysis of complex voltammetric systems may be approached and understood. © 2012 Elsevier B.V. All rights reserved

The influence of substrate effects when investigating new nanoparticle modified electrodes exemplified by the electroanalytical determination of aspirin on NiO nanoparticles supported on graphite

The apparent electrocatalytic detection of aspirin and salicylic acid is compared using NiO nanoparticles and microparticles supported on graphitic electrodes using abrasive and non-abrasive (drop-dry) immobilisation. However control experiments revealed that, the observed voltammetry is not due to the immobilised NiO materials, but is instead due to the underlying graphitic substrates. Abrasive immobilisation of NiO microparticles on a graphite electrode abrades the underlying electrode surface, introducing more electroactive edge-plane defects. Even when drop-dry immobilisation is used (i.e. non-abrasive), appropriate control experiments are still required as other experimental methods employed may change the nature of the underlying substrate

Thin-Film Modified Rotating Disk Electrodes: Models of Electron-Transfer Kinetics for Passive and Electroactive Films

This work explores the influence of both passive and electroactive thin films upon the steady-state voltammetric response of a rotating disk electrode, proposing simple physical and algebraic models. In both cases, it is clearly evidenced how the alteration of the mass-transport regime adjacent to the electrochemical interface leads to an apparent change in the electron-transfer kinetics. These results are of great significance because of the wide adoption of the rotating disk electrode technique for studying new electrocatalytic materials

Thin-Film Modified Rotating Disk Electrodes: Models of Electron-Transfer Kinetics for Passive and Electroactive Films

© 2014 American Chemical Society. This work explores the influence of both passive and electroactive thin films upon the steady-state voltammetric response of a rotating disk electrode, proposing simple physical and algebraic models. In both cases, it is clearly evidenced how the alteration of the mass-transport regime adjacent to the electrochemical interface leads to an apparent change in the electron-transfer kinetics. These results are of great significance because of the wide adoption of the rotating disk electrode technique for studying new electrocatalytic materials