Electron Transfer

When redox active molecules are covalently tethered to the surface of the n-doped silicon, light induces their oxidation by the semiconductor. To visualize this charge separation we have followed the formation and decay of the surface photovoltage by an auxiliary transparent electrode, which serves as a capacitive probe that picks up the transient surface photovoltage. This method has been used in electronics and biophysics but is novel for the surface redox chemistry. The probe provides both the direction of the charge transfer and the resolution of the dynamics. Its application is independent of the optical properties of the semiconductor. Laser initiation of the reaction permits quantitative measurements of the reactions with the rate constants ~108-103 s-1. The electron injection from covalently tethered NTCI(A) molecules into silicon was fast (k >109 s-1). The back electron transfer is poly-disperse with the components ranging from ~10 microseconds and up.

The kinetics of oxidation of 16 meta-, ortho-, and para-substituted anilines with nine oxo(salen)chromium(V) ions
have been studied by spectrophotometric, ESIMS, and EPR techniques. During the course of the reaction, two
new peaks with ìmax at 470 and 730 nm appear in the absorption spectrum, and these peaks are due to the
formation of emeraldine forms of oligomers of aniline supported by the ESIMS peaks with m/z values 274 and 365
(for the trimer and tetramer of aniline). The rate of the reaction is highly sensitive to the change of substituents in
the aryl moiety of aniline and in the salen ligand of chromium(V) complexes. Application of the Hammett equation
to analyze kinetic data yields a F value of -3.8 for the substituent variation in aniline and +2.2 for the substituent
variation in the salen ligand of the metal complex. On the basis of the spectral, kinetic, and product analysis
studies, a mechanism involving an electron transfer from the nitrogen of aniline to the metal complex in the rate
controlling step has been proposed. The Marcus equation has been successfully applied to this system, and the
calculated values are compliant with the measured values

An investigation of the electrochemical activity of human white blood cells (WBC) for biofuel cell (BFC) applications is described. WBCs isolated from whole human blood were suspended in PBS and introduced into the anode compartment of a proton exchange membrane (PEM) fuel cell. The cathode compartment contained a 50 mM potassium ferricyanide solution. Average current densities between 0.9 and 1.6 μA cm-2 and open circuit potentials (Voc) between 83 and 102 mV were obtained, which were both higher than control values. Cyclic voltammetry was used to investigate the electrochemical activity of the activated WBCs in an attempt to elucidate the mechanism of electron transfer between the cells and electrode. Voltammograms were obtained for the WBCs, including peripheral blood mononuclear cells (PBMCs - a lymphocyte-monocyte mixture isolated on a Ficoll gradient), a B lymphoblastoid cell line (BLCL), and two leukemia cell lines, namely K562 and Jurkat. An oxidation peak at about 363 mV vs...

The treatment of ß-and?-cyclodextrins with the half-sandwich complexes of iron afford the inclusion compounds CpFe (L 2) X· CD (ß and?)(X= Cl, I; L= CO; L 2= dppe, dppe=(Ph) 2 P (CH 2) 2 P (Ph) 2),[CpFe (L 2) L-] PF 6· CD (ß and?) L-neutral donor ligands and [(Cp ( ...

A simple procedure was developed to prepare a glassy carbon (GC) electrode modified with carbon nanotubes (CNTs) and catechol compounds. First, 25 μL of DMSO–CNTs solutions (0.4 mg/mL) was cast on the surface of GC electrode and dried in air to form a CNTs film. Then the GC/CNTs modified electrode immersed into a chlorogenic acid, catechine hydrate and caffeic acid solution (electroless deposition) for a short period of time (2–80 s). The cyclic voltammogram of the modified electrode in aqueous solution shows a pair of well-defined, stable and nearly reversible redox couple (quinone/hydroquinone) with surface confined characteristics. The combination of unique electronic and electrocatalytic properties of CNTs and catechol compounds results in a remarkable synergistic augmentation on the response. The electrochemical reversibility and stability of modified electrode prepared with incorporation of catechol compound into CNTs film was evaluated and compared with usual methods for attachment of catechols to electrode surfaces. The transfer coefficient (α), heterogeneous electron transfer rate constants (ks) and surface concentrations (Γ) for GC/CNTs/catechol compound modified electrodes were calculated through the cyclic voltammetry technique. The modified electrodes showed excellent catalytic activity, fast response time and high sensitivity toward oxidation of hydrazine in phosphate buffer solutions at pH range 4–8. The modified electrode retains its initial response for at least 2 months if stored in dry ambient condition. The properties of modified electrodes as an amperometric sensor for micromolar or lower concentration detection of hydrazine have been characterized.

Low dimensional semiconductor crystals structures otherwise known as quantum dots are in possession of unique optoelectronic properties that allow the flow of electrons to be harvested instantaneously. The advent of quantum dot for various technological applications is motivated by their flexibility of their bandgap supporting their capability to tap power from the visible spectrum as well as the invisible infrared through absorbable wavelength ranges from about 700 nanometre to 10 micron. Besides the wide energy harvesting range, quantum dot utilizes small to area for high energy production. The emergence of quantum dot and its application in optoelectronic device such as solar is set to improve the efficiency limit of traditional devices. The configuration of quantum dot in solar cell is discussed as well as electron transfer processes. Their three unique advantages for solar-to-electric energy conversion such as provision of large surface and interfacial areas per unit volume for...

The aim of this work is to the study the influence of the isomer structures of butyl acrylate monomer on the single-electron transfer/degenerative chain transfer mediated living radical polymerization (SET-DTLRP). The kinetic of isobutyl acrylate is determined for the first time by SET-DTLRP in water catalyzed by sodium dithionite. The plots of number-average molecular weight versus conversion and ln([M]0/[M]) versus time are linear, demonstrating a controlled polymerization. The influence of the isomer t-butyl, i-butyl, and n-butyl on the kinetics, properties, and stereochemistry of the reactions was assessed. To the best of our knowledge, there is no previous report dealing with the synthesis of PiBA by any LRP approach in aqueous medium. The results presented in this work suggest that the stability provided by the acrylate side group has an important influence in the polymerization process. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6542–6551, 2008

The lead dioxide electrodeposition (LDE) from nitrate electrolytes is studied by the rotating disk electrode, cyclic voltammetry, and electrode impedance methods. A four-stage kinetic scheme of the LDE reaction is proposed: (1) the electron transfer and generation of oxygen-containing species on the electrode surface; (2) the species interact with lead ions, forming an oxygen-containing intermediate product of Pb(III) of the type Pb(OH)2+, which is not fixed on the electrode surface; (3) the product is oxidized, with the transfer of the second electron, forming compounds of Pb(IV) associated with oxygen (of the type Pb(OH)2+2); and (4) the latter decomposes via a chemical mechanism to form PbO2. The rate-determining stage of the LDE process is essentially dependent on the potential and state of the electrode surface, concentration of Pb(II) ions in solution, and hydrodynamic conditions of experiment. The proposed scheme explains within a unified mechanism of the LDE reaction all the...

We introduce a new, non-invasive technique to measure linear electron transfer in intact leaves under steady-state illumination. Dark-interval relaxation kinetic or 'DIRK' analysis is based on measurements of the initial rates of relaxation of steady-state absorbance signals upon a rapid light-dark transition. We show that estimates of electron flux by DIRK analysis of absorbance signals, reflecting redox changes in the photosynthetic electron transfer chain, can yield quantitative information about photosynthetic flux when the light-dependent partitioning of electrons among redox components of the electron transfer chain are considered. This concept is modeled in computer simulations and then demonstrated in vivo with tobacco plants under non-photorespiratory conditions resulting in linear relationships between DIRK analysis and gross carbon assimilation (A(G)). Estimation based on DIRK analysis of the number of electrons transferred through the photosynthetic apparatus for...