An ultramicroelectrode study of ferrocene diffusion and heterogeneous electron transfer rate in polyelectrolyte

Steady-state voltammograms at a microdisk electrode are used to measure the diffusion coefficient (D) and standard heterogeneous rate constant (k(s)) of ferrocene in polyelectrolyte PEG.MClO(4). The diffusion coefficient and standard heterogeneous rate constant of ferrocene are both smaller in polymer solvents than in monomeric solvents. The D and k(s) of ferrocene have been estimated in PEG containing different concentrations and cations of supporting electrolytes, and the dependencies of D and k(s) on temperature have been observed. These results show that the D and k(s) of ferrocene increase with increasing temperature in polyelectrolyte, and with increasing cation radius of supporting electrolyte, eg D and k(s) increase in the order Bu(4)NClO(4) > NaClO4 > LiClO4. On the other hand, D and k(s) increase with decreasing concentration of supporting electrolyte. The dependence of the half-wave potential (E(1/2)) on the concentration of the supporting electrolyte is also observed. E(1/2) shifts in the negative direction as the concentration of supporting electrolyte increases. (C) 1997 Elsevier Science Ltd.

C-118 from fullerenols: Formation, structure and intermolecular nC(2) transfer reactions in mass spectrometry

In fast atom bombardment, two fullerenols C-60(OH)(x) (x=13-15) and C-60(OH)(x) (x-24-26) gave rise to a group of ions centered at C-118 with intervals of 24 mass units in the high mass region. In contrast, no such ions appeared in the mass spectra of pure C-60, C-70 and other fullerene derivatives such as C-60(C6H5)(10), under the same conditions. It is proposed that the pinacol rearrangement of C-60(OH)(2), resulting from partial rupture of the polyhydroxy molecules, produces C-59 with two carbon atoms bearing an unpaired electron, and that dimerization of this reactive intermediate is responsible for the formation of the predominant product C-118. An intermolecular nC(2) transfer process is used to explain the symmetrical abundance distribution of these product ions in the spectra of fullerenols.

PROMOTER EFFECT OF POLY(4-VINYLPYRIDINE) ON THE DIRECT ELECTRON-TRANSFER BETWEEN CYTOCHROME-C AND GOLD ELECTRODE

The electrochemistry of cytochrome c was studied at the PVP-modified gold electrode. It was found that the promoter effect is related to the amount of PVP at the gold electrode. From our results, it can be seen that the nitrogen element in the polymer is important for accelerating the electron transfer of cytochrome c.

DIRECT ELECTROCHEMICAL REACTIONS OF CYTOCHROME-C AT IODIDE-MODIFIED ELECTRODES

Quasi-reversible and direct electron transfer was observed between an iodide-modified Au electrode and cytochrome c, as well as between cytochrome c in an iodide-containing solution and a bare Au electrode. The results suggest that an electrostatic intera

APPLICATIONS OF RAPID SCAN SPECTROELECTROCHEMISTRY - DETERMINATION OF HETEROGENEOUS ELECTRON-TRANSFER RATE-CONSTANT OF BILIVERDIN OXIDATION

The rapid scan spectrometer was used to determine the heterogeneous electron transfer rate parameters for the oxidation of Biliverdin in DMF by single potential step thin layer spectroelectrochemical techniques and yielded an average formal heterogeneous electron transfer rate constant K(s, h)0' = 2.45 (+/-0.12) x 10(-4) cm s-1, electrochemical transfer coefficient alpha = 0.694+/-0.008. The oxidation process of Biliverdin was also studied and the formal potential E0 = 0.637 V (vs. Ag/AgCl) was obtained.

EFFECT OF PH ON THE ELECTRON-TRANSFER OF CYTOCHROME-C ON A GOLD ELECTRODE MODIFIED WITH BIS(4-PYRIDYL)DISULPHIDE

The adsorption of bis(4-pyridyl)disulphide (PySSPy) and 4.4'-bipyridyl (PyPy) on a gold electrode was studied using cyclic voltammetry. The adsorption isotherms and equilibrium constants (1 X 10(6) mol-1 l for PyPy and 6 x 10(6) Mol-1 l for PySSPy) were determined. The effect of pH on the electrochemical behaviour of cytochrome c was studied on the PySSPy-modified gold electrode. The results show that cytochrome c can only transfer electrons on a deprotonated electrode surface. When the pH is decreased, the standard heterogeneous rate constant of cytochrome c on the modified gold electrode decreases and the electrochemical behaviour changes from a quasi-reversible to an irreversible process.

Interplay between partial incoherence, partial inelasticity, resonance, and heterogeneity in long-range electron transfer and transport

A generalized scattering matrix formalism is constructed to elucidate the interplay of electron resonance, coherence, dephasing, inelastic scattering, and heterogeneity, which play important roles in the physics of long-range electron transfer/transport. The theory consists of an extension of the standard Buttiker phase-breaking model and an analytical expression of the electron transmission coefficient for donor-bridge-acceptor systems with arbitrary length and sequence. The theory incorporates the following features: Dephasing-assisted off-resonance enhancement, inelasticity-induced turnover, resonance enhancement and its dephasing-induced suppression, dephasing-induced smooth superexchange-hopping transition, and heterogeneity effects. (C) 2002 American Institute of Physics.

Average energy loss measured in single and double electron capture collisions of He2 on Ar at low velocities

Employing the recoil ion momentum spectroscopy we investigate the collision between He2+ and argon atoms. By measuring the recoil longitudinal momentum the energy losses of projectile are deduced for capture reaction channels. It is found that in most cases for single- and double-electron capture, the inner electron in the target atom is removed, the recoil ion is in singly or multiply excited states (hollow ion is formed), which indicates that electron correlation plays an important role in the process. The captured electrons prefer the ground states of the projectile. It is experimentally demonstrated that the average energy losses are directly related to charge transfer and electronic configuration.

Two Electron Transfer and Stabilization in Slow O6+ and Rare-Gas Collisions

The stabilization ratios.. for double-electron transfer, i.e., the cross section ratios of true double capture to total double-electron transfer, are measured in O6++ He, Ne and Ar collisions at 6 keV/u. A high.. value about 68% is obtained for the He target, while for the Ar target, the.. value is only 8%. The high R value for the He target is due to the significant direct population of the (2l, nl') configurations with high n For the Ar target, the (quasi) symmetric configurations (3l, nl') lead to the much lower.. value. Neglecting the core effects, the O6+ ion can be taken as a bare ion C6+ except the occupied 1s shell, and then the measured R values are compared with previous experimental results of C6+ projectile ions at similar impact velocity. It yields good agreement with the Ne and Ar target, while the occupied 1s shell for the O6++ He system results in a higher R value than that in C6++He collisions.

Proton transfer reactions within the pyridazine-methanol cluster ion

The multiphoton ionization of the hydrogen-bonding cluster pyridazine-methanol (C4H4N2-CH3OH) was studied using a time-of-flight mass spectrometer at the wavelengths of 355 and 532 nm. At both wavelengths, a series of protonated C4H4N2-(CH3OH)(n)-H+ cluster ions were obtained. Relevant ab initio calculations were performed with HF and B3LYP methods. Equilibrium geometries of both neutral and ionic C4H4N2-CH3OH clusters, and dissociation channels and dissociation energies of ionic clusters, are presented. The results show that when C4H4N2-CH3OH is vertically ionized, C4H4N2H+ and CH3O are the dominant products via proton transfer reaction. A high energy barrier makes another channel corresponding to the production of C4H4N2H+ and CH2OH disfavored. (C) 2002 Elsevier Science B.V. All rights reserved.

Relationship between charge transfer energies of Yb3+ and Sm3+ and crystal environmental factor

Relationship between charge transfer energies E-CT of Yb3+ and Sm3+ and environmental factors h(e) in various crystals was investigated using a dielectric chemical bond method. Both results show that they have an exponential relation E-CT = A+B exp(-kh(e)), but the exponential factors are different, which indicates that the interaction between the rare earth ions and environment is connected with the kind of rare earth ion. This result provides a method of determining charge transfer energies of Yb3+ and Sm3+ from a crystal structure.

Anticancer Drug-DNA Interactions Measured Using a Photoinduced Electron-Transfer Mechanism Based on Luminescent Quantum Dots

A sensing system based on the photoinduced electron transfer of quantum dots (QDs) was designed to measure the interaction of anticancer drug and DNA, taking mitoxantrone (MTX) as a model drug. MTX adsorbed on the surface of QDs can quench the photoluminescence (PL) of QDs through the photoinduced electron-transfer process; and then the addition of DNA will bring the restoration of QDs PL intensity, as DNA can bind with MTX and remove it from QDs. Sensitive detection of MTX with the detection limit of 10 nmol L-1 and a linear detection range from 10 nmol L-1 to 4.5 mu mol L-1 was achieved. The dependence of PL intensity on DNA amount was successfully utilized to investigate the interactions between MTX and DNA. Both the binding constants and the sizes of binding site of MTX-DNA interactions were calculated based on the equations deduced for the PL recovery process. The binding constant obtained in our experiment was generally consistent with previous reports. The sensitive and speedy detection of MTX as well as the avoidance of modification or immobilization process made this system suitable and promising in the drug-DNA interaction studies.

Direct electron transfer between cytochrome c and a gold nanoparticles modified electrode

Quasi-reversible and direct electrochemistry of cytochrome c (cyt. c) has been obtained at a novel electrochemical interface constructed by self-assembling gold nanoparticles (GNPs) onto a three-dimensional silica gel network, without polishing or any modification of the surface. A cleaned gold electrode was first immersed in a hydrolyzed sol of the precursor (3-mercaptopropyl)-trimethoxysilane to assemble three-dimensional silica gel, then the GNPs were chemisorbed onto the thiol groups of the sol-gel network and modified the kinetic barrier of this self-assembled silicate film. Cyclic voltammetry and AC impendance spectroscopy were performed to evaluate electrochemical properties of the as prepared interface. These nanoparticle inhibits the adsorption of cyt. c onto bare electrode and acts as a bridge of electron transfer between protein and electrode.

Luminescence and energy transfer properties of Ca2Gd8(SiO4)(6)O-2 : A(A = Pb2+, Tm3+) phosphors

Ca2Gd8(SiO4)(6)O-2: A(A = Ph2+, Tm3+) phosphors were prepared through the sol-gel process. X-ray diffraction (XRD), scanning electron microseopy(SEM) and photoluminescence spectra were used to characterize the resulting phosphors. The results of XRD indicate that the phosphors crystallized completely at 1000 degreesC. SEM study reveals that the average grain size is 300 similar to 1000 nm. In Ca2Gd8(SiO4)(6)O-2: Tm3+ phosphors, the Tm3+ shows its characteristic blue emission at 456 nm (D-1(2)-F-3(4)) upon excitation into its H-3(6)-D-1(2)(361 nm), with an optimum doping concentration of 1 mol% of Gd3+ in the host lattices. In Ca2Gd8(SiO4)(6)O-2: Pb2+, Tm3+ phosphors, excitation into the Ph2+ at 266 nm (S-1(0)-P-3(1)) yields the emissions of Gd3+ at 311 nm (P-6-S-8) and Tm3+ at 367 nm (D-1(2)-H-3(6)) and 456 our (D-1(2)-F-3(4)), indicating that energy transfer processes of Pb2+-Gd3+ and Ph2+-Tm3+ have occur-red in the host lattices.