19052-44-9Relevant academic research and scientific papers
Electron Transfer. 134. Reduction of Bound Ruthenium(III) by Indium(I)
Chandra, Swapan K.,Gould, Edwin S.
, p. 3485 - 3487 (1997)
Aqueous solutions of the hypovalent state indium(I) react with oxidants of the type [(NH3)5RuIII(Lig)]3+, in which the sixth ligand, Lig , is devoid of groups allowing inner-sphere bridging. Reaction stoichiometry conforms to the relationship InI + 2RuIII → InIII + 2RuII. Kinetic profiles are consistent with a two-step sequence initiated by the formation of metastable InII, which then reacts rapidly with RuIII. Rate constants for the rate-determining steps in this series (kRu,In values) are proportional to those for reductions of the corresponding (NH3)5CoIII oxidants with V2+(aq), Cr2+(aq), Eu2+(aq), and U3+(aq), even though, for each comparison, no metal center is common to the two series chosen. This implies that changes in ΔG?redox arising from substitution of one N-donor ligand for another are nearly independent of the metal centers involved in the net transfer. The rate for the reduction of (NH3)6Ru3+, considered in the framework of the Marcus model, leads to an estimated rate constant of 10-9 M-1 s-1 for electron self-exchange in the system In2+/+. This value lies well below the range characteristic of the most usual aqua-substituted cationic couples, suggesting a more severe H2O-metal bond contraction in going from the uni- to the dipositive cation.
PULSE RADIOLYSIS STUDIES OF ELECTRON TRANSFER BETWEEN POLYMER AND ZWITTERIONIC VIOLOGEN RADICALS
Sakamoto, Tetsuo,Ohsako, Tatsuya,Matsuo, Taku,Mulac, William A.,Meisel, Dan
, p. 1893 - 1896 (1984)
The reaction between viologen polymer radicals(PV+.) and Ru(NH3)6(3+) via zwitterionic viologen as excellent mediator, has been studied using the pulse radiolysis technique.Kinetic analysis provided quantitative measurement of the rate of elect
Hydration of the carbonyl groups in 1,10-phenanthroline-5,6-dione induced by binding protons or metal cations to the pyridine nitrogen sites
Lei, Yabin,Anson, Fred C.
, p. 9849 - 9854 (1995)
In acidic solutions, the chemical or slow electrochemical reduction of the organic ligand - oxidant 1,10-phenanthroline-5,6-dione consumes two electrons and two protons. However, when the electrochemical reduction is examined on shorter time scales using cyclic or rotating disk voltammetry, fewer than two electrons are consumed in the reduction. The magnitude of the electron deficit depends upon pH and the deficit is eliminated at pH values where the pyridine nitrogen sites on the molecule are not protonated. Complexation of metal cations, e.g., Os(II) or Ni(II), to the 1,10-phenanthroline portion of the molecule also produces an electron deficit in electrochemical reductions of the dione. A proton- or metal ion-induced addition of H2O to the quinone carbonyl groups is shown to be responsible for the observed behavior. Rate and equilibrium constants for the hydration - dehydration equilibrium were evaluated by fitting experimental and calculated parameters in a digital simulation. The possible consequences of the results to studies in which the dione is used to oxidize amines and other organic reductants are pointed out.
Interrogation of surfaces for the quantification of adsorbed species on electrodes: Oxygen on gold and platinum in neutral media
Rodríguez-López, Joaquín,Alpuche-Avilés, Mario A.,Bard, Allen J.
, p. 16985 - 16995 (2008)
We introduce a new in situ electrochemical technique based on the scanning electrochemical microscope (SECM) operating in a transient feedback mode for the detection and direct quantification of adsorbed species on the surface of electrodes. A SECM tip generates a titrant from a reversible redox mediator that reacts chemically with an electrogenerated or chemically adsorbed species at a substrate of about the same size as the tip, which is positioned at a short distance from it (ca.1 μm). The reaction between the titrant and the adsorbate provides a transient positive feedback loop until the adsorbate is consumed completely. The sensing mechanism is provided by the contrast between positive and negative feedback, which allows a direct quantification of the charge neutralized at the substrate. The proposed technique allows quantification of the adsorbed species generated at the substrate at a given potential under open circuit conditions, a feature not attainable with conventional electrochemical methods. Moreover, the feedback mode allows the tip to be both the titrant generator and detector, simplifying notably the experimental setup. The surface interrogation technique we introduce was tested for the quantification of electrogenerated oxides (adsorbed oxygen species) on gold and platinum electrodes at neutral pH in phosphate and TRIS buffers and with two different mediator systems. Good agreement is found with cyclic voltammetry at the substrate and with previous results in the literature, but we also find evidence for the formation of incipient oxides which are not revealed by conventional voltammetry. The mode of operation of the technique is supported by digital simulations, which show good agreement with the experimental results.
Studies of electron transfer through self-assembled monolayers using impedance spectroscopy
Protsailo, Lesia V.,Fawcett, W. Ronald
, p. 3497 - 3505 (2000)
An investigation of the kinetics of reduction of Ru(NH3)3+6 has been carried out at single crystal electrodes modified by alkanethiols of varying chain lengths. Careful study of the impedance of the modified electrode system in the absence of the reaction has shown that there is a highly resistive path in parallel to the capacitance due to the self-assembled monolayer. Analysis of the kinetic data and extrapolation of the Tafel plots show that the standard rate constant for the Ru(NH3)3+/2+6 system is 1.7 cm s-1 at an unmodified Au surface with a transfer coefficient close to 0.5. These parameters are expected for a very fast simple heterogeneous electron transfer reaction. The present results are compared with whose reported previously in the literature.
Microwave reflectance studies of photoelectrochemical kinetics at semiconductor electrodes. 3. Photoelectrochemical reduction of Ru(NH3)63+ at p-Si
Peter, Laurence M.,Ushiroda, Shin
, p. 2660 - 2665 (2004)
The reduction of Ru(NH3)63+ at illuminated p-Si in ammonium fluoride solutions was studied by a light modulated microwave reflectivity method. Ru(NH3)63+ was chosen as an example of a one electron outer sphere redox system that is expected to exhibit facile electron transfer kinetics. The results of the microwave measurements show that the transfer of photogenerated electrons to Ru(NH3)63+ at an illuminated p-Si electrode is very slow compared to an order of magnitude estimate for outer sphere electron transfer. It is concluded that the reduction of Ru(NH3)63+ does not involve direct electron transfer from the conduction band but is instead mediated by photogenerated hydrogen states.
Kinetics of reduction of aqueous hexaammineruthenium(III) ion at Pt and Au microelectrodes: Electrolyte, temperature, and pressure effects
Vijaikanth, Vijendran,Li, Guangchun,Swaddle, Thomas W.
, p. 2757 - 2768 (2013)
Rate constants kel obtained by impedance spectroscopy for the reduction of Ru(NH3)63+ at polycrystalline Pt and Au ultramicroelectrodes depend strongly on the identity and concentration of the anion present in t
Study of nitrosation of hexaammineruthenium(II): Crystal structure of trans-[RuNO(NH3)4Cl]Cl2
Il'in,Emel'Yanov,Baidina,Alferova,Korol'Kov
, p. 62 - 70 (2008/10/09)
The nitrosation of [Ru(NH3)6]2+ in hydrochloric acid and alkaline ammonia media has been studied; the patterns of interconversion of ruthenium complexes in reaction solutions have been proposed. In both cases, nitrogen(II) oxide acts as the nitrosation agent. The procedure for the synthesis of [Ru(NO)(NH3)5]Cl3 ? H2O (yield 75-80%), the main nitrosation product of [Ru(NH 3)6]2+, has been optimized. Thermolysis of [Ru(NO)(NH3)5]Cl3 ? H2O in a helium atmosphere has been studied; the intermediates have been identified. One of these products is polyamidodichloronitrosoruthenium(II) whose subsequent decomposition gives an equimolar mixture of ruthenium metal and dioxide. The structure of trans-[RuNO(NH3)4Cl]Cl2, formed in the second stage of thermolysis and as a by-product in the nitrosation of [Ru(NH3)6]Cl2, has been determined by X-ray diffraction. Nauka/Interperiodica 2007.
Tuning the rate and pH accessibility of a conformational electron transfer gate
Baddam, Saritha,Bowler, Bruce E.
, p. 6338 - 6346 (2008/10/09)
Methods to fine-tune the rate of a fast conformational electron transfer (ET) gate involving a His-heme alkaline conformer of iso-1-cytochrome c (iso-1-Cytc) and to adjust the pH accessibility of a slow ET gate involving a Lys-heme alkaline conformer are described. Fine-tuning the fast ET gate employs a strategy of making surface mutations in a substructure unfolded in the alkaline conformer. To make the slow ET gate accessible at neutral pH, the strategy involves mutations at buried sequence positions which are expected to more strongly perturb the stability of native versus alkaline iso-1-Cytc. To fine-tune the rate of the fast His 73-heme ET gate, we mutate the surface-exposed Lys 79 to Ala (A79H73 variant). This mutation also simplifies ET gating by removing Lys 79, which can serve as a ligand in the alkaline conformer of iso-1-Cytc. To adjust the pH accessibility of the slow Lys 73-heme ET gate, we convert the buried side chain Asn 52 to Gly and also mutate Lys 79 to Ala to simplify ET gating (A79G52 variant). ET kinetics is studied as a function of pH using hexaammineruthenium(II) chloride (a6Ru 2+) to reduce the variants. Both variants show fast direct ET reactions dependent on [a6Ru2+] and slower gated ET reactions that are independent of [a6Ru2+]. The observed gated ET rates correlate well with rates for the alkaline-to-native state conformational change measured independently. Together with the previously reported H73 variant (Baddam, S.; Bowler, B. E. J. Am. Chem. Soc. 2005, 127, 9702-9703), the A79H73 variant allows His 73-heme-mediated ET gating to be fine-tuned from 75 to 200 ms. The slower Lys 73-heme (15-20 s time scale) ET gate for the A79G52 variant is now accessible over the pH range 6-8.
Reduction of hexaammineruthenium(III) ions by a series of tris(polypyridyl)chromium(II) ions - Revisiting the Cr(NN)33+/2+ self-exchange rate
Zahir
, p. 1124 - 1127 (2007/10/03)
The kinetics of the outer-sphere oxidation of Cr(NN)32+ ions (NN = 2,2′-bipyridine, 1,10-phenanthroline, and their substituted analogs) by hexaammineruthenium(III) was studied using laser flash photolysis. The Cr(NN)32+ ions were generated via the reductive quenching of the *Cr(NN)33+ excited states by oxalate ions or by H2edta2-. The second-order rate constants were found to vary with the driving force of the reaction. The rate constants increase from (7.1 ± 0.5) × 106 M-1 s-1 for Cr(5-Clphen)32+ to (2.6 ± 0.2) × 108 M-1 s-1 for Cr(4,7-Me2phen)32+. The self-exchange rate constant for the couple (Cr(NN)33+/2+) was calculated by applying Marcus cross relation to present and other known reactions of Cr(NN)3n+ ions, where n = 3 or 2 with various reactants and is estimated to be (6 ± 4) × 107 M-1 s-1.
