Intramolecular electron transfer rate

In Debye solvents, x is tire longitudinal relaxation time. The prediction tliat solvent polarization dynamics would limit intramolecular electron transfer rates was stated tlieoretically [40] and observed experimentally [41]. 

Intramolecular Electron-Transfer Rates. Experiments were carried out under inert atmosphere by reducing a known concen-... 

Influence of the Amino Acid Linkages on Intramolecular Electron-Transfer Rates. There is a significant drop in the 2... 

Table I. Intramolecular Electron Transfer Rates and Activation Parameters ...

Table 5.12 Intramolecular Electron Transfer Rate Constants in Metalloproteins at 25°C...

Give a reasonable explanation for the intramolecular electron transfer rate constants (k) at 25°C for the following precursor complexes ... 

The high lability of bound N2 in [FeII(CN)5N2]3 regenerates the active site, namely the [FeII(CN)5H20]3 ion, which is able to further bind and process hydrazine. A more detailed kinetic study could be warranted for this interesting set of reactions. Some uncertainties still remain as to the nature of the intramolecular electron-transfer rate processes (91). At the employed concentration levels of the complex, the participation of mixtures of mononuclear and dinuclear complexes complicate the spectral evolution. Even the nature of the dinuclear intermediates (cyano- or hydrazino-bridged) could be put into question (probably both are involved, due to the labile interconversion equilibria). The participation of Fe(III) species, either in the mononuclear or dinuclear species, as reactive intermediate precursors of the formation of diazene and N2... 

Additional information about this Fc GO preparation has been reported elsewhere (112). The intramolecular electron transfer rate constant kmirn calculated using Eq. (36) equals 40 s-1 and is by a factor of 50 higher than that for the randomly modified GO (104). The distance separating the ferrocene unit and FAD in Fc GO is believed to be ca. 19 A, by 2 A shorter than in the most effective electrically contacted enzyme generated by the random modification of GO by ferrocene units. This information supports the hypothesis about the key locations of ferrocene groups that play the dominant role in the electrocatalysis (104). 

A variety of linkage isomer pairs have been produced from somewhat more complex ligands, such as substituted pyridines and benzoic acids, for example (5a) and (5b).77,78 These complexes have been employed in detailed studies of inner-sphere electron transfer reactions in order to assess the importance of the nature and orientation of the bridge between redox centres on intramolecular electron transfer rates.77-80... 

Direct measurement of intramolecular electron transfer rates 364... 

A detailed study of the effect of the medium and temperature on the intramolecular electron transfer rate constant kt in various metal complex systems of the bridge structure has been carried out [25]. The values of kt were found to increase and the activation energy to decrease with increasing polarity of the medium. These effects were accounted for in terms of the modern electron transfer theory (see the case Er > J in Fig. 5 of Chap. 3) by greater changes in the free energy, AG°, due to a higher redox potential of the L/Lr pairs in a more polar medium. 

Turowski P. N. McGuirl M. A. Dooley D. M. Intramolecular electron transfer rate between active-site copper and topa quinone in pea seedling amine oxidase. J. Biol. Chem. 1993, 268, 17680-17682. 

Supramolecular chemistry has proven to be a powerful tool for experimentally testing modern electron transfer theory. It has done so by providing materials for exploring the impact of parameters such as driving force, transfer distance and bridge electronic nature on intramolecular electron transfer rates. 

Intramolecular electron transfer rate constants k (s-1) as a function of the free energy difference for the reaction Biphenyl( )-androstane-/4 —> Biphenyl-androstane-v4( ), estimated from the electrochemical reduction potentials in 2-methyltetra-hydrofuran the inverted region for electron transfer rates is prominent. Redrawn from Miller et al. [10]. 

The transient Q-band EPR experiments provide direct evidence for sequential electron transfer from the primary to the secondary radical pair of the triplet channel in a triad consisting of a zinc-9-desoxo-meso-methylpyrochlorophyllide donor (ZC), a pyromellitimide primary acceptor (PI), and a naphthalene-1,8 4,5-diimide secondary acceptor oriented in a liquid crystal (Heinen et al., 2002). At room temperature this process occurs with an exponential time constant of tT = 50 + 1 ns. In the singlet-initiated channel, the intramolecular electron-transfer rates are too fast for direct EPR detection. The species decay with a time constant of tS = 36 1 ns by charge recombination to the singlet ground state. 

The electron transfer rates in P450BM3, measured by laser flash photolysis using semicarbazide-aetivated 5-deazflavin semiquinone, show that no reduction of the native BMP heme oeeurs even though FMN could be reduced rapidly to the semiquinone (Hazard et al., 1997). In the presence of earbon monoxide, which can displace water from the sixth coordination site of iron and convert the low-spin ferric iron to high spin, the intramolecular electron transfer rate is 18sec". In the presence of both CO and the substrate myristic acid, an intramolecular electron transfer rate of up to 250sec" can be obtained. 

The unimolecular reduction of the trinuclear copper center is caused by intramolecular electron transport from the type-1 copper to the trinuclear copper species. The turnover numbers represented by the values (see Table VII) are one to two orders of magnitudes greater than the observed intramolecular electron transfer rate constants. They should be at least as large as the turnover numbers. The low rates seem to imply that the enzymes are in an inactive form under the conditions of the anaerobic reduction experiments. It will be shown later that there is experimental evidence for this assumption. 

The thermal-induced intramolecular electron transfer rates of mixed-valence biferrocene monocation (Fe(II),Fe(III)) were determined in seven solvents and at various temperatures by the proton paramagnetic relaxation measurements. The rate constants of pico-second order were obtained at 298 K and the frequency factors showed a solvent dependence. The effect of solvent friction on the barrier crossing in the reaction trajectory was examined in the strong adiabatic regime. 

The 10 s order rate constants for the thermal-induced (ground state) intramolecular electron transfer rates of the mixed-valence biferrocene monocation were first elucidated in various solvents by the H-NMR relaxation measurements. The obtained solvent dependent frequency factors indicated significant contribution of the solvent dielectric friction on the barrier crossing. An existence of the faster processes compared with the ET rate such as the internal vibration as an escape route of the reaction dynamics along the solvent coordination was also proposed in some extent. 

Figure 3. Driving force-dependence of intramolecular electron transfer rates in Ru-ammine-His33 modified Zn-substituted cytochrome c ( ), and Ru-bpy-His33 modified Fe-cytochrome c ( ). Solid lines were generated using Eq. 1 and the following parameters Ru-ammine,, i=1.15 eV, Hab = 0.10 cm Ru-bpy, X = 0.74 eV, Hab = 0.095 cm". ...

The cyclodextrin-sandwiched porphyrin 18 of Kuroda [98] effectively recognizes hydrophobic quinones in water, with association constants ranging from A a = 7.4 X 10 M for 1,4-naphthoquinone to Ka > 5 x 10 M for an adamantyl-functionalized benzoquinone. In contrast, the association of p-benzoquinone is negligible. Molecular modeling predicts that the quinone approaches the porphyrin from an out-of-plane direction. Time-resolved fluorescence measurements give an estimate of the intramolecular electron transfer rate constant on the order of 10 s for all quinones studied. 

In very recent years derivatives of biferrocene have witnessed a revival of interest. Thus, alkylated biferrocenium salts have been studied mainly from the point of view of their intramolecular electron-transfer rates [62] and charge localization [63]. Thus,... 

Seven horse heart cytochrome C derivatives, each with a single sarcophaginate [Co(diAMsar)]3+ cation covalently attached to a specific surface carboxylate side chain, were synthesized. The experimental intramolecular electron transfer rate constants is nearly independent of the [Co(diAMsar)] + cation attachment site [320]. 

The use of infrared spectroscopy, either through fingerprint characterisation or by functional group identification, is well established. IR vibrational spectroscopy has thus been applied in spectroelectrochemistry for quite some time. ° The possibility to establish the symmetry of a molecule has made IR-SEC a most valuable tool for mixed-valence chemistry, ° allowing intramolecular electron-transfer rates in the picosecond region to be assessed and electron-transfer isomers to be established. ... 

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