Temperature electron transfer kinetics

EPR studies on electron transfer systems where neighboring centers are coupled by spin-spin interactions can yield useful data for analyzing the electron transfer kinetics. In the framework of the Condon approximation, the electron transfer rate constant predicted by electron transfer theories can be expressed as the product of an electronic factor Tab by a nuclear factor that depends explicitly on temperature (258). On the one hand, since iron-sulfur clusters are spatially extended redox centers, the electronic factor strongly depends on how the various sites of the cluster are affected by the variation in the electronic structure between the oxidized and reduced forms. Theoret-... 

Fiomogeneous cross-reaction electron-transfer kinetic studies suggest that many other Cu(II/I) systems obey Scheme 1. However, few Cu(II/I) systems have been subjected to sufficiently low temperature or rapid-scan CV measurements to demonstrate the presence of rate-limiting conformational changes. 

Electron transfer kinetics from the triplet excited state of TMPD to PA in polystyrene has been monitored by phosphorescence emission decay in ref. 85. The rate constant has been found to be invariant over the temperature interval 77-143 K. Parameters ae and ve calculated from the phosphorescence decay using eqn. (12) were found to be ae = 3.46 A and vc = 104 s 1. 

In view of the lack of a clear understanding of the physical picture of the process, the thermal diffusion model has no predictive power. On its basis, for example, the manner in which the kinetic curves for low-temperature electron transfer reactions should change with changing concentration or kind of spatial distribution of reagents cannot be predicted. By contrast, the model of electron tunneling permits such predictions, and these predictions have been shown above (see, for example, Chap. 6, Sect. 3) to agree with the experiments. 

More detailed investigations [38,39] have shown the kinetics of low-temperature electron transfer reaction (1) in bacteria to have a biphase character, i.e. to consist of two sections, one with a faster and the other with a slower decay of the Pf centres. Also, the type of kinetics of reaction (1) in bacteria at low temperatures has been found to depend on the conditions of sample preparation. The region of fast (t 50 ms) charge recombination at T < 230 K was observed only for the samples frozen in the dark. The extent of P decay was observed to decrease upon freezing the samples in the light. These results were explained by the presence of two channels for the decay of P+ centres by reactions with particles A and Q". The faster decay of P+ was assumed to be due to its reaction with A and the slower decay of P4 to its reaction with Q . The relative amounts of A and Q particles (i.e. the extent of electron transfer from the reduced form of the primary acceptor A to the secondary acceptor Q) was assumed to depend on temperature. This assumption explains why the character of P decay depends on whether P+ species are formed after or in the process of freezing the sample. 

Thus, the study [45] of the kinetics of the charge recombination in the reaction centres of photosystem 1 of subchloroplasts over wide time and temperature intervals has shown an essential difference in the kinetics of the tunneling decay of P700+ at high and low temperatures. The quantitative description of the electron transfer kinetics has proved possible in terms of the assumption of a difference in charge recombination rate constants for different reaction centres. Such a difference may be due, for example, to a non-coincidence, for different reaction centres, of electron tunneling distances or to different conformational states of these centres. 

Tegoni, M., Silvestrini, M. C., Guigliarelli, B., ASSO, M., Brunori, M., and Bertrand, P., 1998, Temperature-jump and potentiometric studies on recombinant wild type and Y143F and Y254F mutants of Saccharomyces cerevisiae flavocytochrome b2 role of the driving force in intramolecular electron transfer kinetics. Biochemistry 37 12761nl2771. 

Kirmaier, C., and Holten, D., 1988, Temperature effects on the ground state absorption spectra and electron transfer kinetics of bacterial reaction centers. In NATO ASI Ser., Ser. A, 149 219n228. 

Kirmaier, C., Holten, D., and Parson, W. W., 1985a, Temperature and detection-wavelength dependence of the picosecond electron transfer kinetics measured in Rhodopseudomonas sphaeroides reaction centers Resolution of new spectral and kinetic components in the primary charge-separation process. Biochim. Biophys. Acta, 810 33n48. 

Kleinfeld, D., Okamura, M. Y., and Feher, G., 1984, Electron transfer kinetics in photosynthetic reaction centres cooled to cryogenic temperatures in the charge-separated state evidence for light-induced structural changes. Biochemistry, 23 5780n5786. 

Figure 2. Electron transfer kinetics of cytochrome c oxidation in Chromatium vinosum [4] and Rhodopseudomonas viridis [16] display temperature independence at low temperature, a herald of tunneling. The early Chromatium data were analyzed as a single phase, while the Rp. viridis data were analyzed into three phases, dominated by very fast (VF) and fast (F) phases at high temperatures, and dominated by slow (S) phase at low temperatures.

CH Bock, Avd Est, K Brettel, and D Stehlik (1989) Nanosecond electron transfer kinetics in photosystem las obtained from transient EPR at room temperature. FEES Lett 247 91-96... 

The electrochemistry of titanium (fV) has been exanuned in acidic l-ethyl-3-methyUmidazolium chloride/AlClj ([EmimJCl/AlClj) in 1990 by Carlin et al. [180]. It was shown that titaifium is reduced to Ti(lll) and Ti(n) in two one-electron steps, both of which exhibit slow electron-transfer kinetics. Ten years later, Mukhopadhyay et al. smdied the deposition of Ti nanowires at room temperature from 0.24 M TiCl in the ionic liquid l-butyl-3-methylimidazohumbis((trifluoromethyl)sulfonyl)amide [181]. They found that up to six wires grow at constant potential over a period of about 20 min wires exhibit a narrow width distribution of 10 2 nm and have a length of more than 100 nm. The chemical and electrochemical behavior of titanium was examined in the Lewis acidic [EmimlCl/AlClj molten salt at 353.2 K. The electrodeposition of Al-Ti alloys at Cu rotating disk and wire electrodes was investigated by Tsuda et al. [55]. It was found that Al-Ti alloys which contain up to 19% (atomic fraction) titanium, could be electrodeposited from saturated solutions of Ti(II) in the... 

FAST ELECTRON TRANSFER KINETICS IN PHOTOSYSTEM I FROM TRANSIENT EPR-SPECTROSOOPY AT ROOM TEMPERATURE... 

Lagrost C, Preda L, Volanschi E, Hapiot P (2005) Heterogeneous electron-transfer kinetics of nitro compounds in room-temperature ionic liquids. J Electroanal Chem 585(l) l-7... 

We have spent some time discussing how to change the interfacial temperature. What do we actually measure We measure the open-circuit potential, thereby passing virtually no external current and circumventing the limitations imposed by solution resistance and/or by the RC time constant produced by the solution resistance in series with the double layer capacitance of the electrode. In this section we will discuss just how the open-circuit potential depends upon the interfacial temperature and upon the interfacial electron-transfer kinetics. 

Thus far we have assumed infinfitely fast electron transfer kinetics where the redox species are always at equilibrium with the interfacial potential at the extant interfacial temperature. When the electron transfer kinetics are slow, the ILIT response will exhibit a relaxation whose amplitude is B [Eq. (55)] and characterized by a first-order rate constant, k. If the interfacial temperature change were a step function, we could simply write ... 

If this condition is met there will be no visible response to electron transfer and therefore no measurable amplitude associated with electron transfer kinetics. Quite simply it means that the experimental conditions are such that the interfadal redox equilibrium is not disturbed by a ehange in the interfadal temperature the system was in equilibrium at T and will be in equilibrium at... 

The response times of neat SAMs in the absence of a redox moiety Our theoretical analysis for the ILIT response has presumed that dC /dt is infinitely fast—if that is not the case, extracting meaningful values of will be difficult, if not impossible. We have already mentioned evidence of a slow response of SAMs formed from 11-mercaptoundecanoic acid [113] (Sec. VII). We expect that the results of these types of experiments will be critically dependent upon the choice of the SAM constituent, the SAM preparation, substrate metal, temperature, the solvent, and the electrolyte ions (the less hydrophobic, the better). A thorough study of the potential of zero response would be important and informative. Establishing which films exhibit the fast responses will be critical for any meaningful studies of fast interfacial electron-transfer kinetics. 

Electron-transfer kinetics using SAMs in nonaqueous solvent systems with obvious concern about the stability of SAMs in these solvents) The decrease in the dielectric constant of the solvent coupled with a likely decrease in the reorganization energy and a likely increase in the accessible temperature range should yield some valuable information. 

Smalley, I, L. Geng, A. Chen, S. Feldberg, N. Lewis, and G. Cali (2003). An indirect laser-induced temperature jump study of the influence of redox couple adsorption on heterogeneous electron transfer kinetics. Journal of Electroanalytical Chemistry 549, 13-24. 

We have attempted to support this explanation for slow electron transfer kinetics by comparing experimental and calculated inner-shell barriers for Mn (TPP) Cl reduction. Table 2 contains data from temperature-dependent electrochemical measurements [11] in several non-aqueous solvents. The experimental barrier is obtained by determining AH real from the temperature dependence of the standard heterogeneous rate constant [12] and subtracting from this quantity the value of AG os calculated by equation 4. This difference, AG is, E. is to be compared with AG is calculated by equation 3. For the... 

At this point, the direct electrochemistry of cytochrome c at a host of solid electrodes had become well controlled, stable, and quasi-reversible. This group began to then use this platform to study properties of cytochrome c using direct electrochemical methods, often conpled with optical probes. Stndies of the temperature dependence of the formal redaction potential and the heterogeneons electron transfer kinetics were subseqnently reported, and reaction center entropy valnes were shown to agree well with earlier reports in work by Kent B. KoUer... 

Parson, W.W., Warshel, A. Dependence of photosynthetic electron-transfer kinetics on temperature and energy in a density-matrix model. J. Phys. Chem. B 108, 10474—10483 (2004)... 

Figure 12.10 shows the CVs for methanol oxidation on a Pt/Ru catalyzed electrode at various temperatures. It can be seen that there is a significant increase in the current density with increasing temperature. From the data in this figure, the kinetic parameters of methanol oxidation can be estimated. For an electrochemical reaction controlled purely by electron transfer kinetics, if the reaction overpotential is large enough (>60mV), the Butler-Volmer equation can be simplified to the form of a Tafel equation, which is similar to Eqn (12.6) ... 

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