Modeling electron transfer from

Fukuzumi S, Mochizuki S, Tanaka T. 1990. Efficient catal)dic systems for electron transfer from an NADH model compound to dioxygen. Inorg Chem 29 653. 

Photoelectrochemical experiments on the pyrite/H2S system, as well as theoretical considerations, led Tributsch et al. (2003) to the conclusion that CO2 fixation at pyrite probably could not have led to the syntheses proposed by Wachtershauser. The reaction mechanism involved in such reactions is likely to be much more complex than had previously been assumed. The Berlin group supports the objection of Schoonen et al. (1999) that, apart from other points, the electron transfer from pyrrhotine to CO2 is hindered by an activation energy which is too high. There is, thus, no lack of different opinions on the model of chemoautotrophic biogenesis hopefully future studies will shed more light on the situation ... 

Carloni et al.91 applied the DFT(PZ) calculations to investigate the electronic structure of various models of oxydized and reduced Cu, Zn superoxide dismutase. The first stage of the enzymatic reaction involves the electron transfer from Cu" ion to superoxide. The theoretical investigations provided a detailed description of the electronic structure of the molecules involved in the electron transfer process. The effect of charged groups, present in the active center, on the electron transfer process were analyzed and the Argl41 residue was shown to play a crucial role. 

Complex I can be regulated by phosphorylation. Demin et al. [28] studied superoxide generation by Complex III using the kinetics model of electron transfer from succinate to cytochrome c. 

In this model, one considers the acetals to be composed of polarizable dipolar moieties that can be stabilized by electron transfer from an electron-rich moiety (non-bonding electron on oxygen low ionisation energy) to adjacent polar and polarizable moieties (high electron affinity). A strong overlap between n(O) and cr c 0 orbitals optimizes this electronic transfer. As these orbitals are not spherical, n(0)/ct c o overlap depends on... 

FIGURE 3.2. Variation of the rate constants of dissociative electron transfer from aromatic anion radicals to butyl and benzyl halides as a function of steric hindrance. Data points from reference 10. Solid lines, best-fit parabola dashed lines, prediction of the Morse curve model, logAf-1 s-1). Adapted from Figure 3 of reference 6b, with permission from the American Chemical Society. 

The oxo-transfer chemistry of molybdenum in sulfite oxidase is probably the best characterized, in terms of synthetic models, structural and mechanistic data, of all the elements we have described up till now. The reaction cycle (Figure 17.5) involves binding of sulfite to the oxidized MoVI, two-electron reduction of the Mo centre and release of sulfate. The Movl centre is restored by successive one-electron transfers from a cytochrome (bs in mammals). The primary oxo-transfer reaction ... 

Fig. 16.1 Schematic model of the electron transfer from Ti02 nanoparticles to CNTs. The inset shows a SEM image of Ti02 nanoparticies supported over a MWCNT. Adapted with permission from Centi and Perathoner [7].

Although it is not an electron transport protein, its primary function involves specific electron transfer from cyt c to a heme center, in which binding plays a key kinetic role. It has thus become a model for understanding the structurally more complex interactions between cytoehrome c and its partners in electron transport. This similar cyt c ccp system has several advantages. 

Binding at the remote site has also been detected in studies on the quenching of the excited states [Cr(phen)3] and [Ru(bipy)3] by French bean plastocyanin [103]. The model adopted allows for electron transfer from the remote and adjacent sites, where at low protein concentrations the adjacent pathway is 10 times faster. At the higher concentrations of protein, up to 4 X 10 M, an interesting feature is the evidence for an adduct in which two PCu(I) molecules are associated with one inorganic complex. The oxidant is believed to be sandwiched between two PCu(I) s. 

Because this reaction must involve two steps, diffusion of selenate into the interlayer spaces of the green rust followed by electron transfer from Fe(ll) green rust, Johnson and Bullen (2003) interpreted this result using a two-step model similar to that discussed above. The diffusion step presumably has very little isotopic fractionation associated with it. Step 2 might be expected to involve a kinetic isotope effect similar to that observed in the HCl reduction experiments. As is discussed above, if the diffusion step is partially rate-limiting, the isotopic fractionation for the overall process should be less than the kinetic isotope effect occurring at the reduction step. This appears to be the case, as the ese(vi)-se(iv) value of 7.4%o is somewhat smaller than that observed for reduction by strong HCl (12%o). 

Most of the work published to date on molecular dynamic studies of interfacial electron transfer involves the simplified assumption of a two-state model for the electronic degrees of freedom. Consider an ion of charge qj near a solution/metal interface. As a result of electron transfer between the ion and the metal surface, the charge of the ion changes to qj. We will consider both forward and backward electron transfer and assume that = <7 - = -1, so that the forward reaction corresponds to a single electron transfer from the metal to the ion, for example + e ... 

Last time, electron-transfer reactions were frequently performed in micellar media. Analyzing temperature effects on electron transfer from aromatic amines to coumarins in aqueous Trilon X-100 micelles, Kumbhakar et al. (2006) deduced that the two-dimensional electron-transfer (2DET) model is more suitable to explain the results obtained than the conventional electron-transfer theories. The model is detailed in the article by Kumbhakar et al. (2006) and references therein. 

The intensity (and also the half-width) of the band due to the XH vibration is greatly increased when the hydrogen bond is formed. This increase has been explained in terms of an increase in the ionic character of the bond (158) and also in terms of a charge transfer (159). Possibly both mechanisms operate together, but recent experiments (160) indicate that the charge transfer model is probably to be preferred. In such a case, the X atom becomes negative by an electron transfer from the Y atom, the... 

Flash photolysis has been used to investigate the kinetics of electron transfer from tyrosine to Ru in [Ru(bpy)2(4-Me-4 -CONH-L-tyrosine ethyl ester-2,2 -bpy)] " as a function of pH and temperature. " Model systems for PSII have moved to di- and trimanganese systems containing... 

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