Electron transfer, intermolecular

In this section we review most of the new experimental data on metal-metal electron transfer reactions in solution, in which the rate law for the primary process (19) can be expressed in the second-order form (20), or in related forms explicable in terms of 

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Wang 0, Akhremitchev B and Walker G 0 1997 Femtosecond infrared and visible spectroscopy of photoinduced intermolecular electron transfer dynamics and solvent-solute reaction geometries Coumarin 337 in dimethylaniline J. Rhys. Chem. A 101 2735-8... 

We will use here the main results obtained for two complex and distinct situations the structural and spectroscopic information gathered for D. gigas [NiFe] hydrogenase and AOR, in order to discuss relevant aspects related to magnetic interaction between the redox centers, intramolecular electron transfer, and, finally, interaction with other redox partners in direct relation with intermolecular electron transfer and processing of substrates to products. 

Transient absorption spectra of the CeoN cluster (C6oN" ) -MePH system following laser excitation at 355 nm indicate that the photoinduced intermolecular electron-transfer from the triplet excited state of PH to the QqN cluster (CfioN) occurs as shown in Figure 15.9a. 

Figure15.9 (a) Reaction scheme of photoinduced intermolecular electron-transfer in C oN cluster- MePH system, (b) MFEs on A = Abs(BT)/Abs(0T) in CeoN -MePH inTHF-HjO (2 1) mixed solvent.

One striking prediction of the energy gap law and eq. 11 and 14 is that in the inverted region, the electron transfer rate constant (kjjj. = ket) should decrease as the reaction becomes more favorable (lnknr -AE). Some evidence has been obtained for a fall-off in rate constants with increasing -AE (or -AG) for intermolecular reactions (21). Perhaps most notable is the pulse radiolysis data of Beitz and Miller (22). Nonetheless, the applicability of the energy gap law to intermolecular electron transfer in a detailed way has yet to be proven. 

The aim in solution studies on metalloprotein is to be able to say more about intermolecular electron transfer processes, first of all by studying outer-sphere reactions with simple inorganic complexes as redox partners. With the information (and experience) gained it is then possible to turn to protein-protein reactions, where each reactant has its own complexities... 

Fig. 4 Integrated molecular systems for information transduction through intermolecular electron transfer and conformation change...

Application of pulse-radiolysis techniques revealed that the following intramolecular and intermolecular electron-transfer reactions all exhibit a significant acceleration with increasing pressure. The reported volumes of activation are -17.7 0.9, 18.3 0.7, and... 

In order to obtain further information on the magnitude of the overall reaction volume and the location of the transition state along the reaction coordinate, a series of intermolecular electron-transfer reactions of cytochrome c with pentaammineruthenium complexes were studied, where the sixth ligand on the ruthenium complex was selected in such a way that the overall driving force was low enough so that the reaction kinetics could be studied in both directions (153, 154). The selected substituents were isonicotinamide (isn), 4-ethylpyr-idine (etpy), pyridine (py), and 3,5-lutidine (lut). The overall reaction can be formulated as... 

Attention should be paid to the fact that the electron motion from a donor to an acceptor or within spread-conjugated ion-radicals generates measurable electromagnetic radiation. In other words, there is one specific way to reveal intramolecular electron motion or intermolecular electron transfer in charge-transfer complexes. To probe electron transfer in this manner, the only fundamental requirements are that the molecule can be oriented in the external magnetic field. This takes place most easily if the species considered has a ground state dipole moment. On photoexcitation, there... 

Electroreductive one-electron initiation of cyclization was described for the series of E,E-, 1-dibenzoyl-l,6-heptadiene and its derivatives (Roh et al. 2002, Felton and Bauld 2004). In this case, the catalytic effect was also observed (the actual consumption of electricity was substantially less than theoretical). The same bis(enones) can also be cyclized on the action of the sodium salt of chrysene anion-radical in THF, but with no catalytic effect. Optimum yields were obtained only when 70-120 mol% of the initiator was used, relative to a substrate (Yang et al. 2004). The authors suggest that tight ion pairing of the sodium cation with the product anion-radical in THF (which is a somewhat nonpolar solvent) slows down the intermolecular electron transfer to the bis(enone) molecules. Such an electron transfer would be required for chain propagation. 

The ket values have been determined by fluorescence quenching of RAcrH+ by electron donors [79]. Figure 5 exhibits the dependence of the observed rate constant for intermolecular electron transfer (ket) on AGet [Eq. (6)], which is assumed to be the same as AGet (Scheme 7) in MeCN (part a) and in... 

Scheme 4 J. Intermolecular electron transfer driven by fast bond cleavage.

In ETD, an anion donor collides with the positively charged peptide and transfers an electron to the peptide subsequent to this intermolecular electron transfer, the peptide undergoes cleavage at one of its N-Ca or S-S bonds to form fragment ions. The mass to charge ratios and intensities of the fragment ions are the raw data that is then used to infer the primary sequence of the original... 

Intermolecular electron transfer initiated peroxide decomposition. . 1231... 

Imahori H, Yamada H, Guldi DM et al (2002) Comparison of reorganization energies for intra- and intermolecular electron transfer. Angew Chem Int Ed 41 2344—2347... 

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