Redox potential trimers

Analysis of the UV-visible, ESR and redox potential data suggests the absence of any exciton couphng between the porphyrin rings and these trimers. Energies of the singlet and charge transfer states are shown in Figure 1. H2 means H2L , Ge means [(L ) Ge (0H)2] and Zn means ML M . 

Cationic sandwich complexes of the type CpCo(arene) + were first prepared by hydride abstraction from cyclohexadi-enyl cations (Section 7.1). They are accessible in broader variation from the reaction of CpCoX half-sandwich complexes with arene in the presence of AICI3. Their electrochemical reductions to the corresponding 19-electron monocations and to 20-electron neutral complexes have been studied. The stability of electron-rich sandwich complexes increases with increasing alkyl substitution in either ring despite the more negative redox potential mass spectrometry studies of bond dissociation energies of (arene)Co+ complexes corroborate these results. However, neutral sandwich complexes are not very stable in the polar solvents necessary for the reduction of mono- or dications and have been isolated only from alkyne trimerization with CpCo precursors in nonpolar solvents (Section 5.1.4). 

A similar structure ofthe energy landscape can be expected for the process of excess electron transfer on the basis ofthe redox potential data available in the literature, see e.g. [10]. However, now the traps have to be pyrimidine deoxynucleobases stacked on the same strand (e.g. TT dimers orTTT triplets), the intermediate states should be associated with the anions T" and/or C", while bridging states will correspond to G and/or A bases (see Fig. 1C). This conclusion directly follows from the hierarchy of the measured reduction potentials, which decrease in the order C T A > G [10]. Electron affinities calculated both for individual nucleobases and for their different trimers exhibit the same trend [11]. 

Simple redox solutes, ferrocene, N, N, N, JV-tetramethyl-l,4-phenylenediam-ine, decamethylferrocene, bis(i-propylcyclopentadienyl) iron(ll), [Ru(phen)j] (0104)2, [Fe(bpy)3](0104)2, [Co(bpy)3](0104)2, and iodine have been studied at electrodes modified with polymeric fullerene films. FuUerene-modified electrodes were prepared by electropolymerization of Cjq initiated by traces of dioxygen or by simultaneous electroreduction of fullerene and Pd(ll) acetate trimer. For the former films, the electrochemical activity decreases upon potential cycling. The electrochemical activity of the film is stabihzed by the redox solute added to the electropolimerization stage due to the catalytic oxidation of the fullerene film by the oxidized form of the redox system. Similarly, positively charged species can also be incorporated into the structure of the film. The reversible behavior of redox solutes decreases with the increase in the thickness of the Pd/C q film. This film also incorporates ferricinium ion, N, N, N, N-tetramethyl-l,4-phenylenediamine cation, decamethylferricinium ion, and to a smaller degree [Co(bpy)3]"+ [53]. 

A model of the ATP synthase, the effector of the chemiosmotic mechanism. A potential and a hydrogen ion gradient is created across the inner membrane of mitochondria, bacteria, and chloroplasts by redox reactions. The energy of this proton motive force is translated into ATP synthesis by rotation of the cluster of c subunits of the F , and this rotation is transmitted via the y stalk to the a-B trimers of the F, complex. The catalytic complex contains three a-6 trimers that rotate with transmission of hydronium ions inward through the c subunit complex of the Fo sector. The two b subunits tether the a-6 trimers via the 6 subunit, and the a subunit is fixed, allowing rotation of the c complex, thus rotating the y stalk. 

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