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Alle hoheren Lebensformen nutzen Sauerstoff als primare Energiequelle. Dieser Sauerstoff entsteht aus Wasser mithilfe von Sonnenlicht in Photosynthese-Membranen. Die Absorption von Licht im Photosystem II (PSII) gruner Pflanzen aktiviert den Elektronentransfer im Sauerstoff entwickelnden Komplex (OEC). Der Mechanismus der Wasseroxidation durch den OEC ist ein wichtiges Forschungsgebiet. Die Verfugbarkeit neuer Proteinstrukturen dank Rontgenkristallographie und EXAFS sowie die Resultate vielzahliger experimenteller und theoretischer Studien bilden nun die Grundlage fur einen Vorschlag, wie Wasser am OEC oxidiert werden konnte. Eine Folge lichtgetriebener Reaktionen, die einen gekoppelten Elektronen-Protonen-Transfer (EPT) nutzen, konnte der Schlussel zur Wasseroxidation sein. Werden diese Reaktionen mit einem Transport von Elektronen uber grose Entfernungen (uber sequenzielle lokale Protonenubertragungen) kombiniert, lasst sich der OEC als komplexe Struktur betrachten, die “fur Protonen geschaltet” wird.

The system ROOH/[Mn3O4(dipy)4(OH2)2](ClO4)4 hydroxylates alkanes and converts ArCRCH2 to ArCRO with extremely high activity and good conversions and yields.

The complex Pt2(pop)44− abstracts hydrogen atoms and electrons from DNA upon photolysis into the d σ ∗ → p σ excited state (pop = P2O5H22−). In duplex DNA, the hydrogen atoms are abstracted from the 4′- and 5′- positions of the deoxynbose functionality, and electrons are abstracted by tunneling from the guanine nucleobase. At high Mg2+ concentrations, the Pt2(pop)44− tetraanion can associate more intimately with the duplex, and both hydrogen atom and electron transfer are efficient; however, at low Mg2+ concentrations, the complex is situated far from the duplex so that the only efficient pathway is electron tunneling. Therefore, the guanine/sugar ratio decreases with increasing Mg2+. The electron transfer pathway can also be examined in the absence of the hydrogen transfer pathway in thermal reactions where the electron is abstracted from guanine by Ru(bpy)33+ (bpy = 2,2′-bipyridine). These reactions can be initiated electrochemically by potentiation of the complex to the 3 + form, which produces catalytic enhancements in cyclic voltammograms. These enhancements show that guanine multiplets are more reactive than dispersed guanines. Finally, binding of DNA to the HhaI methyltransferase causes flipping of a cytosine into the active site of the enzyme, leaving behind an unpaired guanine residue that is more reactive towards electron transfer than the paired guanine, an effect visible in high-resolution electrophoresis gels after photolysis in the presence of Pt2(pop)44−.

The emission properties of [ReO2(py)4]+ in Nafion perfluorosulfonated membranes have been investigated. The excited state of [ReO2(py)4]+is a sensitive probe of microheterogeneous environments in aqueous solution (Thorp el al. (1989) J. Am. Chem. SOC. 111,4364–4368). The absorption and emission maxima indicate that the interior of the membrane is quite polar, similar to ethylene glycol (Z-85). Two well-resolved emission components show different lifetimes (τ1(H2O) = 250 ns, τ2,(H20) = 1.3 μs) and isotope effects (3.0, 2.4), indicative of varying degrees of solvent accessibility. The evidence suggests that [ReO2(py)4]+ occupies two distinct regions in the polymer film, assigned as the interfacial region and the ion-cluster region based on previous electrochemical studies involving other metal ions.

All higher life forms use oxygen and respiration as their primary energy source. The oxygen comes from water by solar-energy conversion in photosynthetic membranes. In green plants, light absorption in photosystem II (PSII) drives electron-transfer activation of the oxygen-evolving complex (OEC). The mechanism of water oxidation by the OEC has long been a subject of great interest to biologists and chemists. With the availability of new molecular-level protein structures from X-ray crystallography and EXAFS, as well as the accumulated results from numerous experiments and theoretical studies, it is possible to suggest how water may be oxidized at the OEC. An integrated sequence of light-driven reactions that exploit coupled electron-proton transfer (EPT) could be the key to water oxidation. When these reactions are combined with long-range proton transfer (by sequential local proton transfers), it may be possible to view the OEC as an intricate structure that is "wired for protons".

Etude des reactions electrochimiques du complexe de manganese sur une electrode de carbone a l'etat vitreux dans de l'acetonitrile

The excited-state properties of the trans complex (Ia) are investigated in acetonitrile solutions.