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Three heterotetranuclear complexes, [{Ru(II)(bpy)(2)(L(n))}(3)Mn(II)](8+) (bpy = 2,2'-bipyridine, n = 2, 4, 6), in which a Mn(II)-tris-bipyridine-like centre is covalently linked to three Ru(II)-tris-bipyridine-like moieties using bridging bis-bipyridine L(n) ligands, have been synthesised and characterised. The electrochemical, photophysical and photochemical properties of these complexes have been investigated in CH(3)CN. The cyclic voltammograms of the three complexes exhibit two successive very close one-electron metal-centred oxidation processes in the positive potential region. The first, which is irreversible, corresponds to the Mn(II)/Mn(III) redox system (E(pa) approximately 0.82 V vs Ag/Ag(+) 0.01 M in CH(3)CN-0.1 M Bu(4)NClO(4)), whereas the second which is, reversible, is associated with the Ru(II)/Ru(III) redox couple (E(1/2) approximately 0.91 V). In the negative potential region, three successive reversible four electron systems are observed, corresponding to ligand-based reduction processes. The three stable dimeric oxidized forms of the complexes, [Mn(2)(III,IV)O(2){Ru(II)(bpy)(2)(L(n))}(4)](11+), [Mn(2)(IV,IV)O(2){Ru(II)(bpy)(2)(L(n))}(4)](12+) and [Mn(2)(IV,IV)O(2){Ru(III)(bpy)(2)(L(n))}(4)](16+) are obtained in fairly good yields by sequential electrolyses after consumption of respectively 1.5, 0.5 and 3 electrons per molecule of initial tetranuclear complexes. The formation of the di-micro-oxo binuclear complexes are the result of the instability of the {[Ru(II)(bpy)(2)(L(n))](3)Mn(III)}(9+) species, which react with residual water, via a disproportionation reaction and the release of one ligand, [Ru(II)(bpy)(2)(L(n))](2+). A quantitative yield can be obtained for these reactions if the electrochemical oxidations are performed in the presence of an added external base like 2,6-dimethylpyridine. Photophysical properties of these compounds have been investigated showing that the luminescence of the Ru(II)-tris-bipyridine-like moieties is little affected by the presence of manganese within the tetranuclear complexes. A slight quenching of the excited states of the ruthenium moieties, which occurs by an intramolecular process, has been observed. Measurements made at low concentration (<1 x 10(-5) M) indicate that some decoordination of Mn(2+) arises in 1a-c. These measurements allow the calculation of the association constants for these complexes. Finally, photoinduced oxidation of the tetranuclear complexes has been performed by continuous photolysis experiments in the presence of a large excess of a diazonium salt, acting as a sacrificial oxidant. The three successive oxidation processes, Mn(II)--> Mn(III)Mn(IV), Mn(III)Mn(IV)--> Mn(IV)Mn(IV) and Ru(II)--> Ru(III) are thus obtained, the addition of 2,6-dimethylpyridine in the medium giving an essentially quantitative yield for the two first photo-induced oxidation steps as found for electrochemical oxidation.

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The structure of ajoene, a molecule extracted from garlic, has been studied by 1H-NMR and its interaction with model membranes by 1H-, 2H-, 31-P-NMR and ESR experiments. This study clearly shows that the ajoene molecule is located deep in the layer and is close to the interlayer medium. Moreover while NMR experiments show that the membrane structure is only slightly affected by the presence of ajoene, ESR experiments reveal significant modifications in phospholipid dynamics. This interaction, observed before with the phenothiazine derivative, promazine, results in an increase of the membrane fluidity in its hydrophobic part and could be related to clinical properties of ajoene.

Three heterotetranuclear complexes [{RuII(bpy)2(LLn)}3FeII]8+ {bpy = 2,2'‐bipyridine, n = 2, 4, 6; denoted [{Ru(LLn)}3Fe]8+}, in which one iron centre is complexed by three RuII‐tris‐bipyridine‐like moieties containing covalently bridging bis‐bipyridine LLn ligands, have been synthesised and characterised. The stability and the electrochemical, photophysical and photochemical properties of these complexes have been investigated in CH3CN. The cyclic voltammograms of all complexes exhibit two successive reversible oxidation processes in the positive region, corresponding to the FeII/FeIII and RuII/RuIII redox couples. These systems are clearly separated (ΔE1/2 about 300 mV), which indicates the absence of an electronic connection between the two subunits. In the negative region, three successive reversible four‐electron systems are observed, corresponding to the ligand‐based reduction processes. The two oxidized forms of the complexes [{RuII(LLn)}3FeIII]9+ and [{RuIII(LLn)}3FeIII]12+, which are obtained by two successive exhaustive electrolyses, are very stable. The [{Ru(LLn)}3Fe]8+ complexes are luminescent, which shows that the covalent linkage between the RuII‐tris‐bipyridine and FeII‐tris‐bipyridine subunits leads to an only partial quenching of the RuII* excited states by energy transfer to the FeII centre. The luminescence lifetime and quantum yield are found to be independent of the complexes’ concentration, thus indicating that the energy‐transfer process is only due to an intramolecular electron‐exchange mechanism. Quantitative photoinduced oxidation of the tetranuclear complexes has been performed by continuous photolysis experiments in the presence of a large excess of a diazonium salt, which plays the role of a sacrificial oxidant. Two successive oxidation processes (FeII → FeIII and RuII → RuIII) are observed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)