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The complexation of lanthanum(III), europium(III), dysprosium(III), erbium(III), and lutetium(III) with D‐gluconic acid (LH) was studied by pH potentiometry and NMR. The set of complexes formed in aqueous solutions and their stability constants β were determined, and the results were compared to those previously found for praseodymium(III) (S. Giroux et al., Polyhedron 2000, 19, 1567). A regular evolution of the β values was observed along the lanthanide series, particularly for the neutral complex MLH−2 (where two hydroxy functions were deprotonated) with a selectivity similar to that of EDTA. For the ML2+ complex, where the ligand was coordinated via the carboxylate groups, the analysis of the 13C NMR pseudo‐contact shift showed that the carboxylate group was not bidentate and that there was a participation of the α‐hydroxy group in the coordination. The study of the complexation of PrIII with other hydroxy carboxylic acids: glyceric, threonic, 2‐hydroxybutanoic, and 3‐hydroxybutanoic acids confirms that in the complex MLH−2 the deprotonated hydroxy groups, that intervene in the coordination with the metal ion, are those in α and γ positions relative to the carboxylate group. (© Wiley‐VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Oxidizing polyazaaromatic Ru(II) complexes containing two TAP ligands (TAP = 1,4,5,8-tetraazaphenanthrene) are able under illumination to cross-link irreversibly the two strands of an oligonucleotide (ODN) duplex by covalent bond formation. The cross-linking proceeds by two successive absorptions of a photon. An adduct of the metallic complex on a guanine (G) base of one ODN strand is first photoproduced, followed by a second photoaddition of the same Ru species to a G base of the complementary strand, provided that the two G moieties are separated by 0 or 1 base pair. These two processes lead to the cross-linking of the two strands. Such a photo-cross-linking is easily detected with [Ru(TAP)(2)(phen)](2+) (1; phen = 1,10-phenanthroline) and [Ru(HAT)(2)(phen)](2+) (2; HAT = 1,4,5,8,9,12-hexaazatriphenylene), whereas it is not observed with [Ru(TAP)(2)TPAC](2+) (3; TPAC = tetrapyridoacridine) at the same level of loading of the duplex by 3. With a concentration of 3 similar to that of 1 and 2, when the loading of the duplex by 3 is much more important than with 1 and 2, the photo-cross-linking with 3 can thus also be observed. As 3 intercalates its TPAC ligand into the base pairs stack, its mobility is restricted in the duplex. In contrast, 1 and 2 can adopt different geometries of interaction, which probably facilitate the photo-cross-linking.