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Dioxygen activation by copper in an inert cage

Final Activity Report Summary - DIOXYGEN ACTIVATION (Dioxygen activation by copper in an inert cage)

Polytopic ligands in which three bidentate (2,2'-bipyridine or catechol) units are linked to a central tris(pyrid-2-yl)amine or tris(pyrid-2-yl)methanol moiety by alkyl spacers were prepared by multistep organic syntheses. The parent tris(pyrid-2-yl) type ligands were shown to be modest to good chelators for Zn2+ and Cu2+ ions in solution. The structural metals FeII and RuII (in case of 2,2'-bipyridine) and FeIII (in case of catechol) smoothly form stable, cage-like 1:1 complexes with the ligands in which the metal ion is coordinated to the tris(bidentate) site. The vacant tris(pyrid-2-yl) site of these complexes is, however, a poor donor site for Zn2+ and Cu2+ ions. Therefore, the structural metals (FeII, FeIII and RuII) might be considered as allosteric effectors which modulates the metal binding properties of the second tris(pyrid-2-yl) site of the ligands. Contrary to expectation, Zn2+ and Cu2+ appear to associate weakly with donor atoms directed toward the exterior of the cage-like complexes, rather than locating in the interior of the container by tripodal coordination to the tris(pyrid-2-yl) site. Consequently, studies on the dioxygen activation by the copper complexes were complicated low metal ion affinity of the container. The synthesis of fluorinated analogs was also attempted, however, stability of amide and imine linkage was found to be rather poor against solvolysis, probably due to the strong electron withdrawing effect of the perfluoro substituents.

In parallel, functionalised fluorescent (bpy)3Ru2+ complexes which lack the second, tris(pyrid-2-yl) binding site were synthesised. Their selective binding to specific target molecules was evaluated. New fluorescent biological probes has been developed and the light-induced activation of dioxygen (photosensitised generation of singlet oxygen) has been shown in living cells.