A series of copper complexes of bis(hydroxysalicylidene)ethylenediamine (hydroxy-salens) have
been synthesized. The hydroxy group in the ortho, meta, or para position on each salicylidene unit was added
to reinforce the stability of the copper complex and to create a hydroquinone system cooperating with the
copper redox system to facilitate the spontaneous formation of oxidizing CuIII species. Cyclic voltammetry
and ESR spectroscopy in combination with electrochemistry and spin trapping experiments have been used to
characterize the structure and the redox state of the hydroxy-salen−copper complexes and to evidence the
production of oxygen-based free radicals. A complete set of magnetic values were determined. In addition, we
studied the capacity of complexes 3a,b,c to cleave DNA in the absence of activating agents. The meta isomer
3b does not generate oxygen radicals, and as a result it cannot cleave DNA. In sharp contrast, the para isomer
3c and to a lower extent the ortho isomer 3a exhibit nuclease activities in relation to their capacities to produce
oxygen radicals. Electrochemistry provides unequivocal evidence for the formation of CuIII species with
compounds 3a and 3c, but not with 3b. The nuclease activity correlates well with the ability of the hydroxy-salens to form the oxidizing CuIII species. The redox properties and therefore the DNA cleaving activities of
the complexes depend crucially on the position of the OH groups which contribute significantly to stabilize
the square planar copper complexes. The present work supports the hypothesis that a hydroquinone system
can cooperate with a redox metal system to trigger DNA cleavage. The design of metallo(hydroxy-salens)
provides an original route for the development of self-activated chemical nucleases.
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