Amphiphilic copper(II) complexes modeled after the metal-complexation subunit of bleomycin antibiotics

A series of lipophilic ligands, structurally related to Bleomycins (BLMs) metal-binding subunit, have been synthesized. They comprise a 4-alkoxypyridine substituted in the 2- and 6-positions with methylhistamine or methylethylenediamine moieties. With respect to native BLMs, pyridine replaces the pyrimidine ring and the amide function in one of the two sidearms has been reduced to amine. Long hydrocarbon chains in the alkoxy moiety provide lipophilicity. Hydrophilic ligands were also synthesized to get insight on the effect of micellization upon protonation and complex formation. All ligands form 1:1 complexes with Cu ^II ions, and those of the lipophilic ligands form micellar aggregates (metallomicelles) with critical micelle concentrations (cmc) in the 9 × 10 ^-5-1.4 × 10 ^-4 M concentration interval. Micellization affects acid/base and coordination equilibria as well, as suggested by titration, ¹H NMR, and UV-vis spectroscopic investigations, but does not affect the geometry of coordination. The information obtained indicates that, upon micellization, the amines become less basic although the difference in basicity between aggregate and nonaggregate systems tends to disappear with the proceeding of the protonation. Micellization affects the pH at which the complexes switch from tetra- to pentacoordinate: this explains the pH and aggregation-dependence of the redox potential of the Cu ^II/Cu ^I couple we have previously reported (Langmuir 1996, 12, 5188) for these systems.