HEMOCYANIN AND TYROSINASE MODELS - SYNTHESIS, AZIDE BINDING, AND ELECTROCHEMISTRY OF DINUCLEAR COPPER(II) COMPLEXES WITH POLY(BENZIMIDAZOLE) LIGANDS MODELING THE MET FORMS OF THE PROTEINS

The new poly(benzimidazole) ligands s(1-methyl-2-benzimidazolyl)methyl ]amino]-m-xylene (L-5,5) and thyl-2-benzimidazolyl)ethyl]amino]-m-xyle ne(L-6,6) and their dicopper(I) and bis(aquo)-dicopper(II) complexes a re reported. The ligands provide one tertiary amino and two benzimidaz ole nitrogen donors to each metal center; each of the two ''arms'' of L-5,5 binds the metal with two adjacent five-membered chelate rings, w hile with L-6,6 these chelate rings are six-membered. The dicopper(I) complexes react with dioxygen to produce the bis(hydroxo)dicopper(II) complexes. The bis(aquo)- and bis(hydroxo)dicopper(II) complexes can b e interconverted in a single step by addition of base and acid, respec tively. The electrochemical behavior of the bis(aquo)dicopper(II) comp lex of L-6,6 shows reversible reduction to the corresponding dicopper( I) complex whereas the analogous complex of L-5,5 is irreversibly redu ced. The bis(hydroxo)dicopper(II) complexes of both ligands also under go irreversible reduction. Azide adducts of the dicopper(II) complexes have been isolated; the anion bridges the two coppers in mu-1,1 fashi on in the L-5,5 derivative and in mu-1,3 fashion in the L-6,6 derivati ve. The spectral properties of the two complexes are significantly dif ferent. Binding studies performed in solution for the bis(aquo)- And b is(hydroxo)dicopper(II) complexes show that up to four azide molecules can bind to the complexes and the affinity of azide decreases with th e charge of the complex. Electrochemistry shows that, upon increasing the number of bound azide groups, the successive reductions of the two copper(II) centers tend to coalesce, thus indicating progressive lowe ring of the electronic communication between the metal centers. The re levance of the spectroscopic and binding data of these azide complexes to hemocyanin and tyrosinase is discussed.