A multi-O-2 complex derived from a copper(I) dendrimer

The high-pressure reaction of 2-vinylpyridine with the primary amines of fo ur consecutive generations of poly(propylene imine) dendrimers (DAB-dendr-( NH2)(n)) (n = 4, 8, 16, 32) yielded dendrimers with bis[2-(2-pyridyl)ethyl] amine (PY2) ligands. The complexation of the new dendrimers with metal ions was investigated by a variety of techniques. The reaction of the first- an d fourth-generation dendrimers (n=4 and 32, respectively) with Zn-II(ClO4)( 2) was studied by H-1 NMR titration, and the complexation of all new dendri mers with Cu-II(ClO4)(2) was investigated by UV/Vis and EPR spectroscopy. Q uantitative coordination of one metal ion per PY2 group was demonstrated in all cases. A UV/Vis titration of the fourth-generation dendrimer DAB-dendr -(PY2)(32) in dichloromethane with [Cu-1(CH3CN)(4)](ClO4) in acetonitrile r eveaIed that approximately 30 Cu-I ions were bound. Low-temperature UV/Vis spectroscopy of this complex in dichloromethane at -85 degrees C in the pre sence of dioxygen showed that approximately 60-70% of the copper centers ca n bind dioxygen, corresponding to 10 - 11 of these molecules per dendrimer molecule. This complex can be considered a synthetic analogue of hemocyanin , the copper-containing oxygen transport protein from the hemolymph of moll uscs and arthropods.