Abstract
The imidazolate-bridged dicopper complex of a macrocyclic ligand with two hydroxyethyl pendants L, L=3,6,9,17,20,23-hexaza-6,20-bis(2-hydroxyethyl)-tricyclo[23.3.1.1. 11,15]triaconta-1(29),11(30),12,14,25,27-hexaene, has been synthesized as a possible model for Cu,Zn-SOD. Single-crystal X-ray analysis revealed the geometry of the imidazolate-bridged CuCu center, and the distance between the two Cu(II) ions is 5.8135(9) Å. The two metals are each pentacoordinated with geometries between trigonal-bipyramid (TBP) and tetragonal-pyramid (TP). Magnetic measurement of the imidazolate-bridged dicopper complex exhibited the presence of an antiferromagnetic exchange interaction with a coupling constant of −2 J=72.8 cm −1. Investigation on the pH-dependent ESR of the complex in frozen 50% aqueous DMSO solution at 110 K revealed the existence of the imidazolate-bridged dicopper structure in solution mainly in the range 5.5≤pH≤12. The SOD activity of the complex has been evaluated by the nitro blue tetrazolium assay and the complex catalyzed the dismutation of superoxide at pH 7.8 with an IC 50 value of 0.36 μmol dm −3.
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