Interaction of metal ions with 6-oxopurine nucleotides. Part 1. X-Ray structures of ternary cobalt(III) complexes with inosine 5′-monophosphate or guanosine 5′-monophosphate

Abstract

The crystal structures of two ternary metal nucleotide complexes of cobalt, [Co(en)₂(H₂O)₂]-[Co(5′-IMP)₂(H₂O)₄]Cl₂·4H₂O (1) and [Co(en)₂(H₂O)₂][Co(5′-GMP)₂(H₂O)₄]Cl₂·4H₂O (2), have been analysed by X-ray diffraction (en = ethylenediamine, 5′-IMP = inosine 5′-monophosphate, and 5′-GMP = guanosine 5′-monophosphate). Both complexes crystallize in the orthorhombic space group C222₁ with a= 8.725(1), b= 25.891(5), c= 21.212(5)Å, Z= 4 for (1) and a= 8.733(2), b= 26.169(4), c= 21.288(4)Å, Z= 4 for (2). The structure of (1) was solved by the heavy-atom method, while that of (2) was deduced from (1). The structures were refined to R values of 0.09 and 0.10 for 1 546 and 1 572 reflections for (1) and (2) respectively. The two structures are isomorphous. A novel feature is that the chelate ligand en and the nucleotide are not co-ordinated to the same metal ion. One of the metal ions lying on the two-fold a axis is octahedrally co-ordinated by two chelating en molecules and two water oxygens, while the other on the two-fold b axis is octahedrally co-ordinated by two N(7) atoms of symmetry-related nucleotides in a cis position and four water oxygens. The conformations of the nucleotides are C(2′)-endo, anti, and gauche–gauche. In both (1) and (2) the charge-neutralising chloride ions are disordered in the vacant space between the molecules. These structures bear similarities to the mode of nucleotide co-ordination to Pt^II complexes of 6-oxopurine nucleotides, which are the proposed models for intrastrand cross-linking in DNA by a metal complex.