Preparation and Structures of Ternary Copper(II) Complexes of ADP and ATP Models for Enzyme-Metal Ion-Nucleoside Polyphosphate Complexes

Abstract

Abstract The stable ternary copper(II) complexes of ATP and ADP, [Cu(H2ATP)(phen)]2 · 7 H2O (2) and [Cu4(HADP)2(bipy)4(H2O)2(NO3)2] · 2 NO3 (3), have been isolated from aqueous solution at respective pH values of 2.8 and 4.0. Their structures have been established by single crystal X-ray diffraction. Tridentate coordination of each of the Cu atoms by ono α-, one β- and one γ-phosphate O atom of one ATP molecule is observed in 2. The binding Oα atoms occupy axial positions in a distorted octahedral geometry at Cu and the Cu- Oα interactions are weak. The other axial position is occupied by a γ-phosphate O atom of the second ATP molecule, leading to a dimeric structure. The basic structure of 3 is similar with, in this case, bidentate coordination of each of the central Cu atoms by one α- and one β-phosphate O atom of ono ADP molecule. In this case, however, the third terminal β-phosphate O atoms each bind a further Cu atom. All four Cu atoms in 3 display square pyramidal coordination. The structures of 2 and 3 are stabilised by intramolecular stacking of adenine and phenanthroline/bipyridyl systems. The significance of these structures as models for enzyme-metal ion-nucleoside polyphosphate complexes is discussed.