Crystal and molecular structure of the ternary complex bis[(adenosine 5'-triphosphato)(2,2'-bipyridine)zinc(II)] tetrahydrate

The crystal structure of the dimeric species [Zn(II)-H2ATP-2,2′-bpy]2· 4H2O has been determined by X-ray diffraction. Cell constants are a = 11.105 (3), b = 25.223 (7), c = 10.539 (3) Å, β = 91.34 (4)°, with monoclinic space group P21. Diffractometer collected reflections (1617) were used for the structure determination and refinement (R = 0.098). The structure of the compound consists of dimeric molecules in which two zinc atoms are held together by two -OPO- bridges from the γ-phosphate groups of two ATP molecules. Both zinc atoms show a distorted octahedral coordination formed by two oxygen atoms from different γ-phosphate groups, one oxygen atom from the β-phosphate group, and the two nitrogen atoms of the bipyridyl ligand. The sixth position is filled by a α-phosphate oxygen atom which is more weakly bound. The five closest Zn-N and Zn-O distances average respectively 2.14 (4) and 2.03 (3) Å. Both ribose rings show the common C3′ endo configuration. The conformation around the exocyclic C4′-C5′ bond is gauche+ for both rings. The structure is held together by strong intermolecular bipyridyl-purine and bipyridyl-bipyridyl stacking interactions. Weaker bipyridyl-purine intramolecular stacking is also observed. The molecule provides a possible model for ATP transport and phosphate group transfer mechanism. © 1981 American Chemical Society.