Characterization of the Binding of Adenosine-5′-monophosphate to a µ-Type Alkoxide-Linked Dinuclear Zinc(II) Complex in Crystal and Solution State

Abstract

Abstract The binding of adenosine-5′-monophosphate dianion (AMP2−) to a µ-type alkoxide-linked dinuclear zinc(II) complex (Zn2L3+) has been studied {L = alkoxide form of 1,3-bis[bis(pyridin-2-ylmethyl)amino]propan-2-ol}. X-ray crystallography and potentiometric pH titration have been used to decipher the structure of 1:1 AMP2−-bound Zn2L3+ complex in crystal and solution state. The crystal analysis of the AMP2−–Zn2L3+ complex demonstrated that the 5′-phosphomonoester dianion binds to the two zinc(II) ions in a µ-η2 bridge coordination mode. Each zinc(II) ion has a distorted trigonal-bipyramidal coordination environment with five donor atoms: two pyridine N, alkoxide O−, tertiary amine N, and phosphate O−. In contrast, 1:1 NO3−-bound Zn2L3+ complex showed that the nitrate anion binds to one of the zinc(II) ions in a monodentate coordination mode and a water molecule coordinates to the other zinc(II) ion. The pH titration study disclosed that the AMP2−–Zn2L3+ complex is remarkably stable in a wide pH range between 5 and 9. The dissociation constant Kd (= [AMP2−][Zn2L3+]/[AMP2−–Zn2L3+]) is an extremely low value of 4.0 nM at 25 °C and I = 0.10 M (NaNO3) in aqueous solution.