Phosphodiester Cleavage Promoted by an Asymmetric Dinuclear Zinc Complex: Synthesis, Structure, and Catalytic Activity

The dinuclear Zn II complex [Zn 2 L(DNBA) 2 ]BPh 4 · EtOH ( 1 ) (DNBA = 3,5‐dinitrobenzonic acid) with an asymmetric dinuclear ligand, N ‐4‐methyl‐homopiperazine‐ N ′‐[ N ‐(2‐pyridylmethyl)‐ N ‐2‐(2‐pyridylethyl)amine]‐1,3‐diamino‐propan‐2‐ol (HL), was synthesized and characterized. Single crystal X‐ray crystallographic analysis shows that the coordination around the two Zn II ions in 1 is significantly asymmetric, and the distance between both atoms is 3.426 Å, which is close to the Zn···Zn distance in related natural dinuclear metalloenzymes. Phosphodiesterase activity of Zn 2 L in situ formed from a 2:1 mixture of Zn 2+ ion and HL was investigated using bis(4‐nitrophenyl) phosphate (BNPP) as substrate. The pH dependence of the BNPP cleavage in aqueous buffer media reveals a bell‐shaped pH‐ k obs profile with an optimum at about pH 7.9, which is parallel to the formation of the dinuclear species Zn 2 L‐OH obtained from the potentiometric titration. The catalytic rate constant ( k cat ) is 6.30 × 10 –4 s –1 at pH 7.9 and 25 °C, which is approx. 10 8 ‐fold higher than that of the uncatalyzed reaction. The homopiperazine bound deprotonated Zn‐OH group is responsible for the hydrolysis reaction. The possible mechanism for the BNPP cleavage promoted by Zn 2 L is proposed on the basis of kinetic and spectral analysis.