The hydrolysis of a 5(/) cap analogue, diadenosinyl-5(/),5(/)-triphosphate (ApppA), and two dinucleoside monophosphates: adenylyl(3(/),5(/))adenosine (ApA) and uridylyl(3(/),5(/))uridine (UpU) promoted by an imidazolate-bridged heterobinuclear copper(II)-zinc(II) complex, Cu(II)-diethylenetriamino-mu-imidazolato-Zn(II)- tris(aminoethyl)amine trisperchlorate (denoted as Cu,Zn-complex in the followings) has been investigated. Kinetic measurements were performed in order to explore the effects of pH, the total concentration of the Cu,Zn-complex and temperature on the cleavage rate. The catalytic activity of the Cu,Zn-complex was quantified by pseudo-first-order rate constants obtained in the excess of the cleaving agent. The results show that the Cu,Zn-complex and its deprotonated forms have phosphoesterase activity and with ApppA the metal complex promoted cleavage takes place selectively within the triphosphate bridge. (C) 2007 Elsevier Inc. All riahts reserved.