Zn(II) coordination to tren-based tris-macrocycles. Activity of their trinuclear Zn(II) complexes in carboxy- and phosphate-ester hydrolysis

Zn(II) binding by two tren-based tris-macrocycles has been analysed by means of potentiometric measurements in aqueous solutions. Both ligands form stable trinuclear Zn(II) complexes. Deprotonation of Zn(II)-coordinated water molecules gives mono-, di- and tri-hydroxo complexes. The ability of these trinuclear complexes as hydrolytic agents has been tested by using p-nitrophenyl acetate and bis(p-nitrophenyl) phosphate (BNPP) as substrates. BNPP cleavage takes place through a bridging interaction of the substrate with at least two metals and simultaneous nucleophilic attack of a Zn-OH function at phosphorus. A significant increase of the hydrolysis rate with respect to the mononuclear Zn(II) complex with [12]aneN(4), is observed.