The cyclen based pyridine complexes (Ln= La (III) and Eu (III)) were synthesised as metallo- ribonuclease mimics and their ability to hydrolytically cleave the phosphodiester of HPNP at 37° C was investigated using UV–vis spectroscopy, whereas the binding of the substrate was evaluated using 31P NMR and Eu (III)-luminescent measurements. In contrast gave rise to fast pH dependent hydrolysis of HPNP, with maximum efficiency at ca. pH8. 2, and with ...