Monoesterase Activity of a Purple Acid Phosphatase Mimic with a Cyclam Platform

The synthesis and characterization of a novel dinucleating ligand L (L=4,11‐dimethyl‐1,8‐bis{2‐[N‐(di‐2‐pyridylmethyl)amino]ethyl}cyclam) and its μ‐oxo‐bridged diferric complex [(H2L){FeIII2(O)}(Cl)4]2+ are reported. This diiron(III) complex is the first example of a truly functional purple acid phosphatase (PAP) mimic as it accelerates the hydrolysis of the activated phosphomonoester 2,4‐dinitrophenyl phosphate (DNPP). The spectroscopic and kinetic data indicate that only substrates that are monodentately bound to one of the two ferric ions can be attacked by a suitable nucleophile. This is, most probably, a terminal iron(III)‐bound hydroxide. DFT calculations support this assumption and also highlight the importance of secondary interactions, exerted by the protonated cyclam platform, for the positioning and activation of the iron(III)‐bound substrate. Similar effects are postulated in the native enzyme but addressed in PAP mimics for the first time. Enzyme models: A protonated cyclam platform helps to fix and activate phosphomonoester substrates through a dinuclear metal site (see figure) and leads to the first functional purple acid phosphatase (PAP) mimic.