A New Heterobinuclear FeCu Complex with a Single Terminal Fe–O(phenolate) Bond. Relevance to Purple Acid Phosphatases and Nucleases

A novel heterobinuclear mixed valence complex [FeCu (BPBPMP)(OAc)2]ClO4, 1, with the unsymmetrical N5O2 donor ligand 2-bis[{(2-pyridylmethyl)aminomethyl}-6-{(2hydroxybenzyl)(2-pyridylmethyl)}aminomethyl]-4-methylphenol (H2BPBPMP) has been synthesized and characterized. A combination of data from mass spectrometry, potentiometric titrations, X-ray absorption and electron paramagnetic resonance spectroscopy, as well as kinetics measurements indicates that in ethanol/water solutions an [Fe–(μ)OH–CuOH2]+ species is generated which is the likely catalyst for 2,4-bis(dinitrophenyl)phosphate and DNA hydrolysis. Insofar as the data are consistent with the presence of an Fe-bound hydroxide acting as a nucleophile during catalysis, 1 presents a suitable mimic for the hydrolytic enzyme purple acid phosphatase. Notably, 1 is significantly more reactive than its isostructural homologues with different metal composition (FeM, where M is Zn, Mn, Ni, or Fe). Of particular interest is the observation that cleavage of double-stranded plasmid DNA occurs even at very low concentrations of 1 (2.5 μM), under physiological conditions (optimum pH of 7.0), with a rate enhancement of 2.7×10 over the uncatalyzed reaction. Thus, 1 is one of the most effective model complexes to date, mimicking the function of nucleases. Electronic Supplementary Material Supplementary material is available for this article at http://dx.doi.org/10.1007/s00775-005-0635-7.