Binding of an oxo-bridged dinuclear iron(III) complex {[Fe(phen)(H2O)3]2O}(SO4)2 to dna and its recognition of single- and double-stranded DNA as determined by electrochemical studies

An oxo-bridged dinuclear iron(III) complex, {[Fe(phen)(H2O)3]2O}(SO4)2, was synthesized and the molecular structure was determined by X-ray crystallography. Cyclic voltammetry shows that the complex has a cathodic peak at +0.325 V and a pair of redox peaks at +1.011 V and +0.811 V, respectively, which can be explained by an EC–C–EC mechanism. The binding property of the complex to fish-sperm DNA was investigated by electronic absorption spectrophotometry and electrochemical methods. The change in the electrochemical behavior of the complex after treatment with DNA shows that the oxo-bridged diiron(III) complex interacts with DNA mainly through electrostatic binding, while the electrochemical and chemical (EC–C) process product interacts mainly by intercalation. This result is further supported by experiments examining the influence of ionic strength. The difference in the binding modes of {[Fe(phen)(H2O)3]2O}(SO4)2 and its EC–C product, namely a mononuclear phen-ligated ferrous complex, to DNA implies that this strategy can be used to distinguish single-stranded (ss-) and double-stranded (ds-) DNA. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)