Synthesis, spectrophotometric pH titrations and DNA binding properties of a cyclometalated iridium(III) complex of tetrapyrido[3,2-a:2′,3′-c:3″,2″-h:2‴,3‴-j]phenazine

A new cyclometalated iridium(III) complex [Ir(ppy)2(tpphz)]Cl {Hppy = 2-phenylpyridine and tpphz = tetrapyrido[3,2-a:2′,3′-c:3″,2″-h:2‴,3‴-j]phenazine} has been synthesized and characterized. The pH effects on UV–vis absorption spectra have been studied, and three ground-state acidity ionization constant values have been derived. The calf thymus (ct) DNA binding properties of the complex have also been investigated with UV–vis absorption spectrophotometric titrations, DNA competitive binding with ethidium bromide, DNA melting experiments, viscosity measurements, and density functional theory calculations. The complex was demonstrated to act as a DNA intercalator with a binding constant of (9.29 ± 1.26) × 105 M−1 more than one order of magnitude greater than that previously reported for DNA intercalator of [Ir(ppy)2(dppz)]+.

Graphical abstractA new cyclometalated Ir(III) complex shown below was demonstrated to act as a DNA intercalator with a binding constant of (9.29 ± 1.26) × 105 M−1 over one order of magnitude greater than that for previously reported DNA intercalator of [Ir(ppy)2(dppz)]+, and to exhibit 3-step successive protonation/deprotonation processes.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► A cyclometalated Ir(III) complex as a DNA intercalator. ► A cyclometalated Ir(III) complex as a DNA intercalator.DNA binding constant is over one order of magnitude greater than that for [Ir(ppy)2(dppz)]+. ► The evident UV–vis spectral changes caused by DNA binding and acid–base processes.