Synthesis, characterization, and binding of [Cr(naphen)(H₂O)₂]⁺ with DNA: experimental and modeling study

Abstract

A chromium(III) complex of naphen, where naphen denotes 1,2-bis(naphthylideneamino)ethane having the basic salen structure, with an extended aromatic system, has been synthesized and characterized using UV–visible, infrared and ESI mass spectra. Absorption titration and thermal denaturation studies revealed that [Cr(naphen)( H₂O)₂]⁺ binds to DNA with moderate strength. Relative viscosity measurements clearly indicate that it binds to DNA by an intercalative mode. This observation is in contrast to an observation with the parent complex, [Cr(salen)( H₂O)₂]⁺, which prefers groove binding. Intercalation of the complex results in a change in the helicity of CT DNA, which is reflected in the CD spectrum of DNA in the presence of [Cr(naphen)( H₂O)₂]⁺. The binding constant of the complex to CT DNA has been estimated to be (0.51 ± 0.07)×10⁴ M^-1 (1 M = mol dm^-3), which is lower than the values reported for classical intercalators. Modeling studies with the dodecamer d(GCGCAATTGCGC) ₂ show that as a result of the intercalation of [Cr(naphen)( H₂O)₂]⁺ the vertical separation of the bases increases by 2.67 Å in one strand and by 1.89 Å in the other.