Spectroscopic studies on the interaction between tryptophan–erbium(III) complex and herring sperm DNA

By means of UV and fluorescence spectra, the binding ratios between Er(III)–Trp and DNA in physiological pH environment (pH 7.40) were determined as nTrp:nEr(III) = 3:1 and nER(III)(Trp)3:nDNA=2:1nER(III)(Trp)3:nDNA=2:1, and the apparent molar absorptivity of ɛEr(III)–Trp–DNA is 4.33 × 105 L mol−1 cm−1 which was confirmed by molar ratio method. The binding constants at different temperatures KB25°Cθ=1.93×104 L mol−1 and KB37°Cθ=5.28×103 L mol−1 were obtained by double reciprocal method. Thermodynamic function computation demonstrates that ΔrHmθ is the primary driving power of the interaction between Er(III)(Trp)3 and DNA. By combination analysis of the Scatchard method and CD spectrometry, we suggested that the interaction mode between Er(III)(Trp)3 complex and herring sperm DNA is groove and intercalation bindings.