A Study on the Aggregation and Calf Thymus DNA Binding Characteristics of Anionic Cobalt(II) Tetrasulfonated Phthalocyanine

The aggregation behavior of anionic Cobalt(II) 4,4′,4ʺ,4‴-tetrasulfonated phthalocyanine, [Co(TSPc)4-] was studied at its various concentrations and different ionic strengths using optical absorption and resonance light scattering (RLS) spectroscopies in 5 mM phosphate buffer, pH 7.0 at 25 °C. The results show no aggregation behavior at concentration range of 5.1 × 10-6-7.5 × 10-5 M. Also, the interaction of [Co(TSPc)4-] with calf thymus DNA (ct-DNA) was studied by UV-Vis absorption, fluorescence spectroscopies and thermal denaturation measurement. The binding constants were obtained at various ct-DNA concentrations using SQUAD software. The thermodynamic parameters were calculated by the van't Hoff equation. The results show that the process is entropy-driven. The fluorescence study represents the quenching effect of [Co(TSPc)4-] on bound ethidium bromide (EtBr) to ct-DNA.