The interaction of native DNA with iron(III)- N, N′-ethylene-bis(salicylideneiminato)-chloride

The interaction between native calf thymus deoxyribonucleic acid (DNA) and Fe III- N, N ′-ethylene-bis (salicylideneiminato)-chloride, Fe(Salen)Cl, was investigated in aqueous solutions by UV–visible (UV–vis) absorption, circular dichroism (CD), thermal denaturation and viscosity measurements. The results obtained from CD, UV–vis and viscosity measurements exclude DNA intercalation and can be interpreted in terms of an electrostatic binding between the Fe(Salen) + cation and the phosphate groups of DNA. The trend of the UV–vis absorption band of the Fe(Salen)Cl complex at different ratios [DNA phosphate]/[Fe(Salen)Cl] and the large increase of the melting temperature of DNA in the presence of Fe(Salen)Cl, support the hypothesis of an external electrostatic interaction between the negatively charged DNA double helix and the axially stacked positively charged Fe(Salen) + moieties, analogously to what reported for a number of porphyrazines and metal–porphyrazine complexes interacting with DNA.