Cobalt(III) salen complex with N,N-dipyridoxyl (1,4-butanediamine) Schiff-base ligand as tetradentate ligand was synthesized and characterized by the elemental and spectroscopic analysis. The interaction of this complex with calf thymus DNA (ct DNA) has been investigated in vitro using UV absorption, fluorescence spectroscopy, thermal denaturation and gel electrophoresis techniques. The binding constant has been estimated to be 1×104 M−1 using UV absorption. The addition of ct DNA to Co(III) salen solution resulted in a fluorescence quenching. The binding constant and site size binding have been calculated in connection with other experimental observations show that the interactive model between Co(III) salen and ct DNA is an intercalative one. The interaction between plasmid DNA (pTZ57R DNA) and this complex is confirmed by gel electrophoresis studies. Furthermore, the interaction between HSA and Cobalt(III) salen complex was investigated by UV absorption, fluorescence spectroscopy and molecular modeling. The binding constant for the interaction of this complex with HSA were found to be 3.854×104 M-1 using UV absorption, which was in good agreement with the binding constant obtained from fluorescence method (3.866×104 M-1). The binding distance between HSA and this complex was estimated to be 2.48 nm according to Förster theory of nonradioactive energy transfer. Molecular modeling studies suggested that hydrophobic interaction was the predominant intermolecular forces stabilizing Co(III) complex-HSA system.

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