Interaction of a new cobalt(II) complex of five-coordinated chiral porphyrin with calf thymus DNA

A new template-directed chiral porphyrin [(TPP)Co(Trp)], where TPP = tetraphenylporphyrin and Trp = 1-tryptophan, was prepared and characterized by various physico-chemical methods. Interaction of [(TPP)Co(Trp)] with calf thymus DNA was studied by u.v.–vis. spectroscopy and cyclic voltammetry. The complex [(TPP)Co(Trp)], after interaction with calf thymus DNA, shows a shift in the absorption spectrum and a large hypochromicity, indicating an intercalating binding mode. This observation was further confirmed by the electrochemical behavior of [(TPP)Co(Trp)] before and after interaction with calf thymus DNA. The complex experiences a negative shift in E_1/2 and a decrease in E_p. The ratio of cathodic to anodic peak currents i_pc/i_pa was 1 for [(TPP)Co(Trp)] while for DNA bound complex i_pc/i_pa 1, suggesting that the calf thymus DNA moiety is bound strongly to the complex [(TPP)Co(Trp)]. Kinetic studies of the DNA-porphyrin complex reveal a psuedo-first order rate law as the plot of k_obsversus calf thymus DNA is linear passing through the origin.