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 _obs versus calf thymus DNA is linear passing through the origin.