Characterization of Catalytic Activities and Heme Coordination Structures of Heme–DNA Complexes Composed of Some Chemically Modified Hemes and an All Parallel-Stranded Tetrameric G-Quadruplex DNA Formed from d(TTAGGG)

Heme binds selectively to the 3′-terminal G-quartet (G6 G-quartet) of an all parallel-stranded tetrameric G-quadruplex DNA, [d(TTAGGG)]4, to form a heme–DNA complex. Complexes between [d(TTAGGG)]4 and a series of chemically modified hemes possessing a heme Fe atom with a variety of electron densities were characterized in terms of their peroxidase activities to evaluate the effect of a change in the electron density of the heme Fe atom (ρFe) on their activities. The peroxidase activity of a complex decreased with a decreasing ρFe, supporting the idea that the activity of the complex is elicited through a reaction mechanism similar to that of a peroxidase. In the ferrous heme–DNA complex, carbon monoxide (CO) can bind to the heme Fe atom on the side of the heme opposite the G6 G-quartet, and a water molecule (H2O) is coordinated to the Fe atom as another axial ligand, trans to the CO. The stretching frequencies of Fe-bound CO (νCO) and the Fe–C bond (νFe–C) of CO adducts of the heme–DNA complexes were dete...