ELECTRON-SPIN-RESONANCE STUDY OF THE BINDING STRUCTURES OF CATIONIC WATER-SOLUBLE METALLOPORPHYRINS ON HIGHLY ORIENTED DEOXYRIBONUCLEIC-ACID FIBERS

The binding structures of several paramagnetic metal complexes of 5,10,15,20-tetrakis(1-methyl-4- or -2-pyridinio)porphyrin (H(2)L(1) or H(2)L(2)) on the highly oriented DNA fibres were investigated by means of ESR spectroscopy and computer simulations of the spectra. The structural parameters characteristic of the sterospecific groove binding were obtained for [CuL(2)]Cl-4, high-spin [FeCl(L(1))]Cl-4 and low-spin [CoL(1)][ClO4](4) and the low-spin monoimidazole adduct [CoL(1)(Him)][ClO4](4). They bind to the DNA with the normals of the porphyrin planes tilted by about 45 degrees from the double helix axes. The low-spin bis(imidazole) adduct [FeCl(L(1))(Him)(2)]Cl-4 binds to A-form DNA with the porphyrin plane nearly parallel to the double helix axis. The complex [CoL(1)][ClO4](4) binds to DNA as an intercalator as well as a groove binder. It was also revealed that some metalloporphyrins stabilize the tertiary structures of DNA around the binding sites.