Mode of interaction and apparent binding constants of meso-tetraaryl porphyrins bearing between one and four positive charges with DNA.

Meso-substituted porphyrins, ((4-N-methyl-pyridyl)n(Ph)4-n)PH2, n = 1 to 4, bearing between 1 and 4 positive charges have been synthetized and studied for their interaction with Calf Thymus DNA. Competition binding experiments using ethidium bromide or one of its dimers show that these porphyrins and some of their Cu(II) or Fe(III)Cl complexes have apparent binding constants between 3 10(5) and 5 10(7) M-1. Fluorescence energy transfer experiments show that not only the tetracationic previously described porphyrin but also the tri- and dicationic porphyrins are able to intercalate into DNA. These data indicate a greater importance of the polyaromatic porphyrin ring than of the number or position of the positive charges for meso-tetra-arylporphyrin interaction with DNA.