Molecular orientation of porphyrins accompanying the formation of chain-aligned DNA films

Porphyrin-containing DNA solid films with several binding orientations were successfully prepared by drying the aqueous solution of porphyrins and DNA in a magnetic field. By the measurement of linear dichroism absorption spectra from three identical spatial directions, the molecular orientations of porphyrins in chain-aligned DNA films were evaluated. Tetra(N-methylpyridinium-4-yl)-porphyrin was found to be bound at the surface of DNA chains like a patch. This orientation is different from the intercalative or groove binding manners observed in solutions. In contrast, tetra(4-sulfonatophenyl)-porphyrin exhibited an orientation perpendicular to the DNA axis, which may be attributed to H-aggregation of porphyrins along the direction parallel to DNA chains. Heme-protein with coiled coil backbone was also aligned along the DNA chains, orienting ferric protoporphyrin parallel to the magnetic field. The major effect for these molecular orientations would be the molecular packing of the rod-disk or the rod-rod systems.