INTERACTIONS OF ROALUMINIUM-TETRAMETHYL-TETRAPYRIDINO-PORPHYRAZINE WITH DNA

The interaction of oroaluminium-tetramethyl-tetrapyridinoporphyrazine (ClAlTMPyPa) with DNA was investigated by absorption/emission and circ ular-dichroic spectroscopy. Formation of a DNA-porphyrazine complex wa s evidenced by quenching of the ClAlTMPyPa fluorescence, a hypochromic red shift of the absorption band in the visible part of the spectrum and induction of a characteristic CD band with high positive elliptici ty. Scatchard analysis of the spectral changes in low ionic strength, buffer suggested an association constant of 9.7+/-0.6X10(7) M-1. Quenc hing of the fluorescence of a DNA-ethidium complex by added ClAlTMPyPa was shown to result from direct DNA-dye interaction rather than the d isplacement of ethidium from DNA. Our data suggest that porphyrazine b inds to the outside of the DNA helix, involving interactions which are not limited to electrostatic forces only. The computer assisted model ling of ClAlTMPyPa-DNA interactions showed that the energy-minimized i ntermolecular orientation involves face-on binding of the ligand, pref erably on the minor DNA groove.