Interaction of novel cationic meso-tetraphenylporphyrins in the ground andexcited states with DNA and nucleotides

The syntheses and aggregation properties of novel cationic meso-tetraphenyl porphyrins substituted in the para-positions with -CH2(pyridinio)(+) (P-1), -CH2N+(CH3)(3) (P-2), -CH2P+(n-butyl)(3) (P-3), -CH2P+(phenyl)(3) (P-4), - CH2S+(CH3)(2) (P-5) and -CH2SC(NH2)(2)(+) (P-6) groups are described. Their use as photosensitizers and their interactions with DNA and nucleotides we re studied by optical methods and their properties were compared with those of anionic meso-tetrakis(4-sulfonatophenyl)porphyrin (TPPS) and cationic m eso-tetrakis(4-N-methylpyridyl)porphyrin (TMPyP). P-1 and P-2 formed stable complexes with calf thymus DNA in phosphate buffer (K(a)similar to 10(6) M -1; outside stacking binding mode) and with some nucleotides in methanol (K (a)similar to 10(3)-10(4) M-1). P-3-P-6 aggregated readily in aqueous solut ion due to their more hydrophobic nature. The cationic porphyrins TMPyP and P-1-P-6 sensitized the decomposition of guanosine 5'-monophosphate (GMP). The rates of GMP decomposition were found to be greater with cationic porph yrins P-1-P-6 than with anionic TPPS, presumably because of Coulombic attra ction between the positively charged porphyrins P-1-P-6 and the anionic GMP . In oxygen-free conditions, GMP decomposition was initiated by interaction of the singlet (P-1, P-2) or triplet (P-1-P-6) excited states of the porph yrins with GMP. In the presence of oxygen, GMP is decomposed predominantly via singlet oxygen mechanism.