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

Abstract

The syntheses and aggregation properties of novel cationic meso-tetraphenylporphyrins substituted in the para-positions with -CH2(pyridinio)+ (P11), -CH2N+(CH3)3 (P22), -CH2P+(n-butyl)3 (P33), -CH2P+(phenyl)3 (P44), -CH2S+(CH3)2 (P55) and -CH2SC(NH2)2+ (P66) groups are described. Their use as photosensitizers and their interactions with DNA and nucleotides were studied by optical methods and their properties were compared with those of anionic meso-tetrakis(4-sulfonatophenyl)porphyrin (TPPS) and cationic meso-tetrakis(4-N-methylpyridyl)porphyrin (TMPyP). P11 and P22 formed stable complexes with calf thymus DNA in phosphate buffer (Ka ≈ 106 M−1; outside stacking binding mode) and with some nucleotides in methanol (Ka ≈ 103–104 M−1). P33–P66 aggregated readily in aqueous solution due to their more hydrophobic nature. The cationic porphyrins TMPyP and P11–P66 sensitized the decomposition of guanosine 5′-monophosphate (GMP). The rates of GMP decomposition were found to be greater with cationic porphyrins P11–P66 than with anionic TPPS, presumably because of Coulombic attraction between the positively charged porphyrins P11–P66 and the anionic GMP. In oxygen-free conditions, GMP decomposition was initiated by interaction of the singlet (P11, P22) or triplet (P11–P66) excited states of the porphyrins with GMP. In the presence of oxygen, GMP is decomposed predominantly via singlet oxygen mechanism.