Photophysics of the cationic 5, 10, 15,20-tetrakis (4-N-methylpyridyl) porphyrin bound to DNA, [poly(dA-dT)]2 and [poly(dG-dC)]2: interaction with molecular oxygen studied by porphyrin triplet—triplet absorption and singlet oxygen luminescence

✍ Scribed by Nicolay N. Kruk; Boris M. Dzhagarov; Victor A. Galievsky; Vladimir S. Chirvony; Pierre-Yves Turpin

• Publisher: Elsevier Science
• Year: 1998
• Tongue: English
• Weight: 927 KB
• Volume: 42
• Category: Article
• ISSN: 1011-1344
• DOI: 10.1016/s1011-1344(98)00068-2

✦ Synopsis

Interaction between molecular oxygen and the cationic fiee-base 5,10,15,20-tetrakis(4-N-methylpyridyl )porphyrin (H2TMpyP 4, ) complexed with [poly(dA-dT)I_+, l poly(dG-dC) ]z and calf thymus DNA, has been monitored in air-saturated heavy water solutions through porphyrin triplet-triplet absorption and singlet oxygen luminescence. Three different rate constants of porphyrin triplet state quenching have been lound which correspond to different accessibilities of molecular oxygen to porphyrins embedded in the duplexes. The longest triplet state lifetime ( 30 txs), found for porphyrin bound to I poly(dG-dC) ],, corresponds to molecules well protected from oxygen. This supports the hypothesis of an intercalative binding mode of the porphyrin between GC base-pairs ("type A' sites). The fraction,f T± of the porphyrin triplet states quenched by molecular oxygen with singlel oxygen generation, is unity. In [poly(dA-dT) ]~-porphyrin complexes, two sites ( 'type B" and 'C" sites of interaction) are involved, yielding very different triplet state lifetimes (5.5 ItS and 20.5 txs) and efficiencies of singlet oxygen generation (fr_ 0.50 and 0.82). Thefr decreases can likely be explained in terms of competition between energy and electron transfer from the porphyrin excited triplet state to molecular oxygen. All three types ( A, B and C) of interaction sites can be expected in porphyrin-DNA complexes.