Binding of the cationic 5-coordinate Zn(II)-5,10,15,20-tetrakis(4-N-methylpyridyl)porphyrin to DNA and model polynucleotides: Ionic-strength dependent intercalation in [poly(dG-dC)]2
✍ Scribed by Vladimir S. Chirvony; Victor A. Galievsky; Sergei N. Terekhov; Boris M. Dzhagarov; Vladimir V. Ermolenkov; Pierre-Yves Turpin
- Publisher
- John Wiley and Sons
- Year
- 1999
- Tongue
- English
- Weight
- 246 KB
- Volume
- 5
- Category
- Article
- ISSN
- 1075-4261
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✦ Synopsis
The localization of the water-soluble cationic porphyrin ZnTMpyP(4) [Zn(II) derivative of 5,10,15,20-tetrakis(4-N-methylpyridyl)porphyrin] in its complex with [poly(dG-dC)] 2 is studied as a function of the solution ionic strength ( ϭ 0.20 -0.03). It is shown that the position of the Soret band maximum of ZnTMpyP(4) shifts from 436 to 446 nm on complexation, while its intensity markedly decreases (ϳ40%) when decreases from 0.20 to 0.03. This suggests that the porphyrin is mainly intercalated in [poly(dG-dC)] 2 at ϭ 0.03. Shifts of resonance Raman marker lines under ZnTMpyP(4) complexation to [poly(dG-dC)] 2 at ϭ 0.03 also support porphyrin intercalation. At last, a time-resolved transient absorption study of the porphyrin triplet state quenching by molecular oxygen shows that, at ϭ 0.03, biexponential kinetics of triplet state quenching is observed with time constants ϳ12 s (40%) and ϳ35 s (60%), that is, much longer than that of the free ZnTMpyP(4) species (ϳ3 s). Such a strong "shielding effect" of [poly(dG-dC)] 2 , resulting in the ϳ35-s component, is characteristic for porphyrin intercalation. The other component at ϳ12 s likely corresponds to a less protected, "partially intercalated" species in the polynucleotide. It is assumed that a decrease of the ionic strength (in terms of Na ϩ concentration) decreases the neutralization of the negative charges of the polynucleotide phosphate groups and, therefore, allows cationic ZnTMpyP(4) molecules to come closer to the nucleotides, this favoring, in a second step, full (or partial) intercalation. Since ZnT-MpyP(4) is known to be axially ligated by a H 2 O molecule, intercalation undoubtedly must result in a loss of its axial ligand. As far as we know, this is the first observation of such an axial ligand release in metalloporphyrin, induced by intercalation in a DNA sequence.