Binding of the cationic 5,10,15,20-tetrakis(4-N-methylpyridyl) porphyrin at 5′CG3′ and 5′GC3′ sequences of hexadeoxyribonucleotides: triplettriplet transient absorption, steady-state and time-resolved fluorescence and resonance Raman studies

✍ Scribed by Nicolay N. Kruk; Svetlana I. Shishporenok; Alexander A. Korotky; Victor A. Galievsky; Vladimir S. Chirvony; Pierre-Yves Turpin

• Publisher: Elsevier Science
• Year: 1998
• Tongue: English
• Weight: 892 KB
• Volume: 45
• Category: Article
• ISSN: 1011-1344
• DOI: 10.1016/s1011-1344(98)00162-6

✦ Synopsis

Intercalative binding of the cationic 5,10,15,20-tetra!&( 4-Wmethylpyridyl) porphyrin (H,TMpyp+ ) at 5'CG3 and 5'GC3' sequences in [ d( TACGTA) ] 2 and [ d( TAGCTA) ] 2 hexadeoxyribonucleotides has been monitored through porphyrin ground-state and transient triplettriplet absorption, steady-state and time-resolved fluorescence as well as resonance Raman scattering. The porphyrin intercalation results in large red shifts and hypochromicity of the Soret absorption band. Charge-transfer processes between guanine residues and intercalated porphyrins, leading to an efficient quenching of the porphyrin S, excited singlet state, occur at both 5'CG3' and 5'GC3' sites. However, not all of the intercalated molecules are involved in these charge-transfer processes. Oxygen accessibility to intercalated porphyrins is practically the same for both sequences, resulting in rate constants of porphyrin triplet-state quenching by oxygen of 0.12 X 10" and 0.14 X 10' (M s) -' for 5'CG3' and 5'GC3' sites, respectively. Minor parts ( 11 and 16% for [d( TACGTA) ] 2 and [d(TAGCTA) ] 2, respectively) oftheporphyrin molecules are externally bound to hexamers, resulting in a higher oxygen accessibility (k,= 0.5 X lo9 and 0.6 X 10' (M s) -' for 5'CG3' and 5'GC3' sites, respectively). The photophysical properties of bound H,TMpyY'+ molecules in hexamers and the local polarity at the binding sites are close to those found at the corresponding binding sites in polynucleotides. The resonance Raman spectra of the H,TMpyp+ porphyrin moieties in both complexes mainly bear features characteristic of an intercalative binding mode, but there is also clear evidence for the existence of groove-bound complexes.