Spectroscopic study on binding of TMPyP⁴⁺ porphyrin to single-stranded poly(rA)

Abstract

Binding of tetracationic porphyrin (TMPyP⁴⁺) to poly(rA) has been studied in neutral buffered solution of low ionic strength in a wide range of molar phosphate-to-dye ratios (P/D) using absorption spectroscopy, polarized fluorescence and fluorimetric titration. Two competitive binding modes were identified: partial intercalation of porphyrin chromophores between adenine bases prevailing at P/D > 20 and its outside binding to poly(rA) backbone dominating at P/D < 6. Both of them were accompanied by enhancement of the porphyrin emission. Absence of the emission quenching near stoichiometric P/D ratios allowed us to assume that external binding occurs without the self-stacking of the chromophores.

Keywords:

• Absorption
• binding
• fluorimetric titration
• polarized fluorescence
• poly(rA)
• TMPyP⁴⁺ porphyrin

Acknowledgment

Authors acknowledge National Academy of Sciences of Ukraine for the financial support (Grant N 0120U100157).