Effect of metal cations on the fluorescence lifetimes of pyrene-labeled G-quadruplex probes

Fluorescence lifetime study of two probes abbreviated as Py-Htelom-Py and Py-TBA-Py, carrying pyrene moieties at both termini and sequences of human telomere and thrombin binding aptamer, respectively are reported. The effect of metal cations (sodium, potassium and strontium) on the photophysical processes was examined in order to elucidate factors that facilitate the production of excimer emission. The fluorescence spectra and emission kinetics data supported the conclusion that pyrene-quadruplex conjugate has multiple conformers in solution and that the relative orientation of pyrene and neighboring nucleobases (guanine, adenine, thymine) play a crucial role in determining both the rate of electron-transfer quenching of pyrene excited state and the efficiency of excimer emission.