Fluorescence quenching effect of guanine interacting with water-soluble cationic porphyrin

The process of association between 5,10,15,20-tetrakis[4-(trimethylammonio)phenyl]-21H,23H-porphine tetra-p-tosylate (H2TTMePP) and guanine has been studied both in NaOH solution and TRIS buffer analysing its absorption and steady-state fluorescence spectra. The fluorescence quenching effect observed during interactions porphyrin-guanine points at the fractional accessibility of the fluorophore for the quencher. The association and fluorescence quenching constants are of the order of magnitude of 105 mol−1. The fluorescence lifetimes and the quantum yields of the porphyrin monoanion form were established. The results demonstrate that guanine can interact with H2TTMePP at basic pH and through formation of stacking complexes is able to quench its ability to emission.