Wavelength Dependant Quenching of 2,5-Diphenyloxazole Fluorescence by Nucleotides

The quenching of 2,5-diphenyloxazole (PPO) fluorescence by nucleotides has been investigated by electronic absorption and steady state fluorescence spectra. Five purine nucleotides AMP, ADP, ATP, GMP and dGMP, one pyrimidine nucleotide UMP and one dinucleotide NAD have been employed in the present study. Electronic absorption studies indicate that there is no ground state complexation between the nucleotides and PPO. The quenching of PPO fluorescence was investigated at two different wavelengths. When excited at 304 nm, the λ _max of PPO, the fluorescence spectra of PPO is quenched following Stern–Volmer kinetics. The quenching ability of nucleotides are in the order NAD > AMP > ADP > GMP > dGMP > UMP. The K _SV and k _q values obtained indicate that AMP is a better quencher of PPO fluorescence than GMP, which is contrary to commonly observed pattern. The quenching is found to be dynamic in nature. However, when excited at 260 nm, the absorption maximum of the nucleotides, the fluorescence intensity of PPO is reduced with increase in the concentration of the nucleotide. This is attributed to the primary inner filter effect arising due to the absorption of the incident radiation by the nucleotides. Thus the inner filter effect phenomenon can be employed to assay the non-fluorescent molecules by fluorimetry.