Quenching and dequenching of pyrene fluorescence by nucleotide- monophosphates in cationic micelles

The fluorescence behaviour of pyrene solubilized in the hexadecyltrimethylammonium bromide (CTAB) aqueous micellar solution in the presence of adenosine 5’monophosphate (AMP) and uridine 5’monophosphate (UMP) was investigated. AMP and UMP were found to influence oppositely the fluorescence of micellized pyrene. UMP acts a quencher while AMP acts as dequencher. Both the effects saturate at high nucleotide concentration (about 40 mM). Dequenching of micellized pyrene fluorescence is induced also by addition of ortophosphate while loading with NaBr quenches the fluorescence. In absence of micelles, pyrene fluorescence depends on the UMP according to the Stern-Volmer relation but is unaffected by AMP. The whole data set was successfully accounted for by tacking into account the competition between bromide and nucleotides for the cationic micellar surface and the different photophysical properties of the UMP and AMP