Quenching Efficiency 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 nucleotides -monophosphates (NMPs) was investigated by monitoring the quenching and dequenching of pyrene steady-state fluorescence. The data clearly show that this kind of molecules influences in different way the fluorescence of micellized pyrene: while guanosine 5’-monophosphate (GMP), uridine 5’-monophosphate (UMP) and thimydine 5’-monophosphate (TMP) lead to a reduction in fluorescence intensity (quenching), adenosine 5’-monophosphate (AMP) and cytosine 5’-monophosphate (CMP) induces an increment in it (dequenching). The quenching and dequenching efficiencies were evaluated with a previously described model based on the assumption that the anionic nucleotides compete with the surfactant counterion (bromide) for the surface of micelle. Results make available the follows quenching efficiency order (GMP>UMP>TMP) and dequenching efficiencies order (AMP>CMP). Moreover, in absence of micelle the fluorescence of pyrene mislays the peculiar saturation model and follows the typical linear behaviour according to the Stern-Volmer relation. Z-potential measurements reveals that different purine and pyrimidine bases do not affect the binding of nucleotides to cationic micellar CTAB and that the predominant interactions occurs between the positively charged micellar surface and the negatively charged phosphate moieties on the nucleotides. The present work clearly highlights that the fluorescence of pyrene solubilized in the CTAB micellar solution can be reduced (quenched) or enhanced (dequenched), depending on the nature of the nucleobase.