Excited State Interaction of Azure Dyes with Phospholipids in Liposome - A Fluorescence Study

The fluorescence spectra of three azure (Az) dyes namely AzA, AzB and AzC have been studied in sonicated aqueous dispersion of posphatidylcholine (PC). Lyso PC, phosphorylcholine chloride (PCC) as calciuln salt and choline chloride. The results show the enhancement of fluorescence intensity of Az dyes in presence of PC, lyso PC and PCC with a red shift indicating excited state interaction of dyes with these except choline chloride. A method is developed to estimate the stability constant, K*, of the dye-phospholipid complex in the excited state. The results show the electron acceptor strengths of AZ dyes forming excited state charge transfer (CT) complex with phospholipids are in the order AzC>AzA>AzB, while the electron donor abilities of phospholipids are in the order PC>lysoPC>PCC. A good correlation is also observed between the fleorescence spectral shifts due to excited state CT interaction and the stability constants of the complexes between the Az dyes and phospholipids.