Photophysics of a beta-carboline based non-ionic probe in anionic and zwitterionic liposome membranes

Interaction of a biologically active beta-carboline based non-ionic probe, 3-acetyl-4-oxo-6,7-dihydro-12H indolo-[2,3-a] quinolizine (AODIQ), with the liposomal vesicles of dimyristoyl-l-alpha-phosphatidylcholine (DMPC) and dimyristoyl-l-alpha-phosphatidylglycerol (DMPG) has been demonstrated using steady-state and time-resolved fluorescence and fluorescence anisotropy techniques. Polarity sensitive intramolecular charge transfer of AODIQ shows a large hypsochromic shift along with an enhancement in the fluorescence quantum yield and fluorescence lifetime in the bilayer membranes compared to those in aqueous buffer solution. Polarity of the immediate vicinity of the probe in the lipid environments has been determined. The fluorometric, quenching and micropolarity determination studies reveal that the fluorophore penetrates deeper in the zwitterionic DMPC membrane compared to the anionic DMPG vesicle. Enhancement in the rotational relaxation time of AODIQ in liposomal membranes suggests that the fluorophore exists in motionally restricted environments.