Interaction of fluorescent quinolin-2-one and coumarin derivatives including dipeptides with lipid bilayers

Abstract

The photophysical properties of two quinolin-2-one and two coumarin derivatives, 3-amino-4-phenylquinolin-2-one (1), N-(tert-butyloxycarbonyl)amino-4-phenylcoumarin (2), and the dipeptides 3 and 4 bearing the quinolin-2-one or the coumarin moiety, respectively, synthesized earlier by some of us, were studied in solvents of varying polarity. Compounds 1 and 2 show a moderate solvent sensitive emission, quinolinone 1 exhibited the highest fluorescence quantum yields (between 0.04 and 0.24). The dipeptide derivatives 3 and 4 present reasonable fluorescence quantum yields in several media, including water (between 0.02 and 0.08). Quinolin-2-one (1 and 3) and coumarin (2 and 4) derivatives were incorporated in lipid vesicles of egg lecithin (egg-PC), DPPC, DPPG and mixed DPPC/DPPG (1 : 1). All compounds are mainly located in the lipid bilayer, feeling the transition between the rigid gel phase and the fluid liquid-crystalline phase. Dynamic light scattering measurements indicated that the liposomes with the encapsulated compounds are generally monodisperse and with hydrodynamic diameters lower than 160 nm, suitable for biomedical applications.