Fluorescence quenching of fluorescein by Merocyanine 540 in liposomes

The fluorescence quenching of fluorescein (FL) by merociyanine 540 (MC540) was examined in L-egg lecithin phosphatidycholine (PC) liposomes using spectroscopic methods. The type of quenching mechanism (dynamic or static) was evaluated using the Stern–Volmer plots. Findings were also supported by the temperature studies and florescence decay measurements. The Stern–Volmer equation was utilized to calculate bimolecular quenching constants (Kq). Furthermore, the bimolecular quenching constant of the quencher in the liposomes (KSV), partition coefficient (Kp), binding constant (K), and corresponding thermodynamic parameters ΔH, ΔS, and ΔG were calculated. The quenching property was also used in determining quantitatively (Kp) the partition coefficient of Merociyanini 540 in PC liposome.The obtained data indicated that static quenching occurred in the system and the KSV values decreased with increasing lipid concentration. In addition, thermodynamic analysis suggested that van der Waals interactions and hydrogen bonding were the main acting forces between fluorescein and merociyanine 540 molecules in the medium.