Non-traditional intrinsic luminescence of amphiphilic-based ionic liquids from oxazolidines: Interaction studies in phosphatidylcholine-composed liposomes and BSA optical sensing in solution

Abstract

This study presents the synthesis in good overall yields of oxazolidine-based ionic compounds obtained from protected l-serine followed by an esterification reaction with bromoalcohols and a reaction with 1-methylimidazole in acetonitrile under reflux. These compounds present in ethanol solution an absorption maxima located around 210 nm, resulting in a non-traditional intrinsic luminescence observed between 350 and 390 nm. According to calculations performed at CAM-B3LYP/6-311++G(d,p), these redshifted emission bands would be related to the increased polarity of these structures (μ > 10 D). Fluorescence titration experiments were also performed, and the partition coefficient in PC liposomes was determined, presenting high values (Kp ~ 104). In addition, their interaction with bovine serum albumin (BSA) in a phosphate buffer solution (PBS) was investigated, presenting a suppression mechanism where the imidazolium seems to play a fundamental role. Docking simulations were also performed to better understand the observed BSA suppression mechanism upon the addition of oxazolidines.