Characterization of liposomes containing Ascorbyl-6-O-conjugated linoleate: Perspective on phase transition and release behavior

Ascorbyl fatty acid esters (AEs) are emerging as promising components in delivery systems due to their antioxidant activity and amphiphilic properties. However, most applications have been limited to ascorbyl palmitate (AP), whose high phase transition temperature (T_m > 60 °C) restricts its utility in thermo-responsive systems. In this study, we synthesized high-purity (> 90 %) ascorbyl-6-O-conjugated linoleate (Asc-CLA), a novel unsaturated AE with a subzero T_m, through esterification and transesterification followed by crystallization and liquid–liquid extraction. Structural characterization using Raman and FT-IR spectroscopy demonstrated that increasing Asc-CLA concentration elevated the gauche/trans ratio of acyl chains and altered hydrogen bonding of head group, indicating enhanced acyl chain disorder and reduced lateral packing density. DSC analysis further confirmed that Asc-CLA lowered both T_m and enthalpy, contributing to increased bilayer fluidity. Calcein release assays showed that Asc-CLA enhanced membrane permeability in a concentration- and temperature-dependent manner. Notably, Asc-CLA/DPPC liposomes (0.7:10 M ratio) remained stable at 37 °C for 5 h but exhibited rapid release within 20 min at 42 °C, confirming their thermosensitive behavior. These results highlight Asc-CLA as a tunable lipid capable of modulating phase behavior and membrane permeability, indicating considerable potential for the development of liposomal formulations for use in both pharmaceutical and food applications, where controlled release of drugs or bioactive compounds is required.