Oxidation-Dependent Behavior of Saturated and Unsaturated Phosphatidylcholine Model Membranes: Insights from Langmuir Monolayers and TBARS Analysis.

Lipid oxidation plays an important role in modifying membrane organization and interfacial behavior, particularly in phospholipids containing unsaturated acyl chains. In this study, Langmuir monolayer measurements and thiobarbituric acid reactive substances (TBARS) analysis were used to investigate the oxidative behavior of saturated and unsaturated phosphatidylcholine model systems. Surface pressure-mean molecular area (π-Mma) isotherms and constant-pressure stability measurements were obtained for DMPC, DPPC, POPC, and PAPC monolayers under ambient and controlled oxidative conditions. Differences in acyl-chain saturation influenced phospholipid packing behavior, monolayer organization, and oxidative response under interfacial conditions. Controlled oxidation using the radical initiator 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH) induced distinct structural responses in PAPC monolayers relative to measurements performed under ambient conditions. TBARS analysis confirmed greater oxidative susceptibility in unsaturated phospholipids, with PAPC exhibiting substantially higher malondialdehyde formation than POPC. Addition of α-tocopherol reduced TBARS formation in oxidized PAPC vesicles, consistent with its established antioxidant role in polyunsaturated lipid systems. These findings demonstrate how phospholipid unsaturation influences monolayer organization and oxidative response under interfacial conditions while highlighting the complementary use of Langmuir and TBARS approaches for investigating oxidation-dependent membrane behavior.