Effect of Ester Moiety on Structural Properties of Binary Mixed Monolayers of Alpha-Tocopherol Derivatives with DPPC

Abstract

Phospholipid membranes are ubiquitous components of cells involved in physiological processes; thus, knowledge regarding their interactions with other molecules, including tocopherol ester derivatives, is of great importance. The surface pressure–area isotherms of pure α-tocopherol (Toc) and its derivatives (oxalate (OT), malonate (MT), succinate (ST), and carbo analog (CT)) were studied in Langmuir monolayers in order to evaluate phase formation, compressibility, packing, and ordering. The isotherms and compressibility results indicate that, under pressure, the ester derivatives and CT are able to form two-dimensional liquid-condensed (LC) ordered structures with collapse pressures ranging from 27 mN/m for CT to 44 mN/m for OT. Next, the effect of length of ester moiety on the surface behavior of DPPC/Toc derivatives’ binary monolayers at air–water interface was investigated. The average molecular area, elastic modulus, compressibility, and miscibility were calculated as a function of molar fraction of derivatives. Increasing the presence of Toc derivatives in DPPC monolayer induces expansion of isotherms, increased monolayer elasticity, interrupted packing, and lowered ordering in monolayer, leading to its fluidization. Decreasing collapse pressure with increasing molar ratio of derivatives indicates on the miscibility of Toc esters in DPPC monolayer. The interactions between components were analyzed using additivity rule and thermodynamic calculations of excess and total Gibbs energy of mixing. Calculated excess area and Gibbs energy indicated repulsion between components, confirming their partial mixing. In summary, the mechanism of the observed phenomena is mainly connected with interactions of ionized carboxyl groups of ester moieties with DPPC headgroup moieties where formed conformations perturb alignment of acyl chains, resulting in increasing mean area per molecule, leading to disordering and fluidization of mixed monolayer.

Assessment of DPPC Liposome Disruption by Embedded Tocopheryl Malonate

“…The information regarding properties of TM in DPPC monolayers, or its destructive effects on cancer cell lines, were revealed previously [9,48]. In this work, we present the results obtained in DPPC liposomes, which serve as a model for biological membranes.…”

Understanding the Retention of Vaping Additives in the Lungs: Model Lung Surfactant Membrane Perturbation by Vitamin E and Vitamin E Acetate

“…Positive deviations suggest repulsive interactions and film expansion, while negative deviations indicate attractive interactions and/or condensation. 21 Excess areas were calculated at surface pressures of 1−15 mN/m since monolayers of α-tocopherol and α-tocopherol acetate collapse by 18 mN/m. For the α-tocopherol mixtures, small negative deviations less than 5 Å 2 /molecule are observed, which decrease as the film is compressed, indicating the presence of attractive interactions between the model membrane and αtocopherol.…”

“…To assess the phospholipid–tocopherol additive interactions in the mixed monolayers, excess molecular areas were calculated for varying molar concentrations of α-tocopherol (Figure a) and α-tocopherol acetate (Figure b). Positive deviations suggest repulsive interactions and film expansion, while negative deviations indicate attractive interactions and/or condensation . Excess areas were calculated at surface pressures of 1–15 mN/m since monolayers of α-tocopherol and α-tocopherol acetate collapse by 18 mN/m.…”