The mixed Langmuir monolayers composed of model constituents of biological membranes, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), 2-oleoyl-1-palmitoyl-sn-glycero-3-phosphocholine (POPC), and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), were investigated to provide information on the intermolecular interactions between these membrane components and the physiologically active vitamin E-α-tocopherol (TF), as well as on the phase behavior of these mixed systems. Additionally, topography of these monolayers transferred onto the mica support was investigated by the inverted metallurgical microscope. Morphological characteristics were directly observed by Brewster angle microscopy (BAM). From the surface pressure-area isotherms and the analysis of physicochemical parameters (compressibility and mean molecular area at the maximum compressibility) it was found that depending on the acyl chains saturation degree, TF has different effect on the phospholipids. In the case of DPPC, the addition of TF to the phospholipid film causes destabilization of the ordered hydrocarbon chains, while in the POPC/DOPC-TF systems, the attractive interactions are responsible for the monolayer increased stability. Thus, the results of these studies confirm the hypothesis that α-tocopherol may play a role in the stabilization of biological membranes.
On aqueous subphases of pH 6, the behavior of syndiotactic poly(methyl methacrylate) (synd-PMMA) (average molecular weight, M w )120 000 g/mol) monolayers at the air/water interface was investigated in the range of temperatures between 15 and 50 °C. The monolayer characteristics of synd-PMMA stereoisomer were studied and compared in terms of surface pressure-area per residue (π-A) isotherms, surface compressional modulus-surface pressure (C s -1 π) curves, hysteresis phenomena, film thickness, and the phase images observed from Brewster angle microscopy (BAM). The results show that synd-PMMA (120 000) monolayer exhibits a phase transition LE-L′E (from a liquid-expanded to another liquid-expanded state) at surface pressures of ca. 15-17 mN/m when the temperature is raised from 25 to 50 °C, which is attributed to the formation of reversible loops and tails in the monolayer. On the other hand, the study of the effect of the molecular weight on the PMMA monolayer behavior showed that the polymer of M w ) 15 000 g/mol exhibits a limiting area of 19.7 Å 2 per monomer repeating unity at 30 °C, which is close to the value for the trans conformation of PMMA at the air-water interface. Nevertheless, the limiting area of PMMA (120 000) was lower (14.1 Å 2 /monomer), suggesting that not all monomers are located at the interface. The morphology and thickness of monolayers confirm at microscopic level the structural characteristics deduced from the π-A isotherms.
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