No abstract

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.

The peptide corresponding to the sequence (279-298) of the Hepatitis G virus (HGV/GBV-C) E2 protein was synthesized, and surface activity measurements, pi-A compression isotherms, and penetration of E2(279-298) into phospholipid monolayers spread at the air-water interface were carried out on water and phosphate buffer subphases. The results obtained indicated that the pure E2(279-298) Langmuir monolayer exhibited a looser packing on saline-buffered than on pure water subphase and suggest that the increase in subphase ionic strength stabilizes the peptide monolayer. To better understand the topography of the monolayer, Brewster angle microscopy (BAM) images of pure peptide monolayers were obtained. Penetration of the peptide into the pure lipid monolayers of dipalmitoylphosphatidylcholine (DPPC) and dimyristoylphosphatidylcholine (DMPC) and into mixtures of dimyristoylphosphatidylcholine/dimyristoylphosphatidylglycerol (DMPC/DMPG) at various initial surface pressures was investigated to determine the ability of these lipid monolayers to host the peptide. The higher penetration of peptide into phospholipids is attained when the monolayers are in the liquid expanded state, and the greater interaction is observed with DMPC. Furthermore, the penetration of the peptide dissolved in the subphase into these various lipid monolayers was investigated to understand the interactions between the peptide and the lipid at the air-water interface. The results obtained showed that the lipid acyl chain length is an important parameter to be taken into consideration in the study of peptide-lipid interactions.