A catanionic lipid/porphyrin monolayer was formed at the air-water interface by the tetra-anionic porphyrin, tetra-sodium-meso-tetra(4-sulfonatophenyl)porphine (TSPP), mixed with the cationic lipid dioctadecyldimethylammonium bromide (DODAB) in a 1:4 molar ratio. This binary mixture (TSPP/4DODAB) was used as the incorporation matrix of beta-lactoglobulin (betaLG). Binary and ternary systems (TSPP/4DODAB/zbetaLG, where z stands for the number of protein residues per TSPP) were characterized by surface pressure versus area (pi-A) measurements and by Brewster angle microscopy (BAM) observation at the air-water interface. Pi-A measurements and BAM images show that protein is incorporated in the expanded regime of the monolayer and is gradually expelled upon compression at high surface pressures. The successive compression-expansion cycles indicate that the protein under adsorbed to the floating film is reincorporated after the expansion of the monolayer. At low subphase pH, TSPP tends to aggregate decreasing the interaction with DODAB molecules. Electrostatic and hydrophobic interactions are responsible for the presence of betaLG at the interfacial film.

中文翻译：

---

在空气/水界面的脂质/卟啉单层中掺入β-乳球蛋白。

阳离子脂质/卟啉单层是由四阴离子卟啉，四钠-间位四（4-磺酰基苯基）卟啉（TSPP）与阳离子脂质二十八烷基二甲基溴化铵（DODAB）混合而在空气-水界面处形成的。摩尔比为1：4。该二元混合物（TSPP / 4DODAB）被用作β-乳球蛋白（βLG）的掺入基质。二元和三元系统（TSPP / 4DODAB / zbetaLG，其中z代表每个TSPP的蛋白质残基数）通过表面压力与面积（pi-A）的测量以及在空气-水处的布儒斯特角显微镜（BAM）观察来表征接口。Pi-A测量和BAM图像显示，蛋白质被掺入单层的扩展结构中，并在高表面压力下被压缩后逐渐排出。连续的压缩-膨胀循环表明，吸附到浮膜上的蛋白质在单层膨胀后被重新掺入。在较低的亚相pH下，TSPP倾向于聚集，从而降低了与DODAB分子的相互作用。静电和疏水相互作用是界面膜上存在βLG的原因。