The interactions of l-arginine (l-arg) with Langmuir monolayers of three most common phospholipids, which are sodium salt of dipalmitoylphosphatidylglycerol (DPPG), dipalmitoylphosphatidylcholine (DPPC) and dipalmitoylphosphatidylethanolamine (DPPE), have been investigated at the air-water interface. The surface pressure-area (π-A) isotherms of these monolayers have been measured with a film balance and monolayer morphology has been observed by a Brewster angle microscopy (BAM). The DPPG monolayers on pure water do not show any phase transition but show irregular shaped condensed phases formed just after evaporation of the solvent at 20 °C. However, this monolayer on l-arg solution subphase indicates a first-order phase transition from liquid expanded to liquid condensed (LE-LC) phases and forms LC domains at the same temperature. With an increase in the l-arg concentration in the subphase up to 5.0 × 10⁻⁴ M, the π-A shows an overall increasingly greater expansion in the molecular area. All of the π-A isotherms recorded on ≥5.0 × 10⁻⁴ M l-arg solution subphases almost coincide with each other. These changes in the phase behavior have been explained by the fact that l-arg having guanidinium cationic group undergoes strong hydrogen bonding interaction with the anionic phosphatidylglycerol (PG-) head group. The bonding between two molecules is further strengthened by electrostatic attraction between cationic l-arg and anionic PG- ions. The BAM observation of the monolayer morphology supports this explanation. On the other hand, a very negligible interaction has been observed between l-arg and DPPC or DPPE monolayers. The π-A isotherms in the presence of l-arg for both the amphiphiles show a very little expansion only in the LE phase region, but coincide in the so called solid phase region. The monolayer morphology of both the monolayers also supports these results. This little effect of expansion in the LE region may be explained by the ion-pair formation between cationic l-arg and anionic head groups in the monolayers at lower pressures. However, due to compression at high pressure, the l-arg molecules are squeezed out from the amphiphile head groups.

l-精氨酸 ( l - arg ) 与三种最常见磷脂的朗缪尔单层的相互作用，它们是二棕榈酰磷脂酰甘油 (DPPG)、二棕榈酰磷脂酰胆碱 (DPPC) 和二棕榈酰磷脂酰乙醇胺 (DPPE) 的钠盐，已在空气-水界面进行了研究。这些单层的表面压力-面积 (π-A) 等温线已用薄膜天平测量，单层形态已通过布鲁斯特角显微镜 (BAM) 观察。纯水中的 DPPG 单层没有显示任何相变，但显示出在 20 °C 下溶剂蒸发后形成的不规则形状的凝聚相。然而，这个单层在l-arg 溶液亚相表示从液体膨胀到液体冷凝 (LE-LC) 相的一级相变，并在相同温度下形成 LC 域。随着亚相中l -arg 浓度增加到 5.0 × 10 ^-4 M，π-A 显示出分子区域中整体越来越大的膨胀。在≥5.0 × 10 ^-4 M l -arg 溶液亚相上记录的所有 π-A 等温线几乎彼此一致。这些变化相行为已经被事实解释升具有胍阳离子基团的 -arg 与阴离子磷脂酰甘油 (PG-) 头部基团发生强氢键相互作用。阳离子l -arg 和阴离子 PG- 离子之间的静电吸引力进一步加强了两个分子之间的键合。单层形态的 BAM 观察支持这种解释。另一方面，在l- arg 和 DPPC 或 DPPE 单层之间观察到非常微不足道的相互作用。存在l 时的 π-A 等温线两亲分子的 -arg 仅在 LE 相区域显示出非常小的膨胀，但在所谓的固相区域中重合。两个单层的单层形态也支持这些结果。LE 区域中这种膨胀的小影响可以通过在较低压力下单层中阳离子l- arg 和阴离子头部基团之间的离子对形成来解释。然而，由于高压下的压缩，l- arg 分子被从两亲分子头基中挤出。