Vila-Romeu N, Nieto-Suarez M, Dynarowicz-Łatka P
Department of Physical Chemistry-Faculty of Sciences, University of Vigo, Campus As Lagoas s/n 32004 Ourense, Spain.
J Phys Chem B. 2005 Aug 11;109(31):14965-70. doi: 10.1021/jp050920+.
The behavior of binary mixed Langmuir monolayers from gramicidin A (GA) and ethyl nonadecanoate (EN), spread on aqueous subphases containing NaCl and CaCl2, was investigated on the basis of the analysis of surface pressure-average area per molecule (pi-A) isotherms complemented with Brewster angle microscopy (BAM) images. Compression modulus versus surface pressure (C(S-1)-pi) curves indicate the existence of interactions in the GA-EN mixed monolayers at low surface pressures (below 5 mN m(-1)). However, for mixtures in which the ester is the predominant component, both GA and EN are miscible within regions from fully expanded to collapse. To examine the interactions between both components in the studied system, values of the mean molecular area per molecule (A12) were plotted as a function of molar fraction of gramicidin A (X(GA)). A12-X(GA) plots exhibit negative deviations from ideality at high surface pressures, wherein beta-helices of GA are vertically oriented in respect to the interface. However, at surface pressures below the plateau transition, which is due to reorientation of GA, the binary system obeys the additive rule. Brewster angle microscopy (BAM) was applied for a direct visualization of the monolayers morphologies. The obtained images prove that for molar ratios of GA > or = 0.3 and at surface pressures above 5 mN m(-1), both components are immiscible at the interface. The observed negative deviations from the additively rule were attributed to the formation of a three-dimensional phase in the mixed film, which provokes its contraction at the interface.
基于对表面压力-每分子平均面积（π-A）等温线的分析，并辅以布鲁斯特角显微镜（BAM）图像，研究了短杆菌肽A（GA）和十九烷酸乙酯（EN）在含有NaCl和CaCl₂的水相亚相上形成的二元混合朗缪尔单分子层的行为。压缩模量与表面压力（C(S⁻¹)-π）曲线表明，在低表面压力（低于5 mN m⁻¹）下，GA-EN混合单分子层中存在相互作用。然而，对于酯为主要成分的混合物，在从完全膨胀到塌陷的区域内，GA和EN都是可混溶的。为了研究所研究体系中两种成分之间的相互作用，绘制了每分子平均分子面积（A₁₂）值与短杆菌肽A摩尔分数（X(GA)）的函数关系图。A₁₂-X(GA)图在高表面压力下呈现出与理想情况的负偏差，其中GA的β-螺旋相对于界面垂直取向。然而，在由于GA重新取向导致的平台转变以下的表面压力下，二元体系遵循加和规则。应用布鲁斯特角显微镜（BAM）直接观察单分子层的形态。获得的图像证明，对于GA摩尔比≥0.3且表面压力高于5 mN m⁻¹的情况，两种成分在界面处是不混溶的。观察到的与加和规则的负偏差归因于混合膜中三维相的形成，这导致其在界面处收缩。
