Structure of poly(γ-benzyl-L-glutamate) monolayers at the gas–water interface: A Brewster angle microscopy and x-ray scattering study
Structure of poly(γ-benzyl-L-glutamate) monolayers at the gas–water interface: A Brewster angle microscopy and x-ray scattering study
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气水界面聚（γ-苄基-L-谷氨酸）单层结构：布鲁斯特角显微镜和 X 射线散射研究
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发表时间：
1999
期刊：
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通讯作者：
D. Tirrell
中科院分区：
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作者：
M. Fukuto;R. Heilmann;P. Pershan;Seungju M. Yu;J. Griffiths;D. Tirrell
用布鲁斯特角显微镜（BAM）、X射线镜面反射率（XR）、掠入射衍射（GID）和离面漫散射（XOSDS）研究了单分散和多分散的α-螺旋聚谷氨酸苄酯（PBLG）在水溶液中形成的单分子膜与面积/单体A的关系。由于分散性不同，微观行为未表现出任何可辨别的影响。在低表面密度下（A> 1021A^2/单体，表面压力1021A^2 =0），BAM图像显示部分表面被固体状单层岛覆盖。GID测量显示对应于棒状PBLG分子的局部平行排列的螺旋间峰，表明它们在没有外部压力的情况下倾向于横向聚集。压缩到A<21A^2/单体，首先导致单层完全均匀地覆盖表面，然后是螺旋间距的急剧上升，伴随着螺旋间距的减小。进一步的压缩导致在λ-A等温线中的恒定λ的平台（λ 11.5<λ <λ 18.5A^2/单体，λ 9dyn/cm），其先前被归因于一级单层-双层转变。界面上的电子密度分布确定的共存平台两侧的XR测量提供了直接的证据，这种转变。的基础上的X-射线散射结果，在高密度侧的平台上的膜被示出由一个新形成的不完整的和不相称的第二层，位于顶部的，并具有较低的平均密度比均匀的第一层。GID测量表明，第二层的特点是较大的螺旋间d-间距比第一层，而XOSDS测量的双层表明，第二层是微观上不均匀的。对于单层和双层，所观察到的GID峰宽的分析表明，平行PBLG杆之间的横向位置相关性的程度范围从几个到不超过10015螺旋间的距离，这意味着短程秩序。
This paper reports Brewster angle microscopy (BAM), x-ray specular reflectivity (XR), grazing incidence diffraction(GID) and off-specular diffuse scattering (XOSDS) measurements of Langmuir monolayers formed on water by both mono- and polydisperse samples of α-helical poly(γ-benzyl L-glutamate) (PBLG) as a function of area/monomer A. The microscopic behavior does not exhibit any discernible effects due to differing dispersity. At low surface densities (A>∼21A^2/monomer,surface pressure Π=0), BAM images reveal partial surface coverage by solidlike monolayer islands. GID measurements show an interhelix peak corresponding to a local parallel alignment of rodlike PBLG molecules, indicating their tendency to aggregate laterally without external pressure. Compression to A<21A^2/monomer first leads to full and uniform surface coverage by the monolayer, followed by a steep rise in Π that is accompanied by a decrease in the interhelix distance. Further compression results in a plateau of constant Π in the Π-A isotherm (∼11.5<A<∼18.5A^2/monomer, Π∼9dyn/cm), which has previously been attributed to a first-order monolayer–bilayer transition. The interfacial electron density profiles determined by the XR measurements on both sides of the coexistence plateau provide direct evidence for this transition. On the basis of x-ray scattering results, the film on the high-density side of the plateau is shown to consist of a newly formed incomplete and incommensurate second layer that sits on top of and has lower average density than a homogeneous first layer. GID measurements indicate that the second layer can be characterized by larger interhelix d-spacing than the first layer, while XOSDS measurements on the bilayer suggest that the second layer is microscopically inhomogeneous. For both mono- and bilayers, the analysis of observed GID peak widths indicates that the extent of lateral positional correlations between parallel PBLG rods ranges from a few to no more than ∼15 interhelix distances, implying short-range order.