Department of Chemistry, Katholieke Universiteit Leuven, Leuven, Belgium.
Nanoscale. 2010 Sep;2(9):1773-80. doi: 10.1039/c0nr00176g. Epub 2010 Jul 13.
Self-assembly of organic molecules at solid-liquid interfaces is a route for developing novel functional materials on surfaces and modeling assembly phenomena in 3D. 5-Alkoxylated isophthalic acids (ISA) are known to self-assemble into two-dimensional (2D) lamellae at the interface between a surface of Au(111) or HOPG (highly oriented pyrolytic graphite) and a solvent. Presently, the self-assembly of 4,6-dialkoxylated isophthalic acid derivatives with variable alkyl chain length is investigated at Au(111)-water, Au(111)-tetradecane and HOPG-tetradecane interfaces with a particular focus on the first one. The main aspect of this study is to evaluate the role of the molecular geometry and different interactions in the 2D assembly of amphiphilic molecules. In contrast to 5-alkoxylated ISA, 4,6-dialkoxylated ISA derivatives self-assemble preferentially into arrays of cyclic pentameric/hexameric structures, which appear as 2D analogues of the inverted hexagonal phase of lipids. As a general trend, the derivatives bearing shorter alkyl chains show a higher level of ordering at Au(111)-liquid interfaces. In particular, at the Au(111)-water interface, the 4,6-diheptyloxy ISA derivative forms exclusively pentamers, which are arranged in a quasi-hexagonal lattice. Moreover, the cyclic pentameric features are not empty but host a single isophthalic acid residue which is found to be dynamic. Finally, the packing of the diheptyloxy derivative shows a distinct potential dependence: while at more negative potentials the pentameric arrangement is converted into lamellae, at more positive potentials a loosely packed zig-zag pattern is formed. The present results show that at different solid-liquid interfaces 4,6-dialkoxylated ISA derivatives tend to form cyclic structures that are 2D analogues of an inverted hexagonal phase, akin to lipids having two hydrophobic alkyl chains and a small polar head group. Moreover, the substrate potential at the Au(111)-water interface can tune the 2D molecular arrangement.
有机分子在固液界面的自组装是在表面上开发新型功能材料和模拟 3D 组装现象的途径。已知 5-烷氧基间苯二甲酸（ISA）在 Au（111）或 HOPG（高定向热解石墨）表面与溶剂之间的界面自组装成二维（2D）层。目前，研究了具有可变烷基链长的 4,6-二烷氧基间苯二甲酸衍生物在 Au（111）-水、Au（111）-十四烷和 HOPG-十四烷界面上的自组装，特别关注第一个界面。本研究的主要方面是评估分子几何形状和不同相互作用在两亲分子 2D 组装中的作用。与 5-烷氧基 ISA 不同，4,6-二烷氧基 ISA 衍生物优先自组装成环五聚体/六聚体结构的阵列，这些结构呈现出脂质反六方相的 2D 类似物。作为一般趋势，具有较短烷基链的衍生物在 Au（111）-液相界面上表现出更高的有序性。特别是在 Au（111）-水界面上，4,6-二庚氧基 ISA 衍生物仅形成五聚体，这些五聚体排列成准六边形晶格。此外，这些环五聚体结构不是空的，而是容纳一个动态的间苯二甲酸残基。最后，二庚氧基衍生物的堆积表现出明显的电位依赖性：在更负的电位下，五聚体排列转化为层状结构，而在更正的电位下，形成松散堆积的锯齿形图案。本研究结果表明，在不同的固液界面上，4,6-二烷氧基 ISA 衍生物倾向于形成类似于具有两个疏水性烷基链和一个小极性头基团的脂质的反六方相的二维环状结构。此外，Au（111）-水界面上的基底电位可以调节 2D 分子排列。
