Degen P, Leick S, Rehage H, Polkowska J, Klärner F-G
Lehrstuhl fur Physikalische Chemie II, Universitat Dortmund, Otto Hahn Strasse 6, 44227 Dortmund, Germany.
Langmuir. 2009 Jun 2;25(11):6094-9. doi: 10.1021/la900072w.
In a series of experiments, we studied the interfacial activity of aromatic aliphatic molecules with rigid gemini-like structures at the interface between toluene and water. These molecules, called clips and tweezers, have rigid central benzene or naphthalene spacer-units, each substituted with two polar groups as well as two rigid aromatic side walls. They can serve as host molecules and selectively bind a variety of electron-deficient aromatic and aliphatic guest molecules. In different experiments, we compared the interfacial tensions with the calculated hydrophilic-lipid-balance (HLB) values of these molecules. The measured interfacial tensions depend as much on the HLB values as on the geometric structure of the water insoluble molecules. The concentration dependence of the surface tension gave evidence for the formation of inverse micellar aggregates, which were formed in the oil phase above a well-defined value of the bulk concentration. The presence of aggregates in the organic liquid could also be investigated by dynamic light scattering measurements. We observed typical diameters of the inverse micellar aggregates in the order of 5.6 nm, and the critical micelle concentrations (cmc's) coincided well with the results of interfacial tension measurements. From the surface excess in the vicinity of the cmc, we calculated the space occupied by a single clip molecule on the self-assembled monolayer. The observed molecular surface area was in agreement with the effective molecular diameters of the molecules. In additional experiments, we could also show that complexes with aromatic guest molecules such as 1,2-4,5-tetracyanobenzene (TCNB) led to a reduction of the amphiphilic clip properties.
在一系列实验中，我们研究了具有刚性类双子结构的芳香脂肪族分子在甲苯与水界面处的界面活性。这些分子被称为夹子和镊子，具有刚性的中心苯或萘间隔单元，每个间隔单元被两个极性基团以及两个刚性芳香侧壁取代。它们可以作为主体分子，选择性地结合各种缺电子的芳香族和脂肪族客体分子。在不同的实验中，我们将界面张力与这些分子计算得到的亲水亲油平衡（HLB）值进行了比较。测得的界面张力既取决于HLB值，也取决于水不溶性分子的几何结构。表面张力的浓度依赖性证明了反胶束聚集体的形成，这些聚集体在本体浓度达到一个明确值以上时在油相中形成。有机液体中聚集体的存在也可以通过动态光散射测量来研究。我们观察到反胶束聚集体的典型直径约为5.6 nm，临界胶束浓度（cmc）与界面张力测量结果吻合良好。根据cmc附近的表面过剩量，我们计算了单个夹子分子在自组装单分子层上占据的空间。观察到的分子表面积与分子的有效直径一致。在额外的实验中，我们还可以表明，与芳香族客体分子如1,2 - 4,5 - 四氰基苯（TCNB）形成的络合物会导致两亲性夹子性质的降低。
