Gemini-like molecular clips and tweezers: the influence of structure and guest binding on interfacial tension.

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 b...