Chromatography of Mechanically Interlocked Molecular Compounds

Catenanes and rotaxanes are molecules composed of mechanically interlocked components which are not linked to each other by covalent bonds. These molecular assemblies behave as discrete molecules with defined properties significantly different from those of the parent "free" components. High-performance liquid chromatography has been employed successfully to characterize some tetracationic catenanes and rotaxanes incorporating either cyclobis(paraquat-p-phenylene) or cyclobis(paraquat-4,4′-biphenylene) as the charged components and either hydroquinone-containing macrocycles or dumbbell-shaped entities as the neutral components. In each case, significant differences in the retention times of the mechanically interlocked molecular compounds, in comparison with those of their components as their "free" forms, were observed.