Monolayers of Chiral Imidazole Amphiphiles: Domain Formation and Metal Complexation

The monolayer characteristics of achiral and chiral imidazole amphiphiles on the air-water interface have been studied by measuring the surface pressure/surface area (II/A) isotherms and by epifluorescence microscopy.Both types of amphiphiles form stable monolayers at the air-water interface with a welldefined liquid-expanded (LE) to liquid-condensed (LC) phase transition.The enantiomerically pure imidazole amphiphiles display the same 11/A isotherms within experimental error.The addition of small concentrations (10-6-10~* M) of transition metal ions (Co(II), Ni(II), Zn(II), and Cu(II)) causes a change in the isotherms, which suggests that these ions bind to the imidazole ligand functions.Epifluoroescence microscopy experiments on monolayers of the imidazole amphiphiles on pure water reveal that Bolid domains are formed when the monolayers are compressed into the LE to LC phase transition region.These domains have dendritic or fractal shapes.Interestingly, in the case of the chiral imidazole amphiphiles the solid domains have a chiral appearance: they turn clockwise or counterclockwise depending on the configuration of the chiral center in the amphiphile.The formation of solid domains is also observed when the chiral imidazole amphiphiles are spread on a subphase containing zinc(II) ions.These domains, however, have no chiral appearance.