Metal ion modulated ultrathin films and nanostructures of tyrosine-based bolaamphiphile at the air/water interface

Supramolecular assemblies at the air/water interface from a newly designed tyrosine-based bolaamphiphile, 1,10-bis(O-l-tyrosine)-decane (C10BT), were investigated. The compound could be spread on water surface and form organized ultrathin film. It was interesting to find that metal ions such as Ag+ and Cu2+ in the subphase can greatly modulate the molecular packing of C10BT and the morphology of the subsequently deposited Langmuir–Blodgett (LB) films. Atomic force microscopic measurements revealed that C10BT LB film from the subphase containing Ag+ ion showed well-ordered layered nanofibers, while Cu2+ ion coordinated C10BT film demonstrated dense cross-linked network. It was suggested that both the strong chelating property to the carboxylate and the different packing mode of hydrocarbon chain resulted in the distinct nanostructures. Fourier transform infrared spectra reveal the difference between the Ag–C10BT complex film and that of Cu2+ ion, and the mechanism of the packing mode of hydrocarbon chain was discussed. Furthermore, the X-ray diffraction and X-ray photoelectron spectra also verified the orderly layer structure and the relative molar ratios compared with different metal ions. While many efforts have been devoted to manipulation of the nanostructures and functions of sophisticated bolaform amphiphiles, we provided a simple method of modulating the organization and morphology of C10BT films through metal ions.