Assembly of Helical Nanostructures: Solvent-Induced Morphology Transition and the Effect on Cell Adhesion.

Precise manipulating both the morphology and chiroptical signals of supramolecular assemblies will help to better understand the natural biological self-assembly mechanism. Herein, two simple L/D-phenylalanine based derivatives (L/DPFM) are designed and their solvent-dependent morphology evolutions are illustrated. It is found that by increasing the content of H2O in the ethanol aqueous solutions, LPFM can self-assemble into right-handed nanofibers, flat fibrous structures and inversed left-handed nanofibers, respectively. The assemblies in ethanol and H2O exhibit opposite conformations and circular dichroism (CD) signals even though they are constructed from the same molecules. Thus, the morphology-dependent cell adhesion and proliferation behaviors are further characterized. Left-handed nanofibers are found to be more favorable for the cell adhesion compared with right-handed nanostructures. The quantitative AFM analysis showed that L929 cell adhesion force on left-handed LPFM fibers is much higher than that on structures with inversed handedness. Besides, the value of cell Young's modulus is lower for left-handed nanofibrous films, which indicates better flexibility. The difference in cell-substrate interactions may lead to different effect on cell behaviors.