Tuning supramolecular architectures of KI4K amphiphiles via varying terminal variations

Abstract

We report here how to manipulate the self-assembly behavior of KI4K by the terminal variations. The results demonstrated that both the supramolecular architectures and their corresponding secondary structure can be tuned just by terminal variations. Twisted or helical ribbons with width over the range of 40–50nm and a bilayed height were dominant for the peptide CH3COKI4KCOOH due to the hydrogen bonding interactions resulted from the uncapping COOH. As a comparison, nanotubes with much larger width but only monolayer wall thickness were dominant for CH3COKI4KCONH2. As for FmocKI4KCOOH, the steric hindrance effect can limit the width growth but the π−π stacking interactions can promote further association of the primary aggregate along the height direction to form nanofiber bundles. Both circular dichroism (CD) and Fourier transform infrared spectroscopy (FTIR) results indicated that the CH3COKI4KCOOH and FmocKI4KCOOH adopted a mixture of β-sheet and random coil structure while random coil structure was dominant for both CH3COKI4KCONH2 and NH2KI4KCOOH. The small angle neutron scattering (SANS) results indicated the basic lamellar structure for both CH3COKI4KCOOH and CH3COKI4KCONH2 but they go through different pathways to form ribbons and nanotubes with varied shape and size. The Thioflavin-T (ThT) results indicated their abilities to enhance ThT fluorescence intensity was possibly correlated with the amount of aggregates in solutions except for the aggregate morphologies. The peptides involved in the present study provide simple molecular models for the investigation of both COOH and Fmoc in contribution to varied non-covalent interactions and the final aggregate morphologies.