Mechanistic process understanding of the self-assembling behaviour of asymmetric bolaamphiphilic short-peptides and their templating for silica and titania nanomaterials

Abstract

Investigation of the self-assembly of peptides is critically important to clarify certain biophysical phenomena, fulfill some biological functions, and construct functional materials. However, it is still a challenge to precisely predict the self-assembled structures of peptides because of their complicated driving forces and various assembling pathways. In this work, to elucidate the effects of noncovalent interactions including hydrogen bonding, molecular geometry, and hydrophobic and electrostatic interactions on the peptide self-assembly, a series of asymmetric bolaamphiphilic short peptides consisting of Ac-EI₃K-NH₂ (EI₃K), Ac-EI₄K-NH₂ (EI₄K), Ac-KI₃E-NH₂ (KI₃E) and Ac-KI₄E-NH₂ (KI₄E) were designed and their self-assembling behaviors at different solution pH values were investigated systematically. The peptides self-assembled into twisted nanofibers under most conditions except for EI₄K in a strongly alkaline solution and KI₄E under a strongly acidic condition, in which they self-assembled into nanotubes via helical monolayer nanosheet intermediates. In particular, KI₄E nanotubes are formed under acidic conditions, and its diameters are ∼500 nm much greater than most of the self-assembled structures from bolaamphiphilic peptides. Moreover, reversible morphological transition between the nanotubes and twisted nanofibers was observed with the change in solution pH. Such tunable self-assembled structures and switchable surface properties of the asymmetric bolaamphiphilic short-peptides allow them to be used as templates to construct advanced materials. Silica and titania nanomaterials faithful to the peptide templates in morphology were prepared at ambient temperature. This work clearly elucidates the effects of noncovalent interactions on the peptide self-assembly and also provides new insights into the design and preparation of complicated inorganic materials from tunable organic templates.