Peptide-amphiphiles with collagen-model head groups and dialkyl chain tails have been shown previously to self-assemble into highly ordered polyPro II-like triple-helical structures when dissolved in aqueous subphases. In the present study, we have examined peptide-amphiphiles containing monoalkyl chain tails for similar self-assembly behaviors. The structure of a collagen-model peptide has been characterized with and without an N-terminal hexanoic acid (C 6 ) modification. Evidence for a self-assembly process of both the peptide and peptide-amphiphile has been obtained from (a) circular dichroism spectra and melting curves characteristic of triple-helices, (b) one-dimensional NMR spectra indicative of stable triple-helical structure at low temperatures and melted triple helices at high temperatures, and (c) pulsed-field gradient NMR experiments demonstrating different self-diffusion coefficients between proposed triple-helical and non-triple-helical species. The peptide-amphiphile appeared to form monomeric triple helices. The thermal stability of the collagen-like structure in the peptide-amphiphile was found to increase as the monoalkyl tail chain length is increased over a range of C 6 to C 16 . The assembly process driven by the hydrophobic tail, albeit monoalkyl or dialkyl, may provide a general method for creating well-defined protein molecular architecture. Peptide-amphiphile structures possessing these alkyl moieties have the potential to be used for biomaterial surface modification to improve biocompatibility or, by mimicing fusion of viral envelopes with cellular membranes, as drug delivery vehicles.

We have used cryo-transmission electron microscopy (cryo-TEM), small-angle neutron scattering (SANS), differential scanning calorimetry (DSC), and circular dichroism (CD) for microstructural characterization of amphiphiles that have a model collagen peptide headgroup. Single-tail amphiphiles and double-tail amphiphiles with short tails such as C12 and C14 formed spheroidal micelles. Further increase in tail length of the double-tail amphiphiles led to the formation of disklike micelles that aggregated to form a strandlike structure. SANS curves for double-tail amphiphiles were obtained at different contrasts by using different fractions of D2O in the D2O/H2O mixture. SANS data analysis using the sphere method confirmed the structures imaged by cryo-TEM and provided a detailed structural characterization. CD data showed that the peptide's capacity to organize into a triple helix by intertwining with two neighboring molecules can be affected by increasing the tail length. Double-tail amphiphiles with tails such as C18 and C20 that are crystalline at room temperature disrupt the association of the triple helix at room temperature. Increasing the temperature to melt the crystalline tails helps restore the triple-helical conformation in the headgroups.