Self-Assembly of Palmitoyl Lipopeptides Used in Skin Care Products

The self-assembly of three cosmetically active peptide amphiphiles C-16-GHK, C-16-KT, and C-16-KTTKS (C-16 denotes a hexadecyl, palmitoyl chain) used in commercial skin care products is examined. A range of spectroscopic, microscopic, and X-ray scattering methods is used to probe the secondary structure, aggregate morphology, and the nanostructure. Peptide amphiphile (PA) C-16-KTTKS forms flat tapes and extended fibrillar structures with high beta-sheet content. In contrast, C-16-KT and C-16-GHK exhibit crystal-like aggregates with, in the case of the latter PA, lower beta-sheet content. All three PA samples show spacings from bilayer structures in small-angle X-ray scattering profiles, and all three have similar critical aggregation concentrations, this being governed by the lipid chain length. However, only C-16-KTTKS is stained by Congo red, a diagnostic dye used to detect amyloid formation, and this PA also shows a highly aligned cross-beta X-ray diffraction pattern consistent with the high beta-sheet content in the self-assembled aggregates. These findings may provide important insights relevant to the role of self-assembled aggregates on the reported collagen-stimulating properties of these PAs.