Aggregation of Polypeptide-Based Amphiphiles in Water

Abstract

The amphiphile, poly(γ-methyl L-glutamate) with a phosphate head group at the terminal (PMG10-P) was prepared. PMG10-P was dispersed in aqueous solution to form a globular assembly after sonication. One hour later, globular assemblies had joined each other to transform into fibrous aggregates. At 24 h, the fibrils assembled to form twisted ribbon-like aggregate. The thickness of the ribbon-like sheet was ca. 4.0 nm which is compatible with the chain length of PMG10-P when in the β-form conformation. The β-form conformation of PMG10-P was confirmed by circular dichroism and fourier transform infrared spectrometry (FT-IR) measurements. The ribbon-like aggregate is βI at room temperature. The phase transition from βI to βII above ca. 35°C was confirmed by differential scanning calorimetry (DSC) measurements. Further increase in temperature induced the disaggregation of PMG10-P whose conformation is in random coil with some α-helix. This conformational behavior is summarized in a temperature-concentration phase diagram.