Aggregation of polypeptide-based amphiphiles in water

The amphiphile, poly(gamma -methyl L-glutamate) with a phosphate head group at the terminal (PMG(10)-P) was prepared. PMG(10)-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 PMG(10)-P when in the beta -form conformation. The beta -form conformation of PMG(10)-P was confirmed by circular dichroism and fourier transform infrared spectrometry (FT-LR) measurements. The ribbon-like aggregate is P, at room temperature. The phase transition from beta (1) to beta (II) above ca. 35 degreesC was confirmed by differential scanning calorimetry (DSC) measurements. Further increase in temperature induced the disaggregation of PMG(10)-P whose conformation is in random coil with some alpha -helix. This conformational behavior is summarized in a temperature-cancentration phase diagram.