Self-Assembly and Molecular Dynamics of Copolymers of γ-Methyl-l-glutamate and Stearyl-l-glutamate

Abstract

We report on the self-assembly and molecular dynamics in a series of poly(γ-methyl-l-glutamate-co-γ-stearyl-l-glutamate) [poly(MLG-co-SLG)] using thermodynamic (differential scanning calorimetry), structural (wide-angle X-ray scattering and 13C solid-state NMR), as well as dynamic (dielectric spectroscopy and site-specific solid-state NMR) techniques. Stearyl crystallization takes place in the copolymers with wPSLG ≥ 18% which reflects changes of the hydrocarbon side chains conformation. Extruded fibers of the copolymers are composed of both α-helical and β-sheet secondary structures oriented along the fiber axis with a bottleneck structure with MLG/SLG sequences forming the neck and more distant SLG sequences forming the bottle. This supramolecular organization has direct consequences on the dynamics. Two dielectrically active processes with strong temperature dependences were found. Site-specific NMR allowed the identification of the geometry of motions. One is associated with small-amplitude motions of...