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 w
PSLG ≥ 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 amorphous segments along the polypeptide backbone
and at the chain ends that freeze at the liquid-to-glass transition. The slower process is associated with the relaxation
of the α-helical peptide secondary structure. The analysis of the dielectric strength associated with the slower
process revealed that helices are objects of low persistence.
The synthesis and characterization of the new silylene(isodicyclopentadienyl)(fluorenyl)zirconium dichloride (5) have been performed. This complex has been characterized by 1 H and 13 C NMR spectroscopy and its solid-state molecular structure has been determined. After activation by methylalumoxane, 5 is shown to initiate the polymerization of ethylene and propylene. S-PP is produced. Quite unusual for a silylene-bridged zirconium complex, good syndiotacticity was observed for propylene polymerization.
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