Dynamics of PBLG Polypeptide Nanorods Embedded into Nanoporous Alumina Templates

Hatice Duran 1Antonios Gitsas 2George Floudas 2M. Steinhart 3Wolfgang Knoll 1

1. Max Planck Institute for Polymer Research (MPIP), Ackermannweg 10, Mainz 55128, Germany
2. University of Ioannina, Department of Physics, and BRI-FORTH, P.O. Box 1186, Ioannina 45110, Greece
3. Max Planck Institute of Microstructure Physics (MPI), Weinberg 2, Halle 06120, Germany

Abstract

In this work, N-carboxy anhydride (NCA) monomer molecules were polymerized on the pore walls of an initiator coated nanoporous alumina template, leading to the formation of polypeptide poly(γ-benzyl-L-glutamate), known as PBLG nanorods. The structure and the associated dynamics have been investigated for a series of PBLG using DSC, XRD, FTIR, and dielectric spectroscopy (DS), respectively. High molecular weight bulk PBLG exhibits a glass transition temperature (Tg) at about 286 K and a broad endothermic peak at around 333-353 K during the first heating run. The dynamic investigation by DS revealed a glass temperature at about 281±2 K for the PBLG nanorods, i.e., slightly lower than the bulk Tg. Studies as a function of pore size are in progress. In addition, DS revealed a local process below Tg, associated with the localized fluctuations of the side-group and a slower process associated with the relaxation of the secondary structure. The intensity of this mode suggested "broken" helices. An "ultra slow" process was also detected that arises from the inhomogeneous medium (Maxwell-Wagner-Sillars polarization). The structural characterization of the pure PBLG showed a strong peak of the lyotropic liquid crystalline phase at 2θ= 6.7°. This reflection corresponds to an intermolecular spacing of alpha-helical chains with a spacing of 13.2 Å. XRD patterns of PBLG nanorods had only one- albeit very broad- reflection at 2θ=6.5°. The broader reflection and the absence of higher order reflections are in agreement with the DS study revealing broken helices.

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Presentation: Oral at E-MRS Fall Meeting 2007, Symposium B, by Hatice Duran
See On-line Journal of E-MRS Fall Meeting 2007

Submitted: 2007-05-11 18:16
Revised:   2009-06-07 00:44
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