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Self assembly of a model amphiphilic phenylalanine peptide/polyethylene glycol block copolymer in aqueous solution

Castelletto, V. and Hamley, I.W. (2009) Self assembly of a model amphiphilic phenylalanine peptide/polyethylene glycol block copolymer in aqueous solution. Biophysical Chemistry, 141 (2-3). pp. 169-174. ISSN 0301-4622

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To link to this article DOI: 10.1016/j.bpc.2009.01.008

Abstract/Summary

There has been great interest recently in peptide amphiphiles and block copolymers containing biomimetic peptide sequences due to applications in bionanotechnology. We investigate the self-assembly of the peptide-PEG amphiphile FFFF-PEG5000 containing the hydrophobic sequence of four phenylalanine residues conjugated to PEG of molar mass 5000. This serves as a simple model peptide amphiphile. At very low concentration, association of hydrophobic aromatic phenylalanine residues occurs, as revealed by circular dichroism and UV/vis fluorescence experiments. A critical aggregation concentration associated with the formation of hydrophobic domains is determined through pyrene fluorescence assays. At higher concentration, defined beta-sheets develop as revealed by FTIR spectroscopy and X-ray diffraction. Transmission electron microscopy reveals self-assembled straight fibril structures. These are much shorter than those observed for amyloid peptides, the finite length may be set by the end cap energy due to the hydrophobicity of phenylalanine. The combination of these techniques points to different aggregation processes depending on concentration. Hydrophobic association into irregular aggregates occurs at low concentration, well-developed beta-sheets only developing at higher concentration. Drying of FFFF-PEG5000 solutions leads to crystallization of PEG, as confirmed by polarized optical microscopy (POM), FTIR and X-ray diffraction (XRD). PEG crystallization does not disrupt local beta-sheet structure (as indicated by FTIR and XRD). However on longer lengthscales the beta-sheet fibrillar structure is perturbed because spheruilites from PEG crystallization are observed by POM. (C) 2009 Elsevier B.V. All rights reserved.

Item Type:Article
Refereed:Yes
Divisions:Faculty of Life Sciences > School of Chemistry, Food and Pharmacy > Department of Chemistry
ID Code:11095
Uncontrolled Keywords:Peptide copolymers, Self-assembly, Beta sheets, Fibrils , SURFACTANT-LIKE PEPTIDES, PROTEIN SECONDARY STRUCTURE, AMYLOID FIBRIL FORMATION, POLY(ETHYLENE OXIDE), POLYELECTROLYTE SOLUTIONS, PEG CRYSTALLIZATION, FORM NANOTUBES, BOVINE INSULIN, NANOFIBERS, FRAGMENTS

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