Structure and Dynamics of Self-Assembled Poly(ethylene glycol) Based Coiled-Coil Nano- Objects Guido W. M. Vandermeulen, [a] Dariush Hinderberger, [a] Hui Xu, [c] Sergei S. Sheiko, [c] Gunnar Jeschke,* [a] and Harm-Anton Klok* [b] Introduction Block copolymer self-assembly is driven by the chemical in- compatibility of the constituent blocks and can lead to a varie- ty of morphologies, both in solution and in the solid state. [1] Due to the unspecific nature of the driving forces for self-as- sembly, structural control at the nanometer level, however, is limited. Solid-state block copolymer morphologies are general- ly characterized by a single typical length scale, and solution self-assembly of block copolymers rarely produces uniform nanostructures but rather an ensemble of objects with a cer- tain size distribution. The limited control over nanostructure formation during block copolymer self-assembly is in great contrast to protein folding and assembly, which can lead to materials with complex internal structures that are hierarchical- ly organized from the nanometer to the micrometer level. The excellent properties of protein-derived materials underline the importance of nanoscale order for macroscopic properties. Conjugation of biological structural motifs to synthetic poly- mers enhances control over nanoscale structure formation and is a versatile strategy for the development of novel self-assem- bled materials with complex internal structures and the poten- tial to interface with biology. [2] In contrast to common block copolymers, the self-assembly of such hybrid polymers is driven by the very specific folding properties of the peptide se- quences. Only a few examples of such hybrid block copoly- mers have been reported, with most of them focusing on con- jugates of b-strand peptide sequences and poly(ethylene glycol) (PEG). [3] Recently, we reported the synthesis and self-as- sembly of hybrid block copolymers based on peptide sequen- ces derived from the a-helical coiled-coil motif and PEG. [4] Cir- cular dichroism (CD) and analytical ultracentrifugation (AUC) experiments demonstrated that the folding properties of the peptide sequences are retained upon conjugation to PEG and showed that the block copolymers self-assemble into uniform dimeric and tetrameric nano-objects in aqueous solution (Figure 1). Addition of 50% (v/v) ethanol was found to result in dissociation of the nano-objects into unimeric block copolymer molecules with a-helical peptide segments. The model in Figure 1 features a PEG shell closely wrapped around a pep- tide core, which consists of two or four helices aligned in paral- lel fashion. This model is based on empirical rules for the design of parallel coiled coils [5] and the results of temperature- dependent CD experiments, which indicated a relatively high thermal stability of the coiled-coil nano-objects. [4] Due to their nanosized dimensions, it is difficult to obtain detailed structur- al information from supramolecular nano-objects using meth- ods such as X-ray and neutron scattering. Although NMR spec- troscopy provides suitable resolution, data analysis from com- plex systems, such as peptide hybrid block copolymers, may be very difficult. In this contribution, we will demonstrate that electron paramagnetic resonance (EPR) spectroscopy is a very powerful technique to characterize the solution structure and dynamics of supramolecular nano-objects and to substantiate the model proposed in Figure 1. [a] Dr. G. W. M. Vandermeulen, D. Hinderberger, Priv.-Doz. Dr. G. Jeschke Max Planck Institute for Polymer Research Ackermannweg 10, 55128 Mainz (Germany) Fax: (+ 49) 6131-379-100 E-mail: jeschke@mpip-mainz.mpg.de [b] Prof. H.-A. Klok …cole Polytechnique Fÿdÿrale de Lausanne Institut des Matÿriaux, Laboratoire des Polymõres B‚timent MX-D, 1015 Lausanne (Switzerland) Fax: (+ 41) 21-693-5650 E-mail: harm-anton.klok@epfl.ch [c] Dr. H. Xu, Prof. S. S. Sheiko Department of Chemistry, CB# 3290 University of North Carolina Chapel Hill, NC 27599-3290 (USA) Herein we describe the structure and dynamics of self-assembled nano-objects generated from poly(ethylene glycol) based (PEG- ylated) coiled-coil hybrid block copolymers. Electron paramagnet- ic resonance (EPR) experiments on spin-labeled samples provided a strong indication for a parallel alignment of the peptide helices in at least the dimeric coiled-coil nano-object and indicated that the PEG chains are folded rather closely around the peptide core of the nano-objects. The EPR results were supported by AFM stud- ies, which revealed the presence of discrete nanosized objects in thin, spin cast films of the block copolymers on mica substrates. Since their size and structure may be engineered via directed mu- tations in the amino acid sequence, these nano-objects may be interesting building blocks for the development of supramolec- ular materials with various potential applications. 488 ¹ 2004 Wiley-VCH Verlag GmbH&Co. KGaA, Weinheim DOI: 10.1002/cphc.200301079 ChemPhysChem 2004, 5, 488 ± 494