Modification of Fluorophore Photophysics through Peptide-Driven Self-Assembly Kevin J. Channon, † Glyn L. Devlin, ‡ Steven W. Magennis, § Chris E. Finlayson, † Anna K. Tickler, † Carlos Silva, | and Cait E. MacPhee* ,§ CaVendish Laboratory, UniVersity of Cambridge, JJ Thomson AVenue, Cambridge, U.K., CB3 0HE, Department of Chemistry, UniVersity of Cambridge, Lensfield Road, Cambridge, U.K., CB2 1EW, SUPA, School of Physics, The UniVersity of Edinburgh, Mayfield Road, Edinburgh, U.K., EH9 3JZ, and Départment de Physique, UniVersité de Montréal, C. P. 6128 succ. centre-Ville, Montréal, Québec, Canada, H3C 3J7 Received November 14, 2007; E-mail: cait.macphee@ed.ac.uk Abstract: We describe the formation of self-assembling nanoscale fibrillar aggregates from a hybrid system comprising a short polypeptide conjugated to the fluorophore fluorene. The fibrils are typically unbranched, ∼7 nm in diameter, and many microns in length. A range of techniques are used to demonstrate that the spectroscopic nature of the fluorophore is significantly altered in the fibrillar environment. Time-resolved fluorescence spectroscopy reveals changes in the guest fluorophore, consistent with energy migration and excimer formation within the fibrils. We thus demonstrate the use of self-assembling peptides to drive the assembly of a guest moiety, in which novel characteristics are observed as a consequence. We suggest that this method could be used to drive the assembly of a wide range of guests, offering the development of a variety of useful, smart nanomaterials that are able to self-assemble in a controllable and robust fashion. Introduction The emerging field of smart materials aims to design materials, at the molecular level, that exhibit specific combina- tions of physical and chemical functionality that may be inaccessible to traditional materials. Because of increased simplicity and flexibility of synthesis, supra-molecular self- assembly approaches for the production of functional materials are generating a great deal of attention. 1–3 Amyloid fibrils have attracted interest as nanomaterial scaffolds because of their potential for chemical and biological functionalization with nanometer precision. 4,5 Amyloid fibrils are large, highly ordered polypeptide aggregates which possess many desirable properties for nanomaterials engineering, such as high mechanical and chemical stability. 6–10 In the most part, this stability is derived from a -sheet structural motif that is common to all amyloid fibrils. In this arrangement, individual peptides are connected through hydrogen bonds in a regular, continuous array, per- pendicular to the fibril axis. This hydrogen-bonded array is thought to form consistently, with only a low sensitivity to the amino acid sequence. 11 Here, we explore the utility of an amyloid-fibril-forming peptide in driving the assembly of a functional element—in this case, the polycyclic, aromatic fluorophore, fluorene. The self- assembly of functional systems represents a substantial chal- lenge, because the molecular processes that drive the assembly can often be perturbed by the incorporation of the functional element. Indeed, previous independent studies have demon- strated that fluorene itself can drive the fibrillar assembly of short peptides via π-π interactions between the fluorophores. 12–14 In this study, a fragment of the transthyretin protein (TTR 105–115 ) that is known to form especially well-ordered amyloid fibrils in Vitro 6 was used as the protein component of the system. By choosing this well-characterized fiber-foming peptide, we aimed to retain the information for assembly exclusively within the peptide element without perturbing assembly significantly with inclusion of the guest molecule (Figure 1). Furthermore, in polymeric form, fluorene has displayed promising functionality as an organic electroluminescent material. 15,16 We thus antici- pated that incorporation of the fluorophore into the nanoscale † Cavendish Laboratory, University of Cambridge. ‡ Department of Chemistry, University of Cambridge. § SUPA, School of Physics, The University of Edinburgh. | Départment de Physique, Université de Montréal. (1) Huie, J. C. Smart Mater. Struct. 2003, 12, 59816–59810. (2) Sarikaya, M.; Tamerler, C.; Jen, A. K.-Y.; Schulten, K.; Baneyx, F. Nat. Mater. 2003, 2, 577–585. (3) Whitesides, G. M.; Grzybowski, B. Science 2002, 295, 2418–2421. (4) MacPhee, C. E.; Woolfson, D. N. Curr. Opin. Solid State Mater. Sci. 2004, 8, 141–149. (5) Yeates, T.; Padilla, J. 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