2012-03-EM Synthetic helical organic nano-architectures for single-molecule electronics (UB1-CBMN, UW-WIN)
Over the last decade, it has been shown that a wide variety of synthetic oligomers possess an ability to adopt folded conformations inspired by the structures of biopolymers. Such oligomers were termed foldamers. Recent progress in this area demonstrated that stepwise chemical synthesis and molecular design allow to produce large helically folded molecular architectures based on aromatic oligoamide backbones with well-defined and predictable conformations. For example, oligomers of 8-amino-2-quinoline carboxylic acid fold into helices comprised of 2.5 units per turn and a helix pitch of 3.5 Angström. A 48-mer gives rise to a 7 nm long helix.
These unprecedented objects may be used as rigid rods to be inserted in otherwise soft colloids; they may serve as scaffolds to display various functional groups at defined positions in space; and they have been shown to convey electrons. They thus represent potentially useful components in variety of contexts in materials science, including organic electronics and soft matter, and as biologically active substances. While the structures of these helical molecules have been well characterized in the solid state by x-ray crystallography, much less is known about their dynamic behavior in solution.
The project to be developed during this PhD thesis will aim at giving a detailed description of the conformation dynamics of long helical oligomers. It will involve both challenging multistep organic synthesis to be carried out at CBMN (UB1, France) and physical investigations, mainly through fluorescence spectroscopy, to be carried out at WIN (UW, Canada). Specifically, oligomers of various lengths (10-50 units) bearing solubilizing groups targeted to different solvents are to be synthesized and equipped at their termini by one or more fluorescent reporters. Fluorescence anisotropy measurements will be used to assess the rigidity and tumbling of the oligomers in which flexible monomers may be introduced at defined positions of their sequences.
Figure 1. a) Helical folding of oligoamides of 8-amino-2-carboxylic acid. Red arrows indicate electrostatic repulsions. b) Crystal structure of an 8mer. c) Crystal structure of a 48mer. d) Functionalization of foldamer helices with pyrene (pyr.) to investigate dynamic behavior in solution, for example bending around a flexible unit introduced in a sequence.
Project Partners and their roles
Chimie et Biologie des Membranes et Nano-Objets (CBMN) at Université Bordeaux 1 (UB1), France
The group of Ivan Huc is hosted at the European Institute of Chemistry and Biology (www.iecb.u-bordeaux.fr) on the Campus of University Bordeaux 1. It has pioneered the design, step-wise synthesis and structural characterization of protein-sized artificial folded architectures -i.e. foldamers - based on aromatic oligoamide backbones. One current research line of investigation concerns the use of these objects in material sciences. The group has access to state-of-the-art facilities to prepare and structurally characterize large foldamers, including high fields NMR (700, 800 MHz) and high flux microfocus X-ray diffractometers. .
Waterloo Institute of Nanostechnology (WIN) at University of Waterloo (UW) – Canada
The main activity of Prof. Jean Duhamel's laboratory is to characterize synthetic and biological macromolecules in solution with fluorescence. DNA, polypeptides, and vinyl polymers constitute the main polymeric backbones that have been studied so far. More recently, the internal dynamics of macromolecules with well-defined structure such as pyrene-labeled dendrimers have been investigated. The group has recognized expertise dealing with the three main fluorescence techniques used for such purposes, namely fluorescence dynamic quenching, fluorescence resonance energy transfer (FRET), and fluorescence anisotropy. It has access to steady-state and time-resolved fluorometers which are located in the laboratory
Industry partner: Solvay-Rhodia