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Project A3: Self-assembled nanoribbons and nanotubes of aromatic diamide-esters

Principal Investigators: G. Reiter (Freiburg) / P. Mésini (Strasbourg)
Collaborators: M. Brinkmann (Strasbourg)
PhD Student: Asad Jamal

Current state of the research

a3There are only few molecules able to self-assemble into nanotubes [1]. The nanotubes form spontaneously in solution through noncovalent interactions, like H-bonds, van der Waals interaction or solvophobic forces. A clear understanding of their formation is hampered by the fact that the resolution of the self-assembled nanotubular structure at the atomic scale is very hard. However, it has been shown that the tubes are formed from ribbons winding first into helical ribbons which then form tubules (see figure above). These objects have triggered much theoretical work by physicists [2-4]. The proposed models explain the helical shape of the formed tapes by treating the chirality of the constituent molecules on a phenomenological basis, but do not take into account the effects of local molecular interactions. Therefore, they cannot explain why nonchiral molecules can also self-assembled into chiral helices.

To advance our  understanding of this interesting self-assembly behavior systematic studies of structural and dynamical aspects are needed. Structural studies could explore the correlation between shape of the resulting aggregates and the conditions of their formation (concentration, temperature, solvent composition), whereas dynamical studies should address the growth of the structures and morphological transitions between them. The present project plans to treat both issues.

Contributions of the participating groups

a31Recently, the Strasbourg group has shown that aromatic diamide esters  self-associate into nanotubes which have a diameter of (about) 30 nm and are several micrometers long (see figure to the right) [5-6]. Since the constituting molecules are not chiral and yet can form helices (i.e., chiral objects), their self-assembly cannot be explained by the current theoretical models [2-4]. This makes the study of the self-assembly of these molecules fundamentally interesting. Furthermore, the self-assembly occurs in various solvent mixtures, which opens the possibility for a systematic study of the role of the solvent on the resulting structures and the assembly process. The Freiburg group will contribute to that because it is specialized in the study of ordered polymeric structures on surfaces, both from the structural and dynamic point of view [7]. By AFM and STM the group has already studied supramolecular polymers and was able to identify the interactions leading to different levels of organization [8]. Recently, the group has explored the nucleation and growth of well-ordered structures in thin films of polypeptide-PS copolymers, and they have shown that even traces of protic solvent can drastically change the formation process of these films [9].

Research project and collaborations

The goal of this project is to control in 2D (at the surface of given substrates) and in 3D (solution or in the bulk) the self-assembly process of aromatic diamide esters that is governed by multiple noncovalent interactions and affected by subtle molecular parameters, like the length of the ester, the solvent, and the substrate. We will study (using AFM and STM) morphological transitions of adsorbed monomolecular layers and aggregates by swelling in various solvents. Results will be compared with the behavior in solution. In collaboration with theorists from the ICS (I. Nyrkova, A. Semenov) a modeling of the various regimes in solutions and thin films should be possible. Orientation of the self-assembly via the substrate (epitaxy) will be tested.

The project strongly benefits from the synergy between the studies in 2D and 3D. The Freiburg group will study the nanostructures formed in 2D and the dynamics of the attendant formation process. These results will be compared, for the same compounds and solvent mixtures, with the behavior in 3D solution in 3D, which will be studied in Strasbourg. The group in Strasburg has focused (so far) on studies at equilibrium; the Freiburg group will bring insight into the dynamic aspects to control the shape of the self-assembly.


[1]T. Shimizu; M. Masuda; H. Minamikawa, Chem. Rev. 2005, 105, 1401.
[2]W. Helfrich; J. Prost, Phys. Rev. A 1988, 38, 3065.
[3]U. Seifert; J. Shillcock; P. Nelson,  Phys. Rev. Lett. 1996, 77, 5237.
[4]J. V. Selinger; M. S. Spector; J. M. Schnur, J. Phys. Chem. B 2001, 105, 7157.
[5]N. Diaz; F. X. Simon; M. Schmutz; M. Rawiso; G. Decher; J. Jestin; P. J. Mésini, Angew. Chem. Int. Ed. Engl. 2005, 44, 3260.
[6]F. X. Simon; N. S. Khelfallah; M. Schmutz; N. Diaz; P. J. Mésini, J. Am. Chem. Soc. 2007, 129, 3788.
[7]G. J. Vancso; G. Reiter, Ordered polymeric nanostructures at surfaces. Springer Berlin / Heidelberg: 2006; Vol. 200.
[8]F. Vonau, D. Suhr, D. Aubel, L. Bouteiller, G. Reiter, L. Simon, Phys. Rev. Lett. 2005, 94, 066103.
[9]I. Botiz; N. Grozev; H. Schlaad; G. Reiter, Soft Matter 2008, 4, 993.


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