Fulleren-Rezeptorkomplexe: Konstruktionselemente für nanodimensionierte Molekulare Maschinen
Final Report Abstract
It was the aim of the project to investigate the feasibility of self-assembled supra-molecular complexes as molecular rotors, using substituted tribenzotri-quinacenes as stators and fullerene-derivatives as rotors. For a self-assembling rotor system, which is held together by van-der-Waals interactions, strong dispersive interactions and thus large contact areas are needed. On the other hand, in order to allow for a revolving motion, the rotor needs to be constructed with a close to spherical symmetry. Thus, fullerene-based rotors are the best, if not the only choice. The question is now, whether the chosen C3 symmetric stators can be designed to match the rotor shape. The results achieved in this project clearly show that this concept is indeed feasible. However, the design of the receptor is crucial and concepts from macroscopic rotors fail for such nano-sized systems. In particular, we found that the idea of increasing the rotor-stator interaction by flexibility of the rotor, allowing it to adapt itself to the shape of the rotor, is not beneficial. The entropic penalty substantially reduces binding in this case. On the other hand, we were able to construct a rigid stator with a very strong binding constant (RB). In addition to that, we have demonstrated the first chiral self-assembled rotor system, which shows an asymmetric rotation profile and is in principle suited for preferential rotation in one direction. An important outcome of this project is the development of an arsenal of theoretical methods and simulation protocols to deal with such systems. We derived a first principles force field and showed that in certain cases MD simulations including explicit solvents are needed to gain insight in the rotor-stator binding and dynamics. Due to the very high complexity of the synthesis and characterization of such complex molecular systems and the difficulties during the conduction of the project not all targets envisioned in the proposal could be realized in the given time. Nevertheless, the project has clearly demonstrated that the approach of assembling molecular ratchets from suitably designed molecular rotors and stators via weak dispersive interactions is feasible and we believe that in the near future tribenzotriquinacene based receptors in particular might be further developed and refined. A strategy worth pursuing might be to include charge transfer rotor/stator interactions in the molecular design. By this means, the complex stability constants might be increased by another 1-3 orders of magnitude and the rotational energy profile for the upright rotation of the dipolar rotor in the axial chiral stator might become even more asymmetric, which seems to be crucial in order to construct supramolecular ratchets driven by external (symmetry-breaking) stimuli, e.g. circular polarized electric fields. Fixing such nano devices at precisely controlled places continues to present the future technical challenge, which, however, will require major additional efforts plus combining expertise from preparative chemists and (surface) physicists, as well as from theoreticians.
Publications
- Dalton Trans. 2012, 41, 5995 – 6002
S. Henne, B. Bredenkötter, A. A. D. Baghi, R. Schmid, D. Volkmer
- Almost Enclosed Buckyball Joints: Synthesis Complex Formation and Computational Simulations of a Pentypticene-Extended Tribenzotriquinacene, ChemPhysChem, Vol 15 Issue 17, December 1, 2014, Pages 3855-3863
S. Henne, B. Bredenkötter, M. Alaghemandi, S. Bureekaew, R. Schmid, D. Volkmer
(See online at https://doi.org/10.1002/cphc.201402475) - Chem. Eur. J. 2014, 20
B. Bredenkötter, M. Grzywa, M. Alaghemandi, R. Schmid, W. Herrebout, P. Bultinck, D. Volkmer
(See online at https://doi.org/10.1002/chem.201304980)
