Abstract
Molecular mobility has attracted considerable attention in supramolecular chemistry and biochemistry, but the simple question of whether a small molecule can move directly between different binding sites of a multitopic host without intermediate dissociation has not been addressed so far. To study such processes, we consider hydrogen/deuterium exchange experiments on a model system comprising complexes formed between 18-crown-6 and oligolysine peptides. Because direct binding-site hopping is indistinguishable in solution from a dissociation/reassociation mechanism, here we show that the high vacuum of a mass spectrometer offers a unique environment for probing such processes. The highly dynamic motion of crown ethers along oligolysine peptide chains proceeds mechanistically by a simultaneous transfer of the crown ether from its ammonium ion binding site to a nearby amino group together with a proton. Furthermore, the exchange experiments unambiguously reveal the zwitterionic structure of the 18-crown-6/oligolysine complexes, highlighting the versatility and potential of gas-phase experiments for investigating non-covalent interactions.
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Change history
23 October 2009
At roughly the same time, the authors of this Article independently submitted a manuscript to Angewandte Chemie, in which the method presented here was applied to polyamino propylene amine dendrimers. The authors forgot to mention this publication and would like to apologize for their mistake. The missing reference is: Winkler, H. D. F., Weimann, D. P., Springer, A. and Schalley, C. A. Dynamic motion in crown ether dendrimer complexes: A "spacewalk" on the molecular scale. Angew. Chem. Int. Ed. 48, 7246-7250 (2009).
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Acknowledgements
We thank Andreas Springer for valuable scientific advice and acknowledge funding from the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie.
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C.A.S., H.D.F.W. and D.P.W. conceived, designed and performed the mass spectrometric experiments and co-wrote the paper. J.A.F. and B.K. contributed the peptides. All authors discussed the results and commented on the manuscript.
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Weimann, D., Winkler, H., Falenski, J. et al. Highly dynamic motion of crown ethers along oligolysine peptide chains. Nature Chem 1, 573–577 (2009). https://doi.org/10.1038/nchem.352
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DOI: https://doi.org/10.1038/nchem.352
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