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The effect of isotopic substitution on the chirality of a self-assembled helix

Abstract

N,N′,N″-trialkylbenzene-1,3,5-tricarboxamides (BTAs) self-assemble by means of strong, threefold α-helix-type intermolecular hydrogen bonding into well-defined, helical, one-dimensional columnar aggregates. When a stereogenic centre is introduced into the alkyl side chains of these BTAs, strong Cotton effects are observed in dilute apolar solutions, indicating the preference for one helical conformation over the other. Here, we report the creation of a helical sense preference in self-assembled BTAs by introducing deuterium/hydrogen isotope chirality into the alkyl side chains. We determine the relative stabilities of the left- and right-handed helical conformations of these deuterated supramolecular polymers by performing a conformational analysis. Our findings show that the results of deuterium/hydrogen substitution in BTA-based supramolecular polymers and helical polyisocyanates are very similar, although the formation mechanisms differ. The selectively deuterated BTAs discussed here represent the first example of supramolecular chirality resulting from isotope substitution.

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Figure 1
Figure 2: Self-assembly behaviour of (S)-D-BTA (1a) in solution.
Figure 3: Amplification of chirality experiments for (S)-D-BTA (1a) and (R)-D-BTA (1b) at 20 °C, c = 5 × 10−5 M, in dodecane.
Figure 4: Formation mechanism of (S)-D-BTA (1a) aggregates in solution.

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Acknowledgements

The authors thank M. M. L. Nieuwenhuizen and T. M. Hermans for assistance with 2D- and 2H-NMR, C. Duxbury and A. Heise from DSM Research for their support during the initial experiments, P. J. M. Stals for providing compounds 2 and 3 and M. M. Green for intriguing discussions. This work was supported by the NRSC-C foundation and the Netherlands Organization for Scientific Research (Spinoza-NWO).

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S.C. performed the experimental work and wrote most of the manuscript. D.W.R.B. contributed to the synthesis of the materials and M.M.J.S. to data analysis. A.R.A.P. and E.W.M. conceived and designed the concepts. All authors contributed to the conception of the experiments and discussion of the results, and commented on the manuscript.

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Correspondence to Anja R. A. Palmans or E. W. Meijer.

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The authors declare no competing financial interests.

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Cantekin, S., Balkenende, D., Smulders, M. et al. The effect of isotopic substitution on the chirality of a self-assembled helix. Nature Chem 3, 42–46 (2011). https://doi.org/10.1038/nchem.889

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