Issue 6, 2023

Maximized axial helicity in a Pd2L4 cage: inverse guest size-dependent compression and mesocate isomerism

Abstract

Helicity is an archetypal structural motif of many biological systems and provides a basis for molecular recognition in DNA. Whilst artificial supramolecular hosts are often helical, the relationship between helicity and guest encapsulation is not well understood. We report a detailed study on a significantly coiled-up Pd2L4 metallohelicate with an unusually wide azimuthal angle (∼176°). Through a combination of NMR spectroscopy, single-crystal X-ray diffraction, trapped ion mobility mass spectrometry and isothermal titration calorimetry we show that the coiled-up cage exhibits extremely tight anion binding (K of up to 106 M−1) by virtue of a pronounced oblate/prolate cavity expansion, whereby the Pd–Pd separation decreases for mono-anionic guests of increasing size. Electronic structure calculations point toward strong dispersion forces contributing to these host–guest interactions. In the absence of a suitable guest, the helical cage exists in equilibrium with a well-defined mesocate isomer that possesses a distinct cavity environment afforded by a doubled Pd–Pd separation distance.

Graphical abstract: Maximized axial helicity in a Pd2L4 cage: inverse guest size-dependent compression and mesocate isomerism

Supplementary files

Article information

Article type
Edge Article
Submitted
01 dec 2022
Accepted
12 jan 2023
First published
19 jan 2023
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY-NC license

Chem. Sci., 2023,14, 1524-1531

Maximized axial helicity in a Pd2L4 cage: inverse guest size-dependent compression and mesocate isomerism

W. M. Bloch, S. Horiuchi, J. J. Holstein, C. Drechsler, A. Wuttke, W. Hiller, R. A. Mata and G. H. Clever, Chem. Sci., 2023, 14, 1524 DOI: 10.1039/D2SC06629G

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