Issue 17, 2020

Selective host–guest chemistry, self-assembly and conformational preferences of m-xylene macrocycles probed by ion-mobility spectrometry mass spectrometry

Abstract

We demonstrated ion-mobility spectrometry mass spectrometry (IMS-MS) as a powerful tool for interrogating and preserving selective chemistry including non-covalent and host–guest complexes of m-xylene macrocycles formed in solution. The technique readily revealed the unique favorability of a thiourea-containing macrocycle MXT to Zn2+ to form a dimer complex with the cation in an off-axis sandwich structure having the Zn–S bonds in a tetrahedral coordination environment. Replacing thiourea with urea generates MXU which formed high-order oligomerization with weak binding interactions to neutral DMSO guests detected at every oligomer size. The self-assembly pathway observed for this macrocycle is consistent with the crystalline assembly. Further transformation of urea into squaramide produces MXS, a rare receptor for probing sulfate in solution. Tight complexes were observed for both monomeric and dimeric of MXS in which HSO4 bound stronger than SO42− to the host. The position of HSO4 at the binding cavity is a 180° inversion of the reported crystallographic SO42−. The MXS dimer formed a prism-like shape with HSO4 exhibiting strong contacts with the 8 amine protons of two MXS macrocycles. By eliminating intermolecular interferences, we detected the low energy structures of MXS with collisional cross section (CCS) matching cistrans and ciscis squaramides-amines, both were not observed in crystallization trials. The experiments collectively unravel multiple facets of macrocycle chemistry including conformational flexibility, self-assembly and ligand binding; all in one analysis. Our findings illustrate an inexpensive and widely applicable approach to investigate weak but important interactions that define the shape and binding of macrocycles.

Graphical abstract: Selective host–guest chemistry, self-assembly and conformational preferences of m-xylene macrocycles probed by ion-mobility spectrometry mass spectrometry

Supplementary files

Article information

Article type
Paper
Submitted
24 Dec 2019
Accepted
14 Apr 2020
First published
14 Apr 2020

Phys. Chem. Chem. Phys., 2020,22, 9290-9300

Author version available

Selective host–guest chemistry, self-assembly and conformational preferences of m-xylene macrocycles probed by ion-mobility spectrometry mass spectrometry

B. A. Link, A. J. Sindt, L. S. Shimizu and T. D. Do, Phys. Chem. Chem. Phys., 2020, 22, 9290 DOI: 10.1039/C9CP06938K

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