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Title: Selective host–guest chemistry, self-assembly and conformational preferences of m -xylene macrocycles probed by ion-mobility spectrometry mass spectrometry
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 Zn 2+ 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 HSO 4 − bound stronger than SO 4 2− to the host. The position of HSO 4 − at the binding cavity is a 180° inversion of the reported crystallographic SO 4 2− . The MXS dimer formed a prism-like shape with HSO 4 − exhibiting strong contacts with the 8 amine protons of two MXS macrocycles. By eliminating intermolecular interferences, we detected the low energy structures of MXS more » with collisional cross section (CCS) matching cis – trans and cis – cis 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. « less
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Physical Chemistry Chemical Physics
Page Range or eLocation-ID:
9290 to 9300
Sponsoring Org:
National Science Foundation
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