Anti-Hofmeister Anion Selectivity via a Mechanical Bond Effect in Neutral Halogen-Bonding [2]Rotaxanes

Angew Chem Int Ed Engl. 2022 Dec 12;61(50):e202214523. doi: 10.1002/anie.202214523. Epub 2022 Nov 17.

Abstract

Exceptionally strong halogen bonding (XB) donor-chloride interactions are exploited for the chloride anion template synthesis of neutral XB [2]rotaxane host systems which contain perfluoroaryl-functionalised axle components, including a remarkably potent novel 4,6-dinitro-1,3-bis-iodotriazole motif. Halide anion recognition properties in aqueous-organic media, determined via extensive 1 H NMR halide anion titration experiments, reveal the rotaxane host systems exhibit dramatically enhanced affinities for hydrophilic Cl- and Br- , but conversely diminished affinities for hydrophobic I- , relative to their non-interlocked axle counterparts. Crucially, this mechanical bond effect induces a binding selectivity which directly opposes Hofmeister bias. Free-energy analysis of this mechanical bond enhancement demonstrates anion recognition by neutral XB interlocked host systems as a rare and general strategy to engineer anti-Hofmeister bias anion selectivity in synthetic receptor design.

Keywords: Anion Recognition; Anti-Hofmeister Bias; Halogen Bonding (XB); Mechanically Interlocked Molecules; Rotaxanes.