Regulation of macrocycle shuttling in [2]rotaxanes by amino-acid speed bumps in organic-aqueous solvent mixtures

TL;DR

This study develops amino-acid containing [2]rotaxanes to control macrocycle shuttling rates, demonstrating amino-acid specific rates that vary over 4 orders of magnitude with minimal solvent influence.

Contribution

It introduces amino-acid units into [2]rotaxanes to precisely tune macrocycle shuttling rates based on steric effects, a novel approach in molecular machine control.

Findings

Shuttling rates vary with amino-acid side chain sterics.

Rates can be tuned over 4 orders of magnitude.

Shuttling shows small dependence on solvent composition.

Abstract

A homologous series of two-station [2]rotaxanes incorporating amino-acid units in the molecular thread has been developed. The degenerate [2]rotaxanes exhibit amino-acid specific shuttling rates between two fumaric stations related to the steric factor associated to the amino-acid side chain, as demonstrated by variable-temperature 1H NMR spectroscopy and exchange spectroscopy (EXSY). This allows tuning of the macrocycle shuttling rate over 4 orders of magnitude, which further has a relatively small solvent dependency.