# Directional Macrocycle Transport, Release, and Recapture Enabled by a Rotaxane Transporter

## TL;DR

This paper describes a molecular machine that can transport, release, and recapture a macrocycle in a controlled, repeatable way using chemical inputs.

## Contribution

The study introduces a rotaxane-based transporter capable of iterative directional macrocycle transport and release.

## Key findings

- The macrocycle shuttles directionally between two stations in the rotaxane upon base treatment.
- Fluoride cleaves the stopper, releasing the macrocycle and half-thread into solution.
- The system can be reassembled and reused for a second cycle of transport and release.

## Abstract

A transporter for a directional macrocycle transport, release, and recapture was constructed. This was achieved using a rotaxane featuring a dibenzo‐24‐crown‐8 macrocycle, dibenzylammonium (DBA)/methyl triazolium (MTA) stations on the thread and anthracene/triisopropylsilyl‐acetylene stoppers, respectively. In the protonated rotaxane, the macrocycle primarily resides on the DBA station, followed by directional shuttling to the MTA station upon treatment with base. Addition of fluoride as an additional chemical input cleaves the triisopropylsilyl stopper, leading to release of the macrocycle and the half‐thread into solution. The released macrocycle can be recaptured by protonation, and the mechanical bond can be reestablished via CuAAC click reaction, enabled by the terminal acetylene unit on the half‐thread. This generates an elongated second‐generation rotaxane transporter, which was used for a second cycle of directional macrocycle transport and release, proving the possibility of an iterative operation of the rotaxane‐transporter in this molecular design.

This study represents a bistable rotaxane that enables the directional shuttling, release, and recapture of a dibenzo‐24‐crown‐8 macrocycle upon addition of suitable chemical stimuli. This two‐step molecular transport and release can be followed by NMR and distinct changes in the molecular fluorescence. Based on rational molecular design, the liberated macrocycle is recaptured on to the thread and the mechanical bond is regenerated which allows for directional macrocycle transport and release in an iterative manner.