A Musclelike [2](2)Rotaxane: Synthesis, Performance, and Molecular Dynamics Simulations

Abstract

A novel bistable symmetric [2](2)rotaxane was prepared by a threading-followed-by-stoppering strategy and characterized with (1)H, (13)C, and 2D ROESY NMR spectroscopy and HR-ESI spectrometry. The symmetric [2](2)rotaxane system consists of an anthracene-based bis(crown ether) as macrocycles, and each of the two dibenzo[24]crown-8 (DB24C8) rings is threaded by the pendant substituents of a symmetrically substituted central rotatable ferrocene subunit that possesses two distinguishable recognition sites for the DB24C8 ring: namely, a dibenzylammonium site and an N-methyltriazolium site. The uniform shuttling motion of the thread relative to the two DB24C8 rings in [2](2)rotaxane can be driven by external acid-base stimuli, which was evidenced by (1)H and 2D ROESY NMR spectroscopy. Furthermore, molecular dynamics simulations of the [2](2)rotaxane were carried out both in protonated (stretched) and in neutral (contracted) forms. The calculated percentage change in molecular length of the [2](2)rotaxane between the two end-capping bis(methoxyl)phenyl groups is about 48% in the two different states (in acetone), which is much larger than the percentage change (∼27%) in human muscle. Moreover, in the two states, the C*-Cp-Cp-C* dihedral angles are computed as -177° in the stretched state and -112° in the contracted state, indicating a correlation between the translational and rotational motions of the [2](2)rotaxane.

One-pot synthesis of a [c2]daisy-chain-containing hetero[4]rotaxane via a self-sorting strategy

“…It is notable that the DBA protons in [2]rotaxane 6 cannot be detected because there are no hydrogen bonding interactions between the crown ether and the DBA hydrogen atoms. 16 Compared with the 1 H NMR spectrum of hetero[4]rotaxane 5 , H 4 and H 5 which are adjacent to the DBA site were observed to shift upfield with a Δ δ of –0.53 ppm in the 1 H NMR spectrum of [2]rotaxane 6 , which confirmed that the DBA sites were not bound by the host macrocycle DB24C8 . Therefore, the phenyl-stopped B21C7 played an important role in inhibiting the dethreading of the daisy chain structure in the middle, this is also called a cascade-stopped strategy.…”

Toward quantum chemical calculations of open shell molecules on quantum computers

“…In conclusion, a potential energy curve (PEC) was mapped for the acidbase switchable [2](2)rotaxane in its two protonation states. The original system must overcome a 10 kcal/mol barrier in order to switch to its other conformation; therefore, we propose a chemically modified system.…”

pH-Controlled motions in mechanically interlocked molecules

“…The similar operation of a bipodal molecular elevator with a ferrocene platform was also demonstrated by Qu. 68…”