Moving into another dimension

A Foldaxane-based Supramolecular Muscle-Like Switch

[cn]daisy chain molecular muscle architectures are self-assemblies of hermaphrodite monomers, which usually contain a macrocycle unit linked to a molecular thread that contains sites of interactions - i. e. molecular stations - for the macrocycle. In these multiply threaded structures, altering with control the affinity between macrocycles and stations allows for contraction and extension of the molecule, which is reminiscent of the operation of a muscle. Besides, the field that consists of combining helix and template-containing rods to design foldaxane supramolecular assemblies is still underexplored. By using foldamer units as surrogates for macrocycles, Gan et al. reported the first supramolecular muscle-like foldamer-containing switch that can adopt, after chemical stimulus, either a contracted co-conformational state or a degenerate-like state for which a slow exchange occurred between the contracted and the stretched state.

Foldaxane-Based Switchable [c2]Daisy Chains

Artificial molecular muscles are highly attractive in the field of molecular machinery due to their unique properties of contraction and stretching motion. However, the synthesis of molecular muscles poses formidable challenges as it is hindered by undesirable yields and poor selectivity. Herein, we present a procedure for the dynamic assembly of foldaxane-based [c2]daisy chains, wherein the hermaphroditic sequences consisting of aromatic helices and peptide rods are interlocked through inter-strand hydrogen-bonding interactions. The binding complementarity facilitates a selective and efficient assembly of [c2]daisy chain structures, inhibiting the creation of by-products. Introducing multiple recognition sites confers the system with contraction and stretching motion actuated by chemical stimuli. The rate of this muscle-like motion is calculated to be 0.8 s-1, which is 107 times faster than that of complex dissociation.

An Interlocked Figure-of-Eight Molecular Shuttle

Here is reported the synthesis and characterization of an interlocked figure-of-eight rotaxane molecular shuttle from a dibenzo-24-crown-8 (DB24C8) derivative. This latter bears two molecular chains, whose extremities are able to react together by click chemistry. One of the two substituting chain holds an ammonium function aimed at driving the self-entanglement through the complexation of the DB24C8 moiety. In the targeted figure-of-eight rotaxane, shuttling of the DB24C8 along the threaded axle from the best ammonium station to the weaker binding site triazolium was performed through deprotonation or deprotonation-then-carbamoylation of the ammonium. This way, two discrete co-conformational states were obtained, in which the folding and size of the two loops could be changed.

Dual and sequential locked/unlocked photo-switching effects on FRET processes by tightened/loosened nano-loops of diarylethene-based [1]rotaxanes

The self-trapping nano-loop structures of [1]rotaxanes exhibited multiple Förster resonance energy transfer (FRET) patterns via dual and sequential locking/unlocking of pH-gated and UV exposure processes. As a tightened and constrained nano-loop in the acidic condition, dithienylethene (DTE) unit was locked in the highly bending open form to forbid ring closure upon UV irradiation.