How To Send Molecules On A One-Way Journey

Researchers in Japan have invented a ratchet-like molecular machine, where a chemical reaction is coupled with unidirectional movement.

AsianScientist (Jul. 2, 2018) – A research group in Japan has invented a ratchet-like molecular machine which allows movement in one direction only. The findings are reported in Scientific Reports.

Life is driven by molecular machines. Found in every cell, these tiny motors convert chemical energy into work to keep the body moving. The invention of synthetic molecular machines, which perform similar jobs to power miniaturized technologies, is a hot topic in nanoscience.

In this study, researchers at Osaka University, Japan, have invented a ratchet-like molecular machine that could become a potential component of sophisticated molecular devices.

A classic design for molecular machines is a symmetric ‘dumbbell’: a large cyclic molecule trapped between bulky blockers—or stations—at each end, linked by a spacer. Inspired by this pattern, known as rotaxane, the Osaka team created a pseudo-rotaxane, where all three parts—the two stations and the central cyclic molecule—are small rings.

Both stations of their molecular machine were made from pyridinium, a six-membered cyclic molecule. Methyl groups were attached to each station, like barbed hooks. However, one station carried a single methyl group, while the other end had two.

“This asymmetry sets up an axis along the molecule’s length, favoring movement toward the double-hooked end, which acts like a stopper,” said study first author Associate Professor Akihito Hashidzume.

The concept was demonstrated using α-cyclodextrin (α-CD), a molecule made of six glucose rings. The α-CD ring is wide enough to fit over the single-hooked end and slide along the ratchet toward the stopper. On the way, it interacts with the stations and the central ring. In fact, α-CD catalyzes a chemical reaction in which the ratchet-like molecule exchanges hydrogen atoms with the water solvent.

Labeling experiments confirmed that this exchange occurred only at one end of the ratchet. When the reaction was carried out in heavy water (D2O), deuterium (D) atoms were found on the methyl groups of the single-hooked station and the central ring as well as on the methylene of the second station, but not the double-hooked stopper. The researchers suggested that the α-CD passed over the central ring but was blocked from reaching the methyl groups of the stopper.

“Here, we have a chemical reaction coupled with motion biased in one direction,” said corresponding author Professor Akira Harada. “We call it ‘face-selective translation,’ as α-CD prefers to move from one face of pseudo-rotaxane to the other. We take our cue from nature: by ratcheting movement in one direction, we hope to harness chemical energy in a similar way to biomolecular motors, like those in muscles.”

The article can be found at: Hashidzume et al. (2018) Toward a Translational Molecular Ratchet: Face-selective Translation Coincident With Deuteration in a Pseudo-rotaxane.


Source: Osaka University; Photo: Shutterstock.
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