A reported synthetic molecular motor can be switched off with acid and switched back on with base. Acid helps hold the motor’s rotating arm inside a molecular socket; base removes the proton that enables this hold. In the locked state, light does not make it rotate. Once unlocked, light and heat drive its rotation cycle.
How the molecular lock works
The motor reported by Ben Feringa’s group has two molecular halves joined by a carbon–carbon double bond. One half includes a rotating arm with a plug containing an NH2 group. A dibenzo[24]crown-8 ring acts as the socket that receives the plug.
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In the locked state, acid protonates the plug’s NH2 group. Hydrogen bonding then holds the plug in the crown ether socket, preventing the motor’s rotation cycle from proceeding. A strong base removes the protons, breaks those hydrogen bonds and releases the plug. Chemistry World reported Feringa explaining that irradiation does nothing while the motor is locked, but deprotonation unlocks it: If you irradiate it with light when it’s in the locked state it doesn’t do anything, but as soon as you deprotonate it unlocks.
The report identified him as a University of Groningen researcher. Chemistry World’s 2010 report describes the mechanism.
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| State | What happens at the plug and socket | Can the rotation cycle proceed? |
|---|---|---|
| Acidified, locked | Protonation enables hydrogen bonding that holds the plug in the crown ether socket. | No. Irradiating the locked motor does not make it rotate, according to the report. |
| Basified, unlocked | Base removes protons, breaking the hydrogen bonds and releasing the plug. | Yes. Light and heat drive the isomerization steps that produce rotation. |
What powers the rotation, and how fast is it?
Unlocking makes the motor’s light-and-heat-driven cycle possible; light alone is not described as the lock-release mechanism. The reported cycle uses photochemical and thermal isomerization steps, with the thermal steps limiting its pace. Chemistry World gave the time for one complete rotation as more than half an hour for this particular design. Feringa described the work as a demonstration of the locking principle, rather than an effort to optimize speed. This figure applies to the reported 2010 motor, not to molecular motors generally. Chemistry World identified the underlying paper as a 2010 Angewandte Chemie International Edition article, DOI 10.1002/anie.200906064; the paper itself was not accessible for independent verification of further experimental details.
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What the result does—and does not—demonstrate
The reported result is a molecular-scale proof of principle: chemical conditions can gate whether a light-driven motor’s rotation cycle proceeds. The report discussed possible future connections between molecular rotation and piston-like motion, but those were prospective ideas, not a demonstrated device application. Research across the wider field of light-driven molecular shuttles explores areas such as catalysis, drug delivery and ion transport; a 2022 review of that field is not evidence that this particular motor performs those functions. The review also discusses broader challenges in translating molecular motion into useful device behavior.
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