Spinning motion of a molecular rotor detected

Tag : rotor spinning
Trying to observe such rotational motion on the molecular scale isan extremely difficult undertaking. Japanese researchers at theUniversities of Osaka and Kyoto have now met this challenge. AsAkira Harada and his team report in the journal Angewandte Chemie , they were able to get snapshots of individual molecular rotorscaught in motion.

As the subject of their study the researchers chose a rotaxane.This is a two-part molecular system: A rod-shaped molecule isthreaded by a second, ring-shaped molecule like a cuff while astopper at the end of the rod prevents the ring from coming off.The researchers attached one end of the rod to a glass support. Toobserve the rotational motions of the cuff around the sleeve, thescientists attached a fluorescing side chain to the cuff as aprobe.

To observe the rotation of the ring around the rod, the researchersused a microscopic technique called defocused wide-field totalinternal reflection fluorescence microscopy. This gave snapshots ofindividual rotaxane molecules in the form of emission patterns. Insimplified terms, if the cuff is motionless, the patterns make itpossible to calculate the direction in which the probe emits itsfluorescent light. This makes it possible to calculate theorientation of the cuff, which remains constant for every snapshot.However, if the cuff is rotating, the emission pattern does notreveal the spatial orientation of the probe.