ScienceDaily (July 23, 2008) — Humans have long been trying to make the dream of nanoscopic robots come true. The dream is, in fact, taking on some aspects of reality. Nanoscience has produced components for molecular-scale machines. One such device is a rotor, a movable component that rotates around an axis.

Trying to observe such rotational motion on the molecular scale is an extremely difficult undertaking. Japanese researchers at the Universities of Osaka and Kyoto have now met this challenge. As Akira Harada and his team report in the journal Angewandte Chemie, they were able to get “snapshots” of individual molecular rotors caught in motion.

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

To observe the rotation of the ring around the rod, the researchers used a microscopic technique called defocused wide-field total internal reflection fluorescence microscopy. This gave snapshots of individual rotaxane molecules in the form of emission patterns. In simplified terms, if the cuff is motionless, the patterns make it possible to calculate the direction in which the probe emits its fluorescent light.

This makes it possible to calculate the orientation of the cuff, which remains constant for every snapshot. However, if the cuff is rotating, the emission pattern does not reveal the spatial orientation of the probe.

The researchers showed that the cuff of the rotaxane does not rotate if the sample is dry. However, when it is wet they can see very rapid rotational and vibrational motion. The cuff rotates faster than the time required to snap a picture: the rotational speed is thus over 360° in 300 milliseconds.

Story Source:

Adapted from materials provided by Wiley-Blackwell.

Journal Reference:

1. Akira Harada et al. Single-Molecule Imaging of Rotaxanes Immobilized on Glass Substrates: Observation of Rotary Movement. Angewandte Chemie International Edition, 2008, 47, 6077%u20136079 DOI: 10.1002/anie.200801431

Observing rotational motion on the molecular scale. (Credit: Copyright Wiley-VCH)

Related Stories

Single Molecule Is In Driver's Seat Of Molecular Machine (July 31, 2005) — The downsides of conventional molecular machines are that they are driven as an ensemble, by external light or chemistry, for example, and they are big -- made up of many molecules. These factors ...  > read more

New Rotors Could Help Develop Nanoscale Generators (May 29, 2009) — Scientists have developed a molecular structure that could help create current-generating machines at the ...  > read more

The First Molecular Keypad Lock (Jan. 11, 2007) — How can defense or intelligence agencies safeguard the security of top-secret data protected by a computation device the size of a single molecule? With cryptography approaching that sobering new ...  > read more

New Unidirectional Molecular Rotor May Lead To Tiny Sensors, Pumps, Switches (Oct. 7, 2005) — A University of Colorado at Boulder team has developed the first computer-generated model of a tiny, waterwheel-like molecular rotor that has been harnessed to rotate in one direction at different ...  > read more

Search ScienceDaily

Detecting Disease In Less Than 60 Seconds