Molecular Machine Opens and Closes in Response to Light

Michael J. Lander

Equipped with tools that can manipulate single molecules, researchers may be able to construct molecular robotic devices for numerous applications. Although a number of groups have produced tools with such potential, until recently none had succeeded in using them for controlled manipulation of another molecule.

A computer-generated representation shows a scissorlike molecular machine bound at two sites to a guest molecule. Courtesy of Takuzo Aida, University of Tokyo.

Kazushi Kinbara, Takuzo Aida and their colleagues at the University of Tokyo, however, have created a system that operates like a pair of scissors under varying illumination and have used it to twist and untwist a bound molecule. They presented their work at the March 25 national meeting of the American Chemical Society in Chicago.

At a length of 3 nm, the machine comprised three varieties of molecules bound together to form parts analogous to the blades, pivot and handle of the common cutting tool. The blade molecules could readily attach to nitrogenous bases, and the pivot component rotated freely under lab conditions. Under visible light above 420 nm, the handle unit existed in its long form, which kept the blades in proximity. When exposed to UV light at 350 nm, the short form prevailed, and the scissors opened.

After allowing noncovalent binding to occur between the blades and a separate rotary molecule, the researchers tested the machine’s twisting ability. Exposure to visible and UV light from a xenon arc lamp with a bandpass filter resulted in clockwise and counterclockwise rotation of the attached molecule.

In nanotechnology applications, the researchers state that the device may be especially useful for catalysis. In this context, the tool would destabilize captured substrates by deforming them, which also would allow scientists to study associated changes in the substrates’ physical and chemical properties. The machine may have further applications in manipulation of biologically relevant molecules.

The group is working on a system composed of more than three molecular units. They predict that widespread practical application of their creations could occur within the next five to 10 years.