Molecular 'Scissors' Work in Response to Light

A pair of molecular-scale "scissors" has been developed that open and close in response to wavelengths of light, representing the first example of a molecular machine capable of mechanically manipulating molecules through light energy, its creators said.

The scissors measure just three nanometers in length, small enough to deliver drugs into cells or manipulate genes and other biological molecules, said principal investigator Takuzo Aida, professor of chemistry and biotechnology at the University of Tokyo.

“Chemists and biochemists may also use the scissors to precisely control the activity of proteins,” Aida said. He presented details of the new technique yesterday at the 233rd national meeting of the American Chemical Society, the world’s largest scientific society, at the Hyatt Regency Chicago.

Researchers in Japan have developed a pair of molecular-scale "scissors" that open and close in response to different wavelengths of light. The tiny device, 3 nm long, is the first example of a molecular machine capable of mechanically manipulating molecules by using light and could be used to deliver drugs into cells or manipulate genes and other biological molecules. The research was presented this week at the American Chemical Society meeting in Chicago. (Photo courtesy of Takuzo Aida)

Scientists have long been looking for ways to develop molecular-scale tools that operate in response to specific stimuli, such as sound or light. Biologists, in particular, are enthusiastic about development of such techniques because it would provide them with a simple way to manipulate genes and other molecules.

“It is known, for example, that near-infrared light can reach deep parts of the body,” said Kazushi Kinbara, associate professor of chemistry and biotechnology at the University of Tokyo and co-investigator of the study. “Thus, by using a multiphoton excitation technique, the scissors can be manipulated in the body for medicinal applications such as gene delivery.”

The scissors-like molecular machine uses a photoresponsive chemical group that extends or folds when light of different wavelengths falls upon it. Just like "real" scissors, the molecular scissors consist of a pivot, blades and handles. The pivot part of the scissors is a double-decker structure made of chiral ferrocene, with a spherical iron (II) atom sandwiched between two carbon plates. The three-piece unit creates a shaft that allows the scissors to rotate and swivel.

Driving the motion are two handles strapped with photoresponsive molecules called azobenzene, which not only has the ability to absorb light, but comes in two isomeric forms: a long-form and short-form. Upon exposure to ultraviolet (UV) light, the long-form of azobenzene is converted into the short-form. Exposure to visible light transforms the short-form into the long-form.

When UV and visible light are used interchangeably, the length of the azobenzene decreases and increases, which drives the handles in an open-close motion. The movement activates the pivot, followed by an opening-closing motion of the blades.

Attached to the scissors’ blades are organometallic units called "zinc porphyrin." When the zinc atom in the zinc porphyrin binds with a nitrogen-containing molecule, such as DNA, the zinc and nitrogen act like magnets, securing a firm grip on the molecule.

“As the blades open and close, the guest molecules remain attached to the zinc porphyrin, and as a result, they are twisted back and forth,” Kinbara said.

In a recent study, the scientists demonstrated how the light-driven scissors could be used to grasp and twist molecules. The group is now working to develop a larger scissors system that can be manipulated remotely. Practical applications still remain five to 10 years away, the scientists said.

For more information, visit: www.acs.org