Molecule's dance captured by 'ultimate slo-mo' technique
Method could be used in future to watch proteins in action
Canadian scientists have found a way to shoot frame-by-frame video, in millionths of a millionth of a second, of key movements made by a molecule, revealing how it undergoes a fascinating transformation.
"It's the ultimate in slo-mo," said R. J. Dwayne Miller, a University of Toronto chemistry and physics professor and director of the Max Planck Research Group at the University of Hamburg. He was the principal investigator of the team that developed the technique to capture the ultra-ultra-fast movements and slow them down to a visible speed.
The video reveals, step-by-step, a process that was previously a big mystery — exactly how an organic molecule known as EDO-TTF changes its shape in order to go from being an insulator to conducting electricity when hit with laser light of a certain colour.
It's a type of transformation in the nature of a material called a phase change, like the one that turns water into ice.
The research team, which included scientists in Germany and Japan, was interested in seeing how the molecule's shape-shifting affected its ability to conduct electricity.
The shape-shifting is of interest because closely related molecules have the potential to be superconductors, said Meng Gao, the graduate student who led the study. Superconductors are used to operate devices such as MRI machines for medical imaging.
Miller, who is Gao's supervisor, said the phase change in EDO-TTF was impossible to understand without witnessing directly how it happened: "You had to see all the details in their full atomic splendour."
The video shows how the molecules slide, bend and unbend during the transformation. In the insulating state, half the molecules are bent, making it impossible for electrons to move between them.
During the phase transition, the molecules reconfigure so they are all lying flat and electrons can move easily between them, making the material conductive.
The results were published Wednesday online in the journal Nature.
Miller's team had previously been able to shoot movies of simpler, more robust inorganic materials, such as melting aluminum, by pulsing a beam of electrons at the material very quickly, like a camera flash or shutter. However, the beam wasn't concentrated or "bright" enough to capture the motions of big, "dark," complex organic molecules such as EDO-TTF.
Bunching up electrons
The problem with the original technique was that the electrons in the beam tended to repel each other, Gao said, and they quickly move apart, resulting in a very dim, diffuse beam.
Gao and his colleagues figured out a way to bunch the electrons back together again using radio waves, essentially focusing and brightening the light before it hit the EDO-TTF.
When the electrons hit the atoms in the molecule, the force generates wavelets like the ones that form in the water around the posts of a pier.
This "footprint" can be used to reconstruct the position of the atoms. And the researchers created their video by capturing an ultra-quick set of these footprints in order to generate a series of reconstructions showing exactly how the molecule moves.
The researchers hope that ultimately, their technique can be used to observe how complex biological molecules such as enzymes — proteins involved in many important biological processes — do their work inside living things.
"Proteins are such big, complicated things — there are so many complicated actions that no one understands," Gao said. He added that EDO-TTF is a good stepping stone because, like a protein, it's a carbon-based organic molecule, but it is also much smaller than a protein, which can have thousands of atoms.
"It's almost like a small-scale protein."