Imaging Molecular Escapes

From cell biology to petroleum chemistry, numerous scientific and technological processes depend on transport of molecules through nanosized pores in membranes and particles. Yet few methods can probe those processes at the molecular level. Now, researchers led by Eiichi Nakamura of the University of Tokyo have demonstrated that transmission electron microscopy can provide an up close look at hydrocarbon chains passing through nanosized pores (Nat. Nanotechnol., DOI:10.1038/nnano.2008.263).

The team inserted fullerene molecules with long hydrocarbon chains into carbon nanotubes (1.4-nm diameter) and imaged the molecules as they moved within the tubes. The images (top), which were interpreted with molecular modeling techniques (bottom), show molecules undergoing rotations and other types of motions. Some molecules approached holes in the tube walls (arrow at top left), slowly pushed their chains through the holes (right), underwent conformational changes, and then retracted the chains into the tubes.

Many of the observations triggered fundamental questions and ideas for follow-up study, the team says. One of those observations, based on similarities between images recorded at room temperature and at 4 K, indicates that the microscope's electron beam is the primary energy source that drives the molecular motion.