Watching Rings Cycle

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Science  30 Jul 2010:
Vol. 329, Issue 5991, pp. 493
DOI: 10.1126/science.329.5991.493-b
CREDIT: ADAPTED FROM YE ET AL., ACS NANO 4, 10.1021/NN100545R (2010)

In biomolecules, changes in external conditions can shift the balance of weak interactions and alter the secondary structure. In artificial systems, the controlled movement of a chemical group through changes in weak interactions can be achieved with rotaxane molecules. A chemical ring (blue) can move between different sites along a “thread”—a backbone chain—that is terminated with bulky groups (gray), which act as stoppers to keep the ring on the thread. The drivers of movement can include light or changes in redox conditions that alter the charge interactions at the binding sites (red and green). Such changes have been inferred through spectroscopic measurements in solution, but direct visualization of this process with methods such as scanning tunneling microscopy have been difficult because of the flexibility of the rotaxane molecules. Ye et al. synthesized rotaxane molecules with disulfide groups on the stoppers and used these groups to bind the rotaxanes to gold surfaces (yellow) in order to reduce their mobility. They imaged these molecules and observed changes in ring binding that accompanied changes in redox state.

ACS Nano 4, 10.1021/nn100545r (2010).

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