Mar 26, 2004
Molecular motor spins ahead
Scientists at the University of California, Los Angeles, US, and the Hebrew University of Jerusalem in Israel have used both simple electron transfer processes and photoexcitation to control the rotary motion of a molecule. The resulting molecular machines could have applications as nanovalves or in modifying surface properties.
The molecule contained two hemispherical dicarbollide ligands separated by a nickel centre that acted as the axle for rotation. The two dicarbollide ligands of the Ni(III)bis-[η5-nido-7,8-C2B9H11]2- metallacarborane have transoid carbon vertices. One-electron oxidation causes the vertices to rotate with respect to each other, forming a unique Ni(IV) species with cisoid carbon vertices. The process is reversible and the direction of rotation depends on the configuration of atoms or groups of atoms substituting for carbon atoms in the ligands.
“The nickel metallacarborane is unique in chemistry since it can be made to deliver useful work upon command and provide pre-determined unidirectional rotation,” Fred Hawthorne of UCLA told nanotechweb.org. “The rotation of the motor is reversed by one-electron oxidation or reduction at low applied voltages. We know of no other man-made rotary machines capable of carrying out controlled useful work.”
Each oxidation or reduction step caused the ligands to rotate by 144° with respect to each other; the scientists also found that photoexcitation caused similar geometrical changes. To get larger rotations the team coupled two or more of the machines together. Bonding one of the dicarbollide ligands to a surface so that it could not rotate and rotating the other ligand would create a molecular machine, or “nanowagger”.
Initially, the devices could be used to rotate an attached arm, either to form a nanovalve by physically blocking a pore opening, or to change the nature of a surface from hydrophobic to hydrophilic by exposing or hiding functional groups. The devices could also change surface roughness or expose charged or hydrogen bonding functional groups.
“The motor could conceivably be used to open or close access to homo- or heterogenous catalyst centres, thus leading to sensors,” added Hawthorne. “Motors could also function as reversible switches for molecular electronics applications or information storage.”
Now, Hawthorne and colleagues plan to attach several variations of the original motor to solid surfaces to investigate the effects of motor action on surface properties and to develop nanovalves.
The researchers reported their work in Science.
About the author
Liz Kalaugher is editor of nanotechweb.org.