This award in the Inorganic, Bioinorganic and Organometallic Chemistry program supports research by Professor Frederick Hawthorne at the Univesity of Missouri at Rolla to transform redox-dependent molecular conformers (a "nanowagger") into a molecular rotary motor with the potential for powering nanomachines. The driving motion consists of two stable bis-7,8-dicarbollynickel structures having formal Ni(III) and Ni(IV) oxidation states that are interconverted by single-electron redox processes accompanied by a reversible rotational change of the metallocarborane structure from cisoid Ni(IV) to transoid Ni(III) (with respect to cage-C atoms). The proposed research focuses on: (1) A study of the dynamics of substituted dicarbollide ligand rotation about Ni, Fe, and Co centers in diamagnetic commo-bis-7,8-dicarbollide complexes using both 2H and 10B variable temperature NMR measurements. (2) The NMR elucidation of intramolecular interligand interactions resulting from the rotation of substituted motors which brings these substituents into close proximity to one another in the cisoid conformation. (3) Demonstration in solution of reversible intramolecular excimer formation with pyrene substituents caused by redox-controlled rotation of these substituents from the transoid to the cisoid relationship and the reverse (4) Demonstration of controlled motor rotation in solution by the observation of changes in Forster resonance energy transfer (FRET) between two dye molecules each attached to a separate rotor of a motor. (5) Repetition of the FRET experiments described above, but with the motor molecule anchored by a linker group to a sol gel surface. In this way, the operation of surface-mounted motors immersed in liquids, inert gases or vacuum can be demonstrated.
The industrial and societal applications of successful nanomotors of this type would enable a new generation of nanomolecular and micro devices. Coupling molecular motors to nanodevices could lead to applications including (1) the control of rotary nanovalves, (2) the control of the philicity of surfaces (hydrophilic / hydrophobic), (3) the control of the color or other optical properties of a surface, (4) the throttling of the activity of catalytic sites, (5) the mechanical transference of optical activity between chiral centers and switches for the chemical or electrochemical control of electrons and photons. Since research in this area involves molecular design, computational studies, syntheses, spectroscopy of all types, X-ray diffraction molecular structure studies, electrochemistry and nanodevice construction, students at all levels will receive broad experience for continued research in academia, government or industry.
