Artificial Molecular Machines and Devices

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Under the influence of light, electricity, or chemical reagents, certain interlocked molecules, known as catenanes and rotaxanes-which comprise appropriately matched ring and dumbbell-shaped components-will perform motions (e.g., rotary and linear) at a molecular level reminiscent of the moving parts of macroscopic machines. Such molecular motors hold promise as the intelligent" building blocks for the construction of devices and machines. A team of chemists and engineers from two different institutions (UCLA and nearby CALTECH) will address the fundamental scientific issues surrounding the relationships between controllable molecular machines, nanoscate devices, and the predictable movements of machine components at a macroscopic level.The aims of this collaborative project-which focuses on the NSE RESEARCH THEME of Nanoscale Devices and System Architecture-are to (I) develop the template-directed synthesis (self-assembly) of interlocked molecules (switchable catenanes and rotaxanes) and interpenetrating supermolecules (addressable pseudorotaxanes) as a forerunner to (2) attaching them covalently to frameworks (e.g., silica, alumina) whose (3) synthesis (self-organization) must be established prior to (4) demonstrating the abilities of these machine-like (super)molecules to express different kinds of coherent movements (mainly linear but also possibly rotary ones) characteristic of macroscopic machines when (5) they are activated by chemicals (acids/bases or oxidizing/reducing agents) or electrons or light (redox and electron transfer processes) as a prelude to (6) transducing and amplifying the coherent molecular level movements into macroscopic motions.The specific objectives of the team are to demonstrate transduction of force and motion from the relative mechanical movements of the components present in catenanes, rotaxanes and pseudorotaxanes through the development-on the nanoscale level-of actuating materials and devices reminiscent of (1) engines, (2) levers, (3) muscles, and (4) valves.In thc first instance, we envisage constructing supramolecular two-stroke engines based on two-station pseudorotaxanes with the ring component lodged covalently in appropriately-sized silica pores, leaving the semi-dumbbell-shaped component to act as the piston. In the second example, we propose to design mechanical levers to amplify nanometer motions generated by suitable molecular or supramolecular machines. In the third instance, we propose to graft the ring and thread components of pseudorotaxanes onto separate carbon nanotubes using an aromatic polymer which we have demonstrated wraps itself helically around carbon nanotubes in order to realize artificial muscles and actuators. And, in the final example, we intend to develop molecular valves at the necks of suitably-sized silica pores, lined with pseudorotaxanes that can be induced to associate and dissociate (rings from threads) such that guest molecules located within the pores are, respectively, trapped or free to escape.The anticipated outcome of the proposed program of research includes (I) the synthesis of new molecular motors capable of operating as machines, (2) the synthesis of integrated power supplies for the machines, (3) a bottom-up and top-down integration of frameworks for the machines, (4) new fundamental understanding of forces, friction, etc., on the nanoscale, and (5) a group of students with both broad perspectives and individual expertise in nanoscicnce.With chemists and engineers working side-by-side, this highly integrated project seeks to transform molecular machines from being scientific curiosities into functioning nanosystems with technological potential, to enrich the education of both graduate and undergraduate students, and to promote the public awareness of nano-science and technology through community outreach.