From Molecular Machines to Microscale Motility of Objects: Application as “Smart Materials”, Sensors, and Nanodevices

Abstract

Machinelike operations are common functions in biological systems, and substantial recent research efforts are directed to mimic such processes at the molecular or nanoscale dimensions. The present Feature Article presents three complementary approaches to design machinelike operations: by the signal‐triggered mechanical shuttling of molecular components; by the signal‐triggering of chemical processes on surfaces, resulting in mechanical motion of micro/nanoscale objects; and by the fuel‐triggered motility of biomolecule–metal nanowire hybrid systems. The shuttling of molecular components on molecular wires assembled on surfaces in semirotaxane configurations using electrical or optical triggering signals is described. The control of the hydrophilic/hydrophobic surface properties through molecular shuttling or by molecular bending/stretching processes is presented. Stress generated on microelements, such as cantilevers, results in the mechanical deflection of the cantilever. The deposition of a redox‐active polyaniline film on a cantilever allows the reversible electrochemically induced deflection and retraction of the cantilever by the electrochemical oxidation or reduction of the polymer film, respectively. A micro‐robot consisting of the polypyrrole (PPy) polymer deposited on a multi‐addressable configuration of electrodes is described. Au magnetic core/shell nanoparticles are incorporated into a polyaniline film, and the conductivity of the composite polymer is controlled by an external magnet. Finally, the synthesis of a hybrid nanostructure consisting of two actin filaments tethered to the two ends of a Au nanowire is described. The adenosine triphosphate (ATP)‐fueled motility of the hybrid nanostructure on a myosin monolayer associated with a solid support is demonstrated.

Infrared Study of Intercomponent Interactions in a Switchable Hydrogen‐Bonded Rotaxane

“…This band gradually shifts to 1655 cm À1 in CHCl 3 . In THF and PrCN, a weak band is observed at 1645 and 1648 cm À1 , respectively, which may be attributed to hydrogen-bonded C=O groups of the macrocycle.…”

Light and Redox Switchable Molecular Components for Molecular Electronics

“…[11,23,38,39] Recently we, and others, have employed electrochemistry as both a complimentary switching method to photoswitching as well as a read-out method for demonstrating the retention of photochemical properties of molecules after immobilisation of metal and semiconductor electrodes. [23,40,41] Immobilising photochromic dithienyle thene switches on surfaces as monolayers with high surface coverages allows for both the direct electronic interaction between the surface and the molecule [22] (leading to quenching of photochemistry, changes to molecular orbital energies etc. ), and steric effects, i.e.…”

A Versatile Axle for the Construction of Disassemblage Rotaxanes

“…1 H-NMR (DMSO-d 6 ): δ 1.45 (2H, m), 2.00 (2H, t), 3.22 (2H, t), 3.95-4.05 (4H, m), 6.80-7.00 (16H, m), 7.20 (3H, d). 13 Blocking Group 5: A solution containing 3,5-dimethyl benzoic acid (2.0 g, 13 mmol) in 20 mL of dry DMF was cooled to 0˝C. CDI was added (2.2 g, 15 mmol) to the reaction mixture, which was stirred under Ar.…”

“…1 H-NMR (DMSO-d 6 ): δ 2.30 (6H, s), 2.89 (2H, t), 3.46 (2H, m), 7.08 (1H, s), 7.42 (2H, s). 13 Blocked-Trityl-Axle 6: A solution of trityl-axle 4 (1 g, 2.1mmol) in 10 mL of dry DMF was cooled to 0˝C, and CDI (350 mg, 2.3 mmol) was added. After two hours, blocking group 5 (413 mg, 2.1 mmol) was added to the reaction mixture.…”

“…[2]Rotaxanes comprise a circular molecule (wheel) threaded over a linearly shaped molecule (axle) with large groups (blocking groups) attached to the axle's ends to keep the wheel threaded. Most of the original rotaxane-sensors operated by the wheel switching positions on the axle after an external stimulus is applied to give an observable signal [8][9][10][11][12][13]. While this class of sensors continues to show great promise, we are constructing sensors that operate via the controlled disassemblage of a rotaxane.…”