Researchers designed, built, and tested NanoGear, a device consisting of molecular components interlocked and designed to function like a gear. Since molecules are nanometer objects (1 nanometer = 1 millionth of a millimeter), it is an extremely small device.
The NanoGear molecule belongs to the class of rotaxanes and consists of a ring that can slide along an axis in the center of which a rotor is installed. The ring is free to slide along the axis for its entire length but it cannot escape because two stoppers positioned at the ends of the axis prevent it from slipping off. The rotor is free to rotate around its own axis and has two different blades to facilitate observation of the movement.
The rotor is bonded directly to the shaft with an actual (covalent) chemical bond, while the ring is mechanically locked around the shaft by the presence of the stoppers. Both the translation of the ring and the rotation of the blades are random oscillations determined by the thermal energy of the molecule; the gear is not coupled to any motor and operates “in neutral.” To observe the movements and measure their velocities, refined nuclear magnetic resonance (NMR) techniques were used.
At 65 °C, the ring oscillates linearly from one end of the axis to the other about seven times per minute, passing over the rotor, while in the same period of time, the latter performs about 260 rotations. Therefore, the two motions are not synchronized but mutually influence each other, as demonstrated by experiments carried out on molecules similar to NanoGear but without a rotor or ring.
Another significant and unexpected result is the effect of the medium in which the molecule is located. By changing the solvent, one of the two movements is slowed down while the other is accelerated. This kind of “specific lubrication” constitutes one of the unconventional properties of nanodevices that could lead to radical technological innovations.