Molecular Motors/Rotors/Brakes and Gyroscopes

Anant Babu Marahatta
Ph.D. student in Chemistry
Tohoku University
Japan

One of the current aspects of chemistry is being a watch-dog of the nanoworld. I wonder how many of you are familiar with the microscopic machinery terms used in Chemistry that concentrates especially in the designation of the Molecular Machine. Some of them are Molecular motors, Molecular Rotors, Molecular Brakes, and Molecular Gyroscopes. You may find several of them by consulting the literatures/text books published so far.

I am sure that all of you [for the beginners only] are familiar with the “molecules” and the macroscopic devices such as Motors or Rotors or Brakes or Gyroscopes. But I think, very few of us [including chemists] have got the concrete knowledge about their applications in the nanoworld or in the Molecular machinery. I, a blog writer of “Nepa Chem”, would like to assure our fellows/readers that the detail explanation with the proper schematic illustrations of all the mentioned molecular machinery devices will be posted in the days to come. For now, let me define them very shortly.

Molecular motors, Molecular Rotors, Molecular Brakes, and Molecular Gyroscopes, all these names are derived from their macroscopic analogues. Synthetic/computational chemists have already synthesized/designed the molecules or supra molecules which resembled mechanically to these macroscopic devices. Thus in this stage, you readers are about to catch the main point. I am sure that you all are thinking like this way; if the synthesized molecules/supra molecules resembled mechanically to that of the macroscopic rotating devices, then these molecules are called Molecular rotors. If the synthesized molecules/supra molecules resembled to that of the macroscopic motors [which contain rotors too, complexity arises], then these molecules are called Molecular motors.

The macroscopic Gyroscopes which are used in aircrafts, ships to route them, contain the mechanical parts like rotating axis-axle, rotating part-rotor and the static framework-stator to uphold the rotor by conserving angular momentum. Hurray!!!!The meaning of the molecular Gyroscope is also clarified!!! Do you agree? If not, your level of understanding is not the worst!!!! …lol….The molecules/supra molecules resembled to those of the Macroscopic Gyroscopes mechanically are called Molecular Gyroscopes. You must be very happy!!!!! Aren’t you? Because whatever you were thinking is correct!!!!

The case of the molecular brake is different. You can imagine yourself!!!! Can you? Do you have driving license? Do you brake [be careful, not break, funny writer, isn’t it?] your car? If not, come here in Japan, I rent a TOYOTA car. Anyway, a “Brake” is a device for slowing or stopping the motion. Wow! So sad!!! There must be some parts in motion before applying brake, unlike in rotors/motors and gyroscopes. Thus the challenging part for the computational chemists/synthetic chemists is that the same molecule must possess dynamic parts as well as brake.

According to my experience, some atoms of the molecules, during the rapid motion of the dynamic parts, migrate towards the active site of the same molecule and the motion of the dynamic parts stopped / braked. However, the automatic migration of the atoms which act as a brake is rare. Some of the external sources [electric field, magnetic field, optical field etc.] that initiate this migrating mechanism must be intruded. So far, laser is one of the predominant sources. Similarly, changing the structure after receiving the impulse is also common braking phenomenon. Here is an example of the molecular brake, thousands of times smaller than the width of a human hair, developed by the researchers in Taiwan. It is powered by light and is the first capable of working at room temperature. The animated view of the schematic illustration of the light-driven molecular brake is posted here!!! Enjoy!!!!!
This molecular brake resembles a tiny four-bladed wheel (a rigid pentiptycene group shown in blue in the illustration below) and contains light-sensitive molecules. The paddle-like structure spins freely when a nanomachine is in motion. Exposing the structure to light changes its shape so that the blades stop spinning, 'the braking effect is on'. The braking power can be turned off and on by altering the wavelength of light exposure.

I hope that you readers are able to get the fundamental concepts about these molecular machines. If you are synthetic /computational chemists, I am sure that you will immediately start designing such molecules and contribute into the nano-world. Good luck from my side!!!!!