Chapter 3 - Molecular Switches & Rotors Flashcards
How does the eye detect light?
It has molecular light switches which change from trans to cis state. This is then restored by thermal relaxation. This process produces electrical signals that are interpreted by the brain.
Give an example of what an artificial photoswitch can be used for.
It can be used as an on-off switch for a reduction reaction. If we functionalize a Au-electrode, we can have one state where the oxidation of a certain molecule is allowed. Upon UV-irradiation, the molecules are changed from a trans to cis state, and the electron transfer is no longer allowed.
How can one detect the photo-induces forces of the switching of a polymer based on a molecular photoswitch unit?
We graft it to a surface and a AFM cantilever tip. Then we induce the change by light, and measure the force.
How can we have a photoswitch that changes the molecule from a diamagnetic to paramagnetic state?
By having a pyrridine ring attached to the switch, above a system with a Ni-atom. When we switch it, the pyrridine ring is brought close to the Ni atom, and it makes a cooridnation bond between Ni and N and changes the magnetic properties to a high-spin paramagnetic state.
How can we detect the changes of a photoswitch?
In the example of a tert-butyl-azobenzene, we can see the change quite clear in an STM-measurement.
How can the use of hydrogen tautomerization be used as a molecular switch?
If we have a molecule which is symmetric in every way expect for the middle strucutre, where the hydrogens can sit in one of two positions. Measuring the tunneling current at one point of the molecule will then reveal in which position the hydrogen atoms are placed. Switching can be induced by STM.
What is the name of the molecule which allows switching by hydrogen tautomerization?
TPP - tetraphenyl-porphyrin.
How can we obtain a 4-level conductance switch using TPP?
We use 1H-TPP, and look at one point in the molecule. Depending on one of the four places it is placed, we can obtain four different tunneling currents.
What are catenanes?
Catenanes are systems of two intertwined rings.
What are rotaxanes?
Rotaxanes are systems with one ring surrounding a linear structure, which can be used as a molecular shuttle.
How can we used rotaxanes as molecular shuttles?
By selectively changing the linear chain on which the ring propagates, creating unfavorable positions where we don’t want it to go and favorable positions where we want it to go.
How can we make a molecular elevator?
Using a three-ring rotaxane system and using a chain which can be modified with acid-base concentration to allow the rotaxane to move up and down.
How can we realize data storage elements based on rotaxanes?
We can have them suspended between two nanowires. By applying a voltage, we can then change the position. This was hard to make reliable.
Give example of a biomolecular translation system. How can this be visualized?
The myosin motor system. The propagation occurs by ATP hydrolysis. The movement is unidirectional because of filament polarization (one side is plus the other is minus). By AFM this can be seen.
Give two examples of biomolecular rotational motion.
The flagellae in bacterium, e.g. E.coli
ATP synthase.
