Anne-Sophie is using atomic force microscopy principles to develop a force spectrometer. This spectrometer can measure binding forces at the atomic scale by pulling molecules and reading extremely small force changes as they change configuration or break from the spectrometer tip. It has been used to measure ring/axle assemblies, rotaxanes, molecular rotors, and oligoamide helices.
Presentation: Probing synthetic molecular machines with AFM: Force, motion, dynamics, and function
Do molecular systems have different frequencies of fluctuations?
- Yes, the rate and intensity of fluctuations vary based on the structure.
Have you measured molecular chains [indistinct – referring to a isobenzene polymer system historically measured much earlier. There is discussion about measuring only a single polymer of that system instead of an aggregation.]
- It is difficult because there needs to be sufficient length between the open and contracted form in order to be detected. We should probably calculate the minimum length that can create a clear signal for the force spectrometer.
If you were able to do the same measurement simultaneously on thousands of molecular residues do you think the energy required to move the rotaxane in one direction would be a simple linear combination or do you think there would be a threshold where you get an emergent property and become a material?
- It is not possible to measure simultaneously thousands of molecules. It is possible to do two or three molecules by picking up several molecules at the same time (we try to avoid this). The question is interesting but I don’t know. Pulling the same molecule over and over can show different behaviors. Pulling on thousands may show random behavior.
How does the molecular work you measured vary with temperature?
- We don’t know, it is difficult to measure force at higher temperature because of stability. We could decrease temperature and see the effect – it should have an influence but we didn’t check
What are the biggest challenges for doing this work?
- Finding the right system – I am lucky that people give me amazing molecules and molecular machines. The systems are very nice to study via force spectroscopy. It is difficult to prepare the samples. We need to isolate molecules on a surface so we only pick up one at a time. For each molecule we investigate, there’s a new strategy for isolation.
Is it possible to get resonances from the force fluctuations on the macro-scale cantilever during force spectrometry?
- In principle it can be done but technically it is very challenging.
Seminar summary by Aaron King.