MESA+ University of Twente
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Alberto Gomez Casado (promotion date: 15 July 2011)

Strength and dynamics of multivalent complexes at surfaces

Promotion date: 15. July 2011

Promotor: Prof. dr. ir. Jurriaan Huskens

Co-promotor: Dr. ir. Pascal Jonkheijm

The aim of the work described in this thesis is to study the role of multivalency in the dynamic behavior of multivalent supramolecular systems.

Several supramolecular systems have been employed, ranging from π‐π charge‐transfer complexes to cucurbit[n]uril (CB[n]) and β‐cyclodextrin (βCD) host‐guest complexes.

All these systems have been used before as building blocks to
fabricate nanostructures. Understanding their kinetics potentially allows the design of more stable assemblies, improves drug specificity and the fast‐response of devices.

Was your work application driven?

Though not in a direct way, the systems under investigation have application power, for example in new drug delivery strategies. I studied the strength and stability of multivalent connections. By exerting forces one, two or even three connections can break in a controllable way, allowing the system to diffuse. Some ‘walking and hopping’ behaviour occurred which I could characterize and describe, adding to the knowledge of these systems.

Was there a special moment during your thesis project?

Performing experiments in this field, asks for the right conditions. Especially one moment everything fell into place in a surprising way. I found out that monovalent connections could rupture in parallel, while di- and trivalent could present partial attachments. With this I could explain, for example, why I measured forces characteristic of both mono- and divalent connections when using divalent molecules. Besides the theoretical insight, these attachments are of practical importance as well.

Did you manage to have some nice publications?

I published in The Journal of the American Chemical Society, and also in Nature Chemistry as second author. Next to that I was co-author of several side-publications.

In what way did you grow as a scientist during the project?

Being a bio physicist, first of all I gained a lot of knowledge concerning the chemistry part, being a member of the Molecular Nanofabrication group. Also, I learned that physicists and chemists have distinctive perspectives on science. They possess different working sets of mind, focussing differently on problems, valuing different details of the big picture, so to say.

My method of working systematically is much more mature now than four years ago. In setting up experiments, I work in a consistent way now, building in essential controls. One has to check every step in the procedure in order to prove the findings. Just telling that you see some kind of behaviour is not enough!

Did you feel a member of the Mesa+ institute while working on your thesis project?

That depends on the moment, I guess. After a Mesa+ meeting, I was more aware of being part of the institute for a few months. Mostly I was quite involved in the work of the Molecular Nanofabrication group.

We had some collaborations going on, varying from working together on a daily basis with the Supramolecular Chemistry & Technology group to good contacts with Optical Sciences or Materials Science and Technology of Polymers. Facility sharing was an important part of this collaboration, sharing equipments and sometimes labs.

What, in your opinion, is important for Mesa+ to stay successful in the future?

Mesa+ is very successful already. In my opinion, facing budget cuts it is important to take care of the researchers. Giving priority to them is important as their performance is at the heart of Mesa+.

What are your future plans?

Right now, I am working at the Physics of Complex Fluids group led by professor Frieder Mugele. The subject is quite different, which is a good thing. After four years of doing the same type of experiments I want to avoid getting closed in a box. I am ready now to discover new things and experiences.