Molecular Capsules based on Ionic Interactions in Polar Solvents
Promotion date: 7 May 2004
The main goal was to synthesize molecular containers soluble in water for potential use as drug delivery systems. We wanted to create a molecular container which could encapsulate a guest molecule. We start from two pieces, one is positively charged and the other is negatively charged. The two halves have a cone shape and once they ‘recognize’ each other they form an egg shaped closed structure with a cavity in which you can enclose a guest molecule.
What was your thesis about?
The main goal was to synthesize molecular containers soluble in water for potential use as drug delivery systems. We wanted to create a molecular container which could encapsulate a guest molecule. We start from two pieces, one is positively charged and the other is negatively charged. The two halves have a cone shape and once they ‘recognize’ each other they form an egg shaped closed structure with a cavity in which you can enclose a guest molecule. It has been done before in literature to synthesize molecular capsules from two halves, but the use of ionic interaction for this purpose is relatively new. Our structure showed binding properties for certain guest molecules even in water; this represents the real novelty. Another thing I was not completely satisfied about was the bigger one with four spaces we synthesized. These were very difficult to characterize. But we did have successful results with immobilizing the molecular capsule on a surface by positioning first -one half of the capsule, then the other half, on top of it.. The two halves of the capsule could also be removed from the surface thus proving the reversibility of the methodology.
If this is to be used in the body as a drug delivery system, how does the structure know when to release its guest molecule?
That could be possible by a change in the Ph. But that was not part of our research.
How does an Italian chemist end up at Twente University?
The university where I studied in Italy has a collaboration with the group of Professor Reinhoudt. I wanted to go abroad, so I came here.
Is your research new?
Yes, major parts of it are really ‘my thing’. At the beginning you are given the direction in which to look and from there you develop your own research. I was given a lot of freedom, and I liked that very much.
Could you explain in simple words what was already there?
In literature there were a lot of examples of molecular capsules, but using other interactions.
There were no examples of molecular capsule based on ionic interactions - - that were able to encapsulate guest molecules. And we were able to synthesize the structure in water.
The application of molecular capsules as drug delivery systems is obviously useless if you make it in chloroform or any other organic solvents.
How do you introduce the guest molecule in the structure?
The guest molecule is more or less attracted to the structure. We did a screening on the characteristics of guest molecules, and we found that molecules with a charge were acting as guests for the capsule. The investigation into the behaviour of guest molecules was not an easy task as many factors are of importance, such as the shape and the chemical characteristics.
Is there chance of a practical application in the near future?
The research is very fundamental, there is no way of saying as yet whether it can be applied as a drug delivery system. Basically this research started with me.
What are going to do next?
I am staying here until August as a postdoc writing up some papers and I will be responsible for the NMR (Nuclear Magnetic Resonance) machine, for characterisation of organic compounds. After that I shall look for a job in Italy.
So you are not going to continue this promising research?
No, I will leave that to somebody else. I would like to continue with encapsulation on a surface.
What did you like best of the past for years?
The fact that I had a lot of freedom. You have to show initiative, in fact that is expected of you. That is different from Italy, where tasks are assigned to you.
But I have also had my bad moments. Writing the thesis for instance, where you have to include results on experiments I did four years ago that I would do differently if I could do it again with all that I know now. It helped that I wrote articles in the first years (Journal of American Chemical Society). I could include the data of those first two in my thesis. It is difficult to stop and start writing. You are never satisfied, there is always more to investigate.
For the summary of the thesis, click here.