MMaterialsgateNEWS 2017/05/18

What we couldn’t measure before: the stickiness of molecules

When building with molecules, it is important to understand how they stick together when, amongst others, designing capsules for transportation of medication in the body. After all, how can you construct a car if you don’t know how the components work?

Researchers of the TU Eindhoven enable us to measure how long it takes for small molecules (monomers) to break free from a larger molecular complex (polymer), without influencing the movement of the polymers. Today, biomedical engineer René Lafleur, dr. Xianwen Lou, professor Bert Meijer and colleagues published a paper about this research in Nature Communications.

The movements of molecules is often measured by connecting a coloring to the molecule. However, the coloring is large in size in relation to the molecule, therefore influencing the movement. PhD candidate Lafleur now proved, together with colleague Xianwen Lou, that the technique used for studying the folding of proteins (also a type of polymer), ‘hydrogen/deuterium exchange mass spectrometry (HDX-MS)’, can also be used for studying supramolecular polymers.

Building with molecules

A car mechanic needs to have knowledge of the parts before he can construct a car. The same thing holds for ‘building’ with molecules; for example making capsules to transport medication in the human body or making a medical hydrogel for local release of medication and stem cell therapy.

These types of capsules or materials are often made from polymers; these polymers are built from smaller building blocks, so-called monomers. With self-assembling molecules, these monomers automatically form polymers, for example in the shape of long wires or small spheres in which medication can be transported.

In these self-assembling, supramolecular polymers, the monomers are not attached to each other but they lightly stick together. This enables the monomers to leave the polymer and return to it. The ambient temperature or pH influences this flexibility (how easily they go in and out of the polymer). This dependence on temperature or pH is, amongst others, important when researchers or manufacturers want to apply the capsules in the human body, where pH and temperature tend to differ per location.

Movement 'in view'

So how does it work? After the in water dissolved monomers stuck together to form a polymer, the researchers dissolve the polymers in heavy water. The monomers that leave the polymer will be exposed to the deuterium in the heavy water, resulting in the replacement of the hydrogen atom by a deuterium atom that is just a bit heavier.

The small change in the mass is detected by Lou and Lafleur and is also measureable when the monomer has retaken its place in the polymer. The speed with which the monomers increase their mass is therefore a measure for the speed with which the monomers leave the polymer.

Interestingly enough, the research results show that many monomers already leave the polymer within minutes and therefore gain mass, however others take hours or days. Furthermore, the researchers have shown that a small change in the size of the monomer has an influence on the movements. Larger monomers will remain in the polymer longer and take more time to start moving as compared to smaller monomers. These differences were not measureable before, because the coloring molecules were too large; with the HDX-MS technique, even the influence of small differences in molecular size on the movements of the molecules can now be measured.

Source: TU Eindhoven – 15.05.2017.

Reference:

Xianwen Lou et al., Dynamic diversity of synthetic supramolecular polymers in water as revealed by hydrogen/deuterium exchange, Nature Communications (15 May 2017). DOI: 10.1038/NCOMMS15420.

Investigated and edited by:

Dr.-Ing. Christoph Konetschny, Inhaber und Gründer von Materialsgate
Büro für Material- und Technologieberatung
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