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Finland: Innovation Researchers Develop Flexible Molecular Cups

| Editor: Ahlam Rais

Researchers from the Department of Chemistry and Nanoscience Center, from the University of Jyväskylä prepared flexible cup-shaped molecules, which have similar properties in the solid state and in solution. The molecules wrap around themselves under both conditions. They can be used in supramolecular chemistry as host molecules, which bind metal cations, ammonium ions or neutral guest molecules, such as toluene, inside their cavity by weak interactions. This can be utilised for example in molecular sensors, drug delivery or nanomaterials.

Cup-shaped resorcinarene molecules wrap around themselves in the solid state and in solution.
Cup-shaped resorcinarene molecules wrap around themselves in the solid state and in solution.
(Source: Kaisa Helttunen/ The University of Jyväskylä)

Jyväskylä/Finland – Cup-shaped resorcinarenes are macrocyclic molecules composed of aromatic hydrocarbons. They form in similar reactions as synthetic phenol resins, which are familiar from wood processing. These compounds are studied in supramolecular chemistry as host molecules, which can bind positively charged metal cations, ammonium ions or neutral guest molecules, such as toluene, inside their cavity by weak chemical interactions.

In a recent study, researchers attached toluene groups to the resorcinarene molecules with a hydrocarbon arm, and showed that the chemical composition of the linking group had a significant impact in the shape, aka conformation, of the molecule. When a sulphur and oxygen containing sulfonyl group was used as a linking unit the toluene group was wrapped inside the molecular cup, whereas the toluene group was free to move around when only a hydrocarbon linker was used for the connection. The shape and folding of flexible molecules have direct impacts on molecular properties and functionality. Common examples from everyday life are biological macromolecules, proteins and enzymes.

Molecular Structures Solved In Solution

Researchers from the University of Jyväskylä analysed the weak intramolecular chemical bonds in the solid state using X-ray crystallography. They showed that very weak interactions have an influence on the molecular structures. The molecules were investigated in solution by using nuclear magnetic resonance spectroscopy (NMR). The method is based on the responses of magnetically sensitive isotopes to radio frequency pulses, similar to magnetic resonance imaging commonly used in medicine. The method showed that the movement of the flexible molecules slowed down significantly at -80 centigrade degree temperature, which allowed the positions of the toluene groups to be located.

“The crystal structures of the molecules provide reliable information about the molecular shapes and weak chemical interactions in the solid state. The situation changes when a structurally flexible molecule is placed in a solution where it can move around freely. It is very difficult to guess the shape of the molecule offhand. That is why we were very pleased to solve the structures of the molecules also in solution,” says Academy Research Fellow Kaisa Helttunen from the University of Jyväskylä.

The study was completed in the University of Jyväskylä utilising structural chemistry equipment and the computational resources of CSC in collaboration with the researchers of Nanoscience Center.

The research is funded by the Academy of Finland.

Link to the complete article can be found here: https://chemistry-europe.onlinelibrary.wiley.com/doi/full/10.1002/chem.201905211

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