AsianScientist (Dec. 13, 2018) – In a study published in Nature Chemistry, scientists in Japan have used atomic force microscopy to directly observe the flexibility of crystals in solution.
Porous coordination polymers are crystalline materials that form when metal ions and organic binding molecules, called ligands, self-assemble. Material scientists have taken an interest in these polymers because of their ability to undergo structural changes in the presence of other molecules, or when they are exposed to certain external stimuli.
In this study, researchers led by Dr. Nobuhiko Hosono of Kyoto University’s Institute for Integrated Cell-Material Sciences (iCeMS) in Japan were able to image the dynamic changes that occur on the surface of a porous coordination polymer in the presence of other molecules. They relied on a technique known as atomic force microscopy (AFM).
The surface of the coordination polymer crystal was first examined in solution under stable conditions. The researchers reported that the metal-organic lattices on the surface of the crystal were tetragonal in shape. A biphenyl solution was then added to the crystal in gradually increasing concentrations and AFM images were taken once every 13 seconds.
The team found that the lattices changed to a rhombic shape within ten minutes as the biphenyl concentration reached a maximum of 500 millimoles per liter of solution. Decreasing the biphenyl concentration led to removal of the biphenyl from the material’s surface and resulted in a rapid return to the lattices’ original tetragonal shapes.
“We were surprised to find that the porous coordination polymer surface is exceptionally flexible and constantly fluctuating in solution,” said Hosono. “This is contrary to the common perception that crystals are hard and immobile.”
This highly responsive nature of the porous coordination polymer surface, provides insights that can help guide the development of responsive materials, said the researchers.
The article can be found at: Hosono et al. (2018) Highly Responsive Nature of Porous Coordination Polymer Surfaces Imaged by in Situ Atomic Force Microscopys.
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Source: Kyoto University; Photo: Izumi Mindy Takamiya.
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