New porous gel changes appearance by 'sensing' target molecules through coordination

Researchers at Kyoto University and Tohoku University have developed a new porous polymer gel that selectively recognizes specific molecules (referred to as ‘guests’ in the study) through coordination chemistry and converts these invisible molecular-scale interactions into strikingly visible, macroscale deformation. The study demonstrates how subtle differences in molecular structure can directly alter the shape, color, and mechanical properties of a soft material, opening new possibilities for “smart” stimuli-responsive materials and molecularly programmable soft matter that can sense and react to its environment. 

Molecular recognition is a central concept in supramolecular chemistry and biology, where molecules selectively interact through precisely arranged chemical interactions. While most artificial molecular recognition systems rely on noncovalent interactions such as hydrogen bonding, the present study instead exploits coordination interactions—a type of chemical “handshake”—between metal centers and electron-rich guest molecules. Although coordination chemistry is widely used to construct molecules and porous materials such as metal–organic frameworks (MOFs), its use as a driving force for guest-responsive deformation in soft materials has remained largely unexplored. 

The work, published in Journal of the American Chemical Society, introduces a new class of “MOPEG gels,” constructed from metal–organic polyhedra (MOPs) and flexible polyethylene glycol (PEG) chains. MOPs act as structural junctions that form the polymer network and as molecular recognition sites capable of selectively binding incoming molecules. 

The researchers found that MOPEG gels recognize multitopic molecules with multiple coordinating nitrogen atoms, triggering a distinct color change from green to red and a visible shrinkage of the gel's total volume, whereas structurally similar non-coordinating molecules produced no change. Mechanical measurements further revealed that molecular recognition strengthened MOPEG gel. When coordinating guest molecules that bridge neighboring MOP units, the material's stiffness increased dramatically, indicating that molecular-level guest recognition directly reinforced the internal polymer network of the macroscale material. 

“Our study demonstrates that coordinative molecular recognition can be translated into visible and mechanical responses in gels,” says Professor Shuhei Furukawa of Kyoto University’s Institute for Integrated Cell-Material Sciences (WPI-iCeMS). “By integrating porous MOP into deformable polymer networks, we created a system in which molecular interactions directly control material behavior.”

Dr. Tomoki Tateishi, currently at Tohoku University’s Frontier Research Institute for Interdisciplinary Sciences (FRIS), adds: “This work establishes a synthetic platform that bridges molecular selectivity and macroscale deformation. We believe this concept could lead to next-generation responsive materials capable of sensing, adapting, and mechanically responding to chemical microenvironments.”

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Paper: 
“Coordinative Guest Recognition Triggers Macroscale Deformation of Covalently Linked Metal-Organic Polyhedra Polymer Gels”
Journal of the American Chemical Society｜https://doi.org/10.1021/jacs.6c06620

About Kyoto University’s Institute for Integrated Cell-Material Sciences (iCeMS):
At iCeMS, our mission focuses on the integration of cell biology, chemistry, and materials science to address significant global challenges. We place a primary emphasis on self-assembly—the process by which molecules spontaneously organize into functional structures—to investigate the chemical basis of cells and create life-inspired materials.

iCeMS Website: https://www.icems.kyoto-u.ac.jp/en/

About the World Premier International Research Center Initiative (WPI):
Launched in 2007 by Japan’s Ministry of Education, Culture, Sports, Science and Technology (MEXT), the WPI program fosters globally visible research centers with the highest standards. Administered by the Japan Society for the Promotion of Science (JSPS), these centers operate with high autonomy to drive innovative research and management. 

WPI News Portal: https://www.eurekalert.org/newsportal/WPI

For more information, please contact:
Nashaat Ghanem
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