Scientists at the University of Birmingham have created a molecular gel that can be switched between a solid-like state and a flowing, liquid-like state using ultraviolet light, then rebuilt with heat or dismantled with acid. The material is made from synthetic molecules known as foldamers, which are designed to fold into precise three-dimensional shapes. By combining these shape-changing molecules with palladium ions, the researchers produced a soft material capable of responding to several different chemical and physical signals. The advance could eventually support the development of smart sensors, switchable catalysts, biomedical materials and drug-delivery systems that release their contents only when exposed to a specific trigger.
The new material belongs to a class of substances called metallogels, in which metal ions help connect organic molecules into a three-dimensional network. In this case, helical foldamer molecules are linked by palladium ions that function as four-way molecular junctions. These connections extend throughout the sample, creating a molecular scaffold capable of trapping a liquid. The trapped liquid gives the material its gel-like consistency, while the interconnected molecular framework provides the mechanical structure that prevents it from simply flowing away. Unlike conventional gels, however, this network is not permanently fixed. Its components are held together through reversible interactions, allowing the material to be repeatedly reorganised.
The researchers engineered light-sensitive units into the foldamer molecules. When ultraviolet radiation reaches the gel, these units undergo a change in molecular shape. Although the structural alteration occurs at the scale of individual molecules, its consequences spread through the larger network. The foldamers can no longer maintain the same connections and arrangement, causing the extended framework to lose its ability to support the trapped liquid. As a result, the solid-like gel becomes a liquid-like material that can flow. The transformation demonstrates how a carefully controlled molecular event can be amplified across billions of connected building blocks until it becomes visible at the scale of the entire sample.
The light-triggered transition is reversible. Heating the material allows the foldamer molecules to recover the arrangement needed to reconnect with the palladium ions and rebuild the network. The researchers also found that acid can produce a separate response by disrupting the interactions between the metal ions and the foldamers. This means the material has two chemically distinct routes to disassembly: ultraviolet light changes the shape of the organic building blocks, while acid interferes directly with the metal-mediated connections. The ability to use different signals to produce related but mechanistically separate responses is one of the central features of the new gel.
The team also transformed the original material, which was prepared in an organic solvent, into a hydrogel containing water. This conversion was achieved without destroying the molecular connections responsible for the gel’s behaviour. Hydrogels are especially important in biotechnology and medicine because their water-rich environments resemble aspects of biological tissue and allow them to hold substantial quantities of fluid while retaining a defined structure. A water-based version of a multi-responsive metallogel could therefore be more compatible with biological applications than a material that functions only in organic solvents. The researchers caution that practical medical uses remain a future possibility, but the chemical flexibility demonstrated by the system offers a foundation for further development.
The work brings together three areas of expertise: the design of responsive gels, supramolecular chemistry and atomic-scale structural analysis. Supramolecular materials are assembled through reversible interactions rather than irreversible covalent bonds. That distinction gives scientists a way to construct materials that remain stable under ordinary conditions but can be reorganised when exposed to light, heat or a chemical signal. Dr Sarah Pike, who led the gel-design work, said the project shows how a very small change in molecular shape can create a visible change in the behaviour of a bulk material. Such molecular programming could ultimately allow researchers to tune when and how a gel forms, flows, releases its contents or returns to its original state.
To understand how the material worked, the scientists needed to determine precisely how the palladium atoms were connected to the foldamer molecules. They used dynamic nuclear polarisation-enhanced solid-state nuclear magnetic resonance spectroscopy, known as DNP NMR. Conventional solid-state NMR can provide detailed information about the local chemical environment of atoms, but gels are difficult samples to study because their structures are complex, heterogeneous and often present in only small quantities. DNP improves the sensitivity of the measurement by transferring polarisation from unpaired electrons to nearby nuclei, strengthening the NMR signal and making otherwise impractical experiments possible.
The sensitivity improvement was substantial. An experiment estimated to require approximately seven years using conventional NMR was reduced to about 12 hours with DNP enhancement. The measurements revealed the atomic-level organisation of the gel and showed how palladium ions connect the foldamer molecules to produce the material’s molecular backbone. Dr Dominik Kubicki, who led the structural characterisation, said that observing a material change is only part of the challenge: designing better responsive gels requires knowing how their molecular components are joined. The atomic picture supplied by DNP NMR allowed the researchers to link the material’s macroscopic behaviour to the specific chemical connections within its network.
The findings could influence the design of materials that respond intelligently to their surroundings. A gel that changes state under light might be incorporated into a sensor or a microfluidic device, while a material that responds to acidity could be used to release molecules in environments with a particular pH. In principle, a hydrogel with these properties could be adapted for controlled drug delivery, releasing a therapeutic compound only after encountering a chemical condition associated with diseased tissue. Other possibilities include catalysts that can be switched between active and inactive forms, systems that capture and release selected molecules, and manufacturing materials that can be disassembled and reassembled rather than discarded. The research remains fundamental, but its combination of molecular precision, reversibility and multiple triggers offers a powerful strategy for building soft materials with programmable behaviour.
The study, titled “Dual Photo- and pH-Responsive Foldamer Metallogels,” was published in the Journal of the American Chemical Society. The research was supported by UK Research and Innovation, the Engineering and Physical Sciences Research Council, the Biotechnology and Biological Sciences Research Council, the Royal Society, the Royal Society of Chemistry, the Leverhulme Trust and European research programmes. Specialist low-temperature DNP NMR infrastructure was accessed at the University of Gothenburg. By showing that a foldamer-based network can be switched by light, rebuilt by heat, dismantled by acid and converted into a water-containing hydrogel, the Birmingham team has demonstrated how molecular engineering can turn reversible chemical interactions into a material with striking, controllable behaviour.
Subject of Research: Responsive foldamer metallogels, hydrogels, supramolecular chemistry and controlled molecular assembly.
Article Title: Dual Photo- and pH-Responsive Foldamer Metallogels
News Publication Date: 30-Jul-2026
Web References: Journal of the American Chemical Society article; University of Birmingham School of Chemistry
References: Moosa Wasim, Benjamin M. Gallant, Neha Yadav, Craig Fraser, Sena Öztürk, Louise Male, Dominik J. Kubicki, Maria C. Arno and Sarah J. Pike, “Dual Photo- and pH-Responsive Foldamer Metallogels,” Journal of the American Chemical Society.
Image Credits: Dominik Kubicki
Keywords
Foldamer metallogels, responsive gels, hydrogels, supramolecular chemistry, palladium, ultraviolet light, pH-responsive materials, dynamic nuclear magnetic resonance, DNP NMR, drug delivery, smart materials, molecular chemistry
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