Building a nanoscale “lantern”: chemists tackle precision molecular design

Imagine a tiny capsule that can trap only specific molecules inside. Such technology could one day be used for drug delivery systems or highly selective filters. In chemistry, researchers have been studying these kinds of “molecular cages” since around the 1980s.

Among them, oligophenylene cages made entirely of carbon are especially attractive because they are highly resistant to heat and chemicals. These nanoscale structures resemble lanterns, with upper and lower ring-shaped units connected by three pillar-like molecular units. Scientists hope these cages can act as tiny containers that capture, transport, or sort molecules inside their hollow spaces.

Until now, researchers typically built these cages by connecting two half-cage components at three points. However, this method often failed because the molecular reactions did not occur at the intended positions. Instead, the molecules reacted randomly, producing unwanted clumps rather than the desired cage structures. As a result, it was also difficult to introduce functional groups into the inside of the cage, and the success rate for obtaining the intended cage remained only around 10%.

To solve this problem, a research team led by Associate Professor Kosuke Ono at Institute of Science Tokyo (Science Tokyo) developed a new strategy for constructing oligophenylene cages with functionalized interiors.

The key innovation lies in how the cage is assembled. The pillar-like molecular units already contain functional groups such as –OH (hydroxyl groups) and –NH₂ (amino groups), which later act like “hands” inside the cage. However, during the cage-forming reaction, these groups tend to interfere with the assembly process, making it difficult to build the intended structure.

In conventional methods, all molecular parts were simply mixed together, allowing reactions to occur randomly and often producing unintended structures. The Science Tokyo team introduced a clever solution: they temporarily linked the three pillar molecules together using their functional groups, almost like bundling them with strings before assembly.

This temporary linking kept the molecules in the correct positions while the cage structure formed. Using this method, the success rate for producing the desired cage dramatically improved from about 10% to as high as 68%.

After the cage was completed, the temporary connections could be removed. Importantly, the functional groups remained facing inward, creating a functional inner surface inside the cage. The researchers confirmed that these cages could successfully trap and hold specific molecules such as amino acids within the cavity.

This technology could become a powerful new tool for selectively capturing and handling molecules. For example, it may lead to filters that capture only harmful substances, or artificial enzyme-like systems that accelerate chemical reactions inside the cage.

Because the new method allows researchers to tailor the inside of the cage more freely, it also opens the door to creating more sophisticated molecular structures that were previously difficult to make. Combined with the highly durable carbon framework, these cages could eventually be used in nanoscale chemical systems that operate even under harsh conditions.

Long ago, architects succeeded in building enormous domes once thought impossible by carefully designing structures in which materials naturally supported one another. Our research is similar. By designing a ”template“ that guides molecules into the correct positions, we succeeded in constructing cage structures with high efficiency. Research is not about listing reasons why something cannot be done. It is about asking how it can be done and creating new systems to make it possible. One exciting aspect of science is witnessing the moment when a single new idea turns the impossible into reality.

(Kosuke Ono, Associate Professor, Department of Chemistry, School of Science, Institute of Science Tokyo)

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