Small child building a Lego structure

Molecular structures made to collapse and re-assemble using ultraviolet light

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Researchers at Okinawa Institute of Science and Technology (OIST) have developed self-assembling molecules which can be broken down with ultraviolet (UV) light, then recombined into novel structures.

Large structures are tricky to synthesise, requiring numerous chemicals and complex technique. Instead of synthesising large structures manually, scientists tend to rely on self-assembling molecules.

Self-assembling molecules are compounds which can interact with other, identical molecules to combine into larger structures.

This molecular self-assembly occurs in nature, and is critical to the function of cells. Lipids self-assemble to form membranes, the helical DNA structure is formed through bonding of individual strands, and nanoscale structures combine to give gecko feet their extraordinary “sticky” abilities.

A team of OIST researchers have developed new self-assembling molecules, which can transform into previously unobserved shapes, using just UV light to force them to recombine.

When designing self-assembling structures, scientists normally aim to create the state with minimal energy – the ground state – which is also most stable state. However, being very stable, these states are resistant to being reformed.

In order to bypass this problem, the researchers designed their structures to have a weakness in their ground state. This allowed the researchers to make the structures collapse with a burst of UV light to break bonds within the molecules.

The molecular rubble remained tightly packed after the collapse, allowing it to reassemble into new, less stable states. The researchers observed new, exotic macroscopic structures arise from their self-assembling molecules.

“This report is about a new concept in material science,” said Professor Ye Zhang, who led the study. “We converted a self-assembling phenomenon into co-assembling in a spatially and temporally controllable manner using light.”

“Eventually, we constructed exotic heterogeneous nanostructures inaccessible through conventional synthetic path.”

The ability to create new structures is vital, as “in material science, the function is always related to the structure”, according to Professor Zhang. The OIST research suggests that the final structure assumed by self-assembling molecules depends strongly on their initial conditions. This could be helpful in tailoring structures for specific applications.

“If you create a different structure, you manipulate the function and even create new applications. For example, the toxicity of a molecule in a nanofibre shape might be much lower or higher than the same molecule assembled in a spherical shape.”

Professor Zhang suggests that this method could be helpful in developing new biological and pharmacological applications. For instance, a drug could be sent to its target in a patient’s body, then broken down with UV light and reshaped into a different structure with therapeutic properties.

The next step, she says, is to work on developing more biocompatible materials which could be made to collapse and re-assemble using an alternative to toxic UV light.

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