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Light spurs a new twist for synthetic chemistry

Molecules induced by light to rotate bulky groups around central bonds could be developed into photoactivated bioactive systems, molecular switches, and more.

Researchers at Hokkaido University, led by Assistant Professor Akira Katsuyama and Professor Satoshi Ichikawa of the Faculty of Pharmaceutical Sciences, have expanded the synthetic chemistry toolbox by creating a new class of molecules that can be brought to undergo internal rotation when interacting with light. Similar processes are thought to be important in some natural biological systems. Synthetic versions could be exploited to perform photochemical switching functions in molecular computing and sensing technologies, or in bioactive molecules, including drugs. They report their findings in Natural chemistry.

“Realizing a system like ours was a significant challenge in photochemistry,” explains Katsuyama. “This work makes an important contribution to an emerging field of molecular manipulation.”

Examination of certain natural proteins has provided insight into the possibilities for light to significantly change molecular conformations. These include rhodopsin molecules found in the retina of the eye, which play a crucial role in converting light into electrical signals that create our sense of vision in the brain. Details are emerging about how absorption of light energy can induce a twisting rearrangement of part of the rhodopsin molecule, necessary for it to carry out its biological function.

“Mimicking this in synthetic systems could create switches at the molecular level with various potential applications,” says Katsuyama.

A key innovation of the Hokkaido team was to carry out photo-inductions (that’s to say, driven by light) rotation of molecular groups around a series of chemical bonds that incorporate a nitrogen atom with other linked carbon atoms.

The rotational properties were obtained by adding molecular components containing an atom from the “chalcogen” group of elements of the periodic table, particularly sulfur or selenium, to a simple organic molecule: an amide compound. This has brought a new level of control and versatility to photo-induced synthetic rotation systems.

Some of the chemical groups that revolve around the central bonds were relatively large, based on rings of six bonded carbon atoms. This facilitated large-scale molecular changes that might be necessary for practical use in molecular switching systems.

In addition to demonstrating the photo-induced changes, the team also performed theoretical calculations that provided insight into the likely mechanisms by which the rearrangements took place. The team also explored the effects of temperature on the transformations. The combination of theoretical and experimental work should make it possible to direct future research towards the exploration and control of modifications of systems already produced.

“Our next research priority focuses on the potential of our methods to make novel light-activated bioactive molecules. These could be applied to biological research or possibly developed as drugs,” concludes Ichikawa.

Using light to activate conformational changes allows you to control where and when changes occur. This could be vital for precisely targeted applications in biological systems, including possible therapeutic possibilities.



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