EPR method could lead to new drugs and plastic electronics

A new breakthrough improvement in a technique for studying the behaviour of molecules could advance drug discovery and plastic electronics, researchers claim.

Known as electron paramagnetic resonance (EPR) or electron spin resonance (ESR) spectroscopy, the method is used to detect free radicals — highly reactive chemical species — within chemical compounds.

EPR spectroscopy works by placing a material within a magnetic field and then hitting it with electromagnetic radiation, which causes any unpaired electrons — a characteristic feature of radicals — to switch between different energy states. As they switch back to their normal states, they release electromagnetic energy that reveals details about the molecules in their neighbourhood.

‘Each electron can be thought of as a tiny magnet that senses the magnetic fields caused by atoms in the neighbourhood,’ explained Prof Mark Sherwin, director of the Institute for Terahertz Science and Technology at the University of California Santa-Barbara (UCS).

Although EPR has been known about since the 1940s, it has been limited by the amount of electromagnetic radiation that could be applied to the samples under test, usually of the order of a few tens of gigahertz. The team from UCS, working with researchers from Florida State University, has instead used a free electron laser — the first time one has been used to power EPR — which emits a pulsed beam of electromagnetic radiation at a frequency of 240GHz.

‘This ultra-high-frequency high-power EPR system gives us extremely good time resolution,’ said Susumu Takashiki, lead researcher on the project, which is described in the 20 September edition of Nature. ‘For example, it enables us to film biological molecules in motion.’

Sherwin, who commented on the results in a statement issued by USC, explained that the laser power expands the capability of the technique. ‘We have shattered the electromagnetic bottleneck that EPR has faced, enabling electrons to report on faster motions occurring over longer distances than ever before,’ he said. ‘We look forward to breakthrough science that will lay foundations for discoveries such as new drugs and more efficient plastic solar cells.’