UC Davis Researchers Advance Electron Paramagnetic Resonance for Improved Chemical Insights
To glimpse the molecular and atomic worlds underlying physical matter, researchers rely on a host of analytical techniques, including the ever-popular nuclear magnetic resonance, or NMR, spectroscopy. Magnetic resonance can also be used to examine the spin of electrons.
“In most common chemical species, electrons are spin paired in molecular orbits, quenching their magnetism,” said UC Davis Distinguished Professor of Chemistry R. David Britt, the Winston Ko Chair in Science Leadership. “But many chemical species can also be trapped with unpaired electron spins.”
Transition metals important to both biological and industrial functions, such as iron, copper and manganese, are often found in paramagnetic states with unpaired electrons.
“Electrons are front and center in chemistry and a lot of chemical reactions involve electrons moving from one species to another, in what are called oxidation and reduction reactions,” Britt said.
These electron spin interactions can be probed by another magnetic resonance technique called electron paramagnetic resonance, or EPR.
What is electron paramagnetic resonance spectroscopy?
Traditionally NMR is performed at much higher magnetic fields than EPR. Britt said the technology needed to make higher frequency EPR pulses has lagged behind NMR. This disconnect is known as the “Terahertz Gap” in pulse power technology.
But new research from UC Davis has jumped the proverbial gap.
In a study appearing in Nature Communications, Britt and his colleagues successfully advanced high-power pulse EPR operation by building an instrument that operates at a wide frequency bandwidth centered at 263 GHz. The magnetic field produced by the instrument’s superconducting magnet is nearly 20,000 times stronger than Earth’s magnetic field.
“We’re going a factor of three higher in frequency over the prior high pulse power machines,” Britt said. “The highest frequency high power EPR spectrometers that existed before operate around 95 GHz and we have jumped all the way up to 263 GHz, which is a huge improvement in sensitivity and resolution.”
The advancement was achieved thanks to the use of a new 10-watt, high frequency traveling-wave vacuum tube amplifier, which the team installed in a UC Davis-lab built pulse EPR spectrometer.
The successfully employed their advanced instrumentation to analyze manganese complexes - from manganese impurities in nonmagnetic solids to metal sequestering proteins.
The research, while foundational, bodes well for the future of EPR spectroscopy. Britt said the technique can be used to analyze a variety of chemical processes, including electron flow in batteries, in photosynthesis and oxygen evolution, and in the quantum bits necessary for quantum computing.
A UC Davis project through and through
Britt noted that the research showcases how interdisciplinary research at UC Davis is powering technological advances that can be used around the world. The research was a collaboration between the College of Engineering and the College of Letters and Science.
Britt said the work would have not been possible without the late Neville C. Luhmann Jr., a UC Davis Distinguished Professor with the College of Engineering who specialized in plasma physics and vacuum electronics.
The Britt and Luhmann labs collaborated on methods to advance EPR techniques to these higher frequencies, which give enhanced sensitivity and resolution to the method.
“I was happy that Neville got to see it all working before he passed away,” Britt said. “It’s a very nice memorial for him.”
In addition to Britt and Luhmann, other UC Davis authors include Zikri Hasanbarsi, Shasha Qiu, Guodong Rao, Amanda Caceres, Yuan Zheng, Marie Heffern and Paul Stucky. Authors Erica Debley and Elizabeth M. Nolan, who provided the targeted Mn-binding proteins, are from the Massachusetts Institute of Technology.
The research was supported by the National Science Foundation, the Department of Energy and the National Institutes of Health.
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