Chemists Spin Materials To Improve Magnetic Resonance Data

The American, French And Danish researchers recently discovered that they can obtain more precise data about a material's atomic structure, and do it faster than ever before possible, if they spin the material at just the right speed inside the NMR instrument.

Philip Grandinetti, associate professor of chemistry at Ohio State, and his research partners have named their new technique FASTER, short for "FAst Spinning gives Transfer Enhancement at Rotary resonance."

FASTER eliminates the signal interference that plagues traditional techniques for studying materials using NMR.

In a recent issue of the Journal of Chemical Physics, the chemists reported that spinning samples at speeds of up to 30,000 cycles per second can, in many cases, boost the signal strength of the NMR measurements more than ten times over."This is a big advance for people who want to study the atomic level structure of almost any solid material -- ceramics, plastics, glasses, or catalysts," Grandinetti said. "Even for peptides, proteins, or DNA, FASTER could shorten the time necessary for studying a substance from weeks to mere hours."

Grandinetti worked with three researchers at the French National Center for Scientific Research (CNRS) in Orleans: Thomas Vosegaard, formerly a postdoctoral fellow at CNRS, who is now a research assistant professor in the Laboratory for Biomolecular NMR Spectroscopy at the University of Aarhus, Denmark; Pierre Florian, formerly a postdoctoral fellow at Ohio State, who is now a research associate at CRNS; and Dominique Massiot, who directs the CNRS Center for High-Temperature Materials Research.

NMR works by tuning into the radio waves emitted by atoms within materials, Grandinetti explained.

"Just as astronomers tune into the radio waves emitted by objects in outer space, we tune into radio waves emitted from inner space," he said.

Grandinetti likened the interference that confounds NMR signals to interference between stations on an FM radio. When a station is far away, music from other stations can drown it out.

In the case of atoms and molecules, the radio information that is lost concerns the environment of the atoms. That's because each atom emits radio waves at a particular frequency, depending on the type of atoms that surround them.

"The problem is, when we tune in our NMR 'radios,' we receive a lot of static," Grandinetti said. "We try our best to reduce the noise, but these tiny signals from atomic nuclei are weak to begin with, so it's a battle to get a good signal."

The idea of spinning materials in an NMR instrument to improve the signal isn't new in itself. The original technique, known as magic-angle spinning (MAS), spins materials at a certain angle with respect to the NMR's magnetic field. Unfortunately, MAS doesn't work for 70 percent of known elements.

For these elements, including oxygen, aluminum, and sodium, the rules of quantum mechanics prevent certain nuclear transitions from taking place, and it is those transitions that would reveal a clearer NMR signal.

Typically, researchers must average the test results for these elements over several weeks to reduce the noise. They also must employ very expensive high-power amplifiers to boost the magnetic field.

Performing their experiments on commercially available equipment, Grandinetti and his partners used FASTER to produce the same results in a matter of hours, instead of weeks -- and without a high-power amplifier.

Any NMR machine with an MAS probe can use FASTER, Grandinetti said. High-power, one-kilowatt amplifiers typically cost about $20,000, but FASTER requires an investment of only a few thousand dollars for a low-power amplifier.

The technique could be used by geologists, biologists, chemists, and physicists, as well as materials scientists, since it works for any solid substance -- including minerals, biopolymers, enzymes, and membranes.

Grandinetti plans to apply this advance to several different projects; one involves a study of the complex geochemistry that is occurring under nuclear waste storage tanks at the Department of Energy site in Hanford, Washington. Millions of gallons of radioactive waste from decades of nuclear weapons production are stored at the site, in tanks that are now leaking into the ground.

"It's an environmental nightmare," Grandinetti said, "and we desperately need a remediation strategy based on an accurate understanding of the chemistry taking place under these tanks."

Advances such as FASTER will help scientists characterize the minerals forming under these tanks, and understand their ability to immobilize materials leaking out, he added.

The National Science Foundation and the Department of Energy supported Grandinetti's part in this research.