New technique increases NMR speed
Researchers at the University of Illinois at Chicago have found a way to increase the sensitivity of solid-state nuclear magnetic resonance (SSNMR), which has traditionally been a time-consuming method of imaging and analysis of the chemical makeup of proteins and other biomolecules, and requires large amounts of costly isotope-labeled sample, according to research published online Feb. 8 in Nature Methods.

Yoshitaka Ishii, PhD, associate professor of chemistry, reported that he has found a quicker and more efficient approach to using SSNMR, called paramagnetic relaxation-assisted condensed data collection (PACC).

Ishii and his colleagues have increased the sensitivity of SSNMR by doping samples at varying concentrations with the paramagnetic copper-acid solution Cu-EDTA, a chemical used in many industrial applications. That made the study samples more active transponders, providing strong signals and detailed spectral information with minimal downtime.

"With SSNMR, we collect the signal responses but then have to wait for the SSNMR system to recycle, which takes up to three seconds," said Ishii. "You have to do this hundreds of times. And during most of that time, you're basically doing nothing. By our approach, we've reduced that waiting period by up to 20 times."

The chemists also boosted the SSNMR efficiency by using a spinning speed of 40 kilohertz (kHz), instead of the usual 10 kHz, and doing a fast recycling of low radio frequency field power sequences, which minimizes the amount of irradiation heat surrounding the study sample.

The researchers studied various types of molecules using this new approach, including the amyloid fibrils often associated with Alzheimer's disease, larger globular proteins and cytoskeleton proteins. The new approach worked well with each type.

The doping solution they added to enhance the sensitivity of samples did not change the chemical structure of proteins studied. Ishii said that the approach also enabled his group to get useful spectral signals using much smaller samples.

"We often need samples as large as 10 microliters, but with this approach we can use as little as one microliter or less," he said. "With protein structure work, preparing samples is a major bottleneck, which limits our ability to analyze it. This approach opens up the possibility for more difficult structure determination work."

Ishii said they hope that the PACC approach may be enhanced to achieve even greater SSNMR sensitivity, but noted that the technique, as presently tested, should allow study of molecular structural features that are currently difficult to obtain using other laboratory methods.

The National Science Foundation, the National Institutes of Health, the Dreyfus Foundation and the Alzheimer's Association funded the study.