A new spin on NMR: Rotor redesigned

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  • Published: Nov 15, 2015
  • Author: David Bradley
  • Channels: NMR Knowledge Base
thumbnail image: A new spin on NMR: Rotor redesigned

Rotary innovator

Zirconia rotor for MAS NMR studies under extreme conditions. Courtesy of Chemical Communications, Royal Society of Chemistry

A new rotor design for magic-angle spinning (MAS) NMR experiments allows spectroscopists to carry out studies under more industrially relevant conditions than before, according to work from Pacific Northwest National Laboratory in Richland, Washington, USA, published in the journal Chemical Communications.

There are many conditions under which the use of NMR spectroscopy is limited. For instance, it is difficult to mimic natural conditions underground, in the deep ocean, and in industrial chemical reactors. However, a PNNL team led by Jian Zhi Hu has now developed a sample-holding rotor that acts like the reaction vessels used in industrial organic syntheses and so can mimic those conditions and more while allowing MAS NMR to be carried out with its ability to probe structure at the local level in solid, liquid, gas and mixtures.

Perfectly sealed

"We designed a perfectly sealed all-zirconia rotor that spins samples at high speeds inside a strong magnetic field and performs at extremes of pressure and temperature," explains Hu. This opens up MAS NMR spectroscopy and its potential for high resolution spectra to obtain structures and track changes over time whether a sample is a solid, liquid or mixture and at high temperature or pressures and under supercritical fluid (SCF) conditions. The team suggests that studies of carbon sequestering agents, new solid catalysts, biofuel synthesis, food processing, and even studying disease progression in intact biological tissues might now be possible.

"Limitations in vessels to probe solids and chemical reactions by NMR spectroscopy under more extreme conditions left a large territory of scientific problems related to catalytic reactions and material synthesis unexplored," adds Johannes Lercher, director of the Institute for Integrated Catalysis at PNNL. "Designing a perfectly sealed rotor is critical for gaining chemical insights into catalysts and catalysis while chemical reactions occur."

Broad applications

The PNNL team first developed the reusable rotor to further studies in carbon sequestration knowing that metal and polymer plastic rotors had failed in the past under extreme conditions, so another material was needed. They thus manufactured a rotor from the ceramic zirconia well known for its high mechanical strength. They also ensured that the device was simple in construction having a mere four components: the rotor cylinder, the sealing screw, an O-ring holding the two together, and a spin tip. They carried out various tests ranging from molecular crystallization to a dehydration reaction under both high temperature and high pressure. They also investigated metabolism in biological tissues at requisite very low temperatures for keeping such tissues intact, that would normally hinder the operation of a rotors.

Spectroscopists have sought for a way to emulate various natural and industrial environments in the NMR machine for many years. The PNNL rotor brings a range of contexts within grasping distance now. PNNL researchers themselves will use their universal design zirconia rotor to make measurements and gain understanding never before possible in organic synthesis and biomedical science.

Related Links

Chem. Commun. 2015, 51, 13458-13461: "Sealed Rotors for In Situ High Temperature High Pressure MAS NMR"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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