Quadrupolar Nuclei Successfully Measured Using Zero-Field NMR

Quadrupolar Nuclei Successfully Measured Using Zero-Field NMR
by Robert Schreiber
Berlin, Germany (SPX) Jul 15, 2024

Researchers have long utilized nuclear magnetic resonance (NMR) spectroscopy to explore molecular structures and interactions. Traditionally, NMR requires a powerful magnetic field to align the spins of atomic nuclei, which are then rotated by a weak oscillating magnetic field. The resulting changes in voltage are converted into measurable frequencies, allowing scientists to deduce molecular structures and nuclear spin interactions. However, this method depends on large, complex, and costly equipment and struggles with quadrupolar nuclei, the most common type of nuclei.

Zero-field nuclear magnetic resonance (zero-field NMR) eliminates the need for a strong external magnetic field. In zero-field NMR, the primary interaction is the intramolecular coupling between the spins of magnetically active nuclei. This method produces narrower and sharper spectral lines and allows the examination of samples in metal or other containers. Zero-field NMR has been applied to monitor reactions in metal containers, analyze plants, and holds potential for medical applications. However, shielding against Earth's magnetic field is necessary to detect the small spin interactions, which poses its own challenges.

A collaborative effort by researchers at Johannes Gutenberg University Mainz (JGU), the Helmholtz Institute Mainz (HIM), and the University of California, Berkeley, has achieved the measurement of quadrupolar nuclei using zero-field NMR. "We analyzed an ammonium molecule, NH4+, a cation that plays an important role in various applications," said Dr. Danila Barskiy, head of the JGU team. "We aim to detect these molecules in complex environments, such as reactors and metal containers."

The researchers developed a straightforward experimental setup involving the mixing of ammonium salts with water and varying amounts of deuterium. The spectra were recorded and analyzed using a commercially available magnetometer within a compact analytical system with magnetic shielding.

The team also investigated how the number of deuterium atoms in an ammonium molecule affects the spectrum and the relaxation characteristics of spins. Roman Picazo-Frutos, a student at the JGU Institute of Physics and lead author of the study, noted, "Using our method, it is possible to determine resonance frequencies with a very high level of precision. Because the results produced by this technique can be compared with other experimental data, it can be used for benchmarking quantum chemistry calculations. We hope that our system will become standard practice in the near future."

While current theoretical predictions align closely with the team's results, there are minor deviations. Professor Dmitry Budker of JGU commented, "The work undertaken by the team has considerably extended the range of molecules that can be analyzed by means of zero- to ultralow-field NMR techniques. It may even contribute to the development of innovative applications that could be used to investigate the nuclei of atoms with small atomic numbers by means of their radioactive gamma decay."

Research Report:Zero-field J-spectroscopy of quadrupolar nuclei