Earth’s magnetic field enabled scalar coupling relaxation of 13C nuclei bound to fast-relaxing quadrupolar 14N in amide groups

Abstract Scalar coupling relaxation, which is usually only associated with closely resonant nuclei (e.g., 79 Br– 13 C), can be a very effective relaxation mechanism. While working on hyperpolarized [5- 13 C]glutamine, fast liquid-state polarization decay during transfer to the MRI scanner was observed. This behavior could hypothetically be explained by substantial T 1 shortening due to a scalar coupling contribution (type II) to the relaxation caused by the fast-relaxing quadrupolar 14 N adjacent to the 13 C nucleus in the amide group. This contribution is only effective in low magnetic fields (i.e., less than 800 μT) and prevents the use of molecules bearing the 13 C-amide group as hyperpolarized MRS/MRI probes. In the present work, this hypothesis is explored both theoretically and experimentally. The results show that high hyperpolarization levels can be retained using either a 15 N-labeled amide or by applying a magnetic field during transfer of the sample from the polarizer to the MRI scanner.