Concilio, Maria Grazia, Ilya Kuprov, and Lucio Frydman. “J-Driven Dynamic Nuclear Polarization for Sensitizing High Field Solution State NMR.” Physical Chemistry Chemical Physics 24, no. 4 (2022): 2118–25.
https://doi.org/10.1039/D1CP04186J.
Dynamic nuclear polarization (DNP) is widely used to enhance solid state nuclear magnetic resonance (NMR) sensitivity. Its efficiency as a generic signal-enhancing approach for liquid state NMR, however, decays rapidly with magnetic field B0, unless mediated by scalar interactions arising only in exceptional cases. This has prevented a more widespread use of DNP in structural and dynamical solution NMR analyses. This study introduces a potential solution to this problem, relying on biradicals with exchange couplings Jex of the order of the electron Larmor frequency oE. Numerical and analytical calculations show that in such Jex ~ +/- w_e cases a phenomenon akin to that occurring in chemically induced DNP (CIDNP) happens, leading to different relaxation rates for the biradical singlet and triplet states which are hyperfine-coupled to the nuclear alpha or beta states. Microwave irradiation can then generate a transient nuclear polarization build-up with high efficiency, at all magnetic fields that are relevant in contemporary NMR, and for all rotational diffusion correlation times that occur in small- and mediumsized molecules in conventional solvents.