A Study on the Dynamic Nuclear Polarization Efficiency of a Novel Nitroxide Radical

Abstract: Nuclear magnetic resonance (NMR) mapping, valued for its non‑destructive nature and high resolution, is extensively employed in geological exploration to analyze the distribution of geological structures, mineral resources, and other subsurface targets. However, the intrinsic low sensitivity of NMR limits its utility in weak‑signal environments. Dynamic nuclear polarization (DNP) overcomes this constraint by using radiofrequency excitation to transfer polarization from electron spins to nuclear spins. This mechanism effectively relays the high polarization of electrons to the nuclear spin system, markedly boosting NMR detection sensitivity and serving as a pivotal signal‑enhancement strategy.

Within DNP systems, nitroxide radicals are widely studied due to their chemical stability and synthetic accessibility. However, their polarization efficiency is often limited by the magnetic transition characteristics of the conventional nitrogen nucleus. To address this, the present study established an electron paramagnetic resonance (EPR) spectral simulation method based on software such as Gaussian and ORCA. Guided by this approach, a novel nitroxide radical was designed and synthesized with the aim of enhancing DNP performance at low to medium magnetic fields. EPR experimental results show that this radical exhibits a narrow EPR linewidth and higher unpaired electron transition intensity compared to conventional nitroxide radicals. These properties enable it to overcome the electron transition energy limitations of conventional nitroxide radicals under medium- and low-field conditions, thereby achieving a higher nuclear polarization rate.

In conclusion, this study introduces an efficient design strategy centered on a novel nitroxide radical, which substantially improves DNP signal enhancement and supports the advancement of NMR mapping technology.