Indirect Detection of the Protons in and Around Biradicals and their Mechanistic Role in MAS-DNP

The contribution of protons on or near biradical polarizing agents in Dynamic Nuclear Polarization (DNP) has recently been under scrutiny. Results from selective deuteration and simulations have previously suggested that the role of protons on the biradical molecule depends on the strength of the electron-electron coupling. Here we use the cross effect DNP mechanism to identify and acquire 1H solid-state NMR spectra of the protons that contribute to propagation of the hyperpolarization, via an experimental approach dubbed Nuclear Double Resonance (NUDOR).