Dynamic Nuclear Polarization with Electron Decoupling in Intact Human Cells and Cell Lysates

Dynamic nuclear polarization (DNP) is used to improve the inherently poor sensitivity of nuclear magnetic resonance spectroscopy by transferring spin polarization from electrons to nuclei. However, DNP radicals within the sample can have detrimental effects on nuclear spins close to the polarizing agent. Chirped microwave pulses and electron decoupling (eDEC) attenuate these effects in model systems, but this approach is yet to be applied to intact cells or cellular lysates. Herein, we demonstrate for the first time exceptionally fast ¹H T_1DNP times of just 200 and 300 ms at 90 and 6 K, respectively, using a newly synthesized methylated trityl radical within intact human cells. We further demonstrate that eDEC can also be applied to intact human cells and human and bacterial cell lysates. We investigate eDEC efficiency at different temperatures, with different solvents, and with two trityl radical derivatives. At 90 K, eDEC yields a ¹³C signal intensity increase of 8% in intact human cells and 10% in human and bacterial cell lysates. At 6 K, eDEC provides larger intensity increases of 15 and 39% in intact human cells and cell lysates, respectively. Combining the manipulation of electron spins with frequency-chirped pulses and sample temperatures approaching absolute zero is a promising avenue for executing rapid, high-sensitivity magic-angle spinning DNP in complex cellular environments.