posted on 2020-03-12, 19:40authored byPatrick
T. Judge, Erika L. Sesti, Lauren E. Price, Brice J. Albert, Nicholas Alaniva, Edward P. Saliba, Thomas Halbritter, Snorri Th. Sigurdsson, George B. Kyei, Alexander B. Barnes
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
T1DNP 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.