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cryogenic hyperpolarizer to the reacting centers of interest. Recent studies have
also shown that transferring this hyperpolarization to protons by indirectly detected
methods could successfully give rise to 1 H NMR spectra of hyperpolarized
compounds with a high sensitivity. Harris et al . [ 55 ] demonstrates that indirectly
detected 1 H NMR spectroscopy can also be exploited as time-resolved hyper-
polarized spectroscopy by merging with spatially encoded methods. This method
can successfully deliver a series of hyperpolarized 1 H NMR spectra over a minutes-
long timescale. The principles and opportunities presented by this approach were
demonstrated by following the in vitro phosphorylation of choline by choline
kinase, and by tracking acetylcholine's hydrolysis by acetylcholine esterase, an
important enzyme partaking in synaptic transmission and neuronal degradation
(Fig. 9 )[ 55 ].
Fig. 9 NMR spectral changes revealed by a 5 mm solution of hyperpolarized choline upon
undergoing phosphorylation by 0.5 units of choline kinase. (a) Emergence of the new
phosphocholine resonance shown by directly detected single-pulse 15 N NMR spectroscopy
experiments. (b) Emergence of the 1 H NMR resonance associated with the methylenes in the
C2-position of phosphocholine, (c) Comparison between the expected enzyme kinetics of kinase
with results afforded by the 15 N- (&) and 1 H-detected (^) hyperpolarized experiments, as derived
from the relative peak ratios of the NMR peaks in (a) and (b). The straight line illustrates the best
fit of the combined set of data points, and corresponds to an initial phosphorylation rate of
0.3 mM min 1 under these conditions. Reproduced with permission from [ 55 ]
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