Chemistry Reference
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while preserving z-magnetization was employed. This procedure enables one to
obtain 2D-HMQC spectra over a time frame of the lifetime of the polarization as
exemplified for natural abundance nicotinamide. They have also combined this
pulse sequence with non-uniform sampling to make the best use of the limited
lifetime of the polarization [
84
].
Short acquisition time and single scan capability of gradient-assisted ultrafast
multidimensional spectroscopy make it possible to record 2D spectra of highly
polarized spin systems in the liquid state using DNP in conjunction with fast
dissolution. Panek et al
.
[
85
] presented a slice selective experiment, suitable for
back-to-back acquisition of two independent single-scan 2D experiments from
different sample volumes. This scheme maximizes the amount of information
obtainable from a sample that is prepolarized with a non-repeatable DNP technique.
It is particularly suitable for samples with the short longitudinal relaxation times
common to proton NMR spectroscopy. This technique is demonstrated by applying
two filtered proton 2D COSY experiments on a DNP-polarized mixture of gluta-
mine and glutamate to amplify selectively the correlation pattern of the protons
connected to the beta and gamma carbons of either one of the two amino acids
(Fig.
12
). Particular emphasis was placed on the reproducibility of the experiments,
especially the polarization enhancement. It has been demonstrated that the slice
selective approach is a useful extension of the single-scan 2D spectroscopy tool set,
enabling dynamic studies of DNP-enhanced samples or, alternatively, the acquisi-
tion of different experiments on a single one-time polarized sample.
In addition to the DNP methods described above, laser-polarized xenon can be
used for the development of NMR and MRI techniques, and it is possible to enhance
the nuclear spin polarization of gaseous xenon by four to five orders of magnitude.
More details of this technique can be found in [
86
,
87
].
a
b
Δ
= 16 ms
Δ
= 8 ms
2.0
2.0
Gln
Glx
2.4
2.4
2.8
2.8
Gln
3.2
3.2
Glx
Glx
Glx
3.6
3.6
4.0
3.6
3.2 2.8
1H ppm
2.4
2.0
4.0
3.6
3.2 2.8
1H ppm
2.4
2.0
Fig. 12 DNP enhanced proton COSY spectra of glutamine and glutamate mixture acquired for
two different evolution delays (
D
) in two separate slices. Reproduced with permission from [
85
]
