Chemistry Reference
In-Depth Information
Fig. 11 A pH map of a transverse slice through a mouse implanted with a subcutaneous
lymphoma tumor. (a) The
black and white
1H MR image, obtained at 9.4 T, is shown with the
tumor outlined in
red
.(b) The
false-color
13
C MR pH image is shown separately superimposed
over this; the tumor is acidic compared to the surrounding normal tissue. The spatial distribution of
H
13
CO
3
(c) and
13
CO
2
(d) are also shown in the lower two images. Reproduced with permission
from [
64
]
injection of hyperpolarized H
13
CO
3
[
83
]. This demonstrated that the extracellular
pH in a lymphoma tumor was more acidic than the surrounding tissue (Fig.
11
).
4.4 Multidimensional Time-Domain Experiment for DNP
DNP has become an attractive technique to boost the sensitivity of NMR
experiments. In the case of ex situ polarizations, two-dimensional (2D) spectra
are limited by the short lifetime of the polarization after dissolution and sample
transfer to a high field NMR magnet. This limitation can be overcome by various
approaches. Ludwig et al
.
[
84
] showed how the use of
13
C-labeled acetyl tags can
help to obtain 2D-HMQC spectra for many small molecules, owing to a nuclear
Overhauser enhancement between
13
C spins originating from the long-lived
carbonyl carbon, which extends the lifetimes of other
13
C spins with shorter
longitudinal relaxation times. For two-dimensional spectroscopy, a pulse sequence
using consecutive small flip angle excitations to read out transverse magnetization