Synopsis
This talk will discuss the physical basis of the DNP NMR/MRI
experiment. Attention will focus on
alternatives to do the hyperpolarization component in either solutions or in
the solid state, focusing in particular on the Overhauser, on the Solid and on the
Cross Effects for the sake of maximizing the nuclear polarization. The parameters that each of these methods
requires to work best –including their respective advantages and drawbacks–
will be explained. On the basis of this, the procedures that may then enable
their respective utilization in bioimaging settings will be introduced
Target Audience
Beginning or advanced bioDNP practitioners interested in knowing what
happens in different hyperpolarizers, during the various stages of a DNP
experiment.
Abstract
The
DNP phenomenon, according to which nuclear polarization could be enhanced by
ca. 1000x by irradiating nearby electrons in metals, was publicly introduced as
a theoretical prediction by A. Overhauser in 1953 [1]. The proposal was met by
wide disbelief by an audience that included Bloch, Purcell, Rabi and
Bloembergen –but it was proved to be true a few months later by Slichter [2].
While the DNP effect has remained a tool in the arsenals of chemists and
physicists the ensuing excitement decayed over intervening decades, until the
renaissance that occurred in the early 2000s. Driving this excitement was the
advent of high field solids DNP NMR and of Dissolution DNP MRSI [3,4]. While all DNP experiments share the common
goal of transferring polarization from electrons to nuclei, different
mechanisms operate in the experiments that Slichter, that the solids DNP scientists,
and that dissolution DNP, rely upon. The
physics underlying these different mechanisms are the Overhauser Effect, the
Solid Effect and the Cross Effect, respectively. In this talk their principles will
be presented, and the conditions that make one of these approaches preferable
over the other will be explained, based on the different conditions in which
the sample is studied. Attention will
center on methods that optimize the transfer of polarization from unpaired
electrons to nuclei in the solid state at cryogenic temperatures in the most
complete and rapid way: these are the conditions that predominate in the
dissolution DNP approach, which has seen the widest applications in biological
and clinical settings. The discussion
will also focus on how the subsequent rapid melting of the cryogenic hyperpolarized
pellet using hot vapor enables further investigations that would be impossible
without DNP; which kind of metabolic substrates are and which ones are not
amenable to this kind of procedure, will be rationalized. The overall potential
as well as the limitations of various DNP-based approaches for the sake of
metabolic studies, will also be briefly evaluated.Acknowledgements
Our research in this area has been funded by the Israel Science Foundation (ISF grant 965/18) and by the EU Horizon
2020 programme (Marie Sklodowska-Curie Grant 642773)References
[1] Overhauser,
A.W. (1953). "Polarization of Nuclei in Metals". Phys. Rev. 92 (2):
411–415.
[2]
Carver, T.R.; Slichter, C.P. (1953). "Polarization of Nuclear Spins in
Metals". Phys. Rev. 92 (1): 212–213.
[3] D.A.
Hall; D.C. Maus; G.J. Gerfen; S.J. Inati; L.R. Becerra; F.W. Dahlquist; R.G.
Griffin (1997) “Polarization-enhanced NMR spectroscopy of biomolecules in
frozen solution”, Science, 276: 930-932
[4]
Ardenkjær-Larsen, J. H.; Fridlund, B.; Gram, A.; Hansson, G.; Hansson, L.;
Lerche, M. H.; Servin, R.; Thaning, M.; Golman, K., (2003) “Increase in
signal-to-noise ratio of > 10,000 times in liquid-state NMR”. Proc. Natl.
Acad. Sci. USA 100 (18): 10158-10163.