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Overhauser Dynamic Nuclear Polarization (DNP)

DFG Funded Project: Overhauser Dynamic Nuclear Polarization at high magnetic fields (9.4 T) on Lipid Bilayers



Energy level diagram for electron and proton spins
Ball sizes are proportional to spin populations 		Populations at Bolzmann
thermal equlibrium with
depicted transition
probabilities for nuclei 		Populations at saturation
of EPR spin states with
depicted transition
probabilities for nuclei


The DNP enhancement ɛ is describing the gain in Signal-to-Noise ratio of the NMR signal of a nuclear spin I [1]:




  microwave saturation factor
  DNP coupling factor
  leakage factor



DNP at 9.4 T (400 MHz NMR / 260 GHz EPR)


Helix DNP probehead [2]: application to Malonic acid [3]


Top part of the helix DNP probehead
fabricated at FB14, Goethe University



Sample volume up to 10 nl
of aqueous solution
placed in 50 µm capillary



Malonic acid in CCl4


Stripline-FabryPerot DNP probehead: application to lipid bilayers [4]




Top part of the FabryPerot DNP probehead.
Sample volume up to 200 nl







   (a) 1H NMR of DOPC lipid bilayers.
   (b) 1H NMR spectrum of DOPC
   aligned at stripline,
   doped with TEMPOL radical.
   (c) MW irradiation (5.6 W),
   DNP enhancement
   ɛ = −4.4 for the acyl chain
   proton resonances.
   (d) ɛ increases with the amount
   of TEMPOL in lipid.



DNP for MRI applications

MRI contrast:
  • can be improved by administration of a MRI contrast agents (gadolinium complexes) but with a risk of side effects
  • DNP is promising to get even better contrast by injecting hyperpolarized water


In-bore DNP polarizer for MRI at 1.5 Tesla [5]
can produce upto 3 ml/min continuous flow of hyperpolarized water




AERA Siemens MRI scanner equipped with DNP polarizer



MRI DNP on phantoms


Aorta model[6]


1 - PE tubing (ID =1 mm)
    2.4 ml/min water flow
2-quartz capillary (ID = 0.15 mm)
   1.2 ml/min DNP polarized substrate (30 mM TEPOL)
3 – injection point
Pulse sequence 2D GRE; TR 200 ms, SE 1.46 ms TA 40 sec
ε(CNR)=5


DNP enhanced contrast of aorta in mouse (ex-vivo experiment)



before DNP
(microwaves OFF)
under DNP
(microwaves ON)
subtraction
    
filtered signal from c)
placed on top of image a)


References:

[1] Sezer, D., Prandolini, M. J. and Prisner, T. F.(2009), Dynamic Nuclear Polarization Coupling Factors Calculated from Molecular Dynamics Simulations of a Nitroxide Radical in Water. Phys. Chem. Chem. Phys., 11, 6626 - 6637. doi: 10.1039/B905709A ;
[2] Denysenkov, V. P., Prandolini, M. J., Krahn, A., Gafurov, M., Endeward, B. and Prisner, T. F. (2008), High-Field DNP Spectrometer for Liquids. Appl. Magn. Res., 34, 289 - 299. doi: 10.1007/s00723-008-0127-3;
[3] Orlando, T., Dervisoglu, R., Levien, L., Tkach, I., Prisner, T.F., Andreas, L.B., Denysenkov, V.P. and Bennati, M. (2019), Dynamic Nuclear Polarization of 13C Nuclei in the Liquid State over a 10 Tesla Field Range. Angew. Chem. Int. Ed., 58, 1402–1406 doi: 10.1002/anie.201811892
[4] Jakdetchai, O., Denysenkov, V., Becker-Baldus, J., Dutagaci, B., Prisner, T. F. and Glaubitz, C. (2014), Dynamic Nuclear Polarization-Enhanced NMR on Aligned Lipid Bilayers at Ambient Temperature. J. Am. Chem. Soc., 136, 15533 - 15536 doi: 10.1021/ja509799s
[5] Krummenacker, J., Denysenkov, V., Terekhov, M., Schreiber, L. and Prisner, T. F. (2012), DNP in MRI: An in-Bore Approach at 1,5 T. J. Magn. Reson., 215, 94 - 99. doi: 10.1016/j.jmr.2011.12.015
[6] Denysenkov, V., Terekhov, M., Maeder, R., Fischer, S., Zangos, S., Vogl, T. and Prisner, T. F. (2017), Continuous-Flow DNP Polarizer for MRI Applications at 1.5 T. Sci. Rep., 7, 44010 doi: 10.1038/srep44010