Liquid state DNP using a 260 GHz high power gyrotron

Denysenkov, Vasyl; Prandolini, M. J.; Gafurov, Marat; Sezer, Deniz; Endeward, Burkhard; Prisner, Thomas F.

doi:10.1039/c003697h

Cited by 107 publications

(71 citation statements)

References 23 publications

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“…Moreover, recent developments in high power microwave sources have enabled considerable signal enhancements also in the liquid state at frequencies as high as 263 GHz 4 .…”

Section: Introductionmentioning

confidence: 99%

Correlation of the EPR properties of perchlorotriphenylmethyl radicals and their efficiency as DNP polarizers

Banerjee

Paniagua

Mugnaini

et al. 2011

Phys. Chem. Chem. Phys.

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Water soluble perchlorinated trityl (PTM) radicals were found to be effective 95 GHz DNP (dynamic nuclear polarization) polarizers in ex--situ (dissolution) 13 C DNP (Gabellieri et al, Angew Chem. Int. Ed. 2010, 49, 3360). The degree of the nuclear polarization obtained was reported to depend on the position of the chlorine substituents on the trityl skeleton. In addiiton, on the basis of the DNP frequency sweeps it was suggested that the 13 C NMR signal enhancement is mediated by the Cl nuclei. To understand the DNP mechanism of the PTM radicals we have explored the 95 GHz EPR characteristics of these radicals that are relevant to their performance as DNP polarizers. The EPR spectra of the radicals revealed axially symmetric g--tensors. A comparison of the spectra with the 13 C DNP frequency sweeps showed that although the solid effect mechanism is operational the DNP frequency sweeps reveals some extra width suggesting that contributions from EPR forbidden transitions involving 35,37 Cl nuclear flips are likely. This was substantiated experimentally by ELDOR (electron--electron double resonance) detected NMR measurements, which map the EPR forbidden transitions, and ELDOR experiments that follow the depolarization of the electron spin upon irradiation of the forbidden EPR transitions.DFT (density functional theory) calculations helped to assign the observed transitions and provided the relevant spin Hamiltonian parameters. These results show that the 35,37 Cl hyperfine and nuclear quadrupolar interactions cause a considerable nuclear state mixing at 95 GHz thus facilitating the polarizing of the Cl nuclei upon microwave irradiation. Overlap of Cl nuclear frequencies and the 13 C Larmor frequency further facilitates the polarization of the 13 C nuclei by 2 spin diffusion. Calculation of the 13 C DNP frequency sweep based on the Cl nuclear polarization showed that it does lead to an increase in the width of the spectra, improving the agreement with the experimental sweeps, thus supporting the existence of the new heteronuclear assisted DNP mechanism.

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“…Moreover, recent developments in high power microwave sources have enabled considerable signal enhancements also in the liquid state at frequencies as high as 263 GHz 4 .…”

Section: Introductionmentioning

confidence: 99%

Correlation of the EPR properties of perchlorotriphenylmethyl radicals and their efficiency as DNP polarizers

Banerjee

Paniagua

Mugnaini

et al. 2011

Phys. Chem. Chem. Phys.

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“…At high magnetic fields, the pioneering work has been performed in the solid state [4,5] sparking a surge of new developments and applications [6][7][8][9]. This success triggered attempts to investigate also the potential of DNP in the liquid state at high magnetic fields, e.g., at 3.4 T [10-13] and 9.2 T [14][15][16]. In the liquid state, cross-relaxation between the electron and nuclear spin drive the polarization transfer, called Overhauser DNP.…”

Section: Introductionmentioning

confidence: 99%

Liquid State DNP on Metabolites at 260 GHz EPR/400 MHz NMR Frequency

2012

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We have performed liquid state (''Overhauser'') dynamic nuclear polarization (DNP) experiments at high magnetic field (9.2 T, corresponding to 260 GHz EPR and 400 MHz 1 H-NMR resonance frequency) on solutions of pyruvate, lactate and alanine in water with TEMPOL nitroxide radicals as polarizing agent. We present experimental results showing DNP enhancement on metabolite methyl protons, varying for the different target metabolites. It is shown that the enhancements are achieved through direct coupling between the radicals and the target metabolites in solution, i.e., the effect is not mediated by the solvent water protons. The coupling factors between the TEMPOL radicals and the metabolites observed are a factor of 3-5 smaller compared to direct polarization transfer from TEMPOL to water protons.

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“…The Prisner group has reported proton signal enhancement of water using Fermy's salt radicals at 9.2 T [49]. Enhancement of water and ethanol has been previously demonstrated in our group at 3.4 T [50,51].…”

Section: Static Sample Overhauser Dnpmentioning

confidence: 93%