Cross Polarization for Dissolution Dynamic Nuclear Polarization Experiments at Readily Accessible Temperatures 1.2< T <4.2K

Cross polarization can provide significant enhancements with respect to direct polarization of low-γ nuclei such as 13C. Substantial gains in sample throughput (shorter polarization times) can be achieved by exploiting shorter build-up times τDNP(1H)<τDNP(13C). To polarize protons rather than low-γ nuclei, nitroxide radicals with broad ESR resonances such as TEMPO are more appropriate than Trityl and similar carbon-based radicals that have narrow lines. With TEMPO as polarizing agent, the main Dynamic Nuclear Polarization (DNP) mechanism is thermal mixing (TM). Cross polarization makes it possible to attain higher polarization levels at 2.2K than one can obtain with direct DNP of low-γ nuclei with TEMPO at 1.2K, thus avoiding complex cryogenic technolog

Optimizing dissolution dynamic nuclear polarization

This article is a short review of some of our recent developments in dissolution dynamic nuclear polarization (d-DNP). We present the basic principles of d-DNP, and motivate our choice to step away from conventional approaches. We then introduce a modified d-DNP recipe that can be summed up as follows: (i) Using broad line polarizing agents to efficiently polarize H-1 spins. (ii) Increasing the magnetic field to 6.7 T and above. (iii) Applying microwave frequency modulation. (iv) Applying H-1-C-13 cross polarization. (v) Transferring hyperpolarized solution through a magnetic tunnel. (C) 2015 Elsevier Inc. All rights reserved

Dynamic Nuclear Polarization by Thermal Mixing Under Partial Saturation

We describe a low-temperature thermodynamic model for dynamic nuclear polarization (DNP) via continuous-wave partial saturation of electron spin resonance (ESR) lines that are both homogeneously and inhomogeneously broadened. It is a variant of a reasoning proposed by Borghini, which in turn used Redfield's thermodynamic treatment of saturation. Our variant is furthermore based on Provotorov's insight that under partial saturation of a coupled-spin system two distinct spin temperatures should appear in a thermodynamical theory. We apply our model to DNP results obtained at a temperature of 1.2K and in magnetic fields of 3.35 and 5T on 1-13C labeled sodium acetate dissolved in a frozen D2O/ethanol-d6 solution doped with the free radical TEMP

The role of electron polarization on nuclear spin diffusion

Dynamic nuclear polarization (DNP) is capable of boosting signals in nuclear magnetic resonance by orders of magnitude by creating out-of-equilibrium nuclear spin polarization. The diffusion of nuclear spin polarization in the vicinity of paramagnetic dopants is a crucial step for DNP and remains yet not well understood. In this Letter, we show that the polarization of the electron spin controls the rate of proton spin diffusion in a DNP sample at 1.2 K and 7 T; at increasingly high electron polarization, spin diffusion vanishes. We rationalize our results using a 2 nucleus - 1 electron model and Lindblad s Master equation, which generalizes preexisting models in the literature and qualitatively accounts for the experimental observed spin diffusion dynamics.Comment: Main text: 6 pages, 3 figures Supplement: 9 pages, 4 figure

Proton hyperpolarisation preserved in long-lived states.

International audienceThe polarisation of abundant protons, rather than dilute nuclei with low gyromagnetic ratios, can be enhanced in less than 10 min using dissolution DNP and converted into a long-lived state delocalised over an ensemble of three coupled protons. The process is more straightforward than the hyperpolarisation of heteronuclei followed by magnetisation transfer to protons

Solid-state 1H spin polarimetry by 13CH3 nuclear magnetic resonance

Abstract. Dissolution dynamic nuclear polarization is used to prepare nuclear spin polarizations approaching unity. At present, 1H polarization quantification in the solid state remains fastidious due to the requirement of measuring thermal equilibrium signals. Line shape polarimetry of solid-state nuclear magnetic resonance spectra is used to determine several useful properties regarding the spin system under investigation. In the case of highly polarized nuclear spins, such as those prepared under the conditions of dissolution dynamic nuclear polarization experiments, the absolute polarization of a particular isotopic species within the sample may be directly inferred from the characteristics of the corresponding resonance line shape. In situations where direct measurements of polarization are complicated by deleterious phenomena, indirect estimates of polarization using coupled heteronuclear spins prove informative. We present a simple analysis of the 13C spectral line shape of [2-13C]sodium acetate based on the normalized deviation of the centre of gravity of the 13C peaks, which can be used to indirectly evaluate the proton polarization of the methyl group moiety and very likely the entire sample in the case of rapid and homogeneous 1H–1H spin diffusion. For the case of positive microwave irradiation, 1H polarization was found to increase with an increasing normalized centre of gravity deviation. These results suggest that, as a dopant, [2-13C]sodium acetate could be used to indirectly gauge 1H polarizations in standard sample formulations, which is potentially advantageous for (i) samples polarized in commercial dissolution dynamic nuclear polarization devices that lack 1H radiofrequency hardware, (ii) measurements that are deleteriously influenced by radiation damping or complicated by the presence of large background signals and (iii) situations where the acquisition of a thermal equilibrium spectrum is not feasible. </jats:p

Dynamic Nuclear Polarization by Thermal Mixing Under Partial Saturation

We describe a low-temperature thermodynamic model for dynamic nuclear polarization (DNP) via continuous-wave partial saturation of electron spin resonance (ESR) lines that are both homogeneously and inhomogeneously broadened. It is a variant of a reasoning proposed by Borghini, which in turn used Redfield's thermodynamic treatment of saturation. Our variant is furthermore based on Provotorov's insight that under partial saturation of a coupled-spin system two distinct spin temperatures should appear in a thermodynamical theory. We apply our model to DNP results obtained at a temperature of 1.2 K and in magnetic fields of 3.35 and 5 T on 1-C-13 labeled sodium acetate dissolved in a frozen D2O/ethanol-d(6) solution doped with the free radical TEMPO

Cross Polarization for Dissolution Dynamic Nuclear Polarization Experiments at Readily Accessible Temperatures 1.2 < T < 4.2 K

Cross polarization can provide significant enhancements with respect to direct polarization of low-gamma nuclei such as C-13. Substantial gains in sample throughput (shorter polarization times) can be achieved by exploiting shorter build-up times tau(DNP)(H-1) < tau(DNP)(C-13). To polarize protons rather than low-gamma nuclei, nitroxide radicals with broad ESR resonances such as TEMPO are more appropriate than Trityl and similar carbon-based radicals that have narrow lines. With TEMPO as polarizing agent, the main Dynamic Nuclear Polarization (DNP) mechanism is thermal mixing (TM). Cross polarization makes it possible to attain higher polarization levels at 2.2 K than one can obtain with direct DNP of low-gamma nuclei with TEMPO at 1.2 K, thus avoiding complex cryogenic technology

NMR of Insensitive Nuclei Enhanced by Dynamic Nuclear Polarization

Despite the powerful spectroscopic information it provides, Nuclear Magnetic Resonance (NMR) spectroscopy suffers from a lack of sensitivity, especially when dealing with nuclei other than protons. Even though NMR can be applied in a straightforward manner when dealing with abundant protons of organic molecules, it is very challenging to address biomolecules in low concentration and/or many other nuclei of the periodic table that do not provide as intense signals as protons. Dynamic Nuclear Polarization (DNP) is an important technique that provides a way to dramatically increase signal intensities in NMR. It consists in transferring the very high electron spin polarization of paramagnetic centers (usually at low temperature) to the surrounding nuclear spins with appropriate microwave irradiation. DNP can lead to an enhancement of the nuclear spin polarization by up to four orders of magnitude. We present in this article some basic concepts of DNP, describe the DNP apparatus at EPFL, and illustrate the interest of the technique for chemical applications by reporting recent measurements of the kinetics of complexation of Y-89 by the DOTAM ligand

Homonuclear decoupling for spectral simplification of carbon-13 enriched molecules in solution-state NMR enhanced by dissolution DNP

Complex overlapping multiplets due to scalar couplings (n)J(C-13, C-13) in fully C-13-enriched molecules can be simplified by polychromatic irradiation of selected spins. The signal intensities of the remaining non-irradiated signals are proportional to the concentrations, as shown in this work for the anomeric C-13 signals of the alpha- and beta-conformers of glucose. Homonuclear decoupling can therefore be useful for quantitative NMR studies. The resulting decoupled lineshapes show residual fine structures that have been investigated by means of numerical simulations. Simulations also show that homonuclear decoupling schemes remain effective despite inhomogeneous static fields that tend to hamper in cellulo and in vivo studies. Homonuclear decoupling schemes can be combined with dissolution DNP to obtain signal enhancements of more than four orders of magnitude. Polychromatic irradiation of selected spins does not cause significant losses of hyperpolarization of the remaining non-irradiated spins