Category Archives: 2H

Heteronuclear DNP of protons and deuterons with TEMPOL #DNPNMR

Kaminker, I., et al., Heteronuclear DNP of protons and deuterons with TEMPOL. Phys Chem Chem Phys, 2016. 18(16): p. 11017-41.

https://www.ncbi.nlm.nih.gov/pubmed/27047995

Dynamic nuclear polarization (DNP) experiments on samples with several types of magnetic nuclei sometimes exhibit “cross-talk” between the nuclei, such as different nuclei having DNP spectra with similar shapes and enhancements. In this work we demonstrate that while at 20 K the DNP spectra of (1)H and (2)H nuclei, in a sample composed of 50% v/v (1)H2O/DMSO-d6 and containing 40 mM TEMPOL, are different and can be analyzed using the indirect cross effect (iCE) model, at 6 K the DNP spectra of both (1)H and (2)H nuclei become identical. In addition we experimentally demonstrate that there exists an efficient polarization exchange between the two nuclear pools at this temperature. Both of these results are hallmark predictions of the thermal mixing (TM) formalism. However, the origin of these observations cannot, in our case, be explained using the standard TM formalism, as in our sample the electron reservoir cannot be described by a single non-Zeeman spin temperature, which is a prerequisite of TM. This conclusion follows from the analysis of the electron electron double resonance (ELDOR) experiments on our sample and is similar to the previously published results. Consequently, another mechanism must be used in order to explain these “cross-talk” effects. The heteronuclear cross effect (hnCE) DNP mechanism, previously introduced based on the simulations of the spin evolution in small model systems, results in “cross-talk” effects between two types of nuclei that are similar to the experimental ones seen in this work. In particular we show that the hnCE mechanism exhibits polarization transfer between the nuclei and that there exists a clear relationship between the steady state polarizations of the two types of nuclei which may, in the future, be correlated with the phenomenon observed in the two types of bulk nuclear signals in samples during DNP experiments. It is suggested that the hnCE electrons are a possible source for the process that equalizes the bulk enhancements of the (1)H and (2)H nuclei and are responsible for the observed cross-talk effects.

High-resolution NMR of hydrogen in organic solids by DNP enhanced natural abundance deuterium spectroscopy

Rossini, A.J., et al., High-resolution NMR of hydrogen in organic solids by DNP enhanced natural abundance deuterium spectroscopy. J Magn Reson, 2015. 259: p. 192-8.

http://www.ncbi.nlm.nih.gov/pubmed/26363582

We demonstrate that high field (9.4 T) dynamic nuclear polarization (DNP) at cryogenic ( approximately 100 K) sample temperatures enables the rapid acquisition of natural abundance (1)H-(2)H cross-polarization magic angle spinning (CPMAS) solid-state NMR spectra of organic solids. Spectra were obtained by impregnating substrates with a solution of the stable DNP polarizing agent TEKPol in tetrachloroethane. Tetrachloroethane is a non-solvent for the solids, and the unmodified substrates are then polarized through spin diffusion. High quality natural abundance (2)H CPMAS spectra of histidine hydrochloride monohydrate, glycylglycine and theophylline were acquired in less than 2h, providing direct access to hydrogen chemical shifts and quadrupolar couplings. The spectral resolution of the (2)H solid-state NMR spectra is comparable to that of (1)H spectra obtained with state of the art homonuclear decoupling techniques.

High-resolution NMR of hydrogen in organic solids by DNP enhanced natural abundance deuterium spectroscopy

Rossini, A.J., et al., High-resolution NMR of hydrogen in organic solids by DNP enhanced natural abundance deuterium spectroscopy. J. Magn. Reson., 2015. 259: p. 192-198.

http://dx.doi.org/10.1016/j.jmr.2015.08.020

We demonstrate that high field (9.4 T) dynamic nuclear polarization (DNP) at cryogenic (∼100 K) sample temperatures enables the rapid acquisition of natural abundance 1H–2H cross-polarization magic angle spinning (CPMAS) solid-state NMR spectra of organic solids. Spectra were obtained by impregnating substrates with a solution of the stable DNP polarizing agent TEKPol in tetrachloroethane. Tetrachloroethane is a non-solvent for the solids, and the unmodified substrates are then polarized through spin diffusion. High quality natural abundance 2H CPMAS spectra of histidine hydrochloride monohydrate, glycylglycine and theophylline were acquired in less than 2 h, providing direct access to hydrogen chemical shifts and quadrupolar couplings. The spectral resolution of the 2H solid-state NMR spectra is comparable to that of 1H spectra obtained with state of the art homonuclear decoupling techniques.

Dynamic nuclear polarization of high-density atomic hydrogen in solid mixtures of molecular hydrogen isotopes

If you are interested in this article, you should also have a look at this article by Can et al., describing the Overhauser Effect in insulating solids:

http://blog.bridge12.com/2014/09/overhauser-effects-in-insulating-solids.html

Sheludiakov, S., et al., Dynamic nuclear polarization of high-density atomic hydrogen in solid mixtures of molecular hydrogen isotopes. Phys Rev Lett, 2014. 113(26): p. 265303.

http://www.ncbi.nlm.nih.gov/pubmed/25615349

We report on magnetic resonance studies of high-density atomic hydrogen and deuterium in solid hydrogen matrices at temperatures below 1 K. Average concentrations of H atoms approximately 3×10^{19} cm^{-3} are obtained in chemical tunneling reactions of isotope exchange with D atoms. The products of these reactions are closely located pairs of H atoms near D_{2} molecules with strong exchange interactions. We discovered a dynamic nuclear polarization effect on H atoms created by pumping the center of the H electron spin resonance spectrum, similar to the Overhauser effect in metals. Our results indicate that H atoms may be arranged inside molecular matrices at separations equivalent to local concentrations of 2.6×10^{21} cm^{-3}. This opens up a way to build a metallic state of atomic hydrogen at zero pressure.

Have a question?

If you have questions about our instrumentation or how we can help you, please contact us.