Category Archives: DNP

Hyperpolarized relaxometry based nuclear T1 noise spectroscopy in diamond

Ajoy, A., B. Safvati, R. Nazaryan, J. T. Oon, B. Han, P. Raghavan, R. Nirodi, et al. “Hyperpolarized Relaxometry Based Nuclear T1 Noise Spectroscopy in Diamond.” Nature Communications 10, no. 1 (December 2019): 5160.

https://doi.org/10.1038/s41467-019-13042-3.

The origins of spin lifetimes in quantum systems is a matter of importance in several areas of quantum information. Spectrally mapping spin relaxation processes provides insight into their origin and motivates methods to mitigate them. In this paper, we map nuclear relaxation in a prototypical system of 13C nuclei in diamond coupled to Nitrogen Vacancy (NV) centers over a wide field range (1 mT-7 T). Nuclear hyperpolarization through optically pumped NV electrons allows signal measurement savings exceeding million-fold over conventional methods. Through a systematic study with varying substitutional electron (P1 center) and 13C concentrations, we identify the operational relaxation channels for the nuclei at different fields as well as the dominant role played by 13C coupling to the interacting P1 electronic spin bath. These results motivate quantum control techniques for dissipation engineering to boost spin lifetimes in diamond, with applications including engineered quantum memories and hyperpolarized 13C imaging.

Small Molecules, Non-Covalent Interactions, and Confinement #DNPNMR

Buntkowsky, Gerd, and Michael Vogel. “Small Molecules, Non-Covalent Interactions, and Confinement.” Molecules 25, no. 14 (July 21, 2020): 3311.

https://doi.org/10.3390/molecules25143311

This review gives an overview of current trends in the investigation of small guest molecules, confined in neat and functionalized mesoporous silica materials by a combination of solid-state NMR and relaxometry with other physico-chemical techniques. The reported guest molecules are water, small alcohols, and carbonic acids, small aromatic and heteroaromatic molecules, ionic liquids, and surfactants. They are taken as characteristic role-models, which are representatives for the typical classes of organic molecules. It is shown that this combination delivers unique insights into the structure, arrangement, dynamics, guest-host interactions, and the binding sites in these confined systems, and is probably the most powerful analytical technique to probe these systems.

Shedding light on the atomic-scale structure of amorphous silica–alumina and its Brønsted acid sites #DNPNMR

Perras, Frédéric A., Zichun Wang, Takeshi Kobayashi, Alfons Baiker, Jun Huang, and Marek Pruski. “Shedding Light on the Atomic-Scale Structure of Amorphous Silica–Alumina and Its Brønsted Acid Sites.” Physical Chemistry Chemical Physics 21, no. 35 (2019): 19529–37.

https://doi.org/10.1039/C9CP04099D

In spite of the widespread applications of amorphous silica–aluminas (ASAs) in many important industrial chemical processes, their high-resolution structures have remained largely elusive. Specifically, the lack of long-range ordering in ASA precludes the use of diffraction methods while NMR spectroscopy has been limited by low sensitivity. Here, we use conventional as well as DNP-enhanced 29Si–29Si, 27Al–27Al, and 29Si–27Al solid-state NMR experiments to shed light on the ordering of atoms in ASAs prepared by flame-spray-pyrolysis. These experiments, in conjunction with a novel Monte Carlo-based approach to simulating RESPDOR dephasing curves, revealed that ASA materials obey Loewenstein’s rule of aluminum avoidance. 3D 17O{1H} and 2D
17O{1H, 27Al} experiments were developed to measure site-specific O–H and HO–Al distances, and show that the Brønsted acid sites originate predominantly from the pseudo-bridging silanol groups.

Microscale Hyperpolarization #DNPNMR

Kiss, Sebastian, Lorenzo Bordonali, Jan G. Korvink, and Neil MacKinnon. “Microscale Hyperpolarization.” In Micro and Nano Scale NMR, by Jens Anders and Jan G. Korvink, 297–351. Advanced Micro and Nanosystems. Weinheim, Germany: Wiley-VCH Verlag GmbH & Co. KGaA, 2018.

https://doi.org/10.1002/9783527697281.ch11.

Magnetic resonance (MR) is a tremendously powerful technique for obtaining both structural and dynamical information non-invasively and with atomic resolution. The primary limitation of MR is sensitivity, with the detected resonant exchange of energy dependent on population differences on the order of tens of parts per million as dictated by Boltzmann statistics. The MR community has implemented various strategies to overcome this inherent limitation, including maximizing the static polarizing magnetic field and cooling the probe electronics. As discussed throughout this book, an alternative strategy is to miniaturize the MR detector in order to maximize resonant energy exchange efficiency between the sample and the instrument electronics. In this chapter, we discuss approaches that aim to overcome Boltzmann population statistics. These hyperpolarization techniques rely on the transfer of a large polarization source to the target nuclear spin system, or the preparation of pure spin states that are transferred into the target spin system. The archetypal example of the former case is dynamic nuclear polarization (DNP), whereas in the latter case para-hydrogen and optically pumped 3He or 129Xe are examples.

Electrochemical Overhauser dynamic nuclear polarization #DNPNMR #ODNP

Tamski, Mika, Jonas Milani, Christophe Roussel, and Jean-Philippe Ansermet. “Electrochemical Overhauser Dynamic Nuclear Polarization.” Physical Chemistry Chemical Physics 22, no. 32 (2020): 17769–76.


https://doi.org/10.1039/D0CP00984A

Nuclear Magnetic Resonance (NMR) spectroscopy suffers from low sensitivity due to the low nuclear spin polarization obtained within practically achievable external magnetic fields. Dynamic Nuclear Polarization (DNP) refers to the techniques that increases NMR signal intensity by transferring spin polarization from electrons to the nuclei.

Dynamic nuclear polarization and ESR hole burning in As doped silicon #DNPNMR

Järvinen, J., D. Zvezdov, J. Ahokas, S. Sheludiakov, L. Lehtonen, S. Vasiliev, L. Vlasenko, Y. Ishikawa, and Y. Fujii. “Dynamic Nuclear Polarization and ESR Hole Burning in As Doped Silicon.” Physical Chemistry Chemical Physics 22, no. 18 (2020): 10227–37.

https://doi.org/10.1039/C9CP06859G

We present an experimental study of the Dynamic Nuclear Polarization (DNP) of 29Si nuclei in silicon crystals of natural abundance doped with As in the temperature range 0.1-1 K and in strong magnetic field of 4.6 T. This ensures very high degree of electron spin polarization, extremely slow nuclear relaxation and optimal conditions for realization of Overhauser and resolved solid effects. We found that the solid effect DNP leads to an appearance of a pattern of holes and peaks in the ESR line, separated by the super-hyperfine interaction between the donor electron and 29Si nuclei closest to the donor. On the contrary, the Overhauser effect DNP mainly affects the remote 29Si nuclei having the weakest interaction with the donor electron. This leads to an appearance of a very narrow ( 3 mG wide) hole in the ESR line. We studied relaxation of the holes after burning, which is caused by the nuclear spin diffusion. Analyzing the dynamics of the hole in the spectrum with a simple one-dimensional diffusion model leads to a value of the diffusion coefficient D = 8(3)10􀀀9 G2/s. Our data indicate that the spin diffusion is not completely prevented even in the frozen core near the donors. The emergence of the narrow hole after the Overhauser DNP may be explained by a partial “softening” of the frozen core caused by decoupling of the donor electron and remote 29Si nuclei.

[NMR] Postdoc position in NMR/DNP of heterogeneous catalysts at

Dear Colleagues,

We are seeking a postdoctoral associate with a background in solid-state NMR spectroscopy for the solid-state NMR investigations of heterogeneous catalysts, by conventional as well as dynamic nuclear polarization (DNP) enhanced solid-state NMR spectroscopy. A significant portion of the work will involve solid-state NMR methods development for instance through the development of novel data analysis tools, pulse sequence development, and the advancement and application of emerging technologies including ultra-fast (100 kHz+) magic-angle-spinning, dynamic nuclear polarization, and ultrahigh magnetic fields. The main focus of the work will be geared towards gaining a dynamic understanding of the structures of heterogeneous catalyst surfaces through multidimensional NMR spectroscopy.

Ames Laboratory is equipped with 9.4 and 14.1 T solid-state NMR spectrometers with MAS probes for rotor diameters ranging from 5 to 0.7-mm. Aside from these instruments, the lab is also equipped with a 9.4 T Bruker MAS-DNP NMR spectrometer with both 3.2 and 1.3-mm MAS-DNP probes. Access to computational resources and synthetic resources will also be available.

Interested people are encouraged to apply for the position. More details can be found at this link:

https://isu.wd1.myworkdayjobs.com/en-US/IowaStateJobs/job/Ames-IA/Postdoctoral-Research-Associate—Ames-Laboratory_R2763

Best,

Frédéric Perras, PhD

Ames Laboratory

US Department of Energy

Ames, IA, 50011

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Enabling Natural Abundance 17O Solid-State NMR by Direct Polarization from Paramagnetic Metal Ions #DNPNMR

Jardón-Álvarez, Daniel, Guy Reuveni, Adi Harchol, and Michal Leskes. “Enabling Natural Abundance 17O Solid-State NMR by Direct Polarization from Paramagnetic Metal Ions.” The Journal of Physical Chemistry Letters 11, no. 14 (July 16, 2020): 5439–45.

https://doi.org/10.1021/acs.jpclett.0c01527.

Dynamic nuclear polarization (DNP) significantly enhances the sensitivity of nuclear magnetic resonance (NMR), increasing applications and quality of NMR as a characterization tool for materials. Efficient spin diffusion among the nuclear spins is considered to be essential for spreading the hyperpolarization throughout the sample enabling large DNP enhancements. This scenario mostly limits the polarization enhancement of low sensitivity nuclei in inorganic materials to the surface sites when the polarization source is an exogenous radical. In metal ions based DNP, the polarization agents are distributed in the bulk sample and act as both source of relaxation and of polarization enhancement. We have found that as long as the polarization agent is the main source of relaxation, the enhancement does not depend on the distance between the nucleus and dopant. As a consequence, the requirement of efficient spin diffusion is lifted and the entire sample can be directly polarized. We exploit this finding to measure high quality NMR spectra of 17O in the electrode material Li4Ti5O12 doped with Fe(III) despite its low abundance and long relaxation time.

Stable isotope resolved metabolomics classification of prostate cancer cells using hyperpolarized NMR data #DNPNMR

Frahm, Anne Birk, Pernille Rose Jensen, Jan Henrik Ardenkjær-Larsen, Demet Yigit, and Mathilde Hauge Lerche. “Stable Isotope Resolved Metabolomics Classification of Prostate Cancer Cells Using Hyperpolarized NMR Data.” Journal of Magnetic Resonance 316 (July 2020): 106750.

https://doi.org/10.1016/j.jmr.2020.106750

Metabolic fingerprinting is a strong tool for characterization of biological phenotypes. Classification with machine learning is a critical component in the discrimination of molecular determinants. Cellular activity can be traced using stable isotope labelling of metabolites from which information on cellular pathways may be obtained. Nuclear magnetic resonance (NMR) spectroscopy is, due to its ability to trace labelling in specific atom positions, a method of choice for such metabolic activity measurements. In this study, we used hyperpolarization in the form of dissolution Dynamic Nuclear Polarization (dDNP) NMR to measure signal enhanced isotope labelled metabolites reporting on pathway activity from four different prostate cancer cell lines. The spectra have a high signal-to-noise, with less than 30 signals reporting on 10 metabolic reactions. This allows easy extraction and straightforward interpretation of spectral data. Four metabolite signals selected using a Random Forest algorithm allowed a classification with Support Vector Machines between aggressive and indolent cancer cells with 96.9% accuracy, -corresponding to 31 out of 32 samples. This demonstrates that the information contained in the few features measured with dDNP NMR, is sufficient and robust for performing binary classification based on the metabolic activity of cultured prostate cancer cells.

Balancing dipolar and exchange coupling in biradicals to maximize cross effect dynamic nuclear polarization #DNPNMR

Equbal, Asif, Kan Tagami, and Songi Han. “Balancing Dipolar and Exchange Coupling in Biradicals to Maximize Cross Effect Dynamic Nuclear Polarization.” Physical Chemistry Chemical Physics 22, no. 24 (2020): 13569–79.

https://doi.org/10.1039/D0CP02051F

Dynamic nuclear polarization (DNP) by the Cross Eect (CE) has become a game changer for solid-state nuclear magnetic resonance (NMR) spectroscopy. The eciency of CE-DNP depends on the strength of the electron-electron coupling in biradical polarizing agents. Hence, the focus lately has been on designing biradicals with a large net exchange (J) and dipolar (D) coupling. In this study, we reveal that the crucial factor for CE-DNP is not the sum, J+D, but rather the relative magnitude of J and D, expressed as the J/D ratio. We show that the mechanistic basis of this interference lies in the isotropic v.s. the anisotropic nature of the J and D couplings, respectively. This interference can lead to a small (eective) electron-electron coupling for many orientations even when J+D is large, resulting in non-adiabatic rotor-events. We find that when 0< jJ/Dj < 1 the CE-DNP eciency is attenuated for the majority of orientations, with greater attenuation observed at higher magnetic elds and faster Magic-Angle Spinning (MAS) frequency. The interference eect of J and D coupling introduced in this study can explain why many biradicals with high or comparable J + D still show signicantly divergent DNP performances. We debut J/D as a consequential criteria for designing ecient biradicals to robustly perform across a large range of B0 elds and MAS frequencies.

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