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.
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)109 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.
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:
Frédéric Perras, PhD
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.
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.
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.
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.
[NMR] Paramagnetic metal ion DNP | Tutorial by Björn Corzilius| Tuesday, September 29, 8:00am California #DNPNMR
Dear NMR Enthusiast,
The 15th Educational Tutorial will be given by Prof. Björn Corzilius, University of Rostock, Germany, on the topic:
\”Paramagnetic metal ions polarizing agents for DNP”.
Paramagnetic metal ions are intriguing alternatives to radical polarizing agents for DNP. In the first part of my presentation I will introduce their magnetic resonance properties and the peculiarities in DNP theory of high-spin metal ion polarizing agents. In the second part I will give an overview of recent DNP applications in biomolecular and materials science using high-spin polarizing agents Mn(II), Fe(III), Cr(III), Gd(III).
2005-2008: PhD, Physical Chemistry, Technical University Darmstadt
2009-2013: Postdoctoral Fellow and Associate, Massachusetts Institute of Technology
2013-2019: Emmy Noether Research Group Leader, Goethe University Frankfurt2019-present: Professor of Physical Chemistry, University of Rostock
Time: Tuesday, September 29, 2020, 08:00 AM California or 11:00 am Boston or 5:00 PM Paris or 8:30 PM Delhi
Join Meeting: https://ucsb.zoom.us/j/92480496788
Meeting ID: 924 8049 6788
Global NMR Discussion Meetings
Adrian Draney (Guido Pintacuda Lab, CRMN lyon)
Amrit Venkatesh (Aaron Rossini Lab, Iowa)
Asif Equbal (Songi Han Lab, UCSB)
Blake Wilson (Robert Tycko Lab, NIH)
Michael Hope (Lyndon Emsley Lab, EPFL)
Mona Mohammadi (Alexej Jerschow, NYU)
PinelopiMoutzouri (Lyndon Emsley Lab, EPFL) ]
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Organic Reaction Monitoring of a Glycine Derivative Using Signal Amplification by Reversible Exchange-Hyperpolarized Benchtop Nuclear Magnetic Resonance Spectroscopy #DNPNMR #SABRE
Chae, Heelim, Sein Min, Hye Jin Jeong, Sung Keon Namgoong, Sangwon Oh, Kiwoong Kim, and Keunhong Jeong. “Organic Reaction Monitoring of a Glycine Derivative Using Signal Amplification by Reversible Exchange-Hyperpolarized Benchtop Nuclear Magnetic Resonance Spectroscopy.” Analytical Chemistry 92, no. 16 (August 18, 2020): 10902–7.
Currently, signal ampliﬁcation by reversible exchange (SABRE) using para-hydrogen is an attractive method of hyperpolarization for overcoming the sensitivity problems of nuclear magnetic resonance (NMR) spectroscopy. Additionally, SABRE, using the spin order of para-hydrogen, can be applied in reaction monitoring processes for organic chemistry reactions where a small amount of reactant exists. The organic reaction monitoring system created by integrating SABRE and benchtop NMR is the ideal combination for monitoring a reaction and identifying the small amounts of materials in the middle of the reaction. We used a laboratory-built setup, prepared materials by synthesis, and showed that the products obtained by esteriﬁcation of glycine were also active in SABRE. The products, which were synthesized esteriﬁed glycine with nicotinoyl chloride hydrochloride, were observed with a reaction monitoring system. The maximum SABRE enhancement among them (approximately 147-fold) validated the use of this method. This study is the ﬁrst example of the monitoring of this organic reaction by SABRE and benchtop NMR. It will open new possibilities for applying this system to many other organic reactions and also provide more fruitful future applications such as drug discovery and mechanism study.
Selective DNP Signal Amplification To Probe Structures of Core–Shell Polymer Hybrid Nanoparticles #DNPNMR
Schäfer, Timmy, Steffen Vowinkel, Hergen Breitzke, Markus Gallei, and Torsten Gutmann. “Selective DNP Signal Amplification To Probe Structures of Core–Shell Polymer Hybrid Nanoparticles.” The Journal of Physical Chemistry C 123, no. 1 (January 10, 2019): 644–52.
An efficient approach for the characterization of core-shell polymer hybrid nanoparticles is presented. Selective signal amplification by dynamic nuclear polarization (DNP) is employed to shed more light on the molecular structure of surface sites and of the shell of the particles. DNP enhanced 29Si solid-state NMR is used to clearly prove the core-shell structure of the nanoparticles as well as the success of their functionalization with low amounts of trimethylsiloxy groups. By combination of DNP enhanced 1H-29Si and 1H-13C cross-polarization magic-angle-spinning (CP MAS) experiments, differently substituted alkoxysilane moieties, namely methacryloxypropyltriethoxysilane (MPSEt), 3- methacryloxypropyltriisopropoxysilane (MPSIsoprop) and 3-methacryloxypropyltris (methoxyethoxy)silane (MPSMeEt) are investigated, revealing various crosslinking capabilities of the particle shell. This knowledge about efficiency of surface functionalization and cross-linking sites strongly influences the application and properties of the core-shell polymer hybrid particles for instance as materials for photonic crystals, particle film formation and coatings. This is of high importance for the design of tailor-made core-shell particle architectures.
Overhauser Dynamic Nuclear Polarization: A Tool for Building Maps of Hydration Water #DNPNMR #ODNP #Review
Franck, John M. “Overhauser Dynamic Nuclear Polarization: A Tool for Building Maps of Hydration Water.” Biophysical Journal 118, no. 3, Supplement 1 (February 7, 2020): 487a.
Coating the surface of every macromolecule or macromolecular assembly, one finds a hydration layer composed of water molecules that move typically between 3× and 10× slower than water molecules in bulk water. The interaction between the water molecules in the hydration layer and the macromolecules contributes to the structural stability and sometimes the function of, e.g., proteins and lipid bilayers. Overhauser Dynamic Nuclear Polarization (ODNP) is an emerging electron-spin nuclear-spin (EPR-NMR) double-resonance tool that has demonstrated a capability of measuring the translational dynamics of water in the hydration layer. Here we discuss our efforts on two fronts: First, we design a scheme for measuring the thickness of the hydration layer and the effect of confinement on translational dynamics, as measured by ODNP, with controlled, appropriately labeled reverse micelle systems. Second, we describe the development of an a priori technique for converting ODNP measurements into a 3D “map” of hydration layer properties in dynamic room temperature samples that explore an ensemble of structures. This latter effort focuses on transmembrane model systems and utilizes the modern structure-prediction tool Rosetta in a fashion analogous to successful efforts to predict NMR order parameters. Particular focus is given to improving the quality and automation of the ODNP measurement, as well as validating predicted ensemble structures against both continuous wave EPR and NMR Paramagnetic Relaxation Enhancement (PRE) data.
Überrück, Till, Michael Adams, Josef Granwehr, and Bernhard Blümich. “A Compact X-Band ODNP Spectrometer towards Hyperpolarized 1H Spectroscopy.” Journal of Magnetic Resonance, April 2020, 106724.
The demand for compact benchtop NMR systems that can resolve chemical shift differences in the ppm to sub-ppm range is growing. However due to material and size restrictions these magnets are limited in field strength and thus in signal intensity and quality. The implementation of standard hyperpolarization techniques is a next step in an effort to boost the signal. Here we present a compact Overhauser Dynamic Nuclear Polarization (ODNP) setup with a permanent magnet that can resolve 1H chemical shift differences in the ppm range. The assembly of the setup and its components are described in detail, and the functionality of the setup is demonstrated experimentally with ODNP enhanced relaxation measurements yielding a maximal enhancement of -140 for an aqueous 4Hydroxy-TEMPO solution. Additionally, 1H spectroscopic resolution and significant enhancements are demonstrated on acetic acid as a solvent.