May 24, 2019

Improved waveguide coupling for 1.3 mm MAS DNP probes at 263 GHz #DNPNMR

Purea, Armin, Christian Reiter, Alexandros I. Dimitriadis, Emile de Rijk, Fabien Aussenac, Ivan Sergeyev, Melanie Rosay, and Frank Engelke. “Improved Waveguide Coupling for 1.3 Mm MAS DNP Probes at 263 GHz.” Journal of Magnetic Resonance 302 (May 2019): 43–49.


We consider the geometry of a radially irradiated microwave beam in MAS DNP NMR probes and its impact on DNP enhancement. Two related characteristic features are found to be relevant: (i) the focus of the microwave beam on the DNP MAS sample and (ii) the microwave magnetic field magnitude in the sample. We present a waveguide coupler setup that enables us to significantly improve beam focus and field magnitude in 1.3 mm MAS DNP probes at a microwave frequency of 263 GHz, which results in an increase of the DNP enhancement by a factor of 2 compared to previous standard hardware setups. We discuss the implications of improved coupling and its potential to enable cutting-edge applications, such as pulsed high-field DNP and the use of low-power solid-state microwave sources.

May 22, 2019

Laser-driven semiconductor switch for generating nanosecond pulses from a megawatt gyrotron

Picard, Julian F., Samuel C. Schaub, Guy Rosenzweig, Jacob C. Stephens, Michael A. Shapiro, and Richard J. Temkin. “Laser-Driven Semiconductor Switch for Generating Nanosecond Pulses from a Megawatt Gyrotron.” Applied Physics Letters 114, no. 16 (April 22, 2019): 164102. 


A laser-driven semiconductor switch (LDSS) employing silicon (Si) and gallium arsenide (GaAs) wafers has been used to produce nanosecond-scale pulses from a 3 ls, 110 GHz gyrotron at the megawatt power level. Photoconductivity was induced in the wafers using a 532 nm laser, which produced 6 ns, 230 mJ pulses. Irradiation of a single Si wafer by the laser produced 110 GHz RF pulses with a 9 ns width and >70% reflectance. Under the same conditions, a single GaAs wafer yielded 24 ns 110 GHz RF pulses with >78% reflectance. For both semiconductor materials, a higher value of reflectance was observed with increasing 110 GHz beam intensity. Using two active wafers, pulses of variable length down to 3 ns duration were created. The switch was tested at incident 110 GHz RF power levels up to 600 kW. A 1-D model is presented that agrees well with the experimentally observed temporal pulse shapes obtained with a single Si wafer. The LDSS has many potential uses in high power millimeter-wave research, including testing of high-gradient accelerator structures.

May 20, 2019

Natural Abundance, Single-Scan 13C– 13C-Based Structural Elucidations by Dissolution DNP NMR #DNPNMR

Otikovs, Martins, Gregory L. Olsen, E̅riks Kupče, and Lucio Frydman. “Natural Abundance, Single-Scan 13C– 13C-Based Structural Elucidations by Dissolution DNP NMR.” Journal of the American Chemical Society 141, no. 5 (February 6, 2019): 1857–61.


While 13C-based INADEQUATE experiments offer an attractive alternative for establishing molecular structures, they suffer from low sensitivities arising from the scarcity of spin pairs present at natural abundance. Herein we demonstrate that dissolution dynamic nuclear polarization (dDNP) provides sufficient sensitivity to acquire 1D 13C INADEQUATE spectra in a single scan and at natural abundance. Moreover, if steps are adopted to endow sub-Hertz precision to these measurements, they allow one to measure carbon-carbon J couplings over both one and multiple bonds for each chemical site. As these JCCcouplings are usually sufficiently distinct to enable univocal pairing of the nuclei involved, essentially the same information as in 2D INADEQUATE can be obtained. The feasibility of the method is demonstrated for a range of compounds, including natural products such as α-pinene, menthol and limonene. Features and extensions of this approach are briefly discussed.

May 13, 2019

Compact, low-cost NMR spectrometer and probe for dissolution DNP

Albannay, Mohammed M., Joachim M. O. Vinther, Jan Raagaard Petersen, Vitaliy Zhurbenko, and Jan Henrik Ardenkjaer-Larsen. “Compact, Low-Cost NMR Spectrometer and Probe for Dissolution DNP.” Journal of Magnetic Resonance, April 25, 2019. 


The desire for higher magnetic resonance sensitivity has led to the development of multiple home-built and commercial dissolution dynamic nuclear polarization polarizers. The emergence of polarizers capable of variable magnetic field strengths desires a versatile standalone spectrometer and NMR circuit to fulfill detection needs at different frequencies. We present a benchtop NMR spectrometer with duplexer capable of serving high-field solid and liquid state NMR applications up to 450 MHz. A detailed view of the employed probe is discussed. Tuning and matching schemes are investigated yielding and experimentally verifying closed-form equations to estimate nutation frequency for a remotely tuned and matched sample coil.

May 11, 2019

Postdoc position in Hyperpolarized 13C MR

Postdoctoral Research Fellowship Position in Hyperpolarized 13C Metabolic Imaging

The University of Maryland School of Medicine has expanded its molecular imaging and interventional research capabilities by establishing the Center for Metabolic Imaging and Therapeutics. The center houses a GE SPINLabTM dynamic nuclear polarizer suitable for preclinical and clinical applications, a GE 3T 750w MR scanner, and a Bruker BioSpec 3T Preclinical Benchtop MR scanner. The GE MR scanner is also integrated with two Insightec 1024-element high-intensity focused ultrasound (HIFU) systems for image-guided interventions. Our goal is to facilitate both basic science and clinical research by exploring novel molecular imaging agent-based technologies for screening, early disease detection and treatment response, and real-time image-guided interventions.

A postdoctoral research fellowship position is available in the Metabolic Imaging Program led by Dr. Dirk Mayer. Specific areas of research include optimized acquisition and reconstruction techniques, kinetic modeling for quantitative analysis, and new probe development. These methods will be applied to animal models (e.g., traumatic brain injury, cancer, liver disease) with translation to patients scheduled for summer 2019. This is an exciting opportunity to work at a site that will do translational/clinical hyperpolarized 13C MRI/MRS.

The candidate should have a Ph.D. (or equivalent degree) in engineering, physics, physical chemistry, or similar fields. The ideal candidate has a strong background in NMR physics with particular emphasis on in vivo imaging and/or spectroscopy, data acquisition and signal/image processing/analysis. Experience in pulse sequence programming (ideally on GE and/or Bruker scanners), knowledge of computer languages, such as C++, Matlab and IDL, and experience in performing small animal and/or human subject imaging is a plus. Qualified applicants should also have a track record of peer-reviewed publications.

Interested individuals should send a letter detailing their research interests, an updated CV and contact information for at least two references to Dirk Mayer (dmayer@som.umaryland.edu, also attending the ISMRM Annual Meeting in Montreal).
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2nd announcement PhD position : "nonlinearities in a controlled DNP-maser" at ENS-Paris, France



A PhD position is available in the NMR group of the Laboratoire des biomolécule, located in the chemistry department of the Ecole Normale Supérieure in Paris, France.

Dynamic nuclear polarisation (DNP) techniques provide unprecedented NMR signal enhancement (by several orders of magnitude) and has made possible experiments that were until recently impossible to achieve by conventional methods. In conditions of very high polarisation, the interaction between the large sample magnetisation with the detection circuit leads to nonlinear behaviour (« radiation damping », maser effect, dipolar field effects).

Very unusual NMR signals have been observed in the solid state at liquid helium temperatures (~1.2 K), that exhibit typical multiple maser effects at short times (< ~100 ms) on the one hand, and persistence for tens of seconds on the other hand, (when solid-state NMR signals are typically expected to last no more than ~500 microsecond).

These signals reflect the combination between complex processes of different nature, involving nonlinearities of the magnetization dynamics and DNP.

The PhD student will in particular:

- contribute to the construction and the implementation of the maser control unit on both polarizers (6.7 T and 9.4 T) in use in the lab;

- perform controlled maser experiments in various experimental conditions in order to access the details of the DNP process;

- contribute to the analysis of the data using various models, through simulations or theoretical calculations;

- contribute to the application of the developed instrumentation to optimize hyperpolarization DNP sequences and their integration in dissolution-DNP experiments.

Applicants should preferably have a physics or chemical physics background (significant knowledge in quantum mechanics will be valued), with a strong interest for both fundamental and applied aspects of magnetic resonance.

The NMR team of the Laboratoire des biomolécules (located in part in the chemistry department at ENS-Paris) is strongly methodology-oriented, in various aspects of NMR. The group is equipped with a 800 MHz spectrometer (liqui/solid/micro-imaging), a 600 MHz spectrometer (liquid/high-resolution relaxometry and two-field NMR), a 400 MHz spectrometer (liquid /solid) and two polarizers for dissolution-DNP (6.7 T and 9.4 T)

The position is for 36 months, and the net monthly salary will be about 1400 €.To apply, please send a CV, a cover letter, and the names of two potential referees who could be contacted to provide a supporting letter, to Daniel Abergel (daniel.abergel@ens.fr)

A publication list of the team is available on the website http://www.paris-en-resonance.fr/
-- Daniel Abergel, MD, PhD Laboratoire des Biomolécules UMR7203 Département de Chimie Ecole Normale Supérieure 24, rue Lhomond, 75005 Paris Tel. : +33 1 44 32 32 65 email : daniel.abergel@ens.fr

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May 10, 2019

Stability of nitroxide biradical TOTAPOL in biological samples

McCoy, Kelsey M., Rivkah Rogawski, Olivia Stovicek, and Ann E. McDermott. “Stability of Nitroxide Biradical TOTAPOL in Biological Samples.” Journal of Magnetic Resonance 303 (June 1, 2019): 115–20.


We characterize chemical reduction of a nitroxide biradical, TOTAPOL, used in dynamic nuclear polarization (DNP) experiments, specifically probing the stability in whole-cell pellets and lysates, and present a few strategies to stabilize the biradicals for DNP studies. DNP solid-state NMR experiments use paramagnetic species such as nitroxide biradicals to dramatically increase NMR signals. Although there is considerable excitement about using nitroxide-based DNP for detecting the NMR spectra of proteins in whole cells, nitroxide radicals are reduced in minutes in bacterial cell pellets, which we confirm and quantify here. We show that addition of the covalent cysteine blocker N-ethylmaleimide to whole cells significantly slows the rate of reduction, suggesting that cysteine thiol radicals are important to in vivo radical reduction. The use of cell lysates rather than whole cells also slows TOTAPOL reduction, which suggests a possible role for the periplasm and oxidative phosphorylation metabolites in radical degradation. Reduced TOTAPOL in lysates can also be efficiently reoxidized with potassium ferricyanide. These results point to a practical and robust set of strategies for DNP of cellular preparations.