Jan 30, 2019

Time domain measurement of electron spin relaxation at high fields and dynamic nuclear polarization at sub-millimeter wavelengths #DNPNMR

Dubroca, Thierry, Johannes McKay, Xiaoling Wang, and Johan van Tol. “Time Domain Measurement of Electron Spin Relaxation at High Fields and Dynamic Nuclear Polarization at Sub-Millimeter Wavelengths.” In 2017 IEEE MTT-S International Microwave Symposium (IMS), 1400–1403. Honololu, HI, USA: IEEE, 2017.


We describe a 395 GHz pulsed electron paramagnetic resonance (EPR) setup, and initial results of relaxation measurements and cw EPR at these frequencies in samples used for liquidand solid-state nuclear magnetic resonance enhanced by dynamic nuclear polarization (DNP). Depending on the amount of spin –orbit coupling, the spin lattice relaxation becomes significantly faster at higher fields and frequencies, which has consequences for some DNP applications at high fields and frequencies. We will discuss the requirements for (sub)millimeter-wave sources and components for DNP and pulsed EPR at even higher frequencies and fields, as even higher magnetic fields will become available in the near future.

Jan 28, 2019

Bridge12 is hiring

Bridge12 is hiring. We currently have an opening for a Hardware Engineer and a Microwave Scientist. Check out our website for more information:


Hardware Engineer
As a Hardware Engineer at Bridge12, you will work on multidisciplinary projects that involve the development of control systems for microwave and terahertz generators, particle accelerators and other scientific instrumentation involving real-time and embedded software, firmware and hardware.

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Scientist – Microwave Systems
As a scientist at Bridge12, you will work on multidisciplinary projects that involve all aspects of the design and development of microwave/terahertz sources and particle. You will also take leadership in conceiving new products based on innovative techniques for generating high THz power in compact systems for scientific and industrial applications and discover new applications for high-power terahertz sources.

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Tunable 13C/1H dual channel matching circuit for dynamic nuclear polarization system with cross-polarization #DNPNMR

Rybalko, Oleksandr, Sean Bowen, Vitaliy Zhurbenko, and Jan Henrik Ardenkjar-Larsen. “Tunable 13C/1H Dual Channel Matching Circuit for Dynamic Nuclear Polarization System with Cross-Polarization.” In 2016 46th European Microwave Conference (EuMC), 1227–30. London, United Kingdom: IEEE, 2016.


In this paper we report initial results of design and practical implementation of tuning and matching circuit to estimate a performance of Dynamic Nuclear Polarization (DNP) at a magnetic field of 6.7 T. It is shown that developed circuit for signal observation is compact, easy to make and provides low return loss (typically better than - 45 dB) at a tuning range ±3 MHz for both resonant frequencies. In addition, transmission parameters measured between 13C and 1H channels are less than - 17 dB and - 50 dB for 71.8 MHz and 285.5 MHz, respectively showing a good isolation between the two channels. Measurement results with a tuning and matching circuit prototype are presented including obtained spectra (13C and 1H) and estimation of the signal-to-noise ratio.

Jan 25, 2019

Unlocking a diazirine long-lived nuclear singlet state via photochemistry: NMR detection and lifetime of an unstabilized diazo-compound

Procacci, Barbara, Soumya S Roy, Philip Norcott, Norman Turner, and Simon B Duckett. “Unlocking a Diazirine Long-Lived Nuclear Singlet State via Photochemistry: NMR Detection and Lifetime of an Unstabilized Diazo-Compound.” Journal of the American Chemical Society, 2018, 19.


Diazirines are important for photoaffinity labeling, and their photoisomerization is relatively well-known. This work shows how hyperpolarized NMR spectroscopy can be used to characterize an unstable diazo-compound formed via photoisomerization of a 15N2-labeled silyl-ether-substituted diazirine. This diazirine is prepared in a nuclear spin singlet state via catalytic transfer of spin order from para-hydrogen. The active hyperpolarization catalyst is characterized to provide insight into the mechanism. The photochemical isomerization of the diazirine into the diazo-analogue allows the NMR invisible nuclear singlet state of the parent compound to be probed. The identity of the diazo-species is confirmed by trapping with N-phenyl maleimide via a cycloaddition reaction to afford bicyclic pyrazolines that also show singlet state character. The presence of singlet states in the diazirine and the diazo-compound is validated by comparison of experimental nutation behavior with theoretical simulation. The magnetic state lifetime of the diazo-compound is determined as 12 ± 1 s in CD3OD solution at room temperature, whereas its chemical lifetime is measured as 100 ± 5 s by related hyperpolarized NMR studies. Indirect evidence for the generation of the photoproduct para-N2 is presented.

Jan 23, 2019

Chemical Exchange Reaction Effect on Polarization Transfer Efficiency in SLIC-SABRE

Pravdivtsev, Andrey N, Ivan Vladimirovich Skovpin, Alexandra I Svyatova, Nikita V Chukanov, Larisa M Kovtunova, Valerii I Bukhtiyarov, Eduard Y Chekmenev, Kirill V Kovtunov, Igor V Koptyug, and Jan-Bernd Hovener. “Chemical Exchange Reaction Effect on Polarization Transfer Efficiency in SLIC-SABRE.” The Journal of Physical Chemistry, 2018, 9107–9114. 


Signal Amplification By Reversible Exchange (SABRE) is a new and rapidly developing hyperpolarization technique. The recent discovery of Spin-Lock Induced Crossing SABRE (SLIC-SABRE) showed that high field hyperpolarization transfer techniques developed so far were optimized for singlet spin order that does not coincide with the experimentally produced spin state. Here, we investigated the SLIC-SABRE approach and the most advanced quantitative theoretical SABRE model to date. Our goal is to achieve the highest possible polarization with SLIC-SABRE at high field using the standard SABRE system, IrIMes catalyst with pyridine. We demonstrated the accuracy of the SABRE model describing the effects of various physical parameters such as the amplitude and frequency of the radio frequency field, and the effects of chemical parameters such as the exchange rate constants. By fitting the model to the experimental data, the effective life time of the SABRE complex was estimated, as well as the entropy and enthalpy of the complex-dissociation reaction. We show, for the first time, that this SLIC-SABRE model can be useful for the evaluation of the chemical exchange parameters that are very important for the production of highly polarized contrast agents via SABRE.

Jan 21, 2019

Temperature-Dependent Nuclear Spin Relaxation Due to Paramagnetic Dopants Below 30 K: Relevance to DNP-Enhanced Magnetic Resonance Imaging #DNPNMR

Chen, Hsueh-Ying, and Robert Tycko. “Temperature-Dependent Nuclear Spin Relaxation Due to Paramagnetic Dopants Below 30 K: Relevance to DNP-Enhanced Magnetic Resonance Imaging.” The Journal of Physical Chemistry B 122, no. 49 (December 13, 2018): 11731–42.


Dynamic nuclear polarization (DNP) can increase nuclear magnetic resonance (NMR) signal strengths by factors of 100 or more at low temperatures. In magnetic resonance imaging (MRI), signal enhancements from DNP potentially lead to enhancements in image resolution. However, the paramagnetic dopants required for DNP also reduce nuclear spin relaxation times, producing signal losses that may cancel the signal enhancements from DNP. Here we investigate the dependence of 1H NMR relaxation times, including T1ρ and T2, under conditions of Lee–Goldburg 1H–1H decoupling and pulsed spin locking, on temperature and dopant concentration in frozen solutions that contain the trinitroxide compound DOTOPA. We find that relaxation times become longer at temperatures below 10 K, where DOTOPA electron spins become strongly polarized at equilibrium in a 9.39 T magnetic field. We show that the dependences of relaxation times on temperature and DOTOPA concentration can be reproduced qualitatively (although not quantitatively) by detailed simulations of magnetic field fluctuations due to flip-flop transitions in a system of dipole-coupled electron spin magnetic moments. These results have implications for ongoing attempts to reach submicron resolution in inductively detected MRI at very low temperatures.

Jan 18, 2019

MAS-DNP Enhancements: Hyperpolarization, Depolarization, and Absolute Sensitivity #DNPNMR

Hediger, Sabine, Daniel Lee, Frédéric Mentink-Vigier, and Gaël De Paëpe. “MAS-DNP Enhancements: Hyperpolarization, Depolarization, and Absolute Sensitivity” 7 (2018): 12. 


Dynamic nuclear polarization at high magnetic fields has made significant progress over the last decades, and this hyperpolarizing technique is currently revolutionizing the impact of solid-state NMR for the study of complex systems in chemistry, material science, and biology. In this article, we emphasize the importance and difficulty in quantifying sensitivity from DNP under magic-angle spinning. To this end, we provide insight into the cross effect, the current main MAS-DNP mechanism. This includes a description of the microwave-induced hyperpolarization phenomenon but also of the reduction of the NMR signal prior to microwave irradiation for samples doped with polarizing agents (bleaching and depolarization effects). We highlight the importance of the nuclear hyperpolarization buildup time in the evaluation of MAS-DNP efficiency. Finally, we discuss other experimental parameters affecting sensitivity in DNP-enhanced spectra and propose a guideline for its proper characterization depending on the type of investigation.

Jan 16, 2019

Determining Cholesterol Binding to Membrane Proteins by Cholesterol 13C Labeling in Yeast and Dynamic Nuclear Polarization NMR #DNPNMR

Elkins, Matthew R, Ivan V Sergeyev, and Mei Hong. “Determining Cholesterol Binding to Membrane Proteins by Cholesterol 13C Labeling in Yeast and Dynamic Nuclear Polarization NMR.” Journal of the American Chemical Society, 2018, 15437–15449. 


We present a general strategy for determining the cholesterol-binding site of eukaryotic membrane proteins in native-like lipid membranes by NMR spectroscopy. The strategy combines yeast biosynthetic 13C enrichment of cholesterol with detection of protein-cholesterol 13C-13C cross peaks in 2D correlation NMR spectra under the dynamic nuclear polarization (DNP) condition. Low-temperature DNP not only allows high-sensitivity detection of weak protein cholesterol cross peaks in 2D spectra but also immobilizes cholesterol and protein to enable intermolecular distance measurements. We demonstrate this approach on the influenza M2 protein, which utilizes cholesterol to conduct membrane scission in the last step of virus budding and release from the host cell plasma membrane. A 13C-13C double-quantum filter was employed to significantly simplify the 2D 13C-13C correlation spectra and facilitate the identification of protein-cholesterol cross peaks. A number of cross peaks between the M2 transmembrane residues’ sidechains and the cholesterol sterol group were detected, which complement recently measured protein contacts to the isooctyl tail of cholesterol to define an extended binding interface. These results provide atomic-level evidence of M2-cholesterol interaction to cause membrane curvature and scission, and the approach is generally applicable to other eukaryotic membrane proteins for understanding the influence of cholesterol on membrane protein function.

Jan 14, 2019

Efficient Hyperpolarization of U- 13C-Glucose Using Narrow-Line UV-Generated Labile Free Radicals #DNPNMR

DNP requires a paramagnetic polarizing agent. This is great for DNP but not so great for the NMR experiment, since the paramagnetic species often causes line broadening due to increase nuclear relaxation. To decrease the unwanted relaxation enhancement some researchers suggested to remove (e.g. filter out) the paramagnetic species after the dissolution step.

The article describes an elegant method, using UV generated radicals for polarization at low temperatures, which recombine once the sample is heated up during the dissolution process, effectively removing the paramagnetic enhanced relaxation process.


Capozzi, Andrea, Saket Patel, Christine Pepke Gunnarsson, Irene Marco-Rius, Arnaud Comment, Magnus Karlsson, Mathilde H. Lerche, Olivier Ouari, and Jan Henrik Ardenkjaer-Larsen. “Efficient Hyperpolarization of U- 13C-Glucose Using Narrow-Line UV-Generated Labile Free Radicals.” Angewandte Chemie, December 20, 2018.


Free radicals generated via irradiation with UV-light of a frozen solution containing a fraction of pyruvic acid (PA), have demonstrated their dissolution Dynamic Nuclear Polarization (dDNP) potential providing up to 30% [1-13C]PA liquid-state polarization. Moreover, their labile nature has proven to pave a way to nuclear polarization storage and transport. Herein, differently from the case of PA, we tackled the issue of providing dDNP UV-radical precursors, trimethylpyruvic acid (TriPA) and its methyl-deuterated form d9-TriPA, not involved in any metabolic pathway. The 13C dDNP performance was evaluated for hyperpolarization of [U-13C6,1,2,3,4,5,6,6-d7]-Dglucose. The generated UV-radical proved to be a versatile and highly efficient polarizing agent providing, after dissolution and transfer (10 s), a 13C liquid-state polarization up to 32%.

Jan 11, 2019

Recent advances in solid-state nuclear magnetic resonance spectroscopy of exotic nuclei #DNPNMR

Leroy, César, and David L. Bryce. “Recent Advances in Solid-State Nuclear Magnetic Resonance Spectroscopy of Exotic Nuclei.” Progress in Nuclear Magnetic Resonance Spectroscopy 109 (December 2018): 160–99.


We present a review of recent advances in solid-state nuclei nuclear magnetic resonance (SSNMR) studies of exotic nuclei. Exotic nuclei may be spin-1/2 or quadrupolar, and typically have low gyromagnetic ratios, low natural abundances, large quadrupole moments (when I > 1/2) , or some combination of these properties, generally resulting in low receptivities and/or prohibitively broad line widths. Some nuclides are little studied for other reasons, also rendering them somewhat exotic. We first discuss some of the recent progress in pulse sequences and hardware development which continues to enable researchers to study new kind of materials as well as previously unfeasible nuclei. This is followed by a survey of applications to a wide range of exotic nuclei (including e.g., 9Be, 25Mg, 33S, 39K, 43Ca, 47/49Ti, 53Cr, 59Co, 61Ni, 67Zn, 73Ge, 75As, 87Sr, 115In, 119Sn, 121/123Sb, 135/137Ba, 185/187Re, 209Bi) , most of them quadrupolar. The scope of the review is the past ten years, i.e., 2007 – 2017

Jan 10, 2019

[NMR] PhD position in NMR crystallography #DNPNMR

A PhD position is available to join the Emsley group at EPFL, Lausanne

We are looking for highly motivated candidates to take up a PhD position developing new methods in NMR spectroscopy to address the challenging problem of atomic-level structure determination in chemistry and materials science. In particular we will be working on dynamic nuclear polarization enhanced NMR methods for materials. Examples of our recent work and the application areas that we work on can be found on our website: http://lrm.epfl.ch/publications/

We are looking for highly motivated candidates with strong scientific background, independence, and who enjoy teamwork. You should hold a relevant qualification in chemistry, physics or related disciplines. Skills in developing experimental multi-dimensional nuclear magnetic resonance are a plus.

Our laboratory at EPFL is part of one the world’s leading chemistry departments, and is located Lausanne on the north shore of Lake Geneva. The laboratory is equipped with unique state of the art NMR spectrometers (including gyrotron DNP accessories at 400 and 900 MHz, a dissolution-DNP machine, and 100 kHz magic angle spinning probes).

Motivated candidates should contact Lyndon Emsley with a CV by email at lyndon.emsley@epfl.ch. Applications will be reviewed from 1st February onwards, until the position is filled. 
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[NMR] parahydrogen-hyperpolarization: PhD student position available at MOIN CC in Kiel, Germany.


Dear colleagues!

the molecular imaging north competence center (MOIN CC) in Kiel, Germany, is looking for a PhD student in the area of parahydrogen hyperpolarization for MRI and NMR.

The PhD position is part of the DFG-funded research training circle 2154 "materials for brain" and more information (will be) available on


Candidates with a physics and engineering background are particularly encouraged to apply. The salary is quite competitive (and the research is excellent!).

Please inquire and apply via email at info@moincc.de.

Merry Christmas!
Jan

__________________________________________________________________
Prof. Dr. Jan-Bernd Hövener

Head, Section Biomedical Imaging and MOIN CC
Head, Emmy Noether Group Molecular and Metabolic MRI - M3

Section Biomedical Imaging, MOIN CC
Am Botanischen Garten 14
D-24118 Kiel

phone: +49 (0) 431 880-5832
fax: +49 (0) 431 880-5852

Office UKSH
Building 522, Room 107
phone: +49 (0) 431 500 16 600

Office Freiburg
Breisacher Straße 60a,
D-79106 Freiburg
phone: +49 (0) 761 270-93910

web:


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[NMR] Postdoc and PhD positions in MAS-DNP / Solid State NMR at the Weizmann Institute of Science #DNPNMR

Several positions are available for postdoctoral researchers and PhD candidates in the group of Michal Leskes at the Department of Materials and Interfaces, Weizmann Institute of science.

The projects, funded by the ERC, include the development of paramagnetic metal ion dopants as endogenous polarization agents for MAS-DNP and application of this approach in the study of energy storage and conversion materials. 

Our lab is equipped with a Bruker 400MHz MAS-DNP spectrometer with LT-DNP MAS probes, as well as a wide range of MAS and static solids NMR probes. In addition to our lab dedicated equipment, extensive NMR and EPR systems are available on campus as part of our research support facilities – these include 400, 500 and 800MHz NMR spectrometers equipped with MAS systems and X and Q band pulse and CW EPR systems. 

Required background for postdoctoral positions: PhD in Chemistry/Physics with extensive hands-on experience in solid state NMR/DNP/EPR. Experience in spin dynamics simulations and/or DFT calculations is an advantage as well experience in materials science.

For PhD applications: BSc and MSc (or equivalent) in Chemistry/Physics/Materials science and engineering are required.

Candidates should have excellent communication skills in English.

Further details on PhD studies and the postdoctoral fellowships can be found here: https://www.weizmann.ac.il/feinberg/about-thefeinberg-graduate-school-fgs

The Weizmann Institute is located in a small, affordable and friendly town, 25 minutes from Tel Aviv and 45 minutes from Jerusalem, and is one of Israel's premier scientific institutions. It is a research centre where the official language is English, and which offers numerous facilities to international visitors, including furnished apartments for postdocs.

For additional information and application please contact Michal Leskes by email at michal.leskes@weizamnn.ac.il.

Applications should include CV, list of publications and contact details of two references.

Further details and relevant publications can be found on our website: http://www.weizmann.ac.il/materials/Leskes/.

----------------------------------------------------------------
Dr. Michal Leskes
Department of Materials and Interfaces
Weizmann Institute of Science
Rehovot 7610001
Israel
Office: +972-8-934-2588
NMR Lab: +972-8-934-2424
Mobile: +972-544224001


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Jan 9, 2019

Oxygen-induced leakage of spin polarization in Overhauser-enhanced magnetic resonance imaging: Application for oximetry in tumors #DNPNMR

Gorodetskii, Artem A., Timothy D. Eubank, Benoit Driesschaert, Martin Poncelet, Emily Ellis, Valery V. Khramtsov, and Andrey A. Bobko. “Oxygen-Induced Leakage of Spin Polarization in Overhauser-Enhanced Magnetic Resonance Imaging: Application for Oximetry in Tumors.” Journal of Magnetic Resonance 297 (December 2018): 42–50.


Overhauser-enhanced Magnetic Resonance Imaging (OMRI) is a double resonance technique applied for oxygen imaging in aqueous samples and biological tissues. In this report, we present an improved OMRI approach of oxygen measurement using the single line ‘‘Finland” trityl spin probe. Compared to a traditional approach, we introduced an additional mechanism of leakage of spin polarization due to an interaction of a spin system with oxygen. The experimental comparison of the new approach with an oxygendependent leakage factor to a traditional approach performed in phantom samples in vitro, and mouse tumor model in vivo, shows improved accuracy of determination of oxygen and contrast agent concentrations.

Jan 7, 2019

Influence of 13C Isotopic Labeling Location on Dynamic Nuclear Polarization of Acetate #DNPNMR

Niedbalski, Peter, Christopher Parish, Andhika Kiswandhi, Zoltan Kovacs, and Lloyd Lumata. “Influence of 13C Isotopic Labeling Location on Dynamic Nuclear Polarization of Acetate.” The Journal of Physical Chemistry A 121, no. 17 (May 4, 2017): 3227–33.


Dynamic nuclear polarization (DNP) via the dissolution method has alleviated the insensitivity problem in liquid-state nuclear magnetic resonance (NMR) spectroscopy by amplifying the signals by several thousand-fold. This NMR signal amplification process emanates from the microwavemediated transfer of high electron spin alignment to the nuclear spins at high magnetic field and cryogenic temperature. Since the interplay between the electrons and nuclei is crucial, the chemical composition of a DNP sample such as the type of free radical used, glassing solvents, or the nature of the target nuclei can significantly affect the NMR signal enhancement levels that can be attained with DNP. Herein, we have investigated the influence of 13C isotopic labeling location on the DNP of a model 13C compound, sodium acetate, at 3.35 T and 1.4 K using the narrow electron spin resonance (ESR) line width free radical trityl OX063. Our results show that the carboxyl 13C spins yielded about twice the polarization produced in methyl 13C spins. Deuteration of the methyl 13C group, while proven beneficial in the liquid-state, did not produce an improvement in the 13C polarization level at cryogenic conditions. In fact, a slight reduction of the solid-state 13C polarization was observed when 2H spins are present in the methyl group. Furthermore, our data reveal that there is a close correlation between the solid-state 13C T1 relaxation times of these samples and the relative 13C polarization levels. The overall results suggest the achievable solid-state polarization of 13C acetate is directly affected by the location of the 13C isotopic labeling via the possible interplay of nuclear relaxation leakage factor and cross-talks between nuclear Zeeman reservoirs in DNP.

Jan 2, 2019

Dynamic Nuclear Polarization of Metal–Organic Frameworks Using Photoexcited Triplet Electrons #DNPNMR

Fujiwara, Saiya, Masanori Hosoyamada, Kenichiro Tateishi, Tomohiro Uesaka, Keiko Ideta, Nobuo Kimizuka, and Nobuhiro Yanai. “Dynamic Nuclear Polarization of Metal–Organic Frameworks Using Photoexcited Triplet Electrons.” Journal of the American Chemical Society 140, no. 46 (November 21, 2018): 15606–10.


While dynamic nuclear polarization based on photoexcited triplet electrons (triplet-DNP) has the potential to hyperpolarize nuclear spins of target substrates in the low magnetic field at room temperature, there has been no triplet-DNP system offering structural rigidity and substrate accessibility. Here, we report the first example of triplet-DNP of nanoporous metal−organic frameworks. Accommodation of a carboxylate-modified pentacene derivative in a partially deuterated ZIF-8 (DZIF-8) results in a clear 1H NMR signal enhancement over thermal equilibrium.