Monday, November 12, 2018

NMR Spectroscopy Unchained: Attaining the Highest Signal Enhancements in Dissolution Dynamic Nuclear Polarization #DNPNMR

Niedbalski, Peter, Andhika Kiswandhi, Christopher Parish, Qing Wang, Fatemeh Khashami, and Lloyd Lumata. “NMR Spectroscopy Unchained: Attaining the Highest Signal Enhancements in Dissolution Dynamic Nuclear Polarization.” The Journal of Physical Chemistry Letters 9, no. 18 (September 20, 2018): 5481–89.


Dynamic nuclear polarization (DNP) via the dissolution method is one of the most successful methods for alleviating the inherently low Boltzmann-dictated sensitivity in nuclear magnetic resonance (NMR) spectroscopy. This emerging technology has already begun to positively impact chemical and metabolic research by providing the much-needed enhancement of the liquid-state NMR signals of insensitive nuclei such as 13C by several thousand-fold. In this Perspective, we present our viewpoints regarding the key elements needed to maximize the NMR signal enhancements in dissolution DNP, from the very core of the DNP process at cryogenic temperatures, DNP instrumental conditions, and chemical tuning in sample preparation to current developments in minimizing hyperpolarization losses during the dissolution transfer process. The optimization steps discussed herein could potentially provide important experimental and theoretical considerations in harnessing the best possible sensitivity gains in NMR spectroscopy as afforded by optimized dissolution DNP technology.

Friday, November 9, 2018

Computationally Assisted Design of Polarizing Agents for Dynamic Nuclear Polarization Enhanced NMR: The AsymPol Family #DNPNMR

Mentink-Vigier, Frédéric, Ildefonso Marin-Montesinos, Anil P. Jagtap, Thomas Halbritter, Johan van Tol, Sabine Hediger, Daniel Lee, Snorri Th. Sigurdsson, and Gaël De Paëpe. “Computationally Assisted Design of Polarizing Agents for Dynamic Nuclear Polarization Enhanced NMR: The AsymPol Family.” Journal of the American Chemical Society 140, no. 35 (September 5, 2018): 11013–19.


We introduce a new family of highly efficient polarizing agents for dynamic nuclear polarization (DNP)-enhanced nuclear magnetic resonance (NMR) applications, composed of asymmetric bis-nitroxides, in which a piperidine-based radical and a pyrrolinoxyl or a proxyl radical are linked together. The design of the AsymPol family was guided by the use of advanced simulations that allow computation of the impact of the radical structure on DNP efficiency. These simulations suggested the use of a relatively short linker with the intention to generate a sizable intramolecular electron dipolar coupling/J-exchange interaction, while avoiding parallel nitroxide orientations. The characteristics of AsymPol were further tuned, for instance with the addition of a conjugated carbon−carbon double bond in the 5-membered ring to improve the rigidity and provide a favorable relative orientation, the replacement of methyls by spirocyclohexanolyl groups to slow the electron spin relaxation, and the introduction of phosphate groups to yield highly water-soluble dopants. An in-depth experimental and theoretical study for two members of the family, AsymPol and AsymPolPOK, is presented here. We report substantial sensitivity gains at both 9.4 and 18.8 T. The robust efficiency of this new family is further demonstrated through high-resolution surface characterization of an important industrial catalyst using fast sample spinning at 18.8 T. This work highlights a new direction for polarizing agent design and the critical importance of computations in this process.

Wednesday, November 7, 2018

Photogenerated Radical in Phenylglyoxylic Acid for in Vivo Hyperpolarized 13C MR with Photosensitive Metabolic Substrates #DNPNMR

Marco-Rius, Irene, Tian Cheng, Adam P. Gaunt, Saket Patel, Felix Kreis, Andrea Capozzi, Alan J. Wright, Kevin M. Brindle, Olivier Ouari, and Arnaud Comment. “Photogenerated Radical in Phenylglyoxylic Acid for in Vivo Hyperpolarized 13 C MR with Photosensitive Metabolic Substrates.” Journal of the American Chemical Society 140, no. 43 (October 31, 2018): 14455–63.


Whether for 13C magnetic resonance studies in chemistry, biochemistry or biomedicine, hyperpolarization methods based on dynamic nuclear polarization (DNP) have become ubiquitous. DNP requires a source of unpaired electrons, which are commonly added to the sample to be hyperpolarized in the form of stable free radicals. Once polarized, the presence of these radicals is unwanted. These radicals can be replaced by nonpersistent radicals created by photo-irradiation of pyruvic acid (PA), which are annihilated upon dissolution or thermalization in the solid state. However, since PA is readily metabolized by most cells, its presence may be undesirable for some metabolic studies. In addition, some 13C substrates are photo-sensitive and, therefore, may degrade during photo-generation of PA radical, which requires ultraviolet (UV) light. We show here that photoirradiation of phenylglyoxylic acid (PhGA) using visible light produces a non-persistent radical that, in principle, can be used to hyperpolarize any molecule. We compare radical yields in samples containing PA and PhGA upon photo-irradiation with broadband and narrowband UV-visible light sources. To demonstrate the suitability of PhGA as a radical precursor for DNP, we polarized the gluconeogenic probe 13C-dihydroxyacetone, which is UV-sensitive, using a commercial 3.35 T DNP polarizer and then injected this into a mouse and followed its metabolism in vivo.

Monday, November 5, 2018

Adiabatic-NOVEL for Nano-Scale Magnetic Resonance Imaging #DNPNMR

Annabestani, Razieh, Maryam Mirkamali, and Raffi Budakian. “Adiabatic-NOVEL for Nano-Scale Magnetic Resonance Imaging.” ArXiv:1712.09128 [Quant-Ph], December 25, 2017.


We propose a highly efficient dynamic nuclear polarization technique that is robust against field in-homogeneity. This technique is designed to enhance the detection sensitivity in nano-MRI, where large Rabi field gradients are required. The proposed technique consists of an adiabatic half passage pulse followed by an adiabatic linear sweep of the electron Rabi frequency and can be considered as an adiabatic version of nuclear orientation via electron spin locking (adiabatic-NOVEL). We analyze the spin dynamics of an electron-nuclear system that is under microwave irradiation at high static magnetic field and at cryogenic temperature. The result shows that an amplitude modulation of the microwave field makes adiabatic-NOVEL highly efficient and robust against both the static and microwave field in-homogeneity.

Friday, November 2, 2018

Determination of binding affinities using hyperpolarized NMR with simultaneous 4-channel detection

Kim, Yaewon, Mengxiao Liu, and Christian Hilty. “Determination of Binding Affinities Using Hyperpolarized NMR with Simultaneous 4-Channel Detection.” Journal of Magnetic Resonance 295 (October 2018): 80–86.


Dissolution dynamic nuclear polarization (D-DNP) is a powerful technique to improve NMR sensitivity by a factor of thousands. Combining D-DNP with NMR-based screening enables to mitigate solubility or availability problems of ligands and target proteins in drug discovery as it can lower the concentration requirements into the sub-micromolar range. One of the challenges that D-DNP assisted NMR screening methods face for broad application, however, is a reduced throughput due to additional procedures and time required to create hyperpolarization. These requirements result in a delay of several tens of minutes in-between each NMR measurement. To solve this problem, we have developed a simultaneous 4-channel detection method for hyperpolarized 19F NMR, which can increase throughput four-fold utilizing a purpose-built multiplexed NMR spectrometer and probe. With this system, the concentration-dependent binding interactions were observed for benzamidine and benzylamine with the serine protease trypsin. A T2 relaxation measurement of a hyperpolarized reporter ligand (TFBC; CF3C6H4CNHNH2), which competes for the same binding site on the trypsin with the other ligands, was used. The hyperpolarized TFBC was mixed with trypsin and the ligand of interest, and injected into four flow cells inside the NMR probe. Across the set of four channels, a concentration gradient was created. From the simultaneously acquired relaxation datasets, it was possible to determine the dissociation constant (KD) of benzamidine or benzylamine without the requirement for individually optimizing experimental conditions for different affinities. A simulation showed that this 4-channel detection method applied to D-DNP NMR extends the screenable KD range to up to three orders of magnitude in a single experiment.

Wednesday, October 31, 2018

Monitoring of hydrogenation by benchtop NMR with parahydrogen-induced polarization

Jeong, Keunhong, Sein Min, Heelim Chae, and Sung Keon Namgoong. “Monitoring of Hydrogenation by Benchtop NMR with Parahydrogen-Induced Polarization.” Magnetic Resonance in Chemistry, August 29, 2018.


Reaction monitoring using nuclear magnetic resonance (NMR) spectroscopy is a powerful tool that provides detailed information on the characteristics and mechanism of the reaction. Although highfield NMR provides more accurate and abundant data, which can be explained in terms of Boltzmann factors, benchtop NMR is commonly used because of its low cost and simple maintenance. Therefore, hyperpolarization of the sample in benchtop NMR is a suitable protocol for real-time reaction monitoring. Herein, the principle-based experimental setup, integrating the reaction monitoring system in a 60-MHz benchtop NMR instrument with a parahydrogen-induced polarization (PHIP) system, is used. Enhanced signals by the ALTADENA mechanism were obtained after PHIP on styrene, and reasonable kinetic data were collected, supporting the known reactivity of Wilkinson’s catalyst. These results should provide a foundation for future applications of NMR-based reaction monitoring systems utilizing hyperpolarization.

Monday, October 29, 2018

A portable ventilator with integrated physiologic monitoring for hyperpolarized 129Xe MRI in rodents

Virgincar, Rohan S., Jerry Dahlke, Scott H. Robertson, Nathann Morand, Yi Qi, Simone Degan, Bastiaan Driehuys, and John C. Nouls. “A Portable Ventilator with Integrated Physiologic Monitoring for Hyperpolarized 129Xe MRI in Rodents.” Journal of Magnetic Resonance 295 (October 2018): 63–71.


Hyperpolarized (HP) 129Xe MRI is emerging as a powerful, non-invasive method to image lung function and is beginning to find clinical application across a range of conditions. As clinical implementation progresses, it becomes important to translate back to well-defined animal models, where novel disease signatures can be characterized longitudinally and validated against histology. To date, preclinical 129Xe MRI has been limited to only a few sites worldwide with 2D imaging that is not generally sufficient to fully capture the heterogeneity of lung disease. To address these limitations and facilitate broader dissemination, we report on a compact and portable HP gas ventilator that integrates all the gas-delivery and physiologic monitoring capabilities required for high-resolution 3D hyperpolarized 129Xe imaging. This ventilator is MR- and HP-gas compatible, driven by inexpensive microcontrollers and open source code, and allows for precise control of the tidal volume and breathing cycle in perorally intubated mice and rats. We use the system to demonstrate data acquisition over multiple breath-holds, during which lung motion is suspended to enable high-resolution 3D imaging of gas-phase and dissolved-phase 129Xe in the lungs. We demonstrate the portability and versatility of the ventilator by imaging a mouse model of lung cancer longitudinally at 2-Tesla, and a healthy rat at 7 T. We also report the detection of subtle spectroscopic fluctuations in phase with the heart rate, superimposed onto larger variations stemming from the respiratory cycle. This ventilator was developed to facilitate duplication and gain broad adoption to accelerate preclinical 129Xe MRI research.

Friday, October 26, 2018

Sensitivity-Enhanced 207 Pb Solid-State NMR Spectroscopy for the Rapid, Non-Destructive Characterization of Organolead Halide Perovskites #DNPNMR

Hanrahan, Michael P., Long Men, Bryan A. Rosales, Javier Vela, and Aaron J. Rossini. “Sensitivity-Enhanced 207 Pb Solid-State NMR Spectroscopy for the Rapid, Non-Destructive Characterization of Organolead Halide Perovskites.” Chemistry of Materials, October 4, 2018. 


Organolead halide and mixed halide perovskites (CH3NH3PbX3, CH3NH3PbX3–nYn, X and Y = Cl–, Br– or I–), are promising materials for photovoltaics and optoelectronic devices. 207Pb solid-state NMR spectroscopy has previously been applied to characterize phase segregation and halide ion speciation in mixed halide perovskites. However, NMR spectroscopy is an insensitive technique that often requires large sample volumes and long signal averaging periods. This is especially true for mixed halide perovskites, which give rise to extremely broad 207Pb solid-state NMR spectra. Here, we quantitatively compare the sensitivity of the various solid-state NMR techniques on pure and mixed halide organolead perovskites and demonstrate that both fast MAS and DNP can provide substantial gains in NMR sensitivity for these materials. With fast MAS and proton detection, high signal-to-noise ratio two-dimensional (2D) 207Pb-1H heteronuclear correlation (HETCOR) NMR spectra can be acquired in less than half an hour from only ca. 5 μL of perovskite material. Modest relayed DNP enhancements on the order of 1 to 20 were obtained for perovskites. The cryogenic temperatures (110 K) used for DNP experiments also provide a significant boost in sensitivity. Consequently, it was possible to obtain the 207Pb solid-state NMR spectrum of a 300 nm thick model thin film of CH3NH3PbI3 in 34 hours by performing solid-state NMR experiments with a sample temperature of 110 K. This result demonstrates the possibility of using NMR spectroscopy for characterization of perovskite thin films.

Thursday, October 25, 2018

[NMR] EPFL post-doc postion #DNPNMR


Dear colleagues, 

A post-doc position will be available at the LPMN group of EPFL, starting in the spring of 2019, to work on high field EPR and gyrotron-DNP. 

A job description can be found at https://recruiting.epfl.ch/Vacancies/680/Description/2
For enquires, please write to jean-philippe.ansermet@epfl.ch

Best regards,
Ansermet
==========================
Prof. Jean-Philippe Ansermet
LPMN-ICMP-FSB-station 3
Ecole Polytechnique Fédérale de Lausanne
1015 Lausanne-EPFL
==========================

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Wednesday, October 24, 2018

Efficiency of Water-Soluble Nitroxide Biradicals for Dynamic Nuclear Polarization in Rotating Solids at 9.4 T: bcTol-M and cyolyl-TOTAPOL as New Polarizing Agents #DNPNMR

Geiger, Michel-Andreas, Anil P. Jagtap, Monu Kaushik, Han Sun, Daniel Stöppler, Snorri T. Sigurdsson, Björn Corzilius, and Hartmut Oschkinat. “Efficiency of Water-Soluble Nitroxide Biradicals for Dynamic Nuclear Polarization in Rotating Solids at 9.4 T: BcTol-M and Cyolyl-TOTAPOL as New Polarizing Agents.” Chemistry - A European Journal 24, no. 51 (September 12, 2018): 13485–94.



Nitroxide biradicals are very efficient polarizing agents in magic angle spinning (MAS) cross effect (CE) dynamic nuclear polarization (DNP) nuclear magnetic resonance (NMR). Many recently synthesized, new radicals show superior DNP-efficiency in organic solvents but suffer from insufficient solubility in water or glycerol/water for biological applications. We report DNP efficiencies for two new radicals, the water-soluble bcTol-M and cyolyl-TOTAPOL, and include a comparison with three known biradicals, TOTAPOL, bcTol, and AMUPol. They differ by linker groups, featuring either a 3-aminopropane-1,2-diol or a urea tether, or by the structure of the alkyl substituents that flank the nitroxide groups. For evaluating their performances, we measured both signal enhancements e and DNP-enhanced sensitivity k, and compared the results to electron spin relaxation data recorded at the same magnetic field strength (9.4 T). In our study, differences in DNP efficiency correlate with changes in the nuclear polarization dynamics rather than electron relaxation.
The ratios of their individual e and k differ by up to 20%, which is explained by starkly different nuclear polarization build-up rates. For the radicals compared here empirically, using proline standard solutions, the new radical bcTol-M performs best while being most soluble in water/glycerol mixtures.

Monday, October 22, 2018

Heterogeneity of Network Structures and Water Dynamics in κ-Carrageenan Gels Probed by Nanoparticle Diffusometry #DNPNMR

Kort, Daan W. de, Erich Schuster, Freek J.M. Hoeben, Ryan Barnes, Meike Emondts, Henk M. Janssen, Niklas Lorén, Songi Han, Henk Van As, and John P.M. van Duynhoven. “Heterogeneity of Network Structures and Water Dynamics in κ-Carrageenan Gels Probed by Nanoparticle Diffusometry.” Langmuir 34, no. 37 (September 18, 2018): 11110–20. 


A set of functionalized nanoparticles (PEGylated dendrimers, d = 2.8 - 9 nm) was used to probe the structural heterogeneity in Na+/K+ induced κ-carrageenan gels. The self-diffusion behavior of these nanoparticles as observed by 1H PFG NMR, FRAP and RICS revealed a fast and a slow component, pointing towards microstructural heterogeneity in the gel network. The self-diffusion behavior of the faster nanoparticles could be modelled with obstruction by a coarse network (average mesh size <100 nm), while the slower-diffusing nanoparticles are trapped in a dense network (lower mesh size limit of 4.6 nm). Overhauser DNP-enhanced NMR relaxometry revealed a reduced local solvent water diffusivity near TEMPO-labelled nanoparticles trapped in the dense network, showing that heterogeneity in the physical network is also reflected in heterogeneous self-diffusivity of water. The observed heterogeneity in mesh sizes and in water self-diffusivity is of interest for understanding and modelling of transport through and release of solutes from heterogeneous biopolymer gels.

Friday, October 19, 2018

EPSRC Industrial CASE PhD Studentship “DNP-enhanced Solid-state NMR Studies of Pharmaceuticals” #DNPNMR

EPSRC Industrial CASE PhD Studentship “DNP-enhanced Solid-state NMR Studies of Pharmaceuticals”

Dr Jeremy Titman, School of Chemistry, University of Nottingham
Dr Tran N. Pham, GSK 

Solid-state nuclear magnetic resonance (NMR) is a powerful method for studying the molecular structure and dynamics of a broad range of systems from heterogeneous materials to biological molecules. In some situations solid-state NMR can suffer from low sensitivity, because of the small nuclear spin polarizations involved, so that long acquisition times or large sample volumes are required. However, weak NMR signals can be dramatically enhanced by dynamic nuclear polarization (DNP), which involves transfer of electron spin polarization from radicals implanted in the sample to nearby nuclei. The substantial enhancements (up to 300-fold) obtained with DNP make NMR studies of dilute species feasible for the first time and have already prompted exciting new NMR applications to interfaces, porous materials and microcrystalline substances.

The University of Nottingham has recently established a DNP-enhanced solid-state NMR Facility (unique in the UK) funded by a grant of £2.5 M from EPSRC. In this collaboration with GSK DNP-enhanced solid-state NMR will be used to study pharmaceutical formulations and drug delivery systems. These are challenging systems to study by solid-state NMR because of the often low concentration of the active pharmaceutical ingredient (API). However, the substantial signal enhancements obtained with DNP will allow natural abundance investigations of polymorphs or hydration states of APIs, of formulations involving amorphous APIs and of the interactions at the interfaces between APIs and excipients such as fillers, binders, lubricants and preservatives.

The PhD studentship is available immediately, and is fully funded for 4 years via a stipend covering PhD tuition fees (at the Home/EU rate) and a tax-free living allowance (£14,777 per annum). As part of the project the student will spend up to three months at the GSK Medicines Research Centre in Hertfordshire UK acquiring skills in formulation science and manufacturing samples.

The student will gain expertise in solid-state NMR spectroscopy, especially as applied to pharmaceutical formulations, as well as experience of DNP-enhanced methods. Transferable skills in computer programming, data analysis and scientific communication will also be acquired. In addition, the student will benefit from hands-on experience in industry, while pursuing a research project in an academic environment, and gain knowledge in the business of drug discovery and development.

Applications are invited from outstanding EU/UK students holding or expecting to gain a good undergraduate degree in Chemistry, Physics or a related subject. Prior experience in solid-state NMR is not essential. Note that the UK government has guaranteed EU eligibility for EPSRC funding for PhDs beginning before the end of the 2018-2019 academic year. Apply online at http://www.nottingham.ac.uk/pgstudy/apply/apply-online.aspx by 15th November 2018. For informal enquiries please contact: Jeremy.Titman@nottingham.ac.uk

The solid-state NMR group at Nottingham works on the design of new solid-state NMR experiments and their application to chemistry, energy research, nanotechnology and environmental science. The group has three solid-state NMR spectrometers, operating at 1H Larmor frequencies of 300, 600 and 800 MHz. A 600 MHz Dynamic Nuclear Polarization MAS NMR spectrometer was installed in Nottingham in November 2015. For more information about the solid-state NMR group see: http://www.solidstatenmr.org.uk/ The University of Nottingham is ranked in the top 100 universities in the world (QS World University Rankings).


--------------------------
Dr Jeremy J Titman
Associate Professor and Reader in Magnetic Resonance,
A43, School of Chemistry, University of Nottingham,
University Park, Nottingham, NG7 2RD, UK
Tel: +44 115 951 3560


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Yoder, J. L., P. E. Magnelind, M. A. Espy, and M. T. Janicke. “Exploring the Limits of Overhauser Dynamic Nuclear Polarization (O-DNP) for Portable Magnetic Resonance Detection of Low γ Nuclei.” Applied Magnetic Resonance 49, no. 7 (July 2018): 707–24.


Nuclear magnetic resonance (NMR) spectroscopy in portable, permanent magnet-based spectrometers is primarily limited to nuclei with higher gyromagnetic ratio, γ, such as 1H, 19F, and 31P due to the limited field strength achievable in these systems. Overhauser effect dynamic nuclear polarization (O-DNP), which transfers polarization from an unpaired electron to a nucleus by saturating an electron paramagnetic resonance transition with an oscillating radio frequency magnetic field, B1e, can increase the polarization of low γ nuclei by hundreds or even thousands, enabling detection in a portable system. We have investigated the potential for O-DNP to enhance signals using (4-amino-2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO hereafter) as a source of unpaired electrons in a homebuilt ultra-low field (ULF) O-DNP-NMR spectrometer. We have found, in general, that larger concentrations of TEMPO are required for effective O-DNP with low γ nuclei, which has a number of important effects. Spin exchange effects cause the EPR lines to overlap and ultimately merge at high concentrations of TEMPO, fundamentally increasing the maximum possible enhancement, while the electron–electron dipolar interaction reduces both longitudinal and transverse relaxation times for the electrons, dramatically increasing the required B1e strength. The relationship between TEMPO concentration, B1e magnitude and O-DNP enhancement is quantified, and strategies for achieving these fields are discussed.

Wednesday, October 17, 2018

Structural Elucidation of Amorphous Photocatalytic Polymers from Dynamic Nuclear Polarization Enhanced Solid State NMR #DNPNMR

Brownbill, Nick J., Reiner Sebastian Sprick, Baltasar Bonillo, Shane Pawsey, Fabien Aussenac, Alistair J. Fielding, Andrew I. Cooper, and Frédéric Blanc. “Structural Elucidation of Amorphous Photocatalytic Polymers from Dynamic Nuclear Polarization Enhanced Solid State NMR.” Macromolecules 51, no. 8 (April 24, 2018): 3088–96. 


Dynamic nuclear polarization (DNP) solid-state nuclear magnetic resonance (NMR) offers a recent approach to dramatically enhance NMR signals and has enabled detailed structural information to be obtained in a series of amorphous photocatalytic copolymers of alternating pyrene and benzene monomer units, the structures of which cannot be reliably established by other spectroscopic or analytical techniques. Large 13C cross-polarization (CP) magic angle spinning (MAS) signal enhancements were obtained at high magnetic fields (9.4− 14.1 T) and low temperature (110−120 K), permitting the acquisition of a 13C INADEQUATE spectrum at natural abundance and facilitating complete spectral assignments, including when small amounts of specific monomers are present. The high 13C signal-to-noise ratios obtained are harnessed to record quantitative multiple contact CP NMR data, used to determine the polymers’ composition. This correlates well with the putative pyrene:benzene stoichiometry from the monomer feed ratio, enabling their structures to be understood.

Monday, October 15, 2018

Illuminating the dark metabolome to advance the molecular characterisation of biological systems #DNPNMR

This is a great review showcasing the capabilities of DNP-enhanced NMR spectroscopy for metabolomic studies.



Jones, Oliver A. H. “Illuminating the Dark Metabolome to Advance the Molecular Characterisation of Biological Systems.” Metabolomics 14, no. 8 (August 2018).

https://doi.org/10.1007/s11306-018-1396-y.

Background  The latest version of the Human Metabolome Database (v4.0) lists 114,100 individual entries. Typically, however, metabolomics studies identify only around 100 compounds and many features identified in mass spectra are listed only as ‘unknown compounds’. The lack of ability to detect all metabolites present, and fully identify all metabolites detected (the dark metabolome) means that, despite the great contribution of metabolomics to a range of areas in the last decade, a significant amount of useful information from publically funded studies is being lost or unused each year. This loss of data limits our potential gain in knowledge and understanding of important research areas such as cell biology, environmental pollution, plant science, food chemistry and health and biomedical research. Metabolomics therefore needs to develop new tools and methods for metabolite identification to advance as a field.

Monday, October 8, 2018

Resolving the Core and the Surface of CdSe Quantum Dots and Nanoplatelets Using Dynamic Nuclear Polarization Enhanced PASS–PIETA NMR Spectroscopy #DNPNMR

Piveteau, Laura, Ta-Chung Ong, Brennan J. Walder, Dmitry N. Dirin, Daniele Moscheni, Barbara Schneider, Janine Bär, et al. “Resolving the Core and the Surface of CdSe Quantum Dots and Nanoplatelets Using Dynamic Nuclear Polarization Enhanced PASS–PIETA NMR Spectroscopy.” ACS Central Science 4, no. 9 (September 26, 2018): 1113–25.


Understanding the surface of semiconductor nanocrystals (NCs) prepared using colloidal methods is a longstanding goal of paramount importance for all their potential optoelectronic applications, which remains unsolved largely because of the lack of site-specific physical techniques. Here, we show that multidimensional 113Cd dynamic nuclear polarization (DNP) enhanced NMR spectroscopy allows the resolution of signals originating from different atomic and magnetic surroundings in the NC cores and at the surfaces. This enables the determination of the structural perfection, and differentiation between the surface and core atoms in all major forms of size- and shape-engineered CdSe NCs: irregularly faceted quantum dots (QDs) and atomically flat nanoplatelets, including both dominant polymorphs (zinc-blende and wurtzite) and their epitaxial nanoheterostructures (CdSe/CdS core/shell quantum dots and CdSe/CdS core/crown nanoplatelets), as well as magic-sized CdSe clusters. Assignments of the NMR signals to specific crystal facets of oleate-terminated ZB structured CdSe NCs are proposed. Significantly, we discover far greater atomistic complexity of the surface structure and the species distribution in wurtzite as compared to zinc-blende CdSe QDs, despite an apparently identical optical quality of both QD polymorphs.

Friday, October 5, 2018

Probing the surface of γ-Al2O3 by oxygen-17 dynamic nuclear polarization enhanced solid-state NMR spectroscopy #DNPNMR

Li, Wenzheng, Qiang Wang, Jun Xu, Fabien Aussenac, Guodong Qi, Xingling Zhao, Pan Gao, Chao Wang, and Feng Deng. “Probing the Surface of γ-Al2O3 by Oxygen-17 Dynamic Nuclear Polarization Enhanced Solid-State NMR Spectroscopy.” Physical Chemistry Chemical Physics 20, no. 25 (June 27, 2018): 17218–25.


γ-Al2O3 is an important catalyst and catalyst support of industrial interest. Its acid/base characteristics are correlated to the surface structure, which has always been an issue of concern. In this work, the complex (sub-)surface oxygen species on surface-selectively labelled γ-Al2O3 were probed by 17O dynamic nuclear polarization surface-enhanced NMR spectroscopy (DNP-SENS). Direct 17O MAS and indirect 1H–17O cross-polarization (CP)/MAS DNP experiments enable observation of the (sub-)surface bare oxygen species and hydroxyl groups. In particular, a two-dimensional (2D) 17O 3QMAS DNP spectrum was for the first time achieved for γ-Al2O3, in which two O(Al)4 and one O(Al)3 bare oxygen species were identified. The 17O isotropic chemical shifts (δcs) vary from 56.7 to 81.0 ppm and the quadrupolar coupling constants (CQ) range from 0.6 to 2.5 MHz for the three oxygen species. The coordinatively unsaturated O(Al)3 species is characterized by a higher field chemical shift (56.7 ppm) and the largest CQ value (2.5 MHz) among these oxygen sites. 2D 1H → 17O HETCOR DNP experiments allow us to discriminate three bridging (Aln)-μ2-OH and two terminal (Aln)-μ1-OH hydroxyl groups. The structural features of the bare oxygen species and hydroxyl groups are similar for the γ-Al2O3 samples isotopically labelled by 17O2 gas or H217O. The results presented here show that the combination of surface-selective labelling and DNP-SENS is an effective approach for characterizing oxides with complex surface species.

Wednesday, October 3, 2018

Exploring Applications of Covalent Organic Frameworks: Homogeneous Reticulation of Radicals for Dynamic Nuclear Polarization #DNPNMR

Cao, Wei, Wei David Wang, Hai-Sen Xu, Ivan V. Sergeyev, Jochem Struppe, Xiaoling Wang, Frederic Mentink-Vigier, et al. “Exploring Applications of Covalent Organic Frameworks: Homogeneous Reticulation of Radicals for Dynamic Nuclear Polarization.” Journal of the American Chemical Society 140, no. 22 (June 6, 2018): 6969–77.


Rapid progress has been witnessed in the past decade in the fields of covalent organic frameworks (COFs) and dynamic nuclear polarization (DNP). In this contribution, we bridge these two fields by constructing radical-embedded COFs as promising DNP agents. Via polarization transfer from unpaired electrons to nuclei, DNP realizes significant enhancement of NMR signal intensities. One of the crucial issues in DNP is to screen for suitable radicals to act as efficient polarizing agents, the basic criteria for which are homogeneous distribution and fixed orientation of unpaired electrons. We therefore envisioned that the crystalline and porous structures of COFs, if evenly embedded with radicals, may work as a new “crystalline sponge” for DNP experiments. As a proof of concept, we constructed a series of proxyl-radical-embedded COFs (denoted as PR(x)-COFs) and successfully applied them to achieve substantial DNP enhancement. Benefiting from the bottom-up and multivariate synthetic strategies, proxyl radicals have been covalently reticulated, homogeneously distributed, and rigidly embedded into the crystalline and mesoporous frameworks with adjustable concentration (x%). Excellent performance of PR(x)-COFs has been observed for DNP 1H, 13C, and 15N solid-state NMR enhancements. This contribution not only realizes the direct construction of radical COFs from radical monomers, but also explores the new application of COFs as DNP polarizing agents. Given that many radical COFs can therefore be rationally designed and facilely constructed with well-defined composition, distribution, and pore size, we expect that our effort will pave the way for utilizing radical COFs as standard polarizing agents in DNP NMR experiments.

Monday, October 1, 2018

Bulk Nuclear Hyperpolarization of Inorganic Solids by Relay from the Surface #DNPNMR

Björgvinsdóttir, Snædís, Brennan J. Walder, Arthur C. Pinon, and Lyndon Emsley. “Bulk Nuclear Hyperpolarization of Inorganic Solids by Relay from the Surface.” Journal of the American Chemical Society 140, no. 25 (June 27, 2018): 7946–51.




NMR is a method of choice to determine structural and electronic features in inorganic materials, and has been widely used in the past, but its application is severely limited by its low relative sensitivity. We show how the bulk of proton-free inorganic solids can be hyperpolarized in a general strategy using impregnation dynamic nuclear polarization through homonuclear spin diffusion between low-g nuclei. This is achieved either through direct hyperpolarization or with a pulse-cooling cross-polarization method, transferring hyperpolarization from protons to heteronuclei at particle surfaces. We demonstrate a factor 50 gain in overall sensitivity for the 119Sn spectrum of powdered SnO2, corresponding to an acceleration of a factor >2500 in acquisition times. The method is also shown for 31P spectra of GaP, for 113Cd spectra of CdTe, and 29Si spectra of α-quartz.

Friday, September 28, 2018

Boosting sensitivity and suppressing artifacts via multi-acquisition in direct polarization NMR experiments with small flip-angle pulses

This is not directly related to DNP spectroscopy but an interesting method to increase the sensitivity specifically in solid-state NMR experiments. This method is compatible with DNP and in combination can lead to even larger sensitivity gains than just DNP.


Fu, Riqiang, and Arturo J. Hernández-Maldonado. “Boosting Sensitivity and Suppressing Artifacts via Multi-Acquisition in Direct Polarization NMR Experiments with Small Flip-Angle Pulses.” Journal of Magnetic Resonance 293 (August 1, 2018): 34–40.


A small flip-angle pulse direct polarization is the simplest method commonly used to quantify various compositions in many materials applications. This method sacrifices the sensitivity per scan in exchange for rapid repeating of data acquisition for signal accumulation. In addition, the resulting spectrum often encounters artifacts from background signals from probe components and/or from acoustic rings leading to a distorted baseline, especially in low-γ nuclei and wideline NMR. In this work, a multi-acquisition scheme is proposed to boost the sensitivity per scan and at the same time effectively suppress these artifacts. Here, an adiabatic inversion pulse is first applied in order to bring the magnetization from the +z to −z axis and then a small flip-angle pulse excitation is used before the data acquisition. Right after the first acquisition, the adiabatic inversion pulse is applied again to flip the magnetization back to the +z axis. The second data acquisition takes place after another small flip-angle pulse excitation. The difference between the two consecutive acquisitions cancels out any artifacts, while the wanted signals are accumulated. This acquisition process can be repeated many times before going into next scan. Therefore, by acquiring the signals multiple times in a single scan the sensitivity is improved. A mixture sample of flufenamic acid and 3,5-difluorobenzoic acid and a titanium silicate sample have been used to demonstrate the advantages of this newly proposed method.

Wednesday, September 26, 2018

Continuous wave electron paramagnetic resonance of nitroxide biradicals in fluid solution #DNPNMR

Biradicals are very important polarizing agents used in DNP-enhanced NMR spectroscopy. Specifically in solid-state experiments they often out-perform monoradicals. Understanding the influence of all the different interactions present in a biradical is still ongoing research and only by using liquid and solid state EPR spectroscopy is it possible to characterize, understand and finally optimize polarizing agents for DNP.


Eaton, Sandra S., Lukas B. Woodcock, and Gareth R. Eaton. “Continuous Wave Electron Paramagnetic Resonance of Nitroxide Biradicals in Fluid Solution.” Concepts in Magnetic Resonance Part A, May 25, 2018, e21426.


Nitroxide biradicals have been prepared with electron-electron spin-spin exchange interaction, J, ranging from weak to very strong. EPR spectra of these biradicals in fluid solution depend on the ratio of J to the nitrogen hyperfine coupling, AN, and the rates of interconversion between conformations with different values of J. For relatively rigid biradicals EPR spectra can be simulated as the superposition of AB splitting patterns arising from different combinations of nitrogen nuclear spin states. For more flexible biradicals spectra can be simulated with a Liouville representation of the dynamics that interconvert conformations with different values of J on the EPR timescale. Analysis of spectra, factors that impact J, and examples of applications to chemical and biophysical problems are discussed.

Monday, September 24, 2018

Electronic control of DNA-based nanoswitches and nanodevices #DNPNMR

Ranallo, Simona, Alessia Amodio, Andrea Idili, Alessandro Porchetta, and Francesco Ricci. “Electronic Control of DNA-Based Nanoswitches and Nanodevices.” Chem. Sci. 7, no. 1 (2016): 66–71.


The exchange (J) interaction of organic biradicals is a crucial factor controlling their physiochemical properties and potential applications, and can be modulated by changing the nature of the linker. In the present work, we for the first time demonstrate the effect of chiral configurations of radical parts on the J values of trityl-nitroxide (TN) biradicals. Four diastereoisomers (TNT1, TNT2, TNL1 and TNL2) of TN biradicals were synthesized and purified by conjugation of a racemic (R/S) nitroxide with the racemic (M/P) trityl radical via L-proline. The absolute configurations of these diastereoisomers were assigned by comparing experimental and calculated electronic circular dichroism (ECD) spectra as (M, S, S) for TNT1, (P, S, S) for TNT2, (M, S, R) for TNL1 and (P, S, R) for TNL2. Electron paramagnetic resonance (EPR) results showed that the configuration of the nitroxide part instead of the trityl part is dominant in controlling the exchange interactions and the order of the J values at room temperature is TNT1 (252 G) > TNT2 (127 G) >> TNL2 (33 G) > TNL1 (14 G). Moreover, the J values of TNL1/ TNL2 with the S configuration in the nitroxide part vary with temperature and polarity of solvents due to their flexible linker, whereas the J values of TNT1/ TNT2 are almost insensitive to these two factors due to the rigidity of their linkers. The distinct exchange interactions between TNT1,2 and TNL1,2 in frozen state led to strongly different high-field dynamic nuclear polarization (DNP) enhancements with ε = 7 for TNT1,2 and 40 for TNL1,2 at 800 MHz DNP conditions.

Friday, September 21, 2018

Orientation-independent room temperature optical 13C hyperpolarization in powdered diamond #DNPNMR

Ajoy, Ashok, Kristina Liu, Raffi Nazaryan, Xudong Lv, Pablo R. Zangara, Benjamin Safvati, Guoqing Wang, et al. “Orientation-Independent Room Temperature Optical 13C Hyperpolarization in Powdered Diamond.” Science Advances 4, no. 5 (May 1, 2018):

Dynamic nuclear polarization via contact with electronic spins has emerged as an attractive route to enhance the sensitivity of nuclear magnetic resonance beyond the traditional limits imposed by magnetic field strength and temperature. Among the various alternative implementations, the use of nitrogen vacancy (NV) centers in diamond—a paramagnetic point defect whose spin can be optically polarized at room temperature—has attracted widespread attention, but applications have been hampered by the need to align the NV axis with the external magnetic field. We overcome this hurdle through the combined use of continuous optical illumination and a microwave sweep over a broad frequency range. As a proof of principle, we demonstrate our approach using powdered diamond with which we attain bulk 13C spin polarization in excess of 0.25% under ambient conditions. Remarkably, our technique acts efficiently on diamond crystals of all orientations and polarizes nuclear spins with a sign that depends exclusively on the direction of the microwave sweep. Our work paves the way toward the use of hyperpolarized diamond particles as imaging contrast agents for biosensing and, ultimately, for the hyperpolarization of nuclear spins in arbitrary liquids brought in contact with their surface.

Wednesday, September 19, 2018

Water Dynamics from the Surface to the Interior of a Supramolecular Nanostructure #DNPNMR #ODNP

Ortony, Julia H., Baofu Qiao, Christina J. Newcomb, Timothy J. Keller, Liam C. Palmer, Elad Deiss-Yehiely, Monica Olvera de la Cruz, Songi Han, and Samuel I. Stupp. “Water Dynamics from the Surface to the Interior of a Supramolecular Nanostructure.” Journal of the American Chemical Society 139, no. 26 (July 5, 2017): 8915–21.


Water within and surrounding the structure of a biological system adopts context-specific dynamics that mediate virtually all of the events involved in the inner workings of a cell. These events range from protein folding and molecular recognition to the formation of hierarchical structures. Water dynamics are mediated by the chemistry and geometry of interfaces where water and biomolecules meet. Here we investigate experimentally and computationally the translational dynamics of vicinal water molecules within the volume of a supramolecular peptide nanofiber measuring 6.7 nm in diameter. Using Overhauser dynamic nuclear polarization relaxometry, we show that drastic differences exist in water motion within a distance of about one nanometer from the surface, with rapid diffusion in the hydrophobic interior and immobilized water on the nanofiber surface. These results demonstrate that water associated with materials designed at the nanoscale is not simply a solvent, but rather an integral part of their structure and potential functions.

Monday, September 17, 2018

Baudin, Mathieu, Basile Vuichoud, Aurélien Bornet, Geoffrey Bodenhausen, and Sami Jannin. “A Cryogen-Consumption-Free System for Dynamic Nuclear Polarization at 9.4 T.” Journal of Magnetic Resonance 294 (September 1, 2018): 115–21.


A novel system for dissolution dynamic nuclear polarization based on a cost-effective “cryogen-free” magnet that can generate fields up to 9.4 T with a sample space that can reach temperatures below 1.4 K in a continuous and stable manner. Polarization levels up to P(1H) = 60 ± 5% can be reached with TEMPOL in about 20 min, and P(13C) = 50 ± 5% can be achieved using adiabatic cross polarization.

Friday, September 14, 2018

13C → 1H transfer of light-induced hyperpolarization allows for selective detection of protons in frozen photosynthetic reaction center #DNPNMR

Bielytskyi, Pavlo, Daniel Gräsing, Kaustubh R. Mote, Karthick Babu Sai Sankar Gupta, Shimon Vega, P. K. Madhu, A. Alia, and Jörg Matysik. “13C → 1H Transfer of Light-Induced Hyperpolarization Allows for Selective Detection of Protons in Frozen Photosynthetic Reaction Center.” Journal of Magnetic Resonance 293 (August 1, 2018): 82–91.


In the present study, we exploit the light-induced hyperpolarization occurring on 13C nuclei due to the solid-state photochemically induced dynamic nuclear polarization (photo-CIDNP) effect to boost the NMR signal intensity of selected protons via inverse cross-polarization. Such hyperpolarization transfer is implemented into 1H-detected two-dimensional 13C–1H correlation magic-angle-spinning (MAS) NMR experiment to study protons in frozen photosynthetic reaction centers (RCs). As a first trial, the performance of such an experiment is tested on selectively 13C labeled RCs from the purple bacteria of Rhodobacter sphaeroides. We observed response from the protons belonging to the photochemically active cofactors in their native protein environment. Such an approach is a potential heteronuclear spin-torch experiment which could be complementary to the classical heteronuclear correlation (HETCOR) experiments for mapping proton chemical shifts of photosynthetic cofactors and to understand the role of the proton pool around the electron donors in the electron transfer process occurring during photosynthesis.

Wednesday, September 12, 2018

Generating para-water from para-hydrogen: A Gedankenexperiment #DNPNMR

Ivanov, Konstantin L., and Geoffrey Bodenhausen. “Generating Para-Water from Para-Hydrogen: A Gedankenexperiment.” Journal of Magnetic Resonance 292 (July 1, 2018): 48–52.


A novel conceptual approach is described that is based on the transfer of hyperpolarization from para-hydrogen in view of generating a population imbalance between the two spin isomers of H2O. The approach is analogous to SABRE (Signal Amplification By Reversible Exchange) and makes use of the transfer of spin order from para-hydrogen to H2O in a hypothetical organometallic complex. The spin order transfer is expected to be most efficient at avoided level crossings. The highest achievable enrichment levels of para- and ortho-water are discussed.

Monday, September 10, 2018

Continuous hyperpolarization with parahydrogen in a membrane reactor #DNPNMR

Lehmkuhl, Sören, Martin Wiese, Lukas Schubert, Mathias Held, Markus Küppers, Matthias Wessling, and Bernhard Blümich. “Continuous Hyperpolarization with Parahydrogen in a Membrane Reactor.” Journal of Magnetic Resonance 291 (June 2018): 8–13. 


Hyperpolarization methods entail a high potential to boost the sensitivity of NMR. Even though the ‘‘Signal Amplification by Reversible Exchange” (SABRE) approach uses para-enriched hydrogen, p-H2, to repeatedly achieve high polarization levels on target molecules without altering their chemical structure, such studies are often limited to batch experiments in NMR tubes. Alternatively, this work introduces a continuous flow setup including a membrane reactor for the p-H2, supply and consecutive detection in a 1 T NMR spectrometer. Two SABRE substrates pyridine and nicotinamide were hyperpolarized, and more than 1000-fold signal enhancement was found. Our strategy combines low-field NMR spectrometry and a membrane flow reactor. This enables precise control of the experimental conditions such as liquid and gas pressures, and volume flow for ensuring repeatable maximum polarization.

Friday, September 7, 2018

Diastereoisomers of L-proline-linked trityl-nitroxide biradicals: synthesis and effect of chiral configurations on exchange interactions #DNPNMR

Zhai, Weixiang, Yalan Feng, Huiqiang Liu, Antal Rockenbauer, Deni Mance, Shaoyong Li, Yuguang Song, Marc Baldus, and Yangping Liu. “Diastereoisomers of L-Proline-Linked Trityl-Nitroxide Biradicals: Synthesis and Effect of Chiral Configurations on Exchange Interactions.” Chemical Science 9, no. 19 (May 16, 2018): 4381–91.


The exchange (J) interaction of organic biradicals is a crucial factor controlling their physiochemical properties and potential applications and can be modulated by changing the nature of the linker. In the present work, we for the first time demonstrate the effect of chiral configurations of radical parts on the J values of trityl-nitroxide (TN) biradicals. Four diastereoisomers (TNT1, TNT2, TNL1 and TNL2) of TN biradicals were synthesized and purified by the conjugation of a racemic (R/S) nitroxide with the racemic (M/P) trityl radical viaL-proline. The absolute configurations of these diastereoisomers were assigned by comparing experimental and calculated electronic circular dichroism (ECD) spectra as (M, S, S) for TNT1, (P, S, S) for TNT2, (M, S, R) for TNL1 and (P, S, R) for TNL2. Electron paramagnetic resonance (EPR) results showed that the configuration of the nitroxide part instead of the trityl part is dominant in controlling the exchange interactions and the order of the J values at room temperature is TNT1 (252 G) > TNT2 (127 G) ≫ TNL2 (33 G) > TNL1 (14 G). Moreover, the J values of TNL1/TNL2 with the S configuration in the nitroxide part vary with temperature and the polarity of solvents due to their flexible linker, whereas the J values of TNT1/TNT2 are almost insensitive to these two factors due to the rigidity of their linkers. The distinct exchange interactions between TNT1,2 and TNL1,2 in the frozen state led to strongly different high-field dynamic nuclear polarization (DNP) enhancements with ε = 7 for TNT1,2 and 40 for TNL1,2 under 800 MHz DNP conditions.

Wednesday, September 5, 2018

Perspective of Overhauser dynamic nuclear polarization for the study of soft materials #DNPNMR

Biller, Joshua R., Ryan Barnes, and Songi Han. “Perspective of Overhauser Dynamic Nuclear Polarization for the Study of Soft Materials.” Current Opinion in Colloid & Interface Science 33 (January 1, 2018): 72–85.


Solution state Overhauser dynamic nuclear polarization (ODNP) has been studied for 60years, but only in recent years has found applications of broad interest to biophysical sciences of hydration dynamics (HD-ODNP) around biomolecules and surfaces. In this review we describe state-of-the-art HD-ODNP methods and experiments, and identify technological and conceptual advances necessary to broadly disseminate HD-ODNP, as well as broaden its scope. Specifically, incomplete treatment of the saturation factor leads to the use of high microwave powers that induce temperature-dependent effects in HD-ODNP that can be detrimental to the stability and property of the sample and/or data interpretation, and thus must be corrected for. Furthermore, direct measurements of the electron spin relaxation times for the nitroxide radical-based spin labels used in HD-ODNP have recently caught up with the ambient solution conditions of relevance to HD-ODNP experiment, allowing us to envision an explicit treatment of the saturation factor. This would enable “single-shot” HD-ODNP at one or two concentrations and power levels, cutting down experimental times from the typical hours to minutes. With the development of a user-friendly and robust operation, the application of HD-ODNP experiments can be broadened for the study of biomolecules, biomaterials, soft polymer materials (i.e. hydrogels) and surfaces. In fact, any hydrated materials that can be viably spin labeled can yield information on local water dynamics and interfaces, and so guide the design of soft materials for medical and pharmaceutical uses. A brief introduction to spin-labeling, and exemplary applications to soft materials is discussed to serve as inspiration for future studies.

Monday, September 3, 2018

Frequency-Swept Integrated and Stretched Solid Effect Dynamic Nuclear Polarization #DNPNMR

Can, T. V., J. E. McKay, R. T. Weber, C. Yang, T. Dubroca, J. van Tol, S. Hill, and R. G. Griffin. “Frequency-Swept Integrated and Stretched Solid Effect Dynamic Nuclear Polarization.” The Journal of Physical Chemistry Letters 9, no. 12 (June 21, 2018): 3187–92. 


We investigate a new time domain approach to dynamic nuclear polarization (DNP), the frequency-swept integrated solid effect (FS-ISE), utilizing a high power, broadband 94 GHz (3.35 T) pulse EPR spectrometer. The bandwidth of the spectrometer enabled measurement of the DNP Zeeman frequency/field profile that revealed two dominant polarization mechanisms, the expected ISE, and a recently observed mechanism, the stretched solid effect (S2E). At 94 GHz, despite the limitations in the microwave chirp pulse length (10 μs) and the repetition rate (2 kHz), we obtained signal enhancements up to ∼70 for the S2E and ∼50 for the ISE. The results successfully demonstrate the viability of the FS-ISE and S2E DNP at a frequency 10 times higher than previous studies. Our results also suggest that these approaches are candidates for implementation at higher magnetic fields.

Friday, August 31, 2018

Electron-driven spin diffusion supports crossing the diffusion barrier in MAS DNP #DNPNMR

Wittmann, Johannes J., Michael Eckardt, Wolfgang Harneit, and Björn Corzilius. “Electron-Driven Spin Diffusion Supports Crossing the Diffusion Barrier in MAS DNP.” Physical Chemistry Chemical Physics 20, no. 16 (2018): 11418–29.



Dynamic nuclear polarization (DNP) can be applied to enhance the sensitivity of solid-state NMR experiments by several orders of magnitude due to microwave-driven transfer of spin polarization from unpaired electrons to nuclei. While the underlying quantum mechanical aspects are sufficiently well understood on a microscopic level, the exact description of the large-scale spin dynamics, usually involving hundreds to thousands of nuclear spins per electron, is still lacking consensus. Generally, it is assumed that nuclear hyperpolarization can only be observed on nuclei which do not experience strong influence of the unpaired electrons and thus being significantly removed from the paramagnetic polarizing agents. At the same time, sufficiently strong hyperfine interaction is required for DNP transfer. Therefore, efficient nuclear spin diffusion from the strongly-interacting nuclei to the NMR-observable bulk is considered to be essential for efficient nuclear hyperpolarization. Based on experimental results obtained on the endohedral fullerene N@C60 as a polarizing agent sparsely diluted in C60, we discuss the effect of the spin-diffusion barrier. We introduce electron-driven spin diffusion (EDSD) as a novel mechanism for nuclear polarization transfer in the proximity of an electron spin which is particularly relevant under magic-angle spinning (MAS) DNP conditions.

Wednesday, August 29, 2018

Amplification of Dynamic Nuclear Polarization at 200 GHz by Arbitrary Pulse Shaping of the Electron Spin Saturation Profile #DNPNMR

Kaminker, Ilia, and Songi Han. “Amplification of Dynamic Nuclear Polarization at 200 GHz by Arbitrary Pulse Shaping of the Electron Spin Saturation Profile.” The Journal of Physical Chemistry Letters 9, no. 11 (June 7, 2018): 3110–15.


Dynamic nuclear polarization (DNP) takes center stage in nuclear magnetic resonance (NMR) as a tool to amplify its signal by orders of magnitude through the transfer of polarization from electron to nuclear spins. In contrast to modern NMR and electron paramagnetic resonance (EPR) that extensively rely on pulses for spin manipulation in the time domain, the current mainstream DNP technology exclusively relies on monochromatic continuous wave (CW) irradiation. This study introduces arbitrary phase shaped pulses that constitute a train of coherent chirp pulses in the time domain at 200 GHz (7 T) to dramatically enhance the saturation bandwidth and DNP performance compared to CW DNP, yielding up to 500-fold in NMR signal enhancements. The observed improvement is attributed to the recruitment of additional electron spins contributing to DNP via the cross-effect mechanism, as experimentally confirmed by two-frequency pump–probe electron–electron double resonance (ELDOR).

Monday, August 27, 2018

Direct observation of Ru-alkylidene forming into ethylene in ring-closing metathesis from hyperpolarized 1H NMR #DNPNMR

Kim, Yaewon, Chia-Hsiu Chen, and Christian Hilty. “Direct Observation of Ru-Alkylidene Forming into Ethylene in Ring-Closing Metathesis from Hyperpolarized 1H NMR.” Chemical Communications 54, no. 34 (2018): 4333–36.



Ring-closing metathesis was monitored using real-time NMR of 1H hyperpolarized olefins at room temperature. By applying a selective saturation to an observable intermediate, its protons were found to transfer to ethylene. The intermediate was thus identified as a Ru-alkylidene species, which appears in the ethylene formation pathway.

Friday, August 24, 2018

Dynamic Nuclear Polarization Opens New Perspectives for NMR Spectroscopy in Analytical Chemistry #DNPNMR

Plainchont, B., P. Berruyer, J. N. Dumez, S. Jannin, and P. Giraudeau. “Dynamic Nuclear Polarization Opens New Perspectives for NMR Spectroscopy in Analytical Chemistry.” Analytical Chemistry 90 (March 20, 2018): 3639–50.


Dynamic nuclear polarization (DNP) can boost sensitivity in nuclear magnetic resonance (NMR) experiments by several orders of magnitude. This Feature illustrates how the coupling of DNP with both liquid- and solid-state NMR spectroscopy has the potential to considerably extend the range of applications of NMR in analytical chemistry.

Wednesday, August 22, 2018

Using a local low rank plus sparse reconstruction to accelerate dynamic hyperpolarized 13C imaging using the bSSFP sequence

Milshteyn, Eugene, Cornelius von Morze, Galen D. Reed, Hong Shang, Peter J. Shin, Peder E. Z. Larson, and Daniel B. Vigneron. “Using a Local Low Rank plus Sparse Reconstruction to Accelerate Dynamic Hyperpolarized 13C Imaging Using the BSSFP Sequence.” Journal of Magnetic Resonance 290 (May 1, 2018): 46–59.

Acceleration of dynamic 2D (T2 Mapping) and 3D hyperpolarized 13C MRI acquisitions using the balanced steady-state free precession sequence was achieved with a specialized reconstruction method, based on the combination of low rank plus sparse and local low rank reconstructions. Methods were validated using both retrospectively and prospectively undersampled in vivo data from normal rats and tumor-bearing mice. Four-fold acceleration of 1–2 mm isotropic 3D dynamic acquisitions with 2–5 s temporal resolution and two-fold acceleration of 0.25–1 mm2 2D dynamic acquisitions was achieved. This enabled visualization of the biodistribution of [2-13C]pyruvate, [1-13C]lactate, [13C, 15N2]urea, and HP001 within heart, kidneys, vasculature, and tumor, as well as calculation of high resolution T2 maps.

Tuesday, August 21, 2018

[NMR] Postdoctoral position in EPR spectroscopy


Dear Colleagues:

The Department of Chemistry at the University of Virginia invites applications for a Postdoctoral Research Associate, who is excited about the opportunity to work in a dynamic and collaborative research environment. The successful candidate will participate in collaborative work in the Membrane Biology Center at the University of Virginia, and will be engaged in research directed at the molecular structure and dynamics of proteins that mediate neuronal exocytosis using modern pulse EPR spectroscopy.

This is a one year appointment; however appointment may be renewed for an additional two, one-year increments, contingent upon available funding and satisfactory performance.

Requirements for the position include the completion of a Ph.D. degree in Chemistry, Biochemistry or a related discipline by the appointment start date, and effective oral and written communication skills. The candidate must have a working knowledge of biochemical and molecular biological laboratory procedures, and should have expertise in the expression and purification of SNAREs or related proteins. The candidate is also expected to have expertise in magnetic resonance spectroscopy, with a familiarity of EPR spectroscopy and modern pulse EPR instrumentation. The successful candidate is also expected to help mentor undergraduates and graduate students in the laboratory. 

To apply, please submit a candidate profile on-line through Jobs@UVA (https://jobs.virginia.edu) and electronically attach the following: cover letter, curriculum vitae, and the contact information for three (3) references; search on posting number 0623594. 

Review of applications will begin July 16, 2018; however, the position will remain open until filled. 

Questions regarding this position should be directed to: 
Prof. David Cafiso 
(434) 924-3067 

Questions regarding the Candidate Profile process or Jobs@UVA should be directed to: 
askHR@virginia.edu or 434-9982-0123 

The University will perform background checks on all new hires prior to making a final offer of employment. 

The University of Virginia is an affirmative action/equal opportunity employer committed to diversity, equity, and inclusiveness. Women Minorities, Veterans and Persons with Disabilities are encouraged to apply. 


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[NMR] Postdoctoral position in NMR of materials for energy storage at UCSB (Santa Barbara, USA)



Postdoctoral position in NMR of materials for energy storage at UCSB (Santa Barbara, USA)

The postdoctoral research position is based at the Materials Department, University of California Santa Barbara (UCSB), in the group of Prof. Raphaële Clément. The position is available from October, 1st, 2018, with an initial one-year contract renewable upon mutual agreement for two additional years.


Project Description

The research program focuses on the study of paramagnetic rechargeable battery materials using a variety of solid-state NMR (and EPR) techniques. The work will be in close collaboration with the Lawrence Berkeley National Laboratory, as well as other U.S. Universities and research groups at UCSB. In addition to developing a deep understanding of structure-property relationships for battery electrode materials, the postdoctoral researcher will be given the opportunity to acquire new experimental skills such as the solid-state synthesis of electrodes, and the preparation and testing of electrochemical cells. A strong emphasis will be placed on the combined use of experimental and theoretical tools to investigate changes in the local structure and electrochemical processes taking place during charge and discharge. Specifically, the interpretation of experimental paramagnetic NMR (and EPR) data will be assisted by first principles calculations of paramagnetic NMR/EPR parameters (an area of expertise of our group), and by insights gained from Monte Carlo and density functional theory simulations of electrode materials at different stages of the charge/discharge cycle (through ongoing collaborations). 
Relevant publications

[1] Lee, J.; Kitchaev, D. A.; Kwon, D.-H.; Lee, C.-W.; Papp, J. K.; Liu, Y.-S.; Lun, Z.; Clément, R. J.; Shi, T.; McCloskey, B. D.; Guo, J.; Balasubramanian, M.; Ceder, G. Nature 2018, 556 (7700), 185.

[2] Lee, J.; Papp, J. K.; Clément, R. J.; Sallis, S.; Kwon, D.-H.; Shi, T.; Yang, W.; McCloskey, B. D.; Ceder, G. Nat. Commun. 2017, 8 (1), 981.

[3] Kitchaev, D. A.; Lun, Z.; Richards, W. D.; Ji, H.; Clément, R. J.; Balasubramanian, M.; Kwon, D.-H.; Dai, K.; Papp, J. K.; Lei, T.; McCloskey, B. D.; Yang, W.; Lee, J.; Ceder, G. Energy Environ. Sci. 2018, 104, 4271.

[4] Clément, R. J.; Pell, A. J.; Middlemiss, D. S.; Strobridge, F. C.; Miller, J. K.; Whittingham, M. S.; Emsley, L.; Grey, C. P.; Pintacuda, G. J. Am. Chem. Soc. 2012, 134 (41), 17178.

[5] Middlemiss, D. S.; Ilott, A. J.; Clément, R. J.; Strobridge, F. C.; Grey, C. P. Chem. Mater. 2013, 25 (9), 1723.
Requirements and Preferred Experience

The requirements for the position are a Ph.D. in Chemistry, Materials Science, Physics or Engineering, and experience with standard solid-state NMR techniques (e.g. CP/MAS, REDOR, etc.). Experience with paramagnetic NMR and/or EPR is a plus. In addition to performing research, the postdoc will be expected to provide assistance with the training of graduate and undergraduate students.

The Magnetic Resonance Facilities at UCSB

The spectroscopy facility of the Materials Research Laboratory at UCSB (see https://www.mrl.ucsb.edu/spectroscopy-facility/instruments) comprises an X-band EPR spectrometer as well as several solid-state NMR spectrometers, including a 300 MHz system equipped with a MRI/diffusion probe, a 400 MHz DNP-NMR spectrometer, and 500 MHz and 800 MHz systems. All spectrometers are equipped with a range of MAS probes, with a fast spinning 1.3 mm probe (60 kHz MAS) available on the 500 MHz system. In addition, the Terahertz facility at UCSB (http://www.itst.ucsb.edu) is uniquely equipped with a high field high power EPR system.


Additional Information

Interested candidates should send a cover letter, a résumé (including a list of publications), and the names and email addresses of at least two references to rclement@ucsb.edu.
---------------------------------------------------------------------------
Raphaële Clément

Assistant Professor, Materials Department
Materials Research Laboratory, Room 3009
University of California, Santa Barbara, CA 93106-5121

Phone: 805-893-4294



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[NMR] postdoctoral position at UC Santa Cruz

Dear Colleagues,
I am please to announce the opening of a postdoctoral researcher position in the Department of Chemistry and Biochemistry at UC Santa Cruz. The selected individual should have demonstrated expertise in Double Electron-Electron Resonance (DEER) EPR. Research will focus on structural biology issues related to neurodegenerative diseases, as well as the facilitation of diverse collaborative studies among California Bay Area labs including UCSF, UC Merced, UC Davis and Stanford. Please see our website: 

and the job posting: 
With best regards,
glenn


Glenn L. Millhauser
Department of Chemistry & Biochemistry
UC Santa Cruz
Santa Cruz, CA 95064
831 459 2176 voice
831 566 3337 cell
831 459 2935 fax





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Monday, August 20, 2018

Effect of water/glycerol polymorphism on dynamic nuclear polarization #DNPNMR

Leavesley, Alisa, Christopher B. Wilson, Mark Sherwin, and Songi Han. “Effect of Water/Glycerol Polymorphism on Dynamic Nuclear Polarization.” Physical Chemistry Chemical Physics 20, no. 15 (April 18, 2018): 9897–9903.


A paramount feature of robust experimental methods is acquiring consistent data. However, in dynamic nuclear polarization (DNP), it has been observed that the DNP-induced NMR signal enhancement of nominally the same sample can vary between different experimental sessions. We investigated the impact of various freezing conditions on the DNP results for a standard sample, a 50/40/10 by volume d8-glycerol/D2O/H2O solution of 40 mM 4-amino TEMPO, and found that annealing the samples 10 K above the glass transition temperature (Tg) causes significant changes to the DNP profiles and enhancements compared to that in rapidly frozen samples. When varying the glycerol composition to yield a solution of 60/30/10 d8-glycerol/D2O/H2O, the DNP performance became markedly more consistent, even for samples prepared under vastly different sample freezing methods, in stark contrast with that of the 50/40/10 solution. The EPR lineshapes, Tm, and glass transition temperature, Tg, were measured under the same sample and experimental conditions as used for the DNP experiments to support the conclusion that different freezing methods change the distribution of 4-amino TEMPO radials in the 50/40/10 solution due to the formation of different polymorphs of the glass, which is mitigated in the 60/30/10 solution and is consistent with the water/glycerol vitrification literature.

Friday, August 17, 2018

Dynamic Nuclear Polarization Surface Enhanced NMR spectroscopy (DNP SENS): Principles, protocols, and practice #DNPNMR

Liao, Wei-Chih, Behnaz Ghaffari, Christopher P. Gordon, Jun Xu, and Christophe Copéret. “Dynamic Nuclear Polarization Surface Enhanced NMR Spectroscopy (DNP SENS): Principles, Protocols, and Practice.” Current Opinion in Colloid & Interface Science 33 (January 1, 2018): 63–71.


Dynamic Nuclear Polarization Surface Enhanced NMR spectroscopy has been demonstrated to significantly improve NMR sensitivity on materials by 1 to 2 orders of magnitude at high magnetic fields. The preferential surface enhancement also allows for selectively probing the solid surface. In this review, we will briefly describe the main mechanism used nowadays, i.e. cross effect, for DNP enhanced solid-state NMR. We will show the typical protocols of sample formulation leading to effective DNP surface enhancements and the key experimental factors in performing DNP SENS experiments. Other important developments in DNP, i.e. shielded polarizing agents for reactive surfaces, hyperpolarizing solid matrices, and high-temperature and high-field DNP, will be discussed as well. Finally, we close the review with a short summary and our perspectives on the directions of future developments in this field.

Wednesday, August 15, 2018

Considering low-rank, sparse and gas-inflow effects constraints for accelerated pulmonary dynamic hyperpolarized 129Xe MRI

Xiao, Sa, He Deng, Caohui Duan, Junshuai Xie, Huiting Zhang, Xianping Sun, Chaohui Ye, and Xin Zhou. “Considering Low-Rank, Sparse and Gas-Inflow Effects Constraints for Accelerated Pulmonary Dynamic Hyperpolarized 129Xe MRI.” Journal of Magnetic Resonance 290 (May 1, 2018): 29–37.


Dynamic hyperpolarized (HP) 129Xe MRI is able to visualize the process of lung ventilation, which potentially provides unique information about lung physiology and pathophysiology. However, the longitudinal magnetization of HP 129Xe is nonrenewable, making it difficult to achieve high image quality while maintaining high temporal-spatial resolution in the pulmonary dynamic MRI. In this paper, we propose a new accelerated dynamic HP 129Xe MRI scheme incorporating the low-rank, sparse and gas-inflow effects (L + S + G) constraints. According to the gas-inflow effects of HP gas during the lung inspiratory process, a variable-flip-angle (VFA) strategy is designed to compensate for the rapid attenuation of the magnetization. After undersampling k-space data, an effective reconstruction algorithm considering the low-rank, sparse and gas-inflow effects constraints is developed to reconstruct dynamic MR images. In this way, the temporal and spatial resolution of dynamic MR images is improved and the artifacts are lessened. Simulation and in vivo experiments implemented on the phantom and healthy volunteers demonstrate that the proposed method is not only feasible and effective to compensate for the decay of the magnetization, but also has a significant improvement compared with the conventional reconstruction algorithms (P-values are less than 0.05). This confirms the superior performance of the proposed designs and their ability to maintain high quality and temporal-spatial resolution.

Monday, August 13, 2018

Magic angle spinning NMR with metallized rotors as cylindrical microwave resonators #DNPNMR

Scott, Faith J., Erika L. Sesti, Eric J. Choi, Alexander J. Laut, Jagadishwar R. Sirigiri, and Alexander B. Barnes. “Magic Angle Spinning NMR with Metallized Rotors as Cylindrical Microwave Resonators.” Magnetic Resonance in Chemistry, May 16, 2018.


We introduce a novel design for millimeter wave electromagnetic structures within magic angle spinning (MAS) rotors. In this demonstration, a copper coating is vacuum deposited onto the outside surface of a sapphire rotor at a thickness of 50 nanometers. This thickness is sufficient to reflect 197 GHz microwaves, yet not too thick as to interfere with radiofrequency fields at 300 MHz or prevent sample spinning due to eddy currents. Electromagnetic simulations of an idealized rotor geometry show a microwave quality factor of 148. MAS experiments with sample rotation frequencies of ωr/2π = 5.4 kHz demonstrate that the drag force due to eddy currents within the copper does not prevent sample spinning. Spectra of sodium acetate show resolved 13C J-couplings of 60 Hz and no appreciable broadening between coated and uncoated sapphire rotors, demonstrating that the copper coating does not prevent shimming and high-resolution NMR spectroscopy. Additionally, 13C Rabi nutation curves of ω1/2π = 103 kHz for both coated and uncoated rotors indicate no detrimental impact of the copper coating on radiofrequency coupling of the nuclear spins to the sample coil. We present this metal coated rotor as a first step towards an MAS resonator. MAS resonators are expected to have a significant impact on developments in electron decoupling, pulsed DNP, room temperature DNP, DNP with low power microwave sources, and EPR detection.

[NMR] DNP postdoctoral position at UCSD

The Debelouchina lab at the University of California, San Diego is looking for a postdoctoral researcher with experience and/or interest in DNP to join our growing team. The position will involve the development of new DNP biradical polarization agents and their application to biological systems and materials. Candidates must hold a Ph.D. in chemistry, physics or a related discipline and have experience in solid-state NMR, hyperpolarization techniques or EPR. The project will take advantage of a new 600 MHz DNP spectrometer, scheduled for installation in the fall of 2018.

In addition, the University of California, San Diego has outstanding resources for high-field NMR spectroscopy, including 900 MHz, 750 MHz, 700 MHz and 500 MHz solid-state NMR spectrometers equipped with MAS and static probes, as well as solution spectrometers operating at 800 MHz, 600 MHz and 500 MHz dedicated to biomolecular NMR applications. The large UCSD scientific community and several research institutes nearby (The Salk Institute for Biological Studies, the Scripps Research Institute and the Sanford Burnham Prebys Medical Discovery Institute) provide a vast network and potential for collaborations and scientific exchange. In addition to a vibrant scientific environment, San Diego also offers beautiful weather all year round and many opportunities for nature and ocean exploration.

Interested candidates should contact Dr. Debelouchina directly at gdebelouchina@ucsd.edu with a cover letter, CV and email addresses of two references.

Representative publications:

  • Debelouchina GT, Bayro MJ, Fitzpatrick AWP, Ladizhansky V, Colvin MT, Caporini MA, Jaroniec CP, Bajaj VS, Rosay M, MacPhee C, Vendruscolo M, Maas WE, Dobson CM, Griffin RG (2013). Higher Order Amyloid Fibril Structure by MAS NMR and DNP Spectroscopy. J. Am. Chem. Soc. 135, 19237-47.
  • Debelouchina GT, Bayro MJ, van der Wel PCA, Caporini MA, Barnes AB, Rosay M, Maas WE, Griffin RG (2010). Dynamic Nuclear Polarization Enhanced Solid-State NMR Spectroscopy of GNNQQNY Crystals and Amyloid Fibrils. Phys. Chem. Chem. Phys. 12, 5911-9.
  • Hu KN, Debelouchina GT, Smith AA, Griffin RG (2011). Quantum Mechanical Theory of Dynamic Nuclear Polarization in Solid Dielectrics. J. Chem. Phys. 134, 125105.
  • Dane EL, Maly T, Debelouchina GT, Griffin RG, Swager TM (2009). Synthesis of a BDPA-TEMPO Biradical. Org. Lett. 11, 1871-4.
___________________________
Galia Debelouchina, Ph.D.
Assistant Professor
Department of Chemistry and Biochemistry
University of California, San Diego
9500 Gilman Drive
La Jolla, CA 92093











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A message from the International EPR Society

Below is a message from the International EPR Society to members for the EPR and Magnetic Resonance Community. I typically don't post these kind of advertisements but I do believe the International EPR Society has done a lot of great work for the community over the many years.

Take a look at https://www.ieprs.org. Membership fees are very low and the EPR Newsletter is a nice treat.



Dear EPR users,

To continue to have a vibrant, diverse, and active EPR community, we will all benefit from a scientific organization that offers a support and communication infrastructure for EPR -- this is what the International EPR Society (https://www.ieprs.org) aspires to offer. 

The most familiar faces of IES may be the EPR Newsletters and the Silver and Gold Medals for EPR. 

IES is the only international scientific organization that represents the whole range of important research fields of electron paramagnetic resonance (EPR) spectroscopy and EPR imaging (EMRI). These methods are used as the main research tools over a very wide range of fields, including physics, chemistry, life sciences, materials research and medicine.

IES is a world-wide association of scientists, and the IES mailing list serves the community to help spread EPR-related information (jobs, post-doc and PhD positions, conferences, etc.) to the world-wide EPR community. It provides public networking, available to IES members, where one can post messages via the EPR Newsletter (EPRNL), the official IES publication. EPRNL not only provides information on the availability of second-hand EPR instrumentation, it also publishes advertisements of prominent manufacturers of EPR instrumentation.

Members of IES have free access to the EPRNL! See: http://www.epr-newsletter.ethz.ch

IES also awards prizes and honors for outstanding contributions to EPR spectroscopy, from senior to young investigators! The newly created IES poster prizes honor excellent young scientists and PhD students for their contributions to international EPR conferences. All these achievements are reported in the EPRNL, and you can find more about "Why IES" here: http://www.ieprs.org/whyjoin.php

The member fees are encouragingly low: $6/year for students, $12/year for emeritus and post-doctoral fellows, and $36/year for full members. We will be happy if you paid the membership dues for several years. See: http://www.apes-ies2018.org/registration
Your membership of the IES is what will keep IES relevant, vibrant and impactful, and give IES the necessary tools to be responsive to the ever emerging field of EPR spectroscopy. 

Sincerely,
Songi Han, Vice President (America) of IES
Thomas Prisner, President of IES