Oct 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.

Oct 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.

Oct 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.

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

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Oct 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.

Oct 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.

Oct 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.

Oct 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.

Oct 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).


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.

Oct 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.

Oct 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.

Oct 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.

Oct 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.