Wednesday, August 30, 2017

Communication: Dissolution DNP reveals a long-lived deuterium spin state imbalance in methyl groups #DNPNMR


Jhajharia, A., et al., Communication: Dissolution DNP reveals a long-lived deuterium spin state imbalance in methyl groups. J Chem Phys, 2017. 146(4): p. 041101.


We report the generation and observation of long-lived spin states in deuterated methyl groups by dissolution DNP. These states are based on population imbalances between manifolds of spin states corresponding to irreducible representations of the C3v point group and feature strongly dampened quadrupolar relaxation. Their lifetime depends on the activation energies of methyl group rotation. With dissolution DNP, we can reduce the deuterium relaxation rate by a factor up to 20, thereby extending the experimentally available time window. The intrinsic limitation of NMR spectroscopy of quadrupolar spins by short relaxation times can thus be alleviated.

Monday, August 28, 2017

Peptide and Protein Dynamics and Low-Temperature/DNP Magic Angle Spinning NMR #DNPNMR


Ni, Q.Z., et al., Peptide and Protein Dynamics and Low-Temperature/DNP Magic Angle Spinning NMR. The Journal of Physical Chemistry B, 2017. 121(19): p. 4997-5006.


In DNP MAS NMR experiments at ∼80–110 K, the structurally important −13CH3 and −15NH3+ signals in MAS spectra of biological samples disappear due to the interference of the molecular motions with the 1H decoupling. Here we investigate the effect of these dynamic processes on the NMR line shapes and signal intensities in several typical systems: (1) microcrystalline APG, (2) membrane protein bR, (3) amyloid fibrils PI3-SH3, (4) monomeric alanine-CD3, and (5) the protonated and deuterated dipeptide N-Ac-VL over 78–300 K. In APG, the three-site hopping of the Ala-Cβ peak disappears completely at 112 K, concomitant with the attenuation of CP signals from other 13C’s and 15N’s. Similarly, the 15N signal from Ala-NH3+ disappears at ∼173 K, concurrent with the attenuation in CP experiments of other 15N’s as well as 13C’s. In bR and PI3-SH3, the methyl groups are attenuated at ∼95 K, while all other 13C’s remain unaffected. However, both systems exhibit substantial losses of intensity at ∼243 K. Finally, with spectra of Ala and N-Ac-VL, we show that it is possible to extract site specific dynamic data from the temperature dependence of the intensity losses. Furthermore, 2H labeling can assist with recovering the spectral intensity. Thus, our study provides insight into the dynamic behavior of biological systems over a wide range of temperatures, and serves as a guide to optimizing the sensitivity and resolution of structural data in low temperature DNP MAS NMR spectra.

Friday, August 25, 2017

Frequency-Swept Integrated Solid Effect #DNPNMR


Can, T.V., et al., Frequency-Swept Integrated Solid Effect. Angew Chem Int Ed Engl, 2017. 56(24): p. 6744-6748.


The efficiency of continuous wave dynamic nuclear polarization (DNP) experiments decreases at the high magnetic fields used in contemporary high-resolution NMR applications. To recover the expected signal enhancements from DNP, we explored time domain experiments such as NOVEL which matches the electron Rabi frequency to the nuclear Larmor frequency to mediate polarization transfer. However, satisfying this matching condition at high frequencies is technically demanding. As an alternative we report here frequency-swept integrated solid effect (FS-ISE) experiments that allow low power sweeps of the exciting microwave frequencies to constructively integrate the negative and positive polarizations of the solid effect, thereby producing a polarization efficiency comparable to (+/-10 % difference) NOVEL. Finally, the microwave frequency modulation results in field profiles that exhibit new features that we coin the "stretched" solid effect.

Wednesday, August 23, 2017

Depolarization of nuclear spin polarized 129Xe gas by dark rubidium during spin-exchange optical pumping


Antonacci, M.A., et al., Depolarization of nuclear spin polarized 129Xe gas by dark rubidium during spin-exchange optical pumping. J Magn Reson, 2017. 279: p. 60-67.


Continuous-flow spin-exchange optical pumping (SEOP) continues to serve as the most widespread method of polarizing 129Xe for magnetic resonance experiments. Unfortunately, continuous-flow SEOP still suffers from as-yet unidentified inefficiencies that prevent the production of large volumes of xenon with a nuclear spin polarization close to theoretically calculated values. In this work we use a combination of ultra-low field nuclear magnetic resonance spectroscopy and atomic absorption spectroscopy (AAS) measurements to study the effects of dark Rb vapor on hyperpolarized 129Xe in situ during continuous-flow SEOP. We find that dark Rb vapor in the optical cell outlet has negligible impact on the final 129Xe polarization at typical experimental conditions, but can become significant at higher oven temperatures and lower flow rates. Additionally, in the AAS spectra we also look for a signature of paramagnetic Rb clusters, previously identified as a source of xenon depolarization and a cause for SEOP inefficiency, for which we are able to set an upper limit of 8.3x1015 Rb dimers per cm3.

Monday, August 21, 2017

Dynamic nuclear polarisation by thermal mixing: quantum theory and macroscopic simulations #DNPNMR


Karabanov, A., et al., Dynamic nuclear polarisation by thermal mixing: quantum theory and macroscopic simulations. Phys. Chem. Chem. Phys., 2016. 18(43): p. 30093-30104.


A theory of dynamic nuclear polarisation (DNP) by thermal mixing is suggested based on purely quantum considerations. A minimal 6-level microscopic model is developed to test the theory and link it to the well-known thermodynamic model. Optimal conditions for the nuclear polarization enhancement and effects of inhomogeneous broadening of the electron resonance are discussed. Macroscopic simulations of nuclear polarization spectra displaying good agreement with experiments, involving BDPA and trityl free radicals, are presented.

Friday, August 18, 2017

Free Radical Imaging Using In Vivo Dynamic Nuclear Polarization-MRI #DNPNMR #ODNP


Utsumi, H. and F. Hyodo, Free Radical Imaging Using In Vivo Dynamic Nuclear Polarization-MRI. Methods Enzymol, 2015. 564: p. 553-71.


Redox reactions that generate free radical intermediates are essential to metabolic processes, and their intermediates can produce reactive oxygen species, which may promote diseases related to oxidative stress. The development of an in vivo electron spin resonance (ESR) spectrometer and its imaging enables us noninvasive and direct measurement of in vivo free radical reactions in living organisms. The dynamic nuclear polarization magnetic resonance imaging (DNP-MRI), also called PEDRI or OMRI, is also a new imaging method for observing free radical species in vivo. The spatiotemporal resolution of free radical imaging with DNP-MRI is comparable with that in MRI, and each of the radical species can be distinguished in the spectroscopic images by changing the frequency or magnetic field of ESR irradiation. Several kinds of stable nitroxyl radicals were used as spin probes to detect in vivo redox reactions. The signal decay of nitroxyl probes, which is determined with in vivo DNP-MRI, reflects the redox status under oxidative stress, and the signal decay is suppressed by prior administration of antioxidants. In addition, DNP-MRI can also visualize various intermediate free radicals from the intrinsic redox molecules. This noninvasive method, in vivo DNP-MRI, could become a useful tool for investigating the mechanism of oxidative injuries in animal disease models and the in vivo effects of antioxidant drugs.

Wednesday, August 16, 2017

Simultaneous and spectroscopic redox molecular imaging of multiple free radical intermediates using dynamic nuclear polarization-magnetic resonance imaging #DNPNMR


Hyodo, F., et al., Simultaneous and spectroscopic redox molecular imaging of multiple free radical intermediates using dynamic nuclear polarization-magnetic resonance imaging. Anal Chem, 2014. 86(15): p. 7234-8.


Redox reactions that generate free radical intermediates are essential to metabolic processes. However, their intermediates can produce reactive oxygen species, which may promote diseases related to oxidative stress. We report here the use of dynamic nuclear polarization-magnetic resonance imaging (DNP-MRI) to conduct redox molecular imaging. Using DNP-MRI, we obtained simultaneous images of free radical intermediates generated from the coenzyme Q10 (CoQ10), flavin mononucleotide (FMN), and flavin adenine dinucleotide (FAD) involved in the mitochondrial electron transport chain as well as the radicals derived from vitamins E and K1. Each of these free radicals was imaged in real time in a phantom comprising a mixture of free radicals localized in either lipophilic or aqueous environments. Changing the frequency of electron spin resonance (ESR) irradiation also allowed each of the radical species to be distinguished in the spectroscopic images. This study is the first to report the spectroscopic DNP-MRI imaging of free radical intermediates that are derived from endogenous species involved in metabolic processes.

Monday, August 14, 2017

EPR Spectroscopy of Nitroxide Spin Probes #EPR #DNPNMR


Nitroxide spin labels are extensively used in EPR for distance measurements and many polarizing agents are based on nitroxides. More recently they are also used in Overhauser DNP measurements (ODNP) to study surface hydration dynamics of larger (membrane) proteins. Although the article is already a bit older, it is a nice review of spin labels and their use in EPR spectroscopy.


Bordignon, E., EPR Spectroscopy of Nitroxide Spin Probes, in eMagRes. 2017, John Wiley & Sons, Ltd. p. 235-254.


In this article, we will introduce the main chemical and spectroscopic properties of nitroxides. These paramagnetic non-endogenous probes have been widely used in EPR spectroscopy in the last decade due to their high stability and simple spectral fingerprint, which provides a wealth of qualitative and quantitative information about their microscopic environment under almost unrestricted experimental conditions. Nitroxides can be covalently or noncovalently introduced into a variety of different materials to monitor viscosity, local dynamics, pH, polarity, H-bond networks, transition temperatures, and distances toward other nitroxide probes. In general, these small probes minimally perturb the system under investigation, and being the unique paramagnetic centers in an otherwise diamagnetic sample, they provide unequivocal information. Here we will focus on their exquisite sensitivity to report molecular motions within defined ‘EPR timescales’ and spin-spin interactions via changes in their spectral lineshape. Additionally, we will discuss some methods to monitor polarity and formation of H-bonds in their microenvironment.

Friday, August 11, 2017

Electron Decoupling with Dynamic Nuclear Polarization in Rotating Solids #DNPNMR


Saliba, E.P., et al., Electron Decoupling with Dynamic Nuclear Polarization in Rotating Solids. J Am Chem Soc, 2017. 139(18): p. 6310-6313.


Dynamic nuclear polarization (DNP) can enhance NMR sensitivity by orders of magnitude by transferring spin polarization from electron paramagnetic resonance (EPR) to NMR. However, paramagnetic DNP polarizing agents can have deleterious effects on NMR signals. Electron spin decoupling can mitigate these paramagnetic relaxation effects. We demonstrate electron decoupling experiments in conjunction with DNP and magic-angle-spinning NMR spectroscopy. Following a DNP and spin diffusion period, the microwave irradiation frequency is quickly tuned on-resonance with electrons on the DNP polarizing agent. The electron decoupling performance shows a strong dependence on the microwave frequency and DNP polarization time. Microwave frequency sweeps through the EPR line shape are shown as a time domain strategy to significantly improve electron decoupling. For 13C spins on biomolecules frozen in a glassy matrix, electron decoupling reduces the line widths by 11% (47 Hz) and increases the intensity by 14%.

Thursday, August 10, 2017

[NMR] Training School on Principles and Applications of Dissolution DNP, Nov 13-17, 2017, Copenhagen


Dear all,
The registration deadline for the training school, Principles and Applications of Dissolution DNP, has been extended to Sep 1.

The training school takes place at the Center for Hyperpolarization in Magnetic Resonance, at the Technical University of Denmark, Kgs Lyngby, Denmark from Nov 13-17, 2017.

We have three fantastic external lecturers signed up for the teaching, Tom Wenckebach, Matthew Merritt and Arnaud Comment, together with the faculty of the group. The school covers DNP theory, relaxation, kinetic modelling, sample preparation, polarizer instrumentation and operation, acquisition strategies as well as in vitro and in vivo applications. There will be plenty of hands-on exercises and in-depth discussion in small groups.

More details of the workshop is available from the website: http://www.hypermag.dtu.dk/Research/Dissolution-DNP-Course.

Please forward this email on to anyone who may be interested.

Thanks, and best regards, Jan

Jan Henrik Ardenkjaer-Larsen
Professor, Center Leader
Center for Magnetic Resonance
Technical University of Denmark
Department of Electrical Engineering
Ørsted Plads, bldg. 349, room 126
DK-2800 Kgs Lyngby
Phone +45 45253918

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Wednesday, August 9, 2017

Role of chiral quantum Hall edge states in nuclear spin polarization


Yang, K., et al., Role of chiral quantum Hall edge states in nuclear spin polarization. Nat Commun, 2017. 8: p. 15084.


Resistively detected NMR (RDNMR) based on dynamic nuclear polarization (DNP) in a quantum Hall ferromagnet (QHF) is a highly sensitive method for the discovery of fascinating quantum Hall phases; however, the mechanism of this DNP and, in particular, the role of quantum Hall edge states in it are unclear. Here we demonstrate the important but previously unrecognized effect of chiral edge modes on the nuclear spin polarization. A side-by-side comparison of the RDNMR signals from Hall bar and Corbino disk configurations allows us to distinguish the contributions of bulk and edge states to DNP in QHF. The unidirectional current flow along chiral edge states makes the polarization robust to thermal fluctuations at high temperatures and makes it possible to observe a reciprocity principle of the RDNMR response. These findings help us better understand complex NMR responses in QHF, which has important implications for the development of RDNMR techniques.

Monday, August 7, 2017

Dynamic Nuclear Polarization NMR as a new tool to investigate the nature of organic compounds occluded in plant silica particles #DNPNMR


Masion, A., et al., Dynamic Nuclear Polarization NMR as a new tool to investigate the nature of organic compounds occluded in plant silica particles. Sci Rep, 2017. 7(1): p. 3430.


The determination of the chemical nature of the organic matter associated with phytoliths remains a challenge. This difficulty mainly stems from amounts of organic carbon (C) that are often well below the detection limit of traditional spectroscopic tools. Conventional solid-state 13C Nuclear Magnetic Resonance (NMR) is widely used to examine the nature and structure of organic molecules, but its inherent low sensitivity prohibits the observation of diluted samples. The recent advent of commercial microwave source in the terahertz range triggered a renewed interest in the Dynamic Nuclear Polarization (DNP) technique to improve the signal to noise ratio of solid-state NMR experiments. With this technique, the 13C spectrum of a phytolith sample containing 0.1% w/w C was obtained overnight with sufficient quality to permit a semi-quantitative analysis of the organic matter, showing the presence of peptides and carbohydrates as predominant compounds. Considering the natural abundance of the 13C isotope, this experiment demonstrates that DNP NMR is sufficiently sensitive to observe spin systems present in amounts as low as a few tens of ppm.

Wednesday, August 2, 2017

Transmembrane Interactions of Full-length Mammalian Bitopic Cytochrome-P450-Cytochrome-b5 Complex in Lipid Bilayers Revealed by Sensitivity-Enhanced Dynamic Nuclear Polarization Solid-state NMR Spectroscopy #DNPNMR


Yamamoto, K., et al., Transmembrane Interactions of Full-length Mammalian Bitopic Cytochrome-P450-Cytochrome-b5 Complex in Lipid Bilayers Revealed by Sensitivity-Enhanced Dynamic Nuclear Polarization Solid-state NMR Spectroscopy. Sci Rep, 2017. 7(1): p. 4116.


The dynamic protein-protein and protein-ligand interactions of integral bitopic membrane proteins with a single membrane-spanning helix play a plethora of vital roles in the cellular processes associated with human health and diseases, including signaling and enzymatic catalysis. While an increasing number of high-resolution structural studies of membrane proteins have successfully manifested an in-depth understanding of their biological functions, intact membrane-bound bitopic protein-protein complexes pose tremendous challenges for structural studies by crystallography or solution NMR spectroscopy. Therefore, there is a growing interest in developing approaches to investigate the functional interactions of bitopic membrane proteins embedded in lipid bilayers at atomic-level. Here we demonstrate the feasibility of dynamic nuclear polarization (DNP) magic-angle-spinning NMR techniques, along with a judiciously designed stable isotope labeling scheme, to measure atomistic-resolution transmembrane-transmembrane interactions of full-length mammalian ~72-kDa cytochrome P450-cytochrome b5 complex in lipid bilayers. Additionally, the DNP sensitivity-enhanced two-dimensional 13C/13C chemical shift correlations via proton driven spin diffusion provided distance constraints to characterize protein-lipid interactions and revealed the transmembrane topology of cytochrome b5. The results reported in this study would pave ways for high-resolution structural and topological investigations of membrane-bound full-length bitopic protein complexes under physiological conditions.