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
├śrsted 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.