Friday, June 29, 2012

Dinitroxides for Solid State Dynamic Nuclear Polarization

Ysacco, C., et al., Dinitroxides for Solid State Dynamic Nuclear Polarization. Appl. Magn. Reson., 2012: p. 1-11.


We have prepared a series of dinitroxides and we investigated their properties as polarizing agents for solid-state nuclear magnetic resonance/dynamic nuclear polarization applications at 100 K, 9.34 T (263 GHz electron paramagnetic resonance and 400 MHz 1 H nuclear magnetic resonance). Our results show that a rigid structure with an orthogonal relative orientation of electron g tensors and the appropriate orientation of the two N-O bonds are required to obtain maximum polarization enhancements. In addition, with dinitroxides exhibiting a long T1e , the saturation of the irradiated electron spin packet is favored leading to more efficient dynamic nuclear polarization.



Wednesday, June 27, 2012

Evaluation of a Shuttle DNP Spectrometer by Calculating the Coupling and Global Enhancement Factors of L-Tryptophan

Lottmann, P., et al., Evaluation of a Shuttle DNP Spectrometer by Calculating the Coupling and Global Enhancement Factors of L-Tryptophan. Appl. Magn. Reson., 2012: p. 1-15.


A liquid state shuttle dynamic nuclear polarization (DNP) spectrometer is presented, featuring several technical modifications that increase stability and improve reproducibility. For the protons of l -tryptophan, the signal enhancement and the DNP spin properties, such as relaxation, were measured and compared with each other. The calculated coupling factors suggest that the proton accessibility for the polarizer molecule has an important influence on the DNP enhancement. In general, short proton spin longitudinal relaxation times without radical reduce the detectable enhancement by decreasing the leakage factor and increasing the relaxation losses during the course of the sample transfer. The usage of a global enhancement factor gives a more complete overview of the capabilities for the described experimental setup. Global enhancements of up to −4.2 for l -tryptophan protons are found compared to pure Boltzmann enhancements of up to −2.4.



Monday, June 25, 2012

Temperature Dependence of the Proton Overhauser DNP Enhancements on Aqueous Solutions of Fremy’s Salt Measured in a Magnetic Field of 9.2 T

Gafurov, M., et al., Temperature Dependence of the Proton Overhauser DNP Enhancements on Aqueous Solutions of Fremy’s Salt Measured in a Magnetic Field of 9.2 T. Appl. Magn. Reson., 2012: p. 1-10.


The temperature dependence of the water-proton dynamic nuclear polarization (DNP) enhancement from Fremy’s salt nitroxide radicals was measured in a magnetic field of 9.2 T (corresponding to 260 GHz microwave (MW) and 392 MHz NMR frequencies) in the temperature range of 15–65 °C. The temperature could be determined directly from the proton NMR line shift of the sample. Very high DNP enhancements of −38 (signal integral) or −81 (peak intensity) could be achieved with a high-power gyrotron MW source. The experimental findings are compared with classical Overhauser theory for liquids, which is based on the translational and rotational motion of the molecules and with molecular dynamics calculations of the coupling factor.



Saturday, June 23, 2012

Comparison of Overhauser DNP at 0.34 and 3.4 T with Frémy’s Salt

Türke, M.T. and M. Bennati, Comparison of Overhauser DNP at 0.34 and 3.4 T with Frémy’s Salt. Appl. Magn. Reson., 2012: p. 1-10.


Dynamic nuclear polarization (DNP) is investigated in the liquid state using a model system of Frémy’s salt dissolved in water. Nuclear magnetic resonance signal enhancements at 0.34 and 3.4 T of the bulk water protons are recorded as a function of the irradiation time and the polarizer concentration. The build-up rates are consistent with the T 1n of the observed water protons at room temperature (for 9 GHz/0.34 T) and for about 50 ± 10 °C at 94 GHz/3.4 T. At 94 GHz/3.4 T, we observe in our setup a maximal enhancement of −50 at 25 mM polarizer concentration. The use of Frémy’s salt allows the determination of the saturation factors at 94 GHz by pulsed ELDOR experiments. The results are well consistent with the Overhauser DNP mechanism and indicate that higher enhancements at this intermediate frequency require higher sample temperatures.



Friday, June 22, 2012

EUROMAR satellite meeting on DNP

The final program for the COST meeting on Spin Hyperpolarisation in NMR and MRI held in Dublin from June 29th to July 1st 2012 is released.

For more information go to: http://euromar2012.org/satellite-meetings/


Thursday, June 21, 2012

Dynamic Nuclear Polarization by Thermal Mixing Under Partial Saturation

Jannin, S., A. Comment, and J. van der Klink, Dynamic Nuclear Polarization by Thermal Mixing Under Partial Saturation. Appl. Magn. Reson., 2012: p. 1-10.


We describe a low-temperature thermodynamic model for dynamic nuclear polarization (DNP) via continuous-wave partial saturation of electron spin resonance (ESR) lines that are both homogeneously and inhomogeneously broadened. It is a variant of a reasoning proposed by Borghini, which in turn used Redfield’s thermodynamic treatment of saturation. Our variant is furthermore based on Provotorov’s insight that under partial saturation of a coupled-spin system two distinct spin temperatures should appear in a thermodynamical theory. We apply our model to DNP results obtained at a temperature of 1.2 K and in magnetic fields of 3.35 and 5 T on 1- 13 C labeled sodium acetate dissolved in a frozen D 2 O/ethanol-d 6 solution doped with the free radical TEMPO.



Tuesday, June 19, 2012

Solvent-Free High-Field Dynamic Nuclear Polarization of Mesoporous Silica Functionalized with TEMPO

Lilly Thankamony, A., et al., Solvent-Free High-Field Dynamic Nuclear Polarization of Mesoporous Silica Functionalized with TEMPO. Appl. Magn. Reson., 2012: p. 1-14.


We report high-field magic-angle spinning dynamic nuclear polarization (MAS DNP) of mesoporous silica functionalized with nitroxide radicals. These results demonstrate that co-condensation can be employed to incorporate DNP polarizing agents into inorganic materials and that solvent-free DNP is feasible for porous materials. For the investigated material, the direct MAS DNP enhances the 29 Si nuclear magnetic resonance (NMR) spectra, whereas the indirect MAS DNP via protons is inapplicable owing to the inefficiency of ${}^{1}\hbox{H}\rightarrow{}^{29}\hbox{Si}$ cross polarization transfer. Furthermore, the 29 Si signals in direct experiments build up in a few seconds at 100 K. This fast polarization buildup improves the NMR sensitivity and will be useful for the investigation of direct DNP below 100 K.



Monday, June 18, 2012

Postdoc in MAS DNP (Grenoble)

Dear colleagues,

We have an opening for a postdoctoral fellowship in MAS-DNP NMR at the Institute for Nanosciences and Cryogenics (CEA - Commissariat à l'Energie Atomique et aux Energies Alternatives) / University of Grenoble). Starting date: before the end of 2012. 

The lab is equipped with a state of the art Bruker MAS-DNP system (400 MHz / 263 GHz) and is currently running a program to access MAS temperatures < 100 K. The lab also hosts a second 400 MHz system equipped with 1.3 / 2.5 / 3.2 / 4 mm probes and can access high field instruments through the French TGIR framework (http://www.tgir-rmn.org/). Access to 9 GHz EPR is possible in the lab and access to high field EPR instruments is also possible on campus (collaboration with LNCMI (CNRS), Grenoble). 

Researchers with a strong background or interest in Dynamic Nuclear Polarization / NMR methodology and its application to bio-molecules/materials are particularly welcome to apply. 

This LABEX fellowship is funded by the French National Research Agency (ANR). The duration is 12 months (possible extension up to 24 months). 

For further information regarding details of the research and of the appointment, interested candidates should contact me directly at gael.depaepe@cea.fr

Gaël De Paëpe 

-- 

Dr Gaël De Paëpe 
Laboratoire de Résonances Magnétiques 
Service de Chimie Inorganique et Biologique 
UMR_E 3 CEA-UJF 
CEA Grenoble/INAC/SCIB/LRM 
Commissariat à l'énergie Atomique 
17, rue des Martyrs 
Bâtiment 51C, P.138 
38054 Grenoble 
Cedex 9 - France 
voice +33 4 38 78 47 26 
fax +33 4 38 78 50 90 


==================================== 
This is the AMPERE MAGNETIC RESONANCE mailing list: 

NMR web database: 

Sunday, June 17, 2012

Development of Dissolution DNP-MR Substrates for Metabolic Research

Karlsson, M., et al., Development of Dissolution DNP-MR Substrates for Metabolic Research. Appl. Magn. Reson., 2012: p. 1-14.


Dissolution dynamic nuclear polarization (DNP) provides a broadly applicable and rather simple means of developing probes for the real-time molecular imaging of cellular functions in vivo. The development of novel dissolution DNP substrate formulations is only rewarding for substrates that yield detectable metabolism within few minutes. In addition, in vivo preparations usually require amorphous samples at molar substrate concentrations for an efficient and reproducible DNP step with sufficient material. The composition ranges of novel substrate preparations need to be established experimentally owing to the solute’s impact on vitrification behavior. Here, we describe simple rationales employed in the development of novel substrate preparations for dissolution DNP-magnetic resonance. Solution state substrate polarizations between 10 and 40 % have been obtained for ~40 metabolic substrates in highly concentrated preparations that yield physiologically tolerable solutions with sufficient T 1 for in vivo nuclear magnetic resonance. Substrate metabolism is observed for novel in vivo substrates such as 3-hydroxybutyrate and aspartate.



Friday, June 15, 2012

Simplified THz Instrumentation for High-Field DNP-NMR Spectroscopy

Our very first paper from Bridge12 Technologies.

Maly, T. and J. Sirigiri, Simplified THz Instrumentation for High-Field DNP-NMR Spectroscopy. Appl. Magn. Reson.: p. 1-14.


We present an alternate simplified concept to irradiate a nuclear magnetic resonance sample with terahertz (THz) radiation for dynamic nuclear polarization (DNP) experiments using the TE 01 circular waveguide mode for transmission of the THz power and the illumination of the DNP sample by either the TE 01 or TE 11 mode. Using finite element method and 3D electromagnetic simulations we demonstrate that the average value of the transverse magnetic field induced by the THz radiation and responsible for the DNP effect using the TE 11 or the TE 01 mode are comparable to that generated by the HE 11 mode and a corrugated waveguide. The choice of the TE 11 /TE 01 mode allows the use of a smooth-walled, oversized waveguide that is easier to fabricate and less expensive than a corrugated waveguide required for transmission of the HE 11 mode. Also, the choice of the TE 01 mode can lead to a simplification of gyrotron oscillators that operate in the TE 0n mode, by employing an on-axis rippled-wall mode converter to convert the TE 0n mode into the TE 01 mode either inside or outside of the gyrotron tube. These novel concepts will lead to a significant simplification of the gyrotron, the transmission line and the THz coupler, which are the three main components of a DNP system.



Wednesday, June 13, 2012

Liquid State DNP on Metabolites at 260 GHz EPR/400 MHz NMR Frequency

Krummenacker, J., V. Denysenkov, and T. Prisner, Liquid State DNP on Metabolites at 260 GHz EPR/400 MHz NMR Frequency. Appl. Magn. Reson., 2012: p. 1-8.


We have performed liquid state (“Overhauser”) dynamic nuclear polarization (DNP) experiments at high magnetic field (9.2 T, corresponding to 260 GHz EPR and 400 MHz 1 H-NMR resonance frequency) on solutions of pyruvate, lactate and alanine in water with TEMPOL nitroxide radicals as polarizing agent. We present experimental results showing DNP enhancement on metabolite methyl protons, varying for the different target metabolites. It is shown that the enhancements are achieved through direct coupling between the radicals and the target metabolites in solution, i.e., the effect is not mediated by the solvent water protons. The coupling factors between the TEMPOL radicals and the metabolites observed are a factor of 3–5 smaller compared to direct polarization transfer from TEMPOL to water protons.



Postdoc in NMR, DNP and MRI : Aarhus, Denmark

See: 
for the original post.



We are seeking a candidate for a post doctoral position for the period 15 July 2012 till 14 May 2014. The position is based at the Center for Insoluble Protein Structures (inSPIN) being part of the Interdisciplinary Nanoscience Center (iNANO), Aarhus University.

The candidate is required to have a documented strong background in nuclear magnetic resonance spectroscopy (NMR) and imaging (MRI). Knowledge of optimal control theory and dissolution dynamic nuclear polarization (DNP) will be an advantage. The candidate must have a PhD in the fields of NMR and/or MRI with a methodology focus.

The successful candidate will be involved in the development and implementation of hyperpolarized, spatial selective MRI to identify amyloid disease states. The candidate will collaborate with people in several research groups in an interdisciplinary fashion.
For further information please contact Director, Professor Niels Chr. Nielsen (ncn@inano.au.dk).

Monday, June 11, 2012

Developing Hyperpolarized 13C Spectroscopy and Imaging for Metabolic Studies in the Isolated Perfused Rat Heart

Weiss, K., et al., Developing Hyperpolarized 13C Spectroscopy and Imaging for Metabolic Studies in the Isolated Perfused Rat Heart. Appl. Magn. Reson., 2012: p. 1-14.


Hyperpolarized 13 C magnetic resonance is a powerful tool for the study of cardiac metabolism. In this work, we have implemented protocols for the real-time hyperpolarized 13 C investigation of Langendorff-perfused rat hearts using both non-selective non-localized spectroscopy and fast spectroscopic imaging. Following [1- 13 C] pyruvate infusion, we observed both catabolic and anaplerotic metabolic processes resulting in a number of metabolites, including bicarbonate, carbon dioxide, lactate, alanine and aspartate. Employing fast spectroscopic imaging, we were able to observe regional variations in pyruvate perfusion as well as in lactate and bicarbonate production.



Saturday, June 9, 2012

Overhauser DNP and EPR in a Mobile Setup: Influence of Magnetic Field Inhomogeneity

Neudert, O., et al., Overhauser DNP and EPR in a Mobile Setup: Influence of Magnetic Field Inhomogeneity. Appl. Magn. Reson., 2012: p. 1-17.


Power-dependent Overhauser dynamic nuclear polarization (DNP) enhancements and continuous-wave electron paramagnetic resonance (EPR) spectra of nitroxide radicals were measured in the magnetic field of a mobile Halbach-array permanent magnet and compared with results from a commercially available electromagnet. DNP saturation factors for varying microwave power were obtained from both measurement series and used to investigate how the increased magnetic field inhomogeneity present in the Halbach magnet affects the saturation efficiency. An EPR detection system was designed to allow continuous-wave EPR measurements at microwave power up to 20 W. Our results show that despite the lower magnetic field homogeneity, a Halbach-array magnet can be used for EPR and DNP-enhanced nuclear magnetic resonance of high quality providing almost the same performance as a more homogeneous electromagnet.



Thursday, June 7, 2012

A Mobile DNP Polarizer for Continuous Flow Applications

Ebert, S., et al., A Mobile DNP Polarizer for Continuous Flow Applications. Appl. Magn. Reson., 2012: p. 1-12.


Despite its wide applicability in natural sciences, nuclear magnetic resonance (NMR) still suffers from its inherently low sensitivity. This could be overcome by hyperpolarization of molecules via dynamic nuclear polarization (DNP). Here, we introduce a substantial improvement of a mobile Overhauser DNP polarizer, based on an inexpensive Halbach magnet operating at 0.35 T. It shows an almost vanishing magnetic flux at its outer side and does not disturb other instruments. It can be placed directly next to a superconducting magnet, thus reducing the transport time of the hyperpolarized liquid. However, two problems for DNP applications remain. Firstly, radicals are needed which are often toxic. This problem becomes crucial with regard to medical applications. Secondly, the sample must be transported from the polarization magnet to the place of detection like a magnetic resonance imaging (MRI) scanner, and polarization losses due to T 1 relaxation may occur. We have implemented a flow system into the mobile DNP polarizer, which overcomes both obstacles. The radicals are immobilized in a gel matrix and the hyperpolarized radical-free fluid is subsequently directly pumped into the MRI scanner. It is shown that even at flow conditions, the NMR signal is enhanced due to Overhauser DNP in the Halbach magnet as well as in the MRI scanner (4.7 T) at a distance of 1.4 m. Acquired images demonstrate the use of enhanced and, due to dipolar coupling, inverted NMR signals, which provide an excellent MRI contrast even for small enhancements.

Tuesday, June 5, 2012

DNP Methods for Cardiac Metabolic Imaging with Hyperpolarized [1-13C]pyruvate Large Dose Injection in Pigs

Flori, A., et al., DNP Methods for Cardiac Metabolic Imaging with Hyperpolarized [1-13C]pyruvate Large Dose Injection in Pigs. Appl. Magn. Reson., 2012: p. 1-12.


In this study we set up and optimized a dynamic nuclear polarization (DNP) procedure for the hyperpolarization of a large dose suitable for cardiac metabolic imaging in vivo in swine models. The dose range proposed in this study allowed chemical shift imaging of cardiac metabolism with hyperpolarized [1- 13 C]pyruvate in pigs. We investigated the typical pattern of distribution of [1- 13 C]pyruvate and its downstream metabolites: we analysed the variation of the maximum value of the normalized [1- 13 C]pyruvate signal and the global pyruvate signal in left ventricle (LV). The study reports data obtained with a large dose increase compared to small animal studies: 20 ml of 230 mM [1- 13 C]pyruvate with 16 ± 3 % polarization (mean ± SD), using a DNP system operating at ~1.4 K with a magnetic field of 3.35 T. A significant correlation between the maximum value of the normalized [1- 13 C]pyruvate signal and the global pyruvate signal in the LV was found. The characterization of the dynamic range of the signal and the optimization of the standardized dose could be a starting point for designing pathophysiological studies in experimental large animal models. With this approach the hyperpolarization of metabolic substrates could be applied in biomedical magnetic resonance, which could become one of the most promising models for cardiovascular imaging.



PhD Position in hyperpolarized (HP) xenon and operando solid state NMR

From the NMR list server:


Dear all, 

If you know a potential candidate for a PhD in my group, please forward this message to him or her. 

kind regards, 
C.Fernandez 

** PhD Position in hyperpolarized (HP) xenon and operando solid state NMR. ** 

A fully funded 36 month PhD position has become available at the Laboratory of Catalysis and Spectrochemistry (LCS), ENSICAEN / University of CAEN, Normandy (France). 

We are seeking a highly motivated individual interested in a PhD project in the group of Christian Fernandez. 

The PhD project, as a part of a more general project involving four laboratories of the center of excellence EMC3 (Energy Materials and Clean Combustion Center), aim at developing the application of Xenon hyperpolarization (HP) and solid state NMR to the study natural polymers used as support of organometallic catalysts and which will be prepared using ionic liquid media. The project involves the participation to the setup and tests of an HP Xenon system, the development of quantitative analytic methods using this HP system to study porosity, diffusion and accessibility of active sites. The use of HP xenon in combination with the operando NMR will also be investigated in addition to other advanced solid state NMR techniques. 

The LCS laboratory is equipped with two NMR spectrometers (operating at 400 and 500 MHz for proton) and additionally has access to high field spectrometers in the frame of a national French NMR network (750 MHz and more). 

Candidates should hold a master degree in chemistry or chemical-physics and are expected to provide the contact details of two scientific referees. 

Interested candidates should contact: 

Prof. Christian Fernandez 

Laboratoire Catalyse et Spectrochimie and Center of excellence EMC3 (Energy Materials and Clean Combustion Center) ENSICAEN, Université de Caen, CNRS 

6 bd du Maréchal Juin, 14050 CAEN, France 

Tel: +33 (0) 2 31 45 28 13 
Fax: +33 (0) 2 31 45 28 22 


==================================== 

This is the AMPERE MAGNETIC RESONANCE mailing list: 
NMR web database: 

Sunday, June 3, 2012

High-Temperature Dynamic Nuclear Polarization Enhanced Magic-Angle-Spinning NMR

Akbey, Ü., A. Linden, and H. Oschkinat, High-Temperature Dynamic Nuclear Polarization Enhanced Magic-Angle-Spinning NMR. Appl. Magn. Reson.: p. 1-10.


Dynamic nuclear polarization (DNP) transfers electron spin-polarization to nuclear spins in close proximity, increasing sensitivity by two-to-three orders of magnitude. This enables nuclear magnetic resonance (NMR) experiments on samples with low concentrations of analyte. The requirement of using cryogenic temperatures in DNP-enhanced solid-state NMR (ssNMR) experiments may impair the resolution and hence limit its broad application to biological systems. In this work, we introduce a “High-Temperature DNP” approach, which aims at increasing spectral resolution by performing experiments at temperatures of around 180 K instead of ~100 K. By utilizing the extraordinary enhancements obtained on deuterated proteins, still sufficiently large DNP enhancements of 11–18 are obtained for proton and carbon, respectively. We recorded high sensitivity 2D 13 C– 13 C spectra in ~9 min with higher resolution than at 100 K, which has similar resolution to the one obtained at room temperature for some favorable residues.



Friday, June 1, 2012

A Super-Wide Bore DNP System for Multiple Sample Polarization: Cryogenic Performance and Polarization at Low Temperature

Crémillieux, Y., et al., A Super-Wide Bore DNP System for Multiple Sample Polarization: Cryogenic Performance and Polarization at Low Temperature. Appl. Magn. Reson.: p. 1-14.


The volume of polarized sample and the delay required between successive polarizations of samples represent serious constraints for dynamic nuclear polarization (DNP) applications. With these limitations in mind, a DNP polarizer, based on a super-wide bore (150-mm diameter) vertical magnet operating at 3.35 T, was designed. The working diameter for loading/unloading samples is equal to 46 mm and the microwave cavity can accommodate up to three samples. The cryostat can be cooled to 4.2 K in typically 2 h and filled with liquid helium in 1 h. Once filled with liquid helium, the cryostat hold time is on the order of 4 h and a minimum temperature of 1.19 K can be reached. In situ polarization levels at low temperature were measured between 5 and 10 % in single and multiple samples of 13 C-labeled urea and glycine.