Friday, September 28, 2012

Cluster formation restricts dynamic nuclear polarization of xenon in solid mixtures

Kuzma, N.N., et al., Cluster formation restricts dynamic nuclear polarization of xenon in solid mixtures. J. Chem. Phys., 2012. 137(10): p. 104508-6.


During dynamic nuclear polarization (DNP) at 1.5 K and 5 T, 129Xe nuclear magnetic resonance (NMR) spectra of a homogeneous xenon/1-propanol/trityl-radical solid mixture exhibit a single peak, broadened by 1H neighbors. A second peak appears upon annealing for several hours at 125 K. Its characteristic width and chemical shift indicate the presence of spontaneously formed pure Xe clusters. Microwave irradiation at the appropriate frequencies can bring both peaks to either positive or negative polarization. The peculiar time evolution of 129Xe polarization in pure Xe clusters during DNP can be modelled as an interplay of spin diffusion and T1 relaxation. Our simple spherical-cluster model offers a sensitive tool to evaluate major DNP parameters in situ, revealing a severe spin-diffusion bottleneck at the cluster boundaries and a significant sample overheating due to microwave irradiation. Subsequent DNP system modifications designed to reduce the overheating resulted in four-fold increase of 129Xe polarization, from 5.3% to 21%.

Wednesday, September 26, 2012

Development and Applications of High—Frequency Gyrotrons in FIR FU Covering the sub-THz to THz Range

Idehara, T. and S. Sabchevski, Development and Applications of High—Frequency Gyrotrons in FIR FU Covering the sub-THz to THz Range. J. Infrared Millim. Te., 2012. 33(7): p. 667-694.


Powerful sources of coherent radiation in the sub-terahertz and in the terahertz frequency range of the electromagnetic spectrum are necessary for a great and continuously expanding number of applications in the physical research and in various advanced technological processes as well as in radars, communication systems, for remote sensing and inspection etc .. In recent years, a spectacular progress in the development of various gyro-devices and in particular of the powerful high frequency (sub-terahertz and terahertz) gyrotron oscillators has demonstrated a remarkable potential for bridging the so-called terahertz power gap and stimulated many novel and prospective applications. In this review paper we outline two series of such devices, namely the Gyrotron FU Series which includes pulsed gyrotrons and Gyrotron FU CW Series which consist of tubes operated in a CW (continuous wave) or long pulse mode, both developed at the FIR FU Center. We present the most remarkable achievements of these devices and illustrate their applications by some characteristic examples. An outlook for the further extension of the Gyrotron FU CW Series is also provided.


Monday, September 24, 2012

Development of a Compact sub-THz Gyrotron FU CW CI for Application to High Power THz Technologies

Idehara, T., et al., Development of a Compact sub-THz Gyrotron FU CW CI for Application to High Power THz Technologies. J. Infrared Millim. Te., 2012. 33(7): p. 724-744.


For application of high frequency gyrotron to high power THz technology, Gyrotron FU CW series is being developed in FIR FU. Gyrotron FU CW CI is developed as one of sub-THz gyrotrons included in the series. The advantage of the gyrotron is compactness using a compact superconducting magnet and compact power supply system, which makes the accesses of the gyrotron to applied large-scale devices easier and extends the applications of gyrotron to wider fields. The designed frequency and cavity mode are 394.5 GHz and TE 26 mode for application to the 600 MHz DNP-NMR spectroscopy. As the operation results, the frequency and the output power were 394.03 GHz and around 30 W, respectively, which are available for the application to the 600 MHz DNP-NMR measurement. In addition, this gyrotron can operate at many other frequencies and cavity modes for application to high power THz technologies in wide fields. In this paper, the design and the operation results including long pulse or CW mode are presented.


Thursday, September 20, 2012

1H relaxation dispersion in solutions of nitroxide radicals: Effects of hyperfine interactions with 14N and 15N nuclei

Kruk, D., et al., 1H relaxation dispersion in solutions of nitroxide radicals: Effects of hyperfine interactions with 14N and 15N nuclei. J. Chem. Phys., 2012. 137(4): p. 044512-12.

1H relaxation dispersion of decalin and glycerol solutions of nitroxide radicals, 4-oxo-TEMPO-d16-15N and 4-oxo-TEMPO-d16-14N was measured in the frequency range of 10 kHz–20 MHz (for 1H) using STELAR Field Cycling spectrometer. The purpose of the studies is to reveal how the spin dynamics of the free electron of the nitroxide radical affects the proton spin relaxation of the solvent molecules, depending on dynamical properties of the solvent. Combining the results for both solvents, the range of translational diffusion coefficients, 10−9–10−11 m2/s, was covered (these values refer to the relative diffusion of the solvent and solute molecules). The data were analyzed in terms of relaxation formulas including the isotropic part of the electron spin – nitrogen spin hyperfine coupling (for the case of 14N and 15N) and therefore valid for an arbitrary magnetic field. The influence of the hyperfine coupling on 1H relaxation of solvent molecules depending on frequency and time-scale of the translational dynamics was discussed in detail. Special attention was given to the effect of isotope substitution (14N/15N). In parallel, the influence of rotational dynamics on the inter-molecular (radical – solvent) electron spin – proton spin dipole-dipole coupling (which is the relaxation mechanism of solvent protons) was investigated. The rotational dynamics is of importance as the interacting spins are not placed in the molecular centers. It was demonstrated that the role of the isotropic hyperfine coupling increases for slower dynamics, but it is of importance already in the fast motion range (10−9m2/s). The isotope effects is small, however clearly visible; the 1H relaxation rate for the case of 15N is larger (in the range of lower frequencies) than for 14N. It was shown that when the diffusion coefficient decreases below 5 × 10−11 m2/s electron spin relaxation becomes of importance and its role becomes progressively more significant when the dynamics slows done. As far as the influence of the rotational dynamics is concerned, it was show that this process is of importance not only in the range of higher frequencies (like for diamagnetic solutions) but also at low and intermediate frequencies.

Friday, September 14, 2012

Theory for cross effect dynamic nuclear polarization under magic-angle spinning in solid state nuclear magnetic resonance: The importance of level crossings

Thurber, K.R. and R. Tycko, Theory for cross effect dynamic nuclear polarization under magic-angle spinning in solid state nuclear magnetic resonance: The importance of level crossings. J. Chem. Phys., 2012. 137(8): p. 084508-14.


We present theoretical calculations of dynamic nuclear polarization (DNP) due to the cross effect in nuclear magnetic resonance under magic-angle spinning (MAS). Using a three-spin model (two electrons and one nucleus), cross effect DNP with MAS for electron spins with a large g-anisotropy can be seen as a series of spin transitions at avoided crossings of the energy levels, with varying degrees of adiabaticity. If the electron spin-lattice relaxation time T(1e) is large relative to the MAS rotation period, the cross effect can happen as two separate events: (i) partial saturation of one electron spin by the applied microwaves as one electron spin resonance (ESR) frequency crosses the microwave frequency and (ii) flip of all three spins, when the difference of the two ESR frequencies crosses the nuclear frequency, which transfers polarization to the nuclear spin if the two electron spins have different polarizations. In addition, adiabatic level crossings at which the two ESR frequencies become equal serve to maintain non-uniform saturation across the ESR line. We present analytical results based on the Landau-Zener theory of adiabatic transitions, as well as numerical quantum mechanical calculations for the evolution of the time-dependent three-spin system. These calculations provide insight into the dependence of cross effect DNP on various experimental parameters, including MAS frequency, microwave field strength, spin relaxation rates, hyperfine and electron-electron dipole coupling strengths, and the nature of the biradical dopants.



Wednesday, September 12, 2012

Gyrotron DNP NMR, post-doc position

A 4 year postdoc position is available at the EPF in Lausanne. More information can be found here:


If the link doesn't work, go to http://www.telejob.ethz.ch/ and search for DNP


Inserat Nr. 21707
Vom Mittwoch, 12. September 2012
Arbeitsort Lausanne
Arbeitsbeginn sofort
Vertragsdauer 4 Jahre
Anstellung 100%


EPFL enjoys a strong position in Dynamic Nuclear Polarization for NMR, because it has developed original designs using several approaches. A campus-wide collaboration in particular with the CRPP (fusion research center, specialized in gyrotrons) has allowed us to design and build a gyrotron for solid state NMR. The physical properties of the gyrotron were first investigated at CRPP. The gyrotron will move to our NMR lab in October. Together with another post-doc already in place, the successful applicant will run all the necessary tests prior to engaging in NMR research activities per say. Funding is of EPFL, implying that the research is not tied to existing proposal. We benefit greatly from a close ties with Swiss-to-12, a company dedicated to the manufacturing of THz components. 

Contact : jean-philippe.ansermet@epfl.ch See : http://www.lpmn.ch

Thursday, September 6, 2012

Liquid state DNP for water accessibility measurements on spin-labeled membrane proteins at physiological temperatures

Doll, A., et al., Liquid state DNP for water accessibility measurements on spin-labeled membrane proteins at physiological temperatures. J. Magn. Reson., 2012. 222(0): p. 34-43.


We demonstrate the application of continuous wave dynamic nuclear polarization (DNP) at 0.35T for site-specific water accessibility studies on spin-labeled membrane proteins at concentrations in the 10-100muM range. The DNP effects at such low concentrations are weak and the experimentally achievable dynamic nuclear polarizations can be below the equilibrium polarization. This sensitivity problem is solved with an optimized home-built DNP probe head consisting of a dielectric microwave resonator and a saddle coil as close as possible to the sample. The performance of the probe head is demonstrated with both a modified pulsed EPR spectrometer and a dedicated CW EPR spectrometer equipped with a commercial NMR console. In comparison to a commercial pulsed ENDOR resonator, the home-built resonator has an FID detection sensitivity improvement of 2.15 and an electron spin excitation field improvement of 1.2. The reproducibility of the DNP results is tested on the water soluble maltose binding protein MalE of the ABC maltose importer, where we determine a net standard deviation of 9% in the primary DNP data in the concentration range between 10 and 100muM. DNP parameters are measured in a spin-labeled membrane protein, namely the vitamin B(12) importer BtuCD in both detergent-solubilized and reconstituted states. The data obtained in different nucleotide states in the presence and absence of binding protein BtuF reveal the applicability of this technique to qualitatively extract water accessibility changes between different conformations by the ratio of primary DNP parameters . The -ratio unveils the physiologically relevant transmembrane communication in the transporter in terms of changes in water accessibility at the cytoplasmic gate of the protein induced by both BtuF binding at the periplasmic region of the transporter and ATP binding at the cytoplasmic nucleotide binding domains.

Tuesday, September 4, 2012

Course on "Dissolution Dynamic Nuclear Polarization for NMR spectroscopy" November 14-16, 2012 at EPFL, Switzerland

Repost from: AMPERE MAGNETIC RESONANCE mailing list: 


We would like to announce a three-day course for PhD students and Post-Docs on 

"Dissolution Dynamic Nuclear Polarization" 

The course will start at 1pm on Wednesday November the 14th and will end at 5pm on Friday 16th, and will be held at the Ecole Polytechnique Fédérale de Lausanne (EPFL), Switzerland, at the Laboratory of Biomolecular Magnetic Resonance (LRMB). 
The course is supported by the COST network 'EuroHyperPol'. Travel stipends will be awarded on a competitive base by an international committee. Students and Post-Docs are invited to describe their interest by email, and forward a letter of support from their supervisors. 

* Registration 
please register at the following adress: 
subscription fees: 100 CHF 

* Information 
geoffrey.bodenhausen (at) epfl.ch
sami.jannin (at) epfl.ch

* Objectives 
Dissolution Dynamic Nuclear Polarization (DNP) provides a way to enhance NMR signals in liquids by more than 4 orders of magnitude. We present the current state-of-the-art and recent advances of this technique. 

* Content 
Lectures and seminars: 11 Hours 
Experimental demonstrations with hands-on participation: 7 Hours 

Day 1: Lectures, 1 pm - 5 pm: Theoretical aspects of DNP 

- Introduction to DNP-enhanced NMR 
- Principles of Dissolution-DNP 
- Low temperature DNP Mechanisms 
- Applications to imaging and chemistry 

Day 2: Lectures, 9 am - 12 am: Experimental aspects of DNP 

- Hardware for DNP 
- Hardware for Dissolution 

Demonstrations, 1 pm - 5 pm 

- Sample Preparation 
- Preparation of a dissolution DNP experiment 

Day 3: Demonstrations, 9 am - 12 am: Practical DNP at the Laboratory of Biomolecular Magnetic Resonance (LRMB) 

- Dissolution DNP experiments 

Seminars, 1 pm - 5 pm 

- All students are expected to give a short presentation on applications of DNP that they wish to implement to enhance their own research subjects 

*Required prior knowledge 
Basic understanding of NMR 

Sami Jannin 
Laboratory of Biomolecular Magnetic Resonance (LRMB) 

Paper mail: 

EPFL 
LRMB - ISIC - SB 
BCH 1534 (Bâtiment de chimie UNIL) 
CH-1015 Lausanne 
Switzerland 

Phone +41 21 693 97 24 
Fax +41 21 693 94 35

[NMR] Postdoc - MAS-DNP at CEA Grenoble

Repost from: AMPERE MAGNETIC RESONANCE mailing list:



Post-Doc (2 years) - CEA INAC (Grenoble/France) 

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 using Helium spinning. 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/). 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 fellowship is funded by the French National Research Agency (ANR). The initial duration is 12 months with an additional 12 months extension upon results. 

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 
Office P.132a / Lab P.138 
38054 Grenoble 
Cedex 9 - France 
voice (office) +33 4 38 78 65 70 
voice (lab) +33 4 38 78 47 26 
fax +33 4 38 78 50 90

Monday, September 3, 2012

Liquid state DNP for water accessibility measurements on spin-labeled membrane proteins at physiological temperatures

Doll, A., et al., Liquid state DNP for water accessibility measurements on spin-labeled membrane proteins at physiological temperatures. J. Magn. Reson., 2012. 222(0): p. 34-43.


We demonstrate the application of continuous wave dynamic nuclear polarization (DNP) at 0.35 T for site-specific water accessibility studies on spin-labeled membrane proteins at concentrations in the 10–100 μM range. The DNP effects at such low concentrations are weak and the experimentally achievable dynamic nuclear polarizations can be below the equilibrium polarization. This sensitivity problem is solved with an optimized home-built DNP probe head consisting of a dielectric microwave resonator and a saddle coil as close as possible to the sample. The performance of the probe head is demonstrated with both a modified pulsed EPR spectrometer and a dedicated CW EPR spectrometer equipped with a commercial NMR console. In comparison to a commercial pulsed ENDOR resonator, the home-built resonator has an FID detection sensitivity improvement of 2.15 and an electron spin excitation field improvement of 1.2. The reproducibility of the DNP results is tested on the water soluble maltose binding protein MalE of the ABC maltose importer, where we determine a net standard deviation of 9% in the primary DNP data in the concentration range between 10 and 100 μM. DNP parameters are measured in a spin-labeled membrane protein, namely the vitamin B12 importer BtuCD in both detergent-solubilized and reconstituted states. The data obtained in different nucleotide states in the presence and absence of binding protein BtuF reveal the applicability of this technique to qualitatively extract water accessibility changes between different conformations by the ratio of primary DNP parameters ϵ. The ϵ-ratio unveils the physiologically relevant transmembrane communication in the transporter in terms of changes in water accessibility at the cytoplasmic gate of the protein induced by both BtuF binding at the periplasmic region of the transporter and ATP binding at the cytoplasmic nucleotide binding domains.