Friday, May 30, 2014

Structural Characterization of Micro- and Mesoporous Carbon Materials Using In Situ High Pressure129Xe NMR Spectroscopy


Oschatz, M., et al., Structural Characterization of Micro- and Mesoporous Carbon Materials Using In Situ High Pressure129Xe NMR Spectroscopy. Chemistry of Materials, 2014. 26(10): p. 3280-3288.


In situ high pressure 129Xe NMR spectroscopy in combination with volumetric adsorption measurements were used for the textural characterization of different carbon materials with well-defined porosity including microporous carbide-derived carbons, ordered mesoporous carbide-derived carbon, and ordered mesoporous CMK-3. Adsorption/desorption isotherms were measured also by NMR up to relative pressures close to p/p0 = 1 at 237 K. The 129Xe NMR chemical shift of xenon adsorbed in porous carbons is found to be correlated with the pore size in analogy to other materials such as zeolites. In addition, these measurements were performed loading the samples with n-nonane. Nonane molecules preferentially block the micropores. However, 129Xe NMR spectroscopy proves that the nonane also influences the mesopores, thus providing information about the pore system in hierarchically structured materials.

Wednesday, May 28, 2014

Synthesis and evaluation of nitroxide-based oligoradicals for low-temperature dynamic nuclear polarization in solid state NMR


Yau, W.-M., K.R. Thurber, and R. Tycko, Synthesis and evaluation of nitroxide-based oligoradicals for low-temperature dynamic nuclear polarization in solid state NMR. J. Magn. Reson., 2014(0).


We describe the synthesis of new nitroxide-based biradical, triradical, and tetraradical compounds and the evaluation of their performance as paramagnetic dopants in dynamic nuclear polarization (DNP) experiments in solid state nuclear magnetic resonance (NMR) spectroscopy with magic-angle spinning (MAS). Under our experimental conditions, which include temperatures in the 25-30 K range, a 9.4 T magnetic field, MAS frequencies of 6.2-6.8 kHz, and microwave irradiation at 264.0 GHz from a 800 mW extended interaction oscillator source, the most effective compounds are triradicals that are related to the previously-described compound DOTOPA-TEMPO (see Thurber et al., J. Magn. Reson., vol. 204, p. 303, 2010), but have improved solubility in glycerol/water solvent near neutral pH. Using these compounds at 30 mM total nitroxide concentration, we observe DNP enhancement factors of 92-128 for cross-polarized 13C NMR signals from 15N,13C-labeled melittin in partially protonated glycerol/water, and build-up times of 2.6-3.8 s for1H spin polarizations. Net sensitivity enhancements with biradical and tetraradical dopants, taking into account absolute 13C NMR signal amplitudes and build-up times, are approximately 2-4 times lower than with the best triradicals.

Monday, May 26, 2014

Perturbation of nuclear spin polarizations in solid state NMR of nitroxide-doped samples by magic-angle spinning without microwaves

Happy Memorial Day, everyone.


Thurber, K.R. and R. Tycko, Perturbation of nuclear spin polarizations in solid state NMR of nitroxide-doped samples by magic-angle spinning without microwaves. J Chem Phys, 2014. 140(18): p. 184201.


We report solid state (13)C and (1)H nuclear magnetic resonance (NMR) experiments with magic-angle spinning (MAS) on frozen solutions containing nitroxide-based paramagnetic dopants that indicate significant perturbations of nuclear spin polarizations without microwave irradiation. At temperatures near 25 K, (1)H and cross-polarized (13)C NMR signals from (15)N,(13)C-labeled L-alanine in trinitroxide-doped glycerol/water are reduced by factors as large as six compared to signals from samples without nitroxide doping. Without MAS or at temperatures near 100 K, differences between signals with and without nitroxide doping are much smaller. We attribute most of the reduction of NMR signals under MAS near 25 K to nuclear spin depolarization through the cross-effect dynamic nuclear polarization mechanism, in which three-spin flips drive nuclear polarizations toward equilibrium with spin polarization differences between electron pairs. When T1e is sufficiently long relative to the MAS rotation period, the distribution of electron spin polarization across the nitroxide electron paramagnetic resonance lineshape can be very different from the corresponding distribution in a static sample at thermal equilibrium, leading to the observed effects. We describe three-spin and 3000-spin calculations that qualitatively reproduce the experimental observations.

Sunday, May 25, 2014

36th Magnetic Resonance Discussion Group Meeting of the Gesellschaft Deutscher Chemiker (GDCh)

From the Ampere Magnetic Resonance List


Dear Colleagues,

The Leibniz-Institut für Molekulare Pharmakologie (FMP), the Physikalisch-Technische Bundesanstalt (PTB), the Max-Delbrück-Centrum (MDC) and the Freie Universität Berlin will be hosting the 36th Magnetic Resonance Discussion Group Meeting of the Gesellschaft Deutscher Chemiker (GDCh) from Sep 29-Oct 2, 2014. The meeting will be hold in conjunction with a DIP satellite meeting "Progress in DNP".

The program will cover a wide range of magnetic resonance topics addressing participants from both academia and industry. These topics will include but are not limited to solution and solid-state NMR spectroscopy, magnetic resonance imaging, and EPR spectroscopy. Applications cover the fields of small molecules and materials, of proteins and nucleic acids, medical imaging, polymers and pharmaceutical compounds, EPR and hyperpolarization, and computational methods.


For further details please follow this link:

Please forward this announcement to anyone who might be interested.

Hartmut Oschkinat Thomas Risse Leif Schröder

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Friday, May 23, 2014

Optimized reverse micelle surfactant system for high-resolution NMR spectroscopy of encapsulated proteins and nucleic acids dissolved in low viscosity fluids


Recently the group of Joshua Wand has described the use of reverse micelles as a platform for DNP for solution-state NMR spectroscopy. Although this article is not directly related to DNP it gives more insight into the use of reverse micelles to obtain high resolution NMR spectra of large marcromolecules.



Dodevski, I., et al., Optimized reverse micelle surfactant system for high-resolution NMR spectroscopy of encapsulated proteins and nucleic acids dissolved in low viscosity fluids. J Am Chem Soc, 2014. 136(9): p. 3465-74.


An optimized reverse micelle surfactant system has been developed for solution nuclear magnetic resonance studies of encapsulated proteins and nucleic acids dissolved in low viscosity fluids. Comprising the nonionic 1-decanoyl-rac-glycerol and the zwitterionic lauryldimethylamine-N-oxide (10MAG/LDAO), this mixture is shown to efficiently encapsulate a diverse set of proteins and nucleic acids. Chemical shift analyses of these systems show that high structural fidelity is achieved upon encapsulation. The 10MAG/LDAO surfactant system reduces the molecular reorientation time for encapsulated macromolecules larger than ~20 kDa leading to improved overall NMR performance. The 10MAG/LDAO system can also be used for solution NMR studies of lipid-modified proteins. New and efficient strategies for optimization of encapsulation conditions are described. 10MAG/LDAO performs well in both the low viscosity pentane and ultralow viscosity liquid ethane and therefore will serve as a general surfactant system for initiating solution NMR studies of proteins and nucleic acids.

Wednesday, May 21, 2014

Enhanced performance large volume dissolution-DNP


Bowen, S. and J.H. Ardenkjaer-Larsen, Enhanced performance large volume dissolution-DNP. J Magn Reson, 2014. 240(0): p. 90-4.


A systematic study of the performance of the dissolution process in dissolution-DNP is presented. A relatively simple set of modifications is made to the standard Hypersense dissolution system to enable polarization of large volume samples. These consist of a large volume sample cup along with supporting modifications to the dissolution head and related components. Additional modifications were made to support the mapping of the temperature/pressure space of the dissolution process as well as enabling the use of large volumes of solvent and improving the robustness of the system. No loss of polarization was observed as sample size was increased to the 1 g capacity of the large volume cup and for a dilution factor as low as 1:10.

Monday, May 19, 2014

The Feasibility of Formation and Kinetics of NMR Signal Amplification by Reversible Exchange (SABRE) at High Magnetic Field (9.4 T)


Barskiy, D.A., et al., The feasibility of formation and kinetics of NMR signal amplification by reversible exchange (SABRE) at high magnetic field (9.4 T). J Am Chem Soc, 2014. 136(9): p. 3322-5.


(1)H NMR signal amplification by reversible exchange (SABRE) was observed for pyridine and pyridine-d5 at 9.4 T, a field that is orders of magnitude higher than what is typically utilized to achieve the conventional low-field SABRE effect. In addition to emissive peaks for the hydrogen spins at the ortho positions of the pyridine substrate (both free and bound to the metal center), absorptive signals are observed from hyperpolarized orthohydrogen and Ir-complex dihydride. Real-time kinetics studies show that the polarization build-up rates for these three species are in close agreement with their respective (1)H T1 relaxation rates at 9.4 T. The results suggest that the mechanism of the substrate polarization involves cross-relaxation with hyperpolarized species in a manner similar to the spin-polarization induced nuclear Overhauser effect. Experiments utilizing pyridine-d5 as the substrate exhibited larger enhancements as well as partial H/D exchange for the hydrogen atom in the ortho position of pyridine and concomitant formation of HD molecules. While the mechanism of polarization enhancement does not explicitly require chemical exchange of hydrogen atoms of parahydrogen and the substrate, the partial chemical modification of the substrate via hydrogen exchange means that SABRE under these conditions cannot rigorously be referred to as a non-hydrogenative parahydrogen induced polarization process.

Friday, May 16, 2014

Dynamic nuclear polarisation enhanced 14N overtone MAS NMR spectroscopy


Rossini, A., L. Emsley, and L.A. O'Dell, Dynamic nuclear polarisation enhanced 14N overtone MAS NMR spectroscopy. Phys. Chem. Chem. Phys., 2014.


Dynamic nuclear polarisation (DNP) has been used to obtain magic angle spinning 14NOT (nitrogen-14 overtone) solid-state NMR spectra from several model amino acids, with both direct and indirect observation of the 14NOT signal. The crystalline solids were impregnated with biradical solutions of organic liquids that do not dissolve the crystalline phase. The bulk phase was then polarized via 1H spin diffusion from the highly-polarized surface 1H nuclei, resulting in 1H DNP signal enhancements of around two orders of magnitude. Cross polarisation from 1H nuclei directly to the 14N overtone transition is demonstrated under magic angle spinning, using a standard pulse sequence with a relatively short contact time (on the order of 100 [small mu ]s). This method can be used to acquire 14N overtone MAS powder patterns that match closely with simulated line shapes, allowing isotropic chemical shifts and quadrupolar parameters to be measured. DNP enhancement also allows the rapid acquisition of 2D 14NOT heteronuclear correlation spectra from natural abundance powder samples. 1H-14NOT HETCOR and 13C-14NOT HMQC pulse sequences were used to observe all single-bond H-N and C-N correlations in histidine hydrochloride monohydrate, with the spectra obtained in a matter of hours. Due to the high natural abundance of the 14N isotope (99.6 %) and the advantages of observing the overtone transition, these methods provide an attractive route to the observation of C-N correlations from samples at natural isotopic abundance and enable the high resolution measurement of 14N chemical shifts and quadrupolar interaction parameters.

Post-doc in hyperpolarized 129Xe MRI - CEA Saclay, France

From the Ampere Magnetic Resonance List:

A project untitled: « Polarized Xenon-MRI for diagnosis and follow up of Chest Tumors » is granted by the French programme « Projets de recherche dans le domaine de la physique, des mathématiques ou des sciences de l'ingénieur appliqués au cancer ».

We are looking for a post-doctoral fellow for one year starting July 2014. The place is CEA-Saclay (25 km in the S-W of Paris).

Abstract

Diagnosis and treatment of early stages of non-small-cell lung cancer (NSCLC) could drastically modify the outcome in terms of disease-free and overall survival.

MRI offers several advantages owing to its low invasiveness, its harmlessness and its spatial in-depth resolution but suffers from poor sensitivity. Very few MRI methods are able to detect events at the air-liquid interface (i.e. lung epithelium), due to the low number of detectable atoms present and the strong local magnetic field inhomogeneity. Different strategies can be used to improve MRI detection threshold in lungs including the use of hyperpolarized gases such as 3He and 129Xe. These species can be detected at very low concentration thanks to the gain by several orders of magnitude in nuclear polarization. 

In the project with Institut Gustave Roussy (IGR) and CEA/DSV, we propose a new approach based on 129Xe MRI biosensors for the early diagnosis of NSCLC and follow up of treatment efficacy.

The candidate will belong to the team having in charge the NMR/MRI part. He/she must have a strong background in MRI, an experience of in vivo experiments, and some notions of spin hyperpolarization. The laboratory owns several high-field spectrometers and two home-built setups for optical pumping of noble gases, and has access to the high-field small animal MR imagers at NeuroSpin (40 meters apart).

Interested candidate must send a detailed curriculum vitae and a letter of motivation to : Patrick Berthault 

CEA Saclay
IRAMIS/NIMBE/UMR3299
PC #9
91191 Gif sur Yvette, France

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Wednesday, May 14, 2014

High field dynamic nuclear polarization NMR with surfactant sheltered biradicals


Kiesewetter, M.K., et al., High field dynamic nuclear polarization NMR with surfactant sheltered biradicals. J Phys Chem B, 2014. 118(7): p. 1825-30.


We illustrate the ability to place a water-insoluble biradical, bTbk, into a glycerol/water matrix with the assistance of a surfactant, sodium octyl sulfate (SOS). This surfactant approach enables a previously water insoluble biradical, bTbk, with favorable electron-electron dipolar coupling to be used for dynamic nuclear polarization (DNP) nuclear magnetic resonance (NMR) experiments in frozen, glassy, aqueous media. Nuclear Overhauser enhancement (NOE) and paramagnetic relaxation enhancement (PRE) experiments are conducted to determine the distribution of urea and several biradicals within the SOS macromolecular assembly. We also demonstrate that SOS assemblies are an effective approach by which mixed biradicals are created through an assembly process.

Monday, May 12, 2014

Dynamic nuclear polarization NMR enables the analysis of sn-Beta zeolite prepared with natural abundance (119)sn precursors


Gunther, W.R., et al., Dynamic nuclear polarization NMR enables the analysis of sn-Beta zeolite prepared with natural abundance (119)sn precursors. J Am Chem Soc, 2014. 136(17): p. 6219-22.


The catalytic activity of tin-containing zeolites, such as Sn-Beta, is critically dependent on the successful incorporation of the tin metal center into the zeolite framework. However, synchrotron-based techniques or solid-state nuclear magnetic resonance (ssNMR) of samples enriched with (119)Sn isotopes are the only reliable methods to verify framework incorporation. This work demonstrates, for the first time, the use of dynamic nuclear polarization (DNP) NMR for characterizing zeolites containing approximately 2 wt % of natural abundance Sn without the need for (119)Sn isotopic enrichment. The biradicals TOTAPOL, bTbK, bCTbK, and SPIROPOL functioned effectively as polarizing sources, and the solvent enabled proper transfer of spin polarization from the radical's unpaired electrons to the target nuclei. Using bCTbK led to an enhancement (epsilon) of 75, allowing the characterization of natural-abundance (119)Sn-Beta with excellent signal-to-noise ratios in <24 h. Without DNP, no (119)Sn resonances were detected after 10 days of continuous analysis.

Friday, May 9, 2014

Toward nanomolar detection by NMR through SABRE hyperpolarization


Eshuis, N., et al., Toward nanomolar detection by NMR through SABRE hyperpolarization. J Am Chem Soc, 2014. 136(7): p. 2695-8.


SABRE is a nuclear spin hyperpolarization technique based on the reversible association of a substrate molecule and para-hydrogen (p-H2) to a metal complex. During the lifetime of such a complex, generally fractions of a second, the spin order of p-H2 is transferred to the nuclear spins of the substrate molecule via a transient scalar coupling network, resulting in strongly enhanced NMR signals. This technique is generally applied at relatively high concentrations (mM), in large excess of substrate with respect to metal complex. Dilution of substrate ligands below stoichiometry results in progressive decrease of signal enhancement, which precludes the direct application of SABRE to the NMR analysis of low concentration (muM) solutions. Here, we show that the efficiency of SABRE at low substrate concentrations can be restored by addition of a suitable coordinating ligand to the solution. The proposed method allowed NMR detection below 1 muM in a single scan.

Wednesday, May 7, 2014

Paramagnet induced signal quenching in MAS-DNP experiments in frozen homogeneous solutions


Corzilius, B., et al., Paramagnet induced signal quenching in MAS-DNP experiments in frozen homogeneous solutions. J Magn Reson, 2014. 240(0): p. 113-23.


The effects of nuclear signal quenching induced by the presence of a paramagnetic polarizing agent are documented for conditions used in magic angle spinning (MAS)-dynamic nuclear polarization (DNP) experiments on homogeneous solutions. In particular, we present a detailed analysis of three time constants: (1) the longitudinal build-up time constant TB for (1)H; (2) the rotating frame relaxation time constant T1rho for (1)H and (13)C and (3) T2 of (13)C, the transverse relaxation time constant in the laboratory frame. These relaxation times were measured during microwave irradiation at a magnetic field of 5 T (140 GHz) as a function of the concentration of four polarizing agents: TOTAPOL, 4-amino-TEMPO, trityl (OX063), and Gd-DOTA and are compared to those obtained for a sample lacking paramagnetic doping. We also report the EPR relaxation time constants T1S and T2S, the DNP enhancements, epsilon, and the parameter E, defined below, which measures the sensitivity enhancement for the four polarizing agents as a function of the electron concentration. We observe substantial intensity losses (paramagnetic quenching) with all of the polarizing agents due to broadening mechanisms and cross relaxation during MAS. In particular, the monoradical trityl and biradical TOTAPOL induce approximately 40% and 50% loss of signal intensity. In contrast there is little suppression of signal intensity in static samples containing these paramagnetic species. Despite the losses due to quenching, we find that all of the polarizing agents provide substantial gains in signal intensity with DNP, and in particular that the net enhancement is optimal for biradicals that operate with the cross effect. We discuss the possibility that much of this polarization loss can be regained with the development of instrumentation and methods to perform electron decoupling.

Monday, May 5, 2014

Observation of strongly forbidden solid effect dynamic nuclear polarization transitions via electron-electron double resonance detected NMR


Smith, A.A., et al., Observation of strongly forbidden solid effect dynamic nuclear polarization transitions via electron-electron double resonance detected NMR. J Chem Phys, 2013. 139(21): p. 214201.


We present electron paramagnetic resonance experiments for which solid effect dynamic nuclear polarization transitions were observed indirectly via polarization loss on the electron. This use of indirect observation allows characterization of the dynamic nuclear polarization (DNP) process close to the electron. Frequency profiles of the electron-detected solid effect obtained using trityl radical showed intense saturation of the electron at the usual solid effect condition, which involves a single electron and nucleus. However, higher order solid effect transitions involving two, three, or four nuclei were also observed with surprising intensity, although these transitions did not lead to bulk nuclear polarization--suggesting that higher order transitions are important primarily in the transfer of polarization to nuclei nearby the electron. Similar results were obtained for the SA-BDPA radical where strong electron-nuclear couplings produced splittings in the spectrum of the indirectly observed solid effect conditions. Observation of high order solid effect transitions supports recent studies of the solid effect, and suggests that a multi-spin solid effect mechanism may play a major role in polarization transfer via DNP.

Friday, May 2, 2014

Quantitation of a spin polarization-induced nuclear Overhauser effect (SPINOE) between a hyperpolarized (13) C-labeled cell metabolite and water protons


Marco-Rius, I., et al., Quantitation of a spin polarization-induced nuclear Overhauser effect (SPINOE) between a hyperpolarized (13) C-labeled cell metabolite and water protons. Contrast Media Mol Imaging, 2014. 9(2): p. 182-6.


The spin polarization-induced nuclear Overhauser effect (SPINOE) describes the enhancement of spin polarization of solvent nuclei by the hyperpolarized spins of a solute. In this communication we demonstrate that SPINOEs can be observed between [1,4-(13) C2 ]fumarate, hyperpolarized using the dissolution dynamic nuclear polarization technique, and solvent water protons. We derive a theoretical expression for the expected enhancement and demonstrate that this fits well with experimental measurements. Although the magnitude of the effect is relatively small (around 2% measured here), the SPINOE increases at lower field strengths, so that at clinically relevant magnetic fields (1.5-3 T) it may be possible to track the passage through the circulation of a bolus containing a hyperpolarized (13) C-labeled substrate through the increase in solvent water (1) H signal.