Friday, August 30, 2013

An apparatus for pulsed ESR and DNP experiments using optically excited triplet states down to liquid helium temperatures


Eichhorn, T.R., et al., An apparatus for pulsed ESR and DNP experiments using optically excited triplet states down to liquid helium temperatures. J. Magn. Reson., 2013. 234(0): p. 58-66.


In standard Dynamic Nuclear Polarization (DNP) electron spins are polarized at low temperatures in a strong magnetic field and this polarization is transferred to the nuclear spins by means of a microwave field. To obtain high nuclear polarizations cryogenic equipment reaching temperatures of 1 K or below and superconducting magnets delivering several Tesla are required. This equipment strongly limits applications in nuclear and particle physics where beams of particles interact with the polarized nuclei, as well as in neutron scattering science. The problem can be solved using short-lived optically excited triplet states delivering the electron spin. The spin is polarized in the optical excitation process and both the cryogenic equipment and magnet can be simplified significantly. A versatile apparatus is described that allows to perform pulsed dynamic nuclear polarization experiments at X-band using short-lived optically excited triplet sates. The efficient 4He flow cryostat that cools the sample to temperatures between 4 K and 300 K has an optical access with a coupling stage for a fiber transporting the light from a dedicated laser system. It is further designed to be operated on a neutron beam. A combined pulse ESR/DNP spectrometer has been developed to observe and characterize the triplet states and to perform pulse DNP experiments. The ESR probe is based on a dielectric ring resonator of 7 mm inner diameter that can accommodate cubic samples of 5 mm length needed for neutron experiments. NMR measurements can be performed during DNP with a coil integrated in the cavity. With the presented apparatus a proton polarization of 0.5 has been achieved at 0.3 T.

Wednesday, August 28, 2013

In vivo magnetic resonance imaging of hyperpolarized silicon particles


Cassidy, M.C., et al., In vivo magnetic resonance imaging of hyperpolarized silicon particles. Nat Nano, 2013. 8(5): p. 363-368.


Silicon-based micro- and nanoparticles have gained popularity in a wide range of biomedical applications due to their biocompatibility and biodegradability in vivo, as well as their flexible surface chemistry, which allows drug loading, functionalization and targeting. Here, we report direct in vivo imaging of hyperpolarized 29Si nuclei in silicon particles by magnetic resonance imaging. Natural physical properties of silicon provide surface electronic states for dynamic nuclear polarization, extremely long depolarization times, insensitivity to the in vivo environment or particle tumbling, and surfaces favourable for functionalization. Potential applications to gastrointestinal, intravascular and tumour perfusion imaging at subpicomolar concentrations are presented. These results demonstrate a new background-free imaging modality applicable to a range of inexpensive, readily available and biocompatible silicon particles.

Monday, August 26, 2013

PostDoc position for gyrotron DNP at EPFL, Lausanne

This came through the AMPERE MAGNETIC RESONANCE list:


A post-doc postion is now opened for gyrotron-DNP and related DNP methods. 

This is an EPFL position so their is no pre-existing proposal. Join a group of 3 post-docs and 2 PhD students working closely together on a home-grown system. Contact : jean-philippe.ansermet@epfl.ch

More information on LPMN | EPFL. About DNP in Lausanne, see Swiss DNP Homepage

Jean-Philippe Ansermet

==========================
Jean-Philippe Ansermet
LPMN-ICMP-FSB-station 3
Ecole Polytechnique Fédérale de Lausanne
1015 Lausanne-EPFL
==========================

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Dynamic Nuclear Polarization Enhanced NMR in the Solid-State


Akbey, Ü., et al., Dynamic Nuclear Polarization Enhanced NMR in the Solid-State. 2013, Springer Berlin Heidelberg. p. 1-48.


Nuclear magnetic resonance (NMR) spectroscopy is one of the most commonly used spectroscopic techniques to obtain information on the structure and dynamics of biological and chemical materials. A variety of samples can be studied including solutions, crystalline solids, powders and hydrated protein extracts. However, biological NMR spectroscopy is limited to concentrated samples, typically in the millimolar range, due to its intrinsic low sensitivity compared to other techniques such as fluorescence or electron paramagnetic resonance (EPR) spectroscopy. Dynamic nuclear polarization (DNP) is a method that increases the sensitivity of NMR by several orders of magnitude. It exploits a polarization transfer from unpaired electrons to neighboring nuclei which leads to an absolute increase of the signal-to-noise ratio (S/N). Consequently, biological samples with much lower concentrations can now be studied in hours or days compared to several weeks. This chapter will explain the different types of DNP enhanced NMR experiments, focusing primarily on solid-state magic angle spinning (MAS) DNP, its applications, and possible means of improvement.

Friday, August 23, 2013

Magnetic Resonance Force Microscopy Detected Long-Lived Spin Magnetization

Chen, L., et al., Magnetic Resonance Force Microscopy Detected Long-Lived Spin Magnetization. Magnetics, IEEE Transactions on, 2013. 49(7): p. 3528-3532.


Magnetic resonance force microscopy (MRFM), which combines magnetic resonance imaging with scanning probe microscopy together, is capable of performing ultra-sensitive detection of spin magnetization. In an attempt to observe dynamic nuclear polarization (DNP) in an MRFM experiment, which could possibly further improve its sensitivity towards a single proton spin, a film of perdeuterated polystyrene doped with a nitroxide electron-spin probe was prepared. A high-compliance cantilever with a 4 micrometer-diameter magnetic tip was brought near the film at a temperature of 7.3 K and in a background magnetic field of ~0.6 T. The film was irradiated with 16.7-GHz microwaves while the resulting transient change in cantilever frequency was recorded in real time. In addition to observing the expected prompt change in cantilever frequency due to saturation of the nitroxide's electron-spin magnetization, we observed a persistent cantilever frequency change. Based on its magnitude, lifetime, and field dependence, we tentatively attribute the persistent signal to polarized deuteron magnetization created via transfer of magnetization from electron spins. Further measurements of the persistent signal's dependence on the cantilever amplitude and tip-sample separation are presented and explained by the cross-effect DNP mechanism in high magnetic field gradients.

Wednesday, August 21, 2013

Postdoc position in EU (ITN) project "pNMR"

From the AMPERE MAGNETIC RESONANCE list:


Bruker-BioSpin GmbH, Rheinstetten, Germany and Ecole Nationale Superieure de Lyon, NMR Laboratory of High Magnetic Fields have an opening for a Postdoc Position in the field of solid-state NMR and is is looking for a candidate with a PhD degree in Physics, Physical Chemistry, Biophysics, or Material Sciences with particular interest in NMR hardware and solid-state NMR.

The prospective candidate will work in an International Training Network (Marie Curie program) financed by the European Union, in a project with the topic Paramagnetic NMR - Low temperature and/or ultra-fast MAS of paramagnetic materials, DNP under ultra-fast MAS conditions, and development of radiofrequency pulse sequences suitable for paramagnetic systems.

The project work will be supervised by Dr. Guido Pintacuda (Directeur de Recherche, CNRS), at CRMN , ENS de Lyon, Prof. Clare Grey, University of Cambridge (UK), Dr. Frank Engelke (head of probe development dept.) and Dr. Sebastian Wegner (head of solid-state NMR application dept.) at Bruker BioSpin.

Scientific qualification:
- PhD in physics, biophysics, chemistry, physical chemistry, or material sciences and engineering.
- Experience in NMR, experience in solid-state NMR is a plus.
- Interest in NMR hardware operation, rf pulse program development and engineering.
- Interest in developing new NMR methodology incorporating hardware aspects, rf pulse sequence philosophy, and paramagnetic systems like, e.g., new cathode materials and catalysts.
- Skills in using NMR related simulation packages (e.g. SIMPSON, SPINEVOLUTION)

The candidate will work in a multidisciplinary environment at the Bruker-Biospin facility in Rheinstetten, at the ENS high-field NMR laboratory in Lyon, and at the NMR laboratory at the University of Cambridge (UK). The duration of the project is three years, the financing of the position is for two years.

Please address your application including your CV until 31st August 2013 to Dr. Frank Engelke, or Dr. Sebastian Wegner, Bruker Biospin GmbH, Silberstreifen 4,

76287 Rheinstetten, Germany

Dr. Sebastian Wegner
Head of Solid State NMR Application 

Bruker BioSpin GmbH 
Silberstreifen
76287 Rheinstetten, Germany 

Phone: +49 721 5161-6082
Fax: +49 721 5161-6297 



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Hyperpolarization Methods and Applications in NMR


Köckenberger, W. and J. Matysik, Hyperpolarization Methods and Applications in NMR, in Encyclopedia of Spectroscopy and Spectrometry (Second Edition), L. Editor-in-Chief: John, Editor. 2010, Academic Press: Oxford. p. 963-970.


Nuclear magnetic resonance (NMR) is a well known and versatile spectroscopic and analytical technique. Its enormous success is due to its capacity to determine structures of molecules and proteins in solutions and amorphous solids, to measure local mobilities, to provide information on reaction mechanisms, and to construct three-dimensional images. The main constraints of NMR are its limitation to microsecond time resolution and the low sensitivity. The latter problem is caused by the weak magnetic properties of nuclei and a resulting unfavorable Boltzmann distribution occurring under equilibrium conditions. Therefore, several methods have been developed to produce non-Boltzmann nuclear spin states leading to hyperpolarization and enhanced sensitivity. These hyperpolarization methods induce spin-chemical processes that overcome the Boltzmann equilibrium of the nuclear spins. Under these conditions, signals enhanced to a factor of more than 10 000 are observed. Hyperpolarization methods use light, microwaves, or chemical reactions and, therefore, link different forms of spectroscopy.

Monday, August 19, 2013

Propagation of Dynamic Nuclear Polarization across the Xenon Cluster Boundaries: Elucidation of the Spin-Diffusion Bottleneck


Pourfathi, M., et al., Propagation of Dynamic Nuclear Polarization across the Xenon Cluster Boundaries: Elucidation of the Spin-Diffusion Bottleneck. J. Magn. Reson., 2013(0).


Earlier dynamic nuclear polarization (DNP) experiments with frozen xenon/1-propanol/trityl mixtures have demonstrated spontaneous formation of pure xenon clusters above 120 K, enabling spectrally-resolved real-time measurements of 129Xe nuclear magnetization in the clusters and in the surrounding radical-rich matrix. A spin-diffusion bottleneck was postulated to explain the peculiar time evolution of 129Xe signals in the clusters as well as the apparent discontinuity of 129Xe polarization across the cluster boundaries. A self-contained abinitio model of nuclear spin diffusion in heterogeneous systems is developed here, incorporating the intrinsic T 1 relaxation towards the temperature-dependent equilibrium along with the spin-diffusion coefficients based on the measured NMR line widths and the known atomic densities in each compartment. This simple model provides the physical basis for the observed spin-diffusion bottleneck and is in a good quantitative agreement with the earlier measurements. A simultaneous fit of the model to the time-dependent NMR data at two different DNP frequencies provides excellent estimates of the cluster size, the intrinsic sample temperature, and 129Xe T 1 constants. The model was also applied to the NMR data acquired during relaxation towards thermal equilibrium after microwaves were turned off to estimate T 1 relaxation time constants inside and outside the clusters. Fitting the model to data during and after DNP provides estimates of cluster size that are in complete agreement.

Friday, August 16, 2013

The EF Loop in Green Proteorhodopsin Affects Conformation and Photocycle dynamics


Mehler, M., et al., The EF Loop in Green Proteorhodopsin Affects Conformation and Photocycle dynamics. Biophysical Journal, 2013. 105(2): p. 385-397.


The proteorhodopsin family consists of retinal proteins of marine bacterial origin with optical properties adjusted to their local environments. For green proteorhodopsin, a highly specific mutation in the EF loop, A178R, has been found to cause a surprisingly large redshift of 20 nm despite its distance from the chromophore. Here, we analyze structural and functional consequences of this EF loop mutation by time-resolved optical spectroscopy and solid-state NMR. We found that the primary photoreaction and the formation of the K-like photo intermediate is almost pH-independent and slower compared to the wild-type, whereas the decay of the K-intermediate is accelerated, suggesting structural changes within the counterion complex upon mutation. The photocycle is significantly elongated mainly due to an enlarged lifetime of late photo intermediates. Multidimensional MAS-NMR reveals mutation-induced chemical shift changes propagating from the EF loop to the chromophore binding pocket, whereas dynamic nuclear polarization-enhanced 13C-double quantum MAS-NMR has been used to probe directly the retinylidene conformation. Our data show a modified interaction network between chromophore, Schiff base, and counterion complex explaining the altered optical and kinetic properties. In particular, the mutation-induced distorted structure in the EF loop weakens interactions, which help reorienting helix F during the reprotonation step explaining the slower photocycle. These data lead to the conclusion that the EF loop plays an important role in proton uptake from the cytoplasm but our data also reveal a clear interaction pathway between the EF loop and retinal binding pocket, which might be an evolutionary conserved communication pathway in retinal proteins.

Wednesday, August 14, 2013

Cryogenic solid state NMR studies of fibrils of the Alzheimer's disease amyloid-beta peptide: perspectives for DNP


Lopez Del Amo, J.M., et al., Cryogenic solid state NMR studies of fibrils of the Alzheimer's disease amyloid-beta peptide: perspectives for DNP. J Biomol NMR, 2013: p. 1-5.


Dynamic Nuclear Polarization solid-state NMR holds the potential to enable a dramatic increase in sensitivity by exploiting the large magnetic moment of the electron. However, applications to biological solids are hampered in uniformly isotopically enriched biomacromolecules due to line broadening which yields a limited spectral resolution at cryogenic temperatures. We show here that high magnetic fields allow to overcome the broadening of resonance lines often experienced at liquid nitrogen temperatures. For a fibril sample of the Alzheimer's disease beta-amyloid peptide, we find similar line widths at low temperature and at room temperature. The presented results open new perspectives for structural investigations in the solid-state.

Monday, August 12, 2013

Russell Varian Prize Goes to Dr. Lucio Frydman

From the Agilent website:

Agilent has awarded the 2013 Russell Varian Prize for Innovation in Nuclear Magnetic Resonance to Dr. Lucio Frydman, a professor at the Weizmann Institute of Science in Rehovot, Israel. Frydman is responsible for introducing a unique technique that records previously inaccessible multidimensional NMR spectra in a single scan.

The Russell Varian Prize honors the memory of the pioneer behind the first commercial nuclear magnetic resonance spectrometers and cofounder of Varian Associates, which is now part of Agilent. The prize is awarded to researchers based on a single innovative contribution (a single paper, patent, lecture or piece of hardware) that has demonstrated broad impact on the state of the art in NMR and original contributions that have triggered important advancements in scientific technology.

For more information visit: http://www.agilent.com/about/newsroom/presrel/2013/01aug-ca13049.html

[NMR] PhD Positions - University of Pavia - Braoadband NMR and DNP

From the AMPERE MAGNETIC RESONANCE mailing list:



Three years PhD grants are available at the Physics Department (http://fisica.unipv.it/EN_index.php) of the University of Pavia (http://www.unipv.eu/site/en/home.html),

Starting from November-December 2013 PhD students can be involved in one of the following research projects:

1) NMR investigation of the low-energy excitations and local magnetic properties in the iron-based superconductors.

2) Experimental study of Dynamical Nuclear Polarization working principles and modellization of the Thermal Mixing Regime in molecules of biomedical interest.

Supervisor: Prof. Pietro Carretta NMR Group (http://arturo.unipv.it)

Applicants will be selected following an evaluation of their CV and an interview according to the rules reported in the application call (see http://fisica.unipv.it/PhD_call_2013.pdf ).

Deadline: 18th of September 2013

For further information please contact pietro.carretta@unipv.it


--

***************************************
Prof. Pietro Carretta
Dipartimento di Fisica
Università degli Studi di Pavia
Via Bassi 6 - 27100 Pavia
Italy

Tel. +39-0382-987478
Fax. +39-0382-987478 (after 4 tones)
e-mail: pietro.carretta@unipv.it
Web site http://arturo.unipv.it

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Perspectives in Enzymology of Membrane Proteins by Solid-State NMR


Ullrich, S.J. and C. Glaubitz, Perspectives in Enzymology of Membrane Proteins by Solid-State NMR. Acc. Chem. Res., 2013.


Membrane proteins catalyze reactions at the cell membrane and facilitate thetransport of molecules or signals across the membrane. Recently researchers have made great progress in understanding the structural biology of membrane proteins, mainly based on X-ray crystallography. In addition, the application of complementary spectroscopic techniques has allowed researchers to develop a functional understanding of these proteins. Solid-state NMR has become an indispensable tool for the structure?function analysis of insoluble proteins and protein complexes. It offers the possibility of investigating membrane proteins directly in their environment, which provides essential information about the intrinsic coupling of protein structure and functional dynamics within the lipid bilayer. However, to date, researchers have hardly explored the enzymology of mem-brane proteins. In this Account, we review the perspectives for investigating membrane-bound enzymes by solid-state NMR. Understanding enzyme mechanisms requires access to kinetic parameters, structural analysis of the catalytic center, knowledge of the 3D structure and methods to follow the structural dynamics of the enzyme during the catalytic cycle. In principle, solid-state NMR can address all of these issues. Researchers can characterize the enzyme kinetics by observing substrate turnover within the membrane or at the membrane interphase in a time-resolved fashion as shown for diacylglycerol kinase. Solid-state NMR has also provided a mechanistic understanding of soluble enzymes including triosephosphate isomerase (TIM) and different metal-binding proteins, which demonstrates a promising perspective also for membrane proteins. The increasing availability of high magnetic fields and the development of new experimental schemes and computational protocols have made it easier to determine 3D structure using solid-state NMR. Dynamic nuclear polarization, a key technique to boost sensitivity of solid-state NMR at low temperatures, can help with the analysis of thermally trapped catalytic intermediates, while methods to improve signal-to-noise per time unit enable the real-time measurement of kinetics of conformational changes during the catalytic cycle.

Friday, August 9, 2013

Lineshape-based polarimetry of dynamically-polarized in solid-state mixtures


Kuzma, N.N., et al., Lineshape-based polarimetry of dynamically-polarized in solid-state mixtures. J. Magn. Reson., 2013. 234(0): p. 90-94.


Dynamic nuclear polarization (DNP) of 15 N 2 O , known for its long-lived singlet-state order at low magnetic field, is demonstrated in organic solvent/trityl mixtures at ∼1.5 K and 5 T. Both 15 N polarization and intermolecular dipolar broadening are strongly affected by the sample’s thermal history, indicating spontaneous formation of N2O clusters. In situ 15 N NMR reveals four distinct powder-pattern spectra, attributed to the chemical-shift anisotropy (CSA) tensors of the two 15N nuclei, further split by the intramolecular dipolar coupling between their magnetic moments. 15 N polarization is estimated by fitting the free-induction decay (FID) signals to the analytical model of four single-quantum transitions. This analysis implies ( 10.2 ± 2.2 ) % polarization after 37 h of DNP, and provides a direct, instantaneous probe of the absolute 15 N polarization, without a need for time-consuming referencing to a thermal-equilibrium NMR signal.

Wednesday, August 7, 2013

Kinetic Study of Propylene Hydrogenation over Pt/Al2O3 by Parahydrogen-Induced Polarization


Salnikov, O.G., et al., Kinetic Study of Propylene Hydrogenation over Pt/Al2O3 by Parahydrogen-Induced Polarization. Appl. Magn. Reson., 2012. 44(1-2): p. 279-288.


Parahydrogen-induced polarization has been successfully used for a kinetic study of propylene hydrogenation over a Pt/Al2O3 catalyst. It was shown that the reaction orders with respect to hydrogen are different for the pairwise and the non-pairwise hydrogen addition and are equal to 0.7 and 0.1, respectively. This observation of different reaction orders confirms the coexistence of different types of active sites which are responsible for the overall and the pairwise hydrogen addition to the propylene C=C double bond. Moreover, 0.7 reaction order with respect to H2 for pairwise hydrogen addition indicates that the contribution of pairwise addition depends on the concentration of molecular hydrogen. Therefore, this observation can be developed into a practical tool for producing fluids with highly polarized nuclear spins by changing the hydrogen concentration.

Monday, August 5, 2013

Open Position at Bridge12: Technician

Bridge12 has currently two job openings, one for a research scientist and one for a technician. You can find the original posting at http://www.bridge12.com/careers

Open Position: Technician
Bridge12 is a privately-held startup company focusing on the development of cutting-edge, high-power microwave and terahertz sources and systems for use in scientific research such as magnetic resonance spectroscopy, communication systems and industrial applications. The company has a worldwide customer base and conducts groundbreaking research on applications of microwaves and terahertz in novel fields and has been successful in launching several innovative products based on Small Business Innovation Research (SBIR) grants from several federal agencies. Bridge12 is in the progress of expanding it’s team and has currently an opening for a Technician.

Generating Parahydrogen-Induced Polarization Using Immobilized Iridium Complexes in the Gas-Phase Hydrogenation of Carbon–Carbon Double and Triple Bonds

Skovpin, I.V., et al., Generating Parahydrogen-Induced Polarization Using Immobilized Iridium Complexes in the Gas-Phase Hydrogenation of Carbon–Carbon Double and Triple Bonds. Appl. Magn. Reson., 2012. 44(1-2): p. 289-300.


Immobilized iridium complexes synthesized using [Ir(COD)Cl]2 by anchoring on hydrous and anhydrous silica gels were studied in terms of generating parahydrogen-induced polarization (PHIP) in the gas-phase hydrogenation of propylene and propyne. Distinguishing differences in the hydrogenations of carbon–carbon double and triple bonds were found. It has been shown that in the double bond hydrogenation both catalysts are very active even at 25 C. The reaction yield in continuous flow experiments is more than 70 %, whereas the obtained PHIP degrees are very low. In the case of the triple bond hydrogenation, a more or less active hydrogenation reaction was observed at relatively high temperatures (&70–80 C) for the catalyst immobilized on anhydrous silica, while the catalyst immobilized on hydrous silica was inactive at these temperatures. Contrary to the double bond hydrogenation, the triple bond hydrogenation provided significant signal enhancements observed in 1H nuclear magnetic resonance spectra for the signals corresponding to protons of vinyl fragments of product propylene in both PASADENA and ALTADENA experiments. The catalyst, however, is not stable under the triple bond hydrogenation reaction conditions, and deactivates within several minutes. It was also found that at higher temperatures (100–120 C), this atalyst demonstrates a reactivation most likely associated with the reduction of Ir(I) that results in the ormation of Ir(0) surface metal nanoparticles.

Friday, August 2, 2013

Generating Parahydrogen-Induced Polarization Using Immobilized Iridium Complexes in the Gas-Phase Hydrogenation of Carbon–Carbon Double and Triple Bonds


Skovpin, I., et al., Generating Parahydrogen-Induced Polarization Using Immobilized Iridium Complexes in the Gas-Phase Hydrogenation of Carbon–Carbon Double and Triple Bonds. Appl. Magn. Reson., 2013. 44(1-2): p. 289-300.


Immobilized iridium complexes synthesized using [Ir(COD)Cl]2 by anchoring on hydrous and anhydrous silica gels were studied in terms of generating parahydrogen-induced polarization (PHIP) in the gas-phase hydrogenation of propylene and propyne. Distinguishing differences in the hydrogenations of carbon–carbon double and triple bonds were found. It has been shown that in the double bond hydrogenation both catalysts are very active even at 25 C. The reaction yield in continuous flow experiments is more than 70 %, whereas the obtained PHIP degrees are very low. In the case of the triple bond hydrogenation, a more or less active hydrogenation reaction was observed at relatively high temperatures (&70–80 C) for the catalyst immobilized on anhydrous silica, while the catalyst immobilized on hydrous silica was inactive at these temperatures. Contrary to the double bond hydrogenation, the triple bond hydrogenation provided significant signal enhancements observed in 1H nuclear magnetic resonance spectra for the signals corresponding to protons of vinyl fragments of product propylene in both PASADENA and ALTADENA experiments. The catalyst, however, is not stable under the triple bond hydrogenation reaction conditions, and deactivates within several minutes. It was also found that at higher temperatures (100–120 C), this atalyst demonstrates a reactivation most likely associated with the reduction of Ir(I) that results in the ormation of Ir(0) surface metal nanoparticles.