Jun 29, 2016

Waveguide transition with vacuum window for multiband dynamic nuclear polarization systems #DNPNMR

Rybalko, O., et al., Waveguide transition with vacuum window for multiband dynamic nuclear polarization systems. Review of Scientific Instruments, 2016. 87(5): p. 054705.

A low loss waveguide transition section and oversized microwave vacuum window covering several frequency bands (94 GHz, 140 GHz, 188 GHz) is presented. The transition is compact and was optimized for multiband Dynamic Nuclear Polarization (DNP) systems in a full-wave simulator. The window is more broadband than commercially available windows, which are usually optimized for single band operation. It is demonstrated that high-density polyethylene with urethane adhesive can be used as a low loss microwavevacuum window in multiband DNP systems. The overall assembly performance and dimensions are found using full-wave simulations. The practical aspects of the window implementation in the waveguide are discussed. To verify the design and simulation results, the window is tested experimentally at the three frequencies of interest.

Jun 27, 2016

HP-Xe to go: Storage and transportation of hyperpolarized 129Xenon

Repetto, M., et al., HP-Xe to go: Storage and transportation of hyperpolarized 129Xenon. J. Magn. Reson., 2016. 265: p. 197-199.

Recently the spin–lattice relaxation time T1 of hyperpolarized (HP)-129Xe was significantly improved by using uncoated and Rb-free storage vessels of GE180 glass. For these cells, a simple procedure was established to obtain reproducible wall relaxation times of about 18 h. Then the limiting relaxation mechanism in pure Xe is due to the coupling between the nuclear spins and the angular momentum of the Xe–Xe van-der-Waals-molecules. This mechanism can be significantly reduced by using different buffer gases of which CO2 was discovered to be the most efficient so far. From these values, it was estimated that for a 1:1 mixture of HP-Xe with CO2 a longitudinal relaxation time of about 7 h can be expected, sufficient to transport HP-Xe from a production to a remote application site. This prediction was verified for such a mixture at a total pressure of about 1 bar in a 10 cm glass cell showing a storage time of T1 ≈ 9 h (for T 1 wall = ( 34 ± 9 ) h) which was transported inside a magnetic box over a distance of about 200 km by car.

Jun 24, 2016

Combined Hyperthermia and Photodynamic Therapy Using a Sub-THz Gyrotron as a Radiation Source

Some researcher may think that using a gyrotron for DNP-NMR spectroscopy seems to be a very exotic application. This article describes another application that is up to now rather unusual - heating up cancer tissue for cancer treatment.

Miyoshi, N., et al., Combined Hyperthermia and Photodynamic Therapy Using a Sub-THz Gyrotron as a Radiation Source. J Infrared Milli Terahz Waves, 2016: p. 1-10.

In this paper, we present results of a hyperthermia treatment of malignant tumors using a gyrotron as a radiation source for heating of the cancerous tissue. They clearly demonstrate the efficiency of the irradiation by sub-THz waves, which leads to steady decrease of the volume of the tumor and finally to its disappearance. A combination of hyperthermia and photodynamic therapy (PDT) that utilizes a novel multifunctional photosensitizer has also been explored. In the latter case, the results are even more convincing and promising. In particular, while after a hyperthermia treatment sometimes a regrowth of the tumor is being observed, in the case of combined hyperthermia and PDT such regrowth has never been noticed. Another combined therapy is based on a preheating of the tumor by gyrotron radiation to temperatures lower than the hyperthermia temperature of 43 °C and followed then by PDT. The results show that such combination significantly increases the efficiency of the treatment. We consider this phenomenon as a synergy effect since it is absent when hyperthermia and PDT are applied separately, and manifests itself only when both methods are combined.

[NMR] Two PhD positions in Solid State NMR in Nijmegen #DNPNMR #HYPERPOLARIZATION

From the Ampere Magnetic Resonance List

Two PhD positions supported by the Dutch science foundation NWO-COAST and by the Netherlands’ Nuclear Magnetic Resonance graduate school NMARRS are available in the department for solid state NMR at the Radboud University in Nijmegen, The Netherlands under the supervision of Prof. Arno Kentgens and dr. Jan van Bentum.

1) Supercritical chromatography hyphenated with hyperpolarized NMR

In our group we develop methods for high sensitivity on-chip NMR detection of mass-limited samples. This flow system allows flexible operation, including high pressures and supercritical solvents such as CO2. In conjunction with a supercritical chromatography this may provide a fast analytical tool to study complex mixtures with superior information content. One of the advantages of supercritical solvents is the fact that fast mobility can lead to efficient liquid state (Overhauser) Dynamic Nuclear Polarization at relatively high magnetic fields. At present a Gyrotron mm-wave source operating at 395 GHz is available for this purpose, coupled to a 600 MHz NMR spectrometer.

2) Low temperature micro-MAS DNP for materials research

Using micro-coil NMR it is possible to generate ultra-high RF fields, combined with an exquisite sensitivity for small sample volumes. A sustained proton decoupling at RF fields of about 1 MHz can help to obtain unprecedented high resolution in the solid state. A combination with low temperature (10-40 K) sample spinning, and including MAS-DNP at 395 GHz, can help to boost sensitivity to study low concentration sites for example at catalytic surfaces. Our main goal is to optimize the DNP-NMR methodology for quadrupolar nuclei.

For both projects we are looking for enthusiastic candidates with a solid background in NMR and with an affinity for ‘out of the box’ methodology development. We offer a stimulating and exciting environment with state of the art NMR spectrometers up to 850 MHz. For more information, visit our website http://www.ru.nl/science/solidstatenmr or send an email to a.kentgens@nmr.ru.nl.

Marian de With
Radboud University | Institute for Molecules and Materials
Secretary for depts. of Biophysical Chemistry and Solid State NMR
Tel. +31 24 3652678 

Visiting address:
Heyendaalseweg 135 | 6525 AJ Nijmegen | HG03.344
Postal address:
Postbox 9010 | Internal postbus 84 | 6500 GL Nijmegen 

Working hours: Monday 9-13, Thursday 9-13, Tuesday, Wednesday and Friday 9-17

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Jun 22, 2016

Determination of long-range scalar (1)H-(1)H coupling constants responsible for polarization transfer in SABRE #DNPNMR

Eshuis, N., et al., Determination of long-range scalar (1)H-(1)H coupling constants responsible for polarization transfer in SABRE. J Magn Reson, 2016. 265: p. 59-66.

SABRE (Signal Amplification By Reversible Exchange) nuclear spin hyperpolarization method can provide strongly enhanced NMR signals as a result of the reversible association of small molecules with para-hydrogen (p-H2) at an iridium metal complex. The conversion of p-H2 singlet order to enhanced substrate proton magnetization within such complex is driven by the scalar coupling interactions between the p-H2 derived hydrides and substrate nuclear spins. In the present study these long-range homonuclear couplings are experimentally determined for several SABRE substrates using an NMR pulse sequence for coherent hyperpolarization transfer at high magnetic field. Pyridine and pyrazine derivatives appear to have a similar approximately 1.2Hz (4)J coupling to p-H2 derived hydrides for their ortho protons, and a much lower (5)J coupling for their meta protons. Interestingly, the (4)J hydride-substrate coupling for five-membered N-heterocyclic substrates is well below 1Hz.

Jun 20, 2016

Constant-variable flip angles for hyperpolarized media MRI #DNPNMR

Deng, H., et al., Constant-variable flip angles for hyperpolarized media MRI. J. Magn. Reson., 2016. 263: p. 92-100.

The longitudinal magnetization of hyperpolarized media, such as hyperpolarized 129Xe, 3He, etc., is nonrenewable. When the MRI data acquisition begins at the k-domain center, a constant flip angle (CFA) results in an image of high signal-to-noise ratio (SNR) but sacrifices the accuracy of spatial information. On the other hand, a variable flip angle (VFA) strategy results in high accuracy but suffers from a low SNR. In this paper, we propose a novel scheme to optimize both the SNR and accuracy, called constant-variable flip angles (CVFA). The proposed scheme suggests that hyperpolarized magnetic resonance signals are firstly acquired through a train of n∗ CFA excitation pulses, followed by a train of N–n∗ VFA excitation pulses. We simulate and optimize the flip angle used in the CFA section, the number of CFA excitation pulses, the number of VFA excitation pulses, and the initial and final variable flip angles adopted in the VFA section. Phantom and in vivo experiments demonstrate the good performance of the CVFA designs and their ability to maintain both high SNR and spatial resolution.

Jun 17, 2016

A peripheral component interconnect express-based scalable and highly integrated pulsed spectrometer for solution state dynamic nuclear polarization #DNPNMR

He, Y., et al., A peripheral component interconnect express-based scalable and highly integrated pulsed spectrometer for solution state dynamic nuclear polarization. Rev Sci Instrum, 2015. 86(8): p. 083101.

High sensitivity, high data rates, fast pulses, and accurate synchronization all represent challenges for modern nuclear magnetic resonance spectrometers, which make any expansion or adaptation of these devices to new techniques and experiments difficult. Here, we present a Peripheral Component Interconnect Express (PCIe)-based highly integrated distributed digital architecture pulsed spectrometer that is implemented with electron and nucleus double resonances and is scalable specifically for broad dynamic nuclear polarization (DNP) enhancement applications, including DNP-magnetic resonance spectroscopy/imaging (DNP-MRS/MRI). The distributed modularized architecture can implement more transceiver channels flexibly to meet a variety of MRS/MRI instrumentation needs. The proposed PCIe bus with high data rates can significantly improve data transmission efficiency and communication reliability and allow precise control of pulse sequences. An external high speed double data rate memory chip is used to store acquired data and pulse sequence elements, which greatly accelerates the execution of the pulse sequence, reduces the TR (time of repetition) interval, and improves the accuracy of TR in imaging sequences. Using clock phase-shift technology, we can produce digital pulses accurately with high timing resolution of 1 ns and narrow widths of 4 ns to control the microwave pulses required by pulsed DNP and ensure overall system synchronization. The proposed spectrometer is proved to be both feasible and reliable by observation of a maximum signal enhancement factor of approximately -170 for (1)H, and a high quality water image was successfully obtained by DNP-enhanced spin-echo (1)H MRI at 0.35 T.

Jun 15, 2016

Polarization enhancement technique for nuclear quadrupole resonance detection #DNPNMR

Kim, Y.J., et al., Polarization enhancement technique for nuclear quadrupole resonance detection. Solid State Nucl Magn Reson, 2014. 61-62: p. 35-8.

We demonstrate a dramatic increase in the signal-to-noise ratio (SNR) of a nuclear quadrupole resonance (NQR) signal by using a polarization enhancement technique. By first applying a static magnetic field to pre-polarize one spin subsystem of a material, and then allowing that net polarization to be transferred to the quadrupole subsystem, we increased the SNR of a sample of ammonium nitrate by one-order of magnitude.

Jun 13, 2016

Homonuclear decoupling for spectral simplification of carbon-13 enriched molecules in solution-state NMR enhanced by dissolution DNP

Chinthalapalli, S., et al., Homonuclear decoupling for spectral simplification of carbon-13 enriched molecules in solution-state NMR enhanced by dissolution DNP. Phys Chem Chem Phys, 2016. 18(16): p. 11480-7.

Complex overlapping multiplets due to scalar couplings (n)J((13)C, (13)C) in fully (13)C-enriched molecules can be simplified by polychromatic irradiation of selected spins. The signal intensities of the remaining non-irradiated signals are proportional to the concentrations, as shown in this work for the anomeric (13)C signals of the alpha- and beta-conformers of glucose. Homonuclear decoupling can therefore be useful for quantitative NMR studies. The resulting decoupled lineshapes show residual fine structures that have been investigated by means of numerical simulations. Simulations also show that homonuclear decoupling schemes remain effective despite inhomogeneous static fields that tend to hamper in cellulo and in vivo studies. Homonuclear decoupling schemes can be combined with dissolution DNP to obtain signal enhancements of more than four orders of magnitude. Polychromatic irradiation of selected spins does not cause significant losses of hyperpolarization of the remaining non-irradiated spins.

Jun 10, 2016

[NMR] PhD Position at PSI, Switzerland f#DNPNMR

From the Ampere Magnetic Resonance List

The Paul Scherrer Institute PSI is the largest research centre for natural and engineering sciences within Switzerland. We perform cutting-edge research in the fields of matter and materials, energy and environment and human health. By performing fundamental and applied research, we work on sustainable solutions for major challenges facing society, science and economy. PSI is committed to the training of future generations. Therefore about one quarter of our staff are post-docs, post-graduates or apprentices. Altogether PSI employs 1900 people.

The Polarized Target Group of the Laboratory for Scientific Developments andNovel Materials (LDM) has since many years been a leading group in developing and applying techniques of dynamic nuclear polarization (DNP) in fields as diverse as particle physics, neutron scattering or magnetic resonance imaging. For the study and the further development of a novel method of DNP and its application in neutron science, we are seeking a highly motivated PhD Student
Development of a novel device for neutron polarization analysis

Your tasks
Your tasks will be to develop a neutron spin filter based on a novel method of dynamic nuclear polarization (DNP) that uses optically excited triplet states in molecular crystals to polarize the nuclei of the filter sample. Various techniques will be used: lasers to excite the short lived triplet states, pulse EPR to characterize them, microwaves to drive the electron-nucleon transitions, NMR to measure the nuclear polarization, cryogenics to cool the sample. You will further employ the novel analyzer to perform neutron small angle scattering experiments with longitudinal polarization analysis in the field of magnetic materials.

Your profile
You have recently got a university degree in physics with excellent grades and you are a skillful and innovative experimentalist. Preferably, you have some practical expertise with lasers and/or NMR/EPR spectroscopy and neutron scattering techniques and enjoy working in a multidisciplinary environment. Team spirit and good communication skills in English and/or German are required.

The PhD studies will be done at the University of Basel, while the main part of the experimental research will be carried out at PSI.

We offer
Our institution is based on an interdisciplinary, innovative and dynamic collaboration. You will profit from a systematic training on the job, in addition to personal development possibilities and our pronounced vocational training culture. If you wish to optimally combine work and family life or other personal interests, we are able to support you with our modern employment conditions and the on-site infrastructure.

For further information please contact Dr Patrick Hautle, phone +41 56 310 32 10.

Please submit your application online including addresses of referees for the position as a PhD Student (index no. 3604-00).

Paul Scherrer Institut, Human Resources Management, Nicole Fricker / Mara Kalt, 5232 Villigen PSI, Switzerland

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Jun 9, 2016

[NMR] Post-doctoral position in hyperpolarization available at the University of Florida, associated with the NHMFL.

From the Ampere Magnetic Resonance List

Post-doctoral position in the University of Florida Department of Biochemistry and Molecular Biology

A post-doctoral position for a researcher in hyperpolarization (dynamic nuclear polarization, DNP, and brute force polarization) physics and its application to biological imaging is available in the lab of Dr. Matthew Merritt at the University of Florida Department of Biochemistry and Molecular Biology (Gainesville, FL). The person will be responsible for a project related to the development of brute force methods of polarization and their application to metabolomics. Further development of DNP strategies for production of hyperpolarized samples suitable for rapid chemical analysis is also a target.

Applicants must have a PhD in physics, or chemistry, with a strong emphasis on hardware development and mathematical skills. Biochemistry training in sample preparation or animal handling would also be applicable skills. The applicant will be responsible for:

  • Develop methods for rapidly dissolving frozen samples and transporting them using microfluidics
  • Preparation of samples for DNP studies
  • Implementing strategies for delivery of different microwave frequencies to the target sample
  • Ensuring proper functioning of the NMR detection circuit within the LHe cooled cryostat (NMR frequency is subject to change)
  • Training of graduate and undergraduate students in the lab

The post is funded for two years through the National High Magnetic Field Laboratory at ~$43000/yr, though more qualified applicants could expect higher pay scales.

Please apply for the position at https://jobs.ufl.edu with job code 497186.

Dr. Matthew Merritt
Associate Professor
University of Florida
Department of Biochemistry and
Molecular Biology
PO Box 100245
Gainesville, FL 32610-0245

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Jun 8, 2016

Static DNP-NMR Spectroscopy to Characterize Active Pharmaceutical Ingredients #DNPNMR

Dynamic Nuclear Polarization in general is no new method, but the focus of modern applications has initially been on bio-macromolecules under magic-angle-spinning (MAS) conditions.

One application that came out-of-the-blue was using DNP-NMR spectroscopy to study surface materials by DNP-NMR spectroscopy (for example Lafon et al., 2011) opening up a complete new research area within material science that traditionally struggled with very low signal-to-noise (S/N) ratios.

Even the application of DNP-NMR spectroscopy to study small molecules was not immediately evident, but as demonstrated in Rossini et al, 2012 DNP offers the possibility to record 13C correlation spectra of unlabeled molecules such as glucose in just 16 hours. Without DNP this experiment would require months of spectrometer time.

The majority of the DNP-NMR experiments that have been reported in recent years use gyrotron-based DNP-NMR systems and MAS-DNP probes operating at about 100 K. Alternatively, there is a small group of researchers that use DNP systems based on a solid-state microwave source. These systems have are typically limited by their output power, which ranges between >80 mW at 263 GHz (400 MHz 1H NMR) to < 200 mW at 197 GHz (300 MHz 1H NMR). At lower frequencies the output power increases and > 500 mW can be reached for systems operating at 95 GHz. A comprehensive overview of low-power DNP-NMR systems can be found in Siaw et al., 2016.

Because of the limited output power, DNP experiments are performed at temperatures < 20 K, which requires cooling with liquid helium (very common for example in EPR experiments) and can be cost-effective when using a cryostat (e.g. at 10 K the consumption is about 0.5 l/hr). Furthermore, with the increasing popularity of cryogen-free systems some cryostats don't require any liquid cryogens anymore for cooling. The main advantage is the reduced cost since a solid-state source based DNP-NMR system typically comes at a 10th of the cost of a gyrotron-based system.

At first sight it seems as if the applications of static DNP are very limited. However, when I was at ENC this year I listened to a talk by David A. Hirsh entitled "35Cl Dynamic Nuclear Polarization Solid-State NMR of Active Pharmaceutical Ingredients". David is a graduate student in the group of Rob Schurko, University of Windsor and gave a very nice talk on using DNP-NMR spectroscopy to characterize Active Pharmaceutical Ingredients (API) using 35Cl solid-state NMR spectroscopy. Since 35Cl is a quadrupole nucleus the corresponding NMR spectra are typically very broad. MAS does only have a small effect, mainly on the center transition, and traditionally wide-line spectra of static solids are recorded.

To overcome sensitivity issues, the group has developed pulse sequences such as WURST-CPMG or BRAIN-CP to rapidly record broad 35Cl patterns even at moderate magnetic field strengths (e.g. 9.4 T, 400 MHz 1H NMR). However, recording a single spectrum often requires several hours of signal averaging to achieve a sufficiently high signal-to-noise (S/N) ratio. With the aid of DNP these acquisition times can be dramatically reduced to just minutes. In his talk at ENC David described using a grytron-based DNP-NMR system, equipped with a MAS-DNP probe head in his experiments. Polarizing the sample is done while the rotor is spinning, but the rotor is stopped prior to recording the wide-line NMR spectrum. 

This experiment seems to be ideally suited for a low-power DNP-NMR system for static solids, using a cryostat for sample cooling. This would greatly simplify the experiment because starting and stopping the rotor is not required anymore. Because the experiment is performed at much lower temperatures, there will be an additional boost in sensitivity and multi-dimensional correlation experiments should be possible, experiments that are close to impossible to perform without the aid of DNP.

In recent years the NMR community has witnessed the transition of DNP-NMR spectroscopy from an exotic method with a limited number of applications to a method with more and more applications. High-field DNP-NMR spectroscopy either based on a gyrotron or using a low-power solid-state source is still a very young method with many possibilities and I'm very excited to see what other applications lie in the future. I am however convinced that DNP-NMR spectroscopy will find their way into many more labs in the future and that the method will become an integral part of the NMR toolbox.

Rotaxane-mediated suppression and activation of cucurbit[6]uril for molecular detection by (129)Xe hyperCEST NMR

Finbloom, J.A., et al., Rotaxane-mediated suppression and activation of cucurbit[6]uril for molecular detection by (129)Xe hyperCEST NMR. Chem Commun (Camb), 2016. 52(15): p. 3119-22.

We report a method for blocking interactions between (129)Xe and cucurbit[6]uril (CB6) until activation by a specific chemical event. We synthesized a CB6-rotaxane that allowed no (129)Xe interaction with the CB6 macrocycle component until a cleavage event released the CB6, which then produced a (129)Xe@CB6 NMR signal. This contrast-upon-activation (129)Xe NMR platform allows for modular synthesis and can be expanded to applications in detection and disease imaging.

Jun 6, 2016

Dynamic nuclear polarization in a magnetic resonance force microscope experiment

Issac, C.E., et al., Dynamic nuclear polarization in a magnetic resonance force microscope experiment. Phys Chem Chem Phys, 2016. 18(13): p. 8806-19.

We report achieving enhanced nuclear magnetization in a magnetic resonance force microscope experiment at 0.6 tesla and 4.2 kelvin using the dynamic nuclear polarization (DNP) effect. In our experiments a microwire coplanar waveguide delivered radiowaves to excite nuclear spins and microwaves to excite electron spins in a 250 nm thick nitroxide-doped polystyrene sample. Both electron and proton spin resonance were observed as a change in the mechanical resonance frequency of a nearby cantilever having a micron-scale nickel tip. NMR signal, not observable from Curie-law magnetization at 0.6 T, became observable when microwave irradiation was applied to saturate the electron spins. The resulting NMR signal's size, buildup time, dependence on microwave power, and dependence on irradiation frequency was consistent with a transfer of magnetization from electron spins to nuclear spins. Due to the presence of an inhomogeneous magnetic field introduced by the cantilever's magnetic tip, the electron spins in the sample were saturated in a microwave-resonant slice 10's of nm thick. The spatial distribution of the nuclear polarization enhancement factor epsilon was mapped by varying the frequency of the applied radiowaves. The observed enhancement factor was zero for spins in the center of the resonant slice, was epsilon = +10 to +20 for spins proximal to the magnet, and was epsilon = -10 to -20 for spins distal to the magnet. We show that this bipolar nuclear magnetization profile is consistent with cross-effect DNP in a approximately 10(5) T m(-1) magnetic field gradient. Potential challenges associated with generating and using DNP-enhanced nuclear magnetization in a nanometer-resolution magnetic resonance imaging experiment are elucidated and discussed.

Jun 3, 2016

Identifying low-coverage surface species on supported noble metal nanoparticle catalysts by DNP-NMR #DNPNMR

Johnson, R.L., et al., Identifying low-coverage surface species on supported noble metal nanoparticle catalysts by DNP-NMR. Chem Commun (Camb), 2016. 52(9): p. 1859-62.

DNP-NMR spectroscopy has been applied to enhance the signal for organic molecules adsorbed on gamma-Al2O3-supported Pd nanoparticle catalysts. By offering >2500-fold time savings, the technique enabled the observation of (13)C-(13)C cross-peaks for low coverage species, which were assigned to products from oxidative degradation of methionine adsorbed on the nanoparticle surface.

Jun 1, 2016

Dynamic nuclear polarization of biocompatible (13)C-enriched carbonates for in vivo pH imaging #DNPNMR

Korenchan, D.E., et al., Dynamic nuclear polarization of biocompatible (13)C-enriched carbonates for in vivo pH imaging. Chem Commun (Camb), 2016. 52(14): p. 3030-3.

A hyperpolarization technique using carbonate precursors of biocompatible molecules was found to yield high concentrations of hyperpolarized (13)C bicarbonate in solution. This approach enabled large signal gains for low-toxicity hyperpolarized (13)C pH imaging in a phantom and in vivo in a murine model of prostate cancer.