Friday, May 25, 2018

Multi-Frequency Pulsed Overhauser DNP at 1.2 Tesla

Schöps, P., E. Spindler Philipp, and F. Prisner Thomas, Multi-Frequency Pulsed Overhauser DNP at 1.2 Tesla, in Z. Phys. Chem. 2017. p. 561.


Dynamic nuclear polarization (DNP) is a methodology to increase the sensitivity of nuclear magnetic resonance (NMR) spectroscopy. It relies on the transfer of the electron spin polarization from a radical to coupled nuclear spins, driven by microwave excitation resonant with the electron spin transitions. In this work we explore the potential of pulsed multi-frequency microwave excitation in liquids. Here, the relevant DNP mechanism is the Overhauser effect. The experiments were performed with TEMPOL radicals in aqueous solution at room temperature using a Q-band frequency (1.2 T) electron paramagnetic resonance (EPR) spectrometer combined with a Minispec NMR spectrometer. A fast arbitrary waveform generator (AWG) enabled the generation of multi-frequency pulses used to either sequentially or simultaneously excite all three 14N-hyperfine lines of the nitroxide radical. The multi-frequency excitation resulted in a doubling of the observed DNP enhancements compared to single-frequency microwave excitation. Q-band free induction decay (FID) signals of TEMPOL were measured as a function of the excitation pulse length allowing the efficiency of the electron spin manipulation by the microwave pulses to be extracted. Based on this knowledge we could quantitatively model our pulsed DNP enhancements at 1.2 T by numerical solution of the Bloch equations, including electron spin relaxation and experimental parameters. Our results are in good agreement with theoretical predictions. Whereas for a narrow and homogeneous single EPR line continuous wave excitation leads to more efficient DNP enhancements compared to pulsed excitation for the same amount of averaged microwave power. The situation is different for radicals with several hyperfine lines or in the presence of inhomogeneous line broadening. In such cases pulsed single/multi-frequency excitation can lead to larger DNP enhancements.

Wednesday, May 23, 2018

(13)C Dynamic Nuclear Polarization Using a Trimeric Gd(3+) Complex as an Additive #DNPNMR

Niedbalski, P., et al., (13)C Dynamic Nuclear Polarization Using a Trimeric Gd(3+) Complex as an Additive. J. Phys. Chem. A, 2017. 121(27): p. 5127-5135.


Dissolution dynamic nuclear polarization (DNP) is one of the most successful techniques that resolves the insensitivity problem in liquid-state nuclear magnetic resonance (NMR) spectroscopy and imaging (MRI) by amplifying the signal by several thousand-fold. One way to further improve the DNP signal is the inclusion of trace amounts of lanthanides in DNP samples doped with trityl OX063 free radical as the polarizing agent. In practice, stable monomeric gadolinium complexes such as Gd-DOTA or Gd-HP-DO3A are used as beneficial additives in DNP samples, further boosting the DNP-enhanced solid-state (13)C polarization by a factor of 2 or 3. Herein, we report on the use of a trimeric gadolinium complex as a dopant in (13)C DNP samples to improve the (13)C DNP signals in the solid-state at 3.35 T and 1.2 K and consequently, in the liquid-state at 9.4 T and 298 K after dissolution. Our results have shown that doping the (13)C DNP sample with a complex which holds three Gd(3+) ions led to an improvement of DNP-enhanced (13)C polarization by a factor of 3.4 in the solid-state, on par with those achieved using monomeric Gd(3+) complexes but only requires about one-fifth of the concentration. Upon dissolution, liquid-state (13)C NMR signal enhancements close to 20000-fold, approximately 3-fold the enhancement of the control samples, were recorded in the nearby 9.4 T high resolution NMR magnet at room temperature. Comparable reduction of (13)C spin-lattice T1 relaxation time was observed in the liquid-state after dissolution for both the monomeric and trimeric Gd(3+) complexes. Moreover, W-band electron paramagnetic resonance (EPR) data have revealed that 3-Gd doping significantly reduces the electron T1 of the trityl OX063 free radical, but produces negligible changes in the EPR spectrum, reminiscent of the results with monomeric Gd(3+)-complex doping. Our data suggest that the trimeric Gd(3+) complex is a highly beneficial additive in (13)C DNP samples and that its effect on DNP efficiency can be described in the context of the thermal mixing mechanism.

Monday, May 21, 2018

Improving Sensitivity of Solid-state NMR Spectroscopy by Rational Design of Polarizing Agents for Dynamic Nuclear Polarization #DNPNMR

Kubicki, D.J. and L. Emsley, Improving Sensitivity of Solid-state NMR Spectroscopy by Rational Design of Polarizing Agents for Dynamic Nuclear Polarization. Chimia (Aarau), 2017. 71(4): p. 190-194.


We review our recent efforts to optimize the efficiency of polarizing agents for Dynamic Nuclear Polarization (DNP) in solid-state MAS NMR spectroscopy. We elucidate the links between DNP performance, molecular structure and electronic relaxation properties of dinitroxide biradicals. We show that deuteration and increased bulkiness lead to slower electronic relaxation and in turn to higher DNP enhancements. We also show that the incorporation of solid dielectric particles into the sample is a general method of amplifying DNP enhancements by about a factor of two.

Friday, May 18, 2018

A radiofrequency system for in vivo hyperpolarized (13) C MRS experiments in mice with a 3T MRI clinical scanner

Giovannetti, G., et al., A radiofrequency system for in vivo hyperpolarized (13) C MRS experiments in mice with a 3T MRI clinical scanner. Scanning, 2016. 38(6): p. 710-719.


Hyperpolarized carbon-13 magnetic resonance spectroscopy (MRS) is a powerful tool to explore tissue metabolic state, by permitting the study of intermediary metabolism of biomolecules in vivo. However, a number of technological problems still limit this technology and need innovative solutions. In particular, the low molar concentration of derivate metabolites give rise to low signal-to-noise ratio (SNR), which makes the design and development of dedicated radiofrequency (RF) coils a fundamental task. In this article, the authors describe the simulation and the design of a RF coils configuration for MR experiments in mice, constituted by a (1) H whole body volume RF coil for imaging and a (13) C single circular loop surface RF coil for performing (13) C acquisitions. After the building, the RF system was employed in an in vivo experiment in a mouse injected with hyperpolarized [1-(13) C]pyruvate by using a 3 T clinical MR scanner. SCANNING 38:710-719, 2016. (c) 2016 Wiley Periodicals, Inc.

Wednesday, May 16, 2018

DNP-enhanced ultrawideline (207)Pb solid-state NMR spectroscopy: an application to cultural heritage science

Kobayashi, T., et al., DNP-enhanced ultrawideline (207)Pb solid-state NMR spectroscopy: an application to cultural heritage science. Dalton Trans, 2017. 46(11): p. 3535-3540. 


Dynamic nuclear polarization (DNP) is used to enhance the (ultra)wideline (207)Pb solid-state NMR spectra of lead compounds of relevance in the preservation of cultural heritage objects. The DNP SSNMR experiments enabled, for the first time, the detection of the basic lead carbonate phase of the lead white pigment by (207)Pb SSNMR spectroscopy. Variable-temperature experiments revealed that the short T'2 relaxation time of the basic lead carbonate phase hinders the acquisition of the NMR signal at room temperature. We additionally observe that the DNP enhancement is twice as large for lead palmitate (a lead soap, which is a degradation product implicated in the visible deterioration of lead-based oil paintings), than it is for the basic lead carbonate. This enhancement has allowed us to detect the formation of a lead soap in an aged paint film by (207)Pb SSNMR spectroscopy; which may aid in the detection of deterioration products in smaller samples removed from works of art.

Tuesday, May 15, 2018

[NMR] Postdoc in hyperpolarized NMR and MRI in the Theis lab at NC State University and close collaboration with Duke University



Dear colleagues,

A postdoctoral position is opening in the Theis lab at the North Carolina State University. The focus of the position will be on development and applications of hyperpolarization technology. In a highly interdisciplinary and collaborative environment we will be advancing parahydrogen induced polarization techniques towards applications in biomolecular structure elucidation, miniaturized NMR, and molecular imaging. Novel hyperpolarized markers and detection schemes will be developed, tested and applied. The position also involves a close collaboration with the Warren lab at Duke University.

We offer access to parahydrogen hyperpolarizers (Duke and NCSU) and dissolution-DNP instrumentation (hypersense at Duke). The hyperpolarizers are installed next to imagers (7T and 1T) and NMR spectrometers (400 MHz). Schemes for optical detection of hyperpolarized signals with sensitive magnetometers will be designed and installed at NCSU. 

At NCSU METRIC (The Molecular Education, Technology and Research Innovation Center) gives access to the following NMR devices in addition to state-of-the-art mass spectrometry and X-Ray Crystallography instrumentation: 

  • Bruker Avance NEO 400 MHz NMR, RT BBO iProbe, VT, and SampleXpress Automatic Sample Changer
  • Bruker Avance NEO 500 MHz NMR, BBO PRODIGY LN2 -Cryoprobe, VT, and SampleCASE automatic Sample Changer
  • Bruker Avance NEO 600 MHz NMR, RT BBO Smart Probe and TXI 1H-13C/15N- 2H Probe, VT, and SampleXpress Automatic Sample Changer
  • Bruker Avance NEO 700 MHz NMR, TCI 1H/19F-13C/15N- 2H LHe Cryoprobe, TXI 1H-13C/15N- 2H Probe, VT, and SampleXPress Automatic Sample Changer
  • Bruker Avance III 700 MHz NMR, TCI 1H-13C/15N- 2H LHe CryoProbe, TXI 1H-13C/15N- 2HProbe, VT, and SampleXpress Automatic Sample Changer
  • Varian Mercury 400 MHz NMR, VT, 5mm ASW 4-nuclei 1H/19F/13C/31P Probe
  • Varian Inova 400 MHz NMR, VT, 5 mm PFG gradient 4-nuclei Probe (1H/19F/13C/31P)
  • Varian Mercury 300 MHz NMR, 5 mm ID Probe (1H/13C)
  • Varian Mercury Plus 300 MHz NMR, 5mm PFG 4-nuclei Probe
  • E500-10/12 EPR System with Digital High-Resolution Hall Field Controller and Dual Channel Signal Processing UnitFurthermore, we offer many collaborations across the Triangle (UNC, Duke, NC State), the US and Europe, and extended opportunities to travel for collaborations and attending conferences. 
The preferred candidate is a highly motivated and collaborative individual with expertise in magnetic resonance technologies and experimental design. Experience with hyperpolarization technologies, imaging and programming are a plus.

Candidates with a strong background in chemical synthesis that wish to broaden their skill-set by combining their strength in chemical design with innovative molecular imaging and spectroscopy approaches are also encouraged to apply. 


For more details please email ttheis@ncsu.edu or see:
The Theis lab is located on the modern centennial campus at NCSU. See: https://centennial.ncsu.edu/
To apply, please send CV/resume with contact information for 2 references to: ttheis@ncsu.edu

_________________________________
Thomas Theis, Ph.D.

Assistant Professor of Chemistry
North Carolina State University 

Adjunct at Duke University, Department of Chemistry 




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[NMR] PhD and Postdoctoral positions available to join the Emsley group at EPFL #DNPNMR

PhD and Postdoctoral positions available to join the Emsley group at EPFL, Lausanne

We are looking for highly motivated candidates to take up PhD and Postdoctoral positions developing new methods in NMR spectroscopy to address challenging problems in chemistry and materials science. In particular we will be working on extending dynamic nuclear polarization enhanced NMR crystallography to complex non-crystalline materials. Examples of our recent work and the application areas that we work on can be found on our website: http://lrm.epfl.ch

We are looking for highly motivated candidates with strong scientific background, independence, and who enjoy teamwork. You should hold a relevant qualification in chemistry, physics or related disciplines. Skills in one of the following fields of expertise are a plus:

• Experimental multi-dimensional nuclear magnetic resonance,
• 
Simulation, Theory, or Modelling of nuclear spin dynamics, NMR properties or chemical structures.
 

Our laboratory at EPFL is part of one the world’s leading chemistry departments, and is located Lausanne on the north shore of Lake Geneva. The laboratory is equipped with unique state of the art NMR spectrometers (including gyrotron DNP accessories at 400 and 900 MHz, a dissolution-DNP machine, and 100 kHz magic angle spinning probes).
 
Motivated candidates should contact Lyndon Emsley by email to lyndon.emsley@epfl.ch


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