Oct 18, 2019

Frequency-chirped dynamic nuclear polarization with magic angle spinning using a frequency-agile gyrotron #DNPNMR

Gao, Chukun, Nicholas Alaniva, Edward P. Saliba, Erika L. Sesti, Patrick T. Judge, Faith J. Scott, Thomas Halbritter, Snorri Th. Sigurdsson, and Alexander B. Barnes. “Frequency-Chirped Dynamic Nuclear Polarization with Magic Angle Spinning Using a Frequency-Agile Gyrotron.” Journal of Magnetic Resonance 308 (November 2019): 106586.

We demonstrate that frequency-chirped dynamic nuclear polarization (DNP) with magic angle spinning (MAS) improves the enhancement of nuclear magnetic resonance (NMR) signal beyond that of continuous-wave (CW) DNP. Using a custom, frequency-agile gyrotron we implemented frequencychirped DNP using the TEMTriPol-1 biradical, with MAS NMR at 7 Tesla. Frequency-chirped microwaves yielded a DNP enhancement of 137, an increase of 19% compared to 115 recorded with CW. The chirps were 120 MHz-wide and centered over the trityl resonance, with 7 W microwave power incident on the sample (estimated 0.4 MHz electron spin Rabi frequency). We describe in detail the design and fabrication of the frequency-agile gyrotron used for frequency-chirped MAS DNP. Improvements to the interaction cavity and internal mode converter yielded efficient microwave generation and mode conversion, achieving >10 W output power over a 335 MHz bandwidth with >110 W peak power. Frequency-chirped DNP with MAS is expected to have a significant impact on the future of magnetic resonance.

Oct 16, 2019

Persistence of Nitroxide Radicals in Solution #EPR #DNPNMR

Elajaili, Hanan, Jessica Sedhom, Sandra S. Eaton, and Gareth R. Eaton. “Persistence of Nitroxide Radicals in Solution.” Applied Magnetic Resonance 50, no. 10 (October 2019): 1177–81.

Data on long-term persistence of nitroxide radicals typically are focused on solid samples. Less information is available for nitroxides in fluid solution. Sealed deoxygenated solutions of a doxyl nitroxide in tetrahydrofuran and a piperidinyl nitroxide in toluene in 4 mm EPR tubes were kept in a laboratory environment at ambient temperature and without protection from light. After more than 40 years, the concentrations of the solutions had decreased by about factors of 12 and 6, respectively. The longevity in solution probably depends strongly on the purity of the solvent, but these results indicate remarkable persistence.

Oct 14, 2019

Identification of Intracellular and Extracellular Metabolites in Cancer Cells Using 13C Hyperpolarized Ultrafast Laplace NMR #DNPNMR

Zhang, Guannan, Susanna Ahola, Mathilde H. Lerche, Ville-Veikko Telkki, and Christian Hilty. “Identification of Intracellular and Extracellular Metabolites in Cancer Cells Using 13C Hyperpolarized Ultrafast Laplace NMR.” Analytical Chemistry 90, no. 18 (September 18, 2018): 11131–37.

Ultrafast Laplace NMR (UF-LNMR), which is based on the spatial encoding of multidimensional data, enables one to carry out 2D relaxation and diffusion measurements in a single-scan. Besides reducing the experiment time to a fraction, it significantly facilitates the use of nuclear spin hyperpolarization to boost experimental sensitivity, because the time consuming polarization step does not need to be repeated. Here we demonstrate the usability of hyperpolarized UF-LNMR in the context of cell metabolism, by investigating the conversion of pyruvate to lactate in the cultures of mouse 4T1 cancer cells. We show that 13C ultrafast diffusion – T2 relaxation correlation measurements, with the sensitivity enhanced by several orders of magnitude by dissolution dynamic nuclear polarization (DDNP), allows the determination of the extra- vs. intracellular location of metabolites due to their significantly different values of diffusion coefficients and T2 relaxation times. Under the current conditions, pyruvate located predominantly in the extracellular pool, while lactate remained primarily intracellular. Contrary to the small flip angle diffusion methods reported in the literature, the UFLNMR method does not require several scans with varying gradient strength, and it provides a combined diffusion and T2 contrast. Furthermore, the ultrafast concept can be extended to various other multidimensional LNMR experiments, which will provide detailed information about the dynamics and exchange processes of cell metabolites.

Oct 11, 2019

High-Field Liquid-State Dynamic Nuclear Polarization in Microliter Samples #DNPNMR

Yoon, Dongyoung, Alexandros I. Dimitriadis, Murari Soundararajan, Christian Caspers, Jeremy Genoud, Stefano Alberti, Emile de Rijk, and Jean-Philippe Ansermet. “High-Field Liquid-State Dynamic Nuclear Polarization in Microliter Samples.” Analytical Chemistry 90, no. 9 (May 2018): 5620–26.

Nuclear hyperpolarization in liquid state by dynamic nuclear polarization (DNP) has been of great interest because of its potential use in NMR spectroscopy of small samples of biological and chemical compounds in aqueous media. Liquid state DNP generally requires microwave resonators in order to generate an alternating magnetic field strong enough to saturate electron spins in the solution. As a consequence, the sample size is limited to dimensions of the order of the wavelength, and this restricts the sample volume to less than 100 nL for DNP at 9 T (~ 260 GHz). We show here a new approach that overcomes this sample size limitation. Large saturation of electron spins was obtained with a high-power (~ 150 W) gyrotron without microwave resonators. Since high power microwaves can cause serious dielectric heating in polar solutions, we designed a planar probe which effectively alleviates dielectric heating. A thin liquid sample of 100 μm of thickness is placed on a block of high thermal conductivity aluminum nitride with a gold coating, that serves both as a ground plane and as a heat sink. A meander or a coil were used for NMR. We performed 1H DNP at 9.2 T (~ 260 GHz) and at room temperature with 10 μL of water, a volume that is more than 100 times larger than reported so far. The 1H NMR signal is enhanced by a factor of about -10 with 70 W of microwave power. We also demonstrated liquid state 31P DNP in fluorobenzene containing triphenylphosphine, and obtained an enhancement of ~200.

[NMR] Announcement: 6th Winter School on Biomolecular SSNMR, January 5-10, 2020


The 6th Winter School on Biomolecular Solid-State NMR
Stowe, Vermont, USA
January 5-10, 2020

Organizers: Tatyana Polenova (U. Delaware), Christopher Jaroniec (Ohio State U.), Mei Hong (MIT) and Bob Griffin (MIT)

Dear Colleagues,

We invite you to encourage your students, postdocs, and senior associates to attend the 6th Winter School on Biomolecular Solid-State NMR, which will be held on January 5-10, 2020, in Stowe, Vermont. Similar to the previous five highly successful Winter Schools, this pedagogical meeting is aimed at students and postdocs in solid-state NMR as well as more senior scientists in related fields who are interested in entering this vibrant field. Our goals are to provide a focused week of teaching of the core concepts and practices in the increasingly multifaceted and complex field of biological solid-state NMR spectroscopy, and to encourage information sharing among different laboratories. Topics to be covered in the 6th Winter School include:

  • Basics of solid-state NMR: orientation-dependent NMR frequencies, MAS, tensors and rotations, density operator and its time evolution, decoupling and recoupling techniques, and average Hamiltonian theory
  • Multidimensional correlation spectroscopy, non-uniform sampling, techniques for resonance assignment and measurement of structural restraints in biomolecules
  • Paramagnetic solid-state NMR techniques
  • Techniques for enhancing sensitivity of solid-state NMR: dynamic nuclear polarization and 1H detection
  • Solid-state NMR techniques for measuring molecular motion
  • Solid-state NMR techniques for structural studies of oriented membrane proteins
  • Solid-state NMR spectra simulations in SPINEVOLUTION
  • Beyond spin 1/2: NMR of quadrupolar nuclei
  • Basics of NMR probe design
In addition to lectures, problem sets and discussion sessions will be given at the meeting.
Speakers: The following have agreed to serve as lecturers:

Tim Cross (Florida State)
Philip Grandinetti (Ohio State)
Bob Griffin (MIT)
Mei Hong (MIT)
Christopher Jaroniec (Ohio State)
Francesca Marassi (Burnham)
Ann McDermott (Columbia)
Guido Pintacuda (ENS Lyon)
Tatyana Polenova (Delaware)
Bernd Reif (Tech Univ Munich)
Melanie Rosay (Bruker)
Robert Tycko (NIH)

Venue and transportation: The meeting will be held at the beautiful and historical Trapp Family Lodge http://www.trappfamily.com/ in Stowe, Vermont. Stowe is accessible from airports in Burlington, VT, Manchester, NH, and Boston, MA. A block of rooms has been reserved at the lodge. We anticipate space for ~70 attendees.

Cost: Room and board will be free for attendees. The registration fee is $750 for academic attendees and $1500 for industrial attendees.

Application: Interested students and postdocs should send the following application materials as a single PDF file to: ssnmr.winterschool@gmail.com. The application materials include: (1) a CV, (2) publication list, and (3) a 1-page description of your current research and your statement of interest in attending the Winter School. Please indicate your gender in the CV for the purpose of hotel room assignment. Please name this application file as: AdvisorLastName_YourLastName_WS2020app.pdf. For example “McDermott_Smith_WS2020app.pdf”.

Application deadline: Friday, November 8, 2019. Given the limited number of available spaces, it may not be possible to accommodate applications received after this date.

Please distribute this announcement to members of your research group as well as to colleagues who may be interested in attending or sending their group members.

With kind regards,
Tatyana, Chris, Mei & Bob

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Oct 10, 2019

[NMR] Dates for the diary: 53rd ESR Group Conference in Manchester

Dear Colleagues,

the next conference in the long series of Electron Spin Resonance meetings organised by the ESR Group of the Royal Society of Chemistry will take place in Manchester between 29th March and 2nd April 2020:

The Meeting is the oldest EPR Spectroscopy conference in the world, as well as the occasion on which the EPR Spectroscopy Bruker Prize is awarded to eminent EPR scientists, Bruker Thesis Prize is given for the best PhD thesis in the preceding two years, and the JEOL Student Prize is awarded for the best student research work presented at the Conference.

The registration will open in November.

Best wishes,

Dr Ilya Kuprov FRSC
Associate Professor of Chemical Physics
Secretary to the RSC ESR Spectroscopy Group
Associate Editor, Science Advances
Office 3041, Building 30,
School of Chemistry, FNES,
University of Southampton,
Southampton, SO17 1BJ, UK.
Tel: +44 2380 594 140

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Oct 9, 2019

Metabolic Measurements of Nonpermeating Compounds in Live Cells Using Hyperpolarized NMR

Liu, Mengxiao, and Christian Hilty. “Metabolic Measurements of Nonpermeating Compounds in Live Cells Using Hyperpolarized NMR.” Analytical Chemistry 90, no. 2 (January 16, 2018): 1217–22.

Hyperpolarization by dissolution dynamic nuclear polarization (D-DNP) has emerged as a technique for enhancing NMR signals by several orders of magnitude, thereby facilitating the characterization of metabolic pathways both in vivo and in vitro. Following the introduction of an externally hyperpolarized compound, real-time NMR enables the measurement of metabolic flux in the corresponding pathway. Spin relaxation however limits the maximum experimental time and prevents the use of this method with compounds exhibiting slow membrane transport rates. Here, we demonstrate that electroporation can serve as a method for membrane permeabilization for use with D-DNP in cell cultures. An electroporation apparatus hyphenated with stopped flow sample injection permits the introduction of the hyperpolarized metabolite within 3 s after the electrical pulse. In yeast cells that do not readily take up pyruvate, the addition of the electroporation pulse to the D-DNP experiment increases the signals of the downstream metabolic products CO2 and HCO3 -, which otherwise are near the detection limit, by 8.2 and 8.6-fold. Modeling of the time dependence of these signals then permits the determination of the respective kinetic rate constants. The observed conversion rate from pyruvate to CO2 normalized for cell density was found to increase by a factor of 12 due to the alleviation of the membrane transport limitation. Using electroporation therefore extends the applicability of D-DNP to in vitro studies to a wider range of metabolites, and at the same time reduces the influence of membrane transport on the observed conversion rates.