Friday, September 29, 2017

Pyruvate cellular uptake and enzymatic conversion probed by dissolution DNP-NMR: the impact of overexpressed membrane transporters


Balzan, R., et al., Pyruvate cellular uptake and enzymatic conversion probed by dissolution DNP-NMR: the impact of overexpressed membrane transporters. Magn Reson Chem, 2017. 55(6): p. 579-583.


Pyruvate membrane crossing and its lactate dehydrogenase-mediated conversion to lactate in cells featuring different levels of expression of membrane monocarboxylate transporters (MCT4) were probed by dissolution dynamic nuclear polarization-enhanced NMR. Hyperpolarized 13 C-1-labeled pyruvate was transferred to suspensions of rodent tumor cell carcinoma, cell line 39. The pyruvate-to-lactate conversion rate monitored by dissolution dynamic nuclear polarization-NMR in carcinoma cells featuring native MCT4 expression level was lower than the rate observed for cells in which the human MCT4 gene was overexpressed. The enzymatic activity of lactate dehydrogenase was also assessed in buffer solutions, following the real-time pyruvate-to-lactate conversion speeds at different enzyme concentrations. Copyright (c) 2016 John Wiley & Sons, Ltd.

Wednesday, September 27, 2017

Hyperpolarized 13 C magnetic resonance evaluation of renal ischemia reperfusion injury in a murine model


Baligand, C., et al., Hyperpolarized 13 C magnetic resonance evaluation of renal ischemia reperfusion injury in a murine model. NMR Biomed, 2017. 30(10): p. e3765-n/a.


Acute kidney injury (AKI) is a major risk factor for the development of chronic kidney disease (CKD). Persistent oxidative stress and mitochondrial dysfunction are implicated across diverse forms of AKI and in the transition to CKD. In this study, we applied hyperpolarized (HP) 13 C dehydroascorbate (DHA) and 13 C pyruvate magnetic resonance spectroscopy (MRS) to investigate the renal redox capacity and mitochondrial pyruvate dehydrogenase (PDH) activity, respectively, in a murine model of AKI at baseline and 7 days after unilateral ischemia reperfusion injury (IRI). Compared with the contralateral sham-operated kidneys, the kidneys subjected to IRI showed a significant decrease in the HP 13 C vitamin C/(vitamin C + DHA) ratio, consistent with a decrease in redox capacity. The kidneys subjected to IRI also showed a significant decrease in the HP 13 C bicarbonate/pyruvate ratio, consistent with impaired PDH activity. The IRI kidneys showed a significantly higher HP 13 C lactate/pyruvate ratio at day 7 compared with baseline, although the 13 C lactate/pyruvate ratio was not significantly different between the IRI and contralateral sham-operated kidneys at day 7. Arterial spin labeling magnetic resonance imaging (MRI) demonstrated significantly reduced perfusion in the IRI kidneys. Renal tissue analysis showed corresponding increased reactive oxygen species (ROS) and reduced PDH activity in the IRI kidneys. Our results show the feasibility of HP 13 C MRS for the non-invasive assessment of oxidative stress and mitochondrial PDH activity following renal IRI.

Monday, September 25, 2017

Dynamic Nuclear Polarization/Solid-State NMR Spectroscopy of Membrane Polypeptides: Free-Radical Optimization for Matrix-Free Lipid Bilayer Samples #DNPNMR


Salnikov, E.S., et al., Dynamic Nuclear Polarization/Solid-State NMR Spectroscopy of Membrane Polypeptides: Free-Radical Optimization for Matrix-Free Lipid Bilayer Samples. ChemPhysChem, 2017. 18(15): p. 2103-2113.


Dynamic nuclear polarization (DNP) boosts the sensitivity of NMR spectroscopy by orders of magnitude and makes investigations previously out of scope possible. For magic-angle-spinning (MAS) solid-state NMR spectroscopy studies, the samples are typically mixed with biradicals dissolved in a glass-forming solvent and are investigated at cryotemperatures. Herein, we present new biradical polarizing agents developed for matrix-free samples such as supported lipid bilayers, which are systems widely used for the investigation of membrane polypeptides of high biomedical importance. A series of 11 biradicals with different structures, geometries, and physicochemical properties were comprehensively tested for DNP performance in lipid bilayers, some of them developed specifically for DNP investigations of membranes. The membrane-anchored biradicals PyPol-C16, AMUPOL-cholesterol, and bTurea-C16 were found to exhibit improved g-tensor alignment, inter-radical distance, and dispersion. Consequently, these biradicals show the highest signal enhancement factors so far obtained for matrix-free membranes or other matrix-free samples and may potentially shorten NMR acquisition times by three orders of magnitude. Furthermore, the optimal biradical-to-lipid ratio, sample deuteration, and membrane lipid composition were determined under static and MAS conditions. To rationalize biradical performance better, DNP enhancement was measured by using the 13 C and 15 N signals of lipids and a peptide as a function of the biradical concentration, DNP build-up time, resonance line width, quenching effect, microwave power, and MAS frequency.

[NMR] Postdoc position on SSNMR at the University of Lille, France #DNPNMR

Fromt the Ampere Magnetic Resonance List



Please forward to potential candidates.

Project title: Development of high-field (DNP)-NMR methods to detect quadrupolar nuclei on catalytic surfaces

A two-year postdoc position in solid-state NMR spectroscopy of advanced materials is available at the University of Lille, Lille, France. It will start preferably in December 2017.

Project description: The development of improved heterogeneous catalysts can be undertaken in a rational way by a better
understanding of their structures. Solid-state NMR spectroscopy is very well suited to the study of heterogeneous catalysts because it can give information on the local structure. However, the lack of sensitivity and resolution poses limit for the characterization of surface sites, notably when they are occupied by quadrupolar nuclei (11B, 17O, 27Al, 67Zn, 95Mo...) exhibiting NMR signal broaden by large quadrupolar interaction. This project aims at developing and applying novel solid-state high-field (DNP)NMR methods to probe the local environment of quadrupolar nuclei. It will provide unique insights into the structure of the catalytic surfaces, which will be useful to improve their performances.

Host and research infrastructure: Lille is a vibrant and handsome city, imbued with a rich history, located in the center of northwestern Europe (only 30 min by high-speed trains from Brussels, 1h from Paris and 1h30 from London). Lille is one of France’s top student cities and the university of Lille is a leading center for magnetic resonance. Lille NMR facility includes 800 and 900 MHz NMR spectrometers and has been selected to host the first 1.2 GHz NMR spectrometer to be installed in France. Our research group is internationally known for the development of solid-state NMR methods, notably for quadrupolar nuclei, and the characterization of heterogeneous catalysts. We have an expertise in high-field solid-state NMR spectroscopy and were among the pioneers of high-field DNP-NMR of hybrid and inorganic materials. 

The person: We seek application from candidates with experience in the development of solid-state NMR methods and/or the NMR characterization of inorganic materials and catalysts. The successful applicant will be given the opportunity to work in an exciting environment with national and international collaborations.

Contact: Applications and informal queries about the lab and research projects should be directed by


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Friday, September 22, 2017

Nanodiamond-enhanced MRI via in situ hyperpolarization


Waddington, D.E.J., et al., Nanodiamond-enhanced MRI via in situ hyperpolarization. Nat Commun, 2017. 8: p. 15118.


Nanodiamonds are of interest as nontoxic substrates for targeted drug delivery and as highly biostable fluorescent markers for cellular tracking. Beyond optical techniques, however, options for noninvasive imaging of nanodiamonds in vivo are severely limited. Here, we demonstrate that the Overhauser effect, a proton-electron polarization transfer technique, can enable high-contrast magnetic resonance imaging (MRI) of nanodiamonds in water at room temperature and ultra-low magnetic field. The technique transfers spin polarization from paramagnetic impurities at nanodiamond surfaces to 1H spins in the surrounding water solution, creating MRI contrast on-demand. We examine the conditions required for maximum enhancement as well as the ultimate sensitivity of the technique. The ability to perform continuous in situ hyperpolarization via the Overhauser mechanism, in combination with the excellent in vivo stability of nanodiamond, raises the possibility of performing noninvasive in vivo tracking of nanodiamond over indefinitely long periods of time.

Wednesday, September 20, 2017

Measuring Nano- to Microstructures from Relayed Dynamic Nuclear Polarization NMR #DNPNMR


Pinon, A.C., et al., Measuring Nano- to Microstructures from Relayed Dynamic Nuclear Polarization NMR. The Journal of Physical Chemistry C, 2017. 121(29): p. 15993-16005.


We show how dynamic nuclear polarization (DNP) NMR can be used in combination with models for polarization dynamics to determine the domain sizes in complex materials. By selectively doping a source component with radicals and leaving the target undoped, we can measure experimental polarization buildup curves which can be compared with simulations based on heterogeneous distributions of polarization within the sample. The variation of the integrated DNP enhancement as a function of the polarization time is found to be characteristic of the geometry. We demonstrate the method experimentally on four different systems where we successfully determine domain sizes between 200 and 20 000 nm, specifically in powdered histidine hydrochloride monohydrate, pore lengths of mesoporous silica materials, and two domain sizes in two-component polymer film coatings. Additionally, we find that even in the apparently homogeneous frozen solutions used as polarization sources in most DNP experiments, polarization is relayed from protons near the radicals to the bulk of the solution by spin diffusion, which explains the experimentally observed buildup times in these samples.

Monday, September 18, 2017

Unprecedented Carbon Signal Enhancement in Liquid-State NMR Spectroscopy #DNPNMR


Pinter, G. and H. Schwalbe, Unprecedented Carbon Signal Enhancement in Liquid-State NMR Spectroscopy. Angew Chem Int Ed Engl, 2017. 56(29): p. 8332-8334.


We shall overcome: As a result of efforts to overcome the sensitivity challenge of liquid-state NMR spectroscopy, a thousand-fold signal enhancement was achieved by dynamic nuclear polarization (DNP) for 13 C signals at high magnetic field (3.4 T) and room temperature, thereby exceeding the predicted limitations of high-field liquid-state in situ DNP.

Friday, September 15, 2017


Barskiy, D.A., et al., NMR Hyperpolarization Techniques of Gases. Chemistry, 2017. 23(4): p. 725-751.


Nuclear spin polarization can be significantly increased through the process of hyperpolarization, leading to an increase in the sensitivity of nuclear magnetic resonance (NMR) experiments by 4-8 orders of magnitude. Hyperpolarized gases, unlike liquids and solids, can often be readily separated and purified from the compounds used to mediate the hyperpolarization processes. These pure hyperpolarized gases enabled many novel MRI applications including the visualization of void spaces, imaging of lung function, and remote detection. Additionally, hyperpolarized gases can be dissolved in liquids and can be used as sensitive molecular probes and reporters. This Minireview covers the fundamentals of the preparation of hyperpolarized gases and focuses on selected applications of interest to biomedicine and materials science.

Thursday, September 14, 2017

[NMR] Nobel Prize winner Nico Bloembergen passed away at age 97


From the Ampere Magnetic Resonance List:

Dear colleagues,

Last week, Nobel laureate Professor Nicolaas Bloembergen, a pioneer in the field of NMR and laser spectroscopy passed away at age of 97. As an undergraduate Bloembergen studied Physics at Utrecht University from 1938 to 1943 and received his PhD in Physics from Leiden University with C.J. Gorter in 1948 on the topic of Nuclear Magnetic Relaxation. His thesis resulted in the famous BPP (Bloembergen, Purcell and Pound) paper which still serves as a point of departure for understanding many NMR relaxation experiments. In 1973 he returned to Leiden and occupied the Lorentz Chair in Physics. In 1981, he was awarded the Nobel Prize in Physics for his work in coherent optics. In 2001 in honour of his achievements, the NMR group at Utrecht University named their laboratory the Bloembergen Building.

For further information on a true scientific giant, please look out for an obituary written by C. Luchinat, R. Boelens, and R. Kaptein that will appear on the Ampere website and in the Ampere newsletter soon.

Also, please see, for example:

Best wishes,
Marc Baldus



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Wednesday, September 13, 2017

Single-scan 13C diffusion-ordered NMR spectroscopy of DNP-hyperpolarised substrates #DNPNMR


Guduff, L., et al., Single-scan 13C diffusion-ordered NMR spectroscopy of DNP-hyperpolarised substrates. Chemistry, 2017: p. n/a-n/a.


Diffusion-ordered NMR spectroscopy (DOSY) is a powerful approach for the analysis of molecular mixtures, yet its application range is limited by the relatively low sensitivity of NMR. We show here that spectrally resolved 13C DOSY data can be collected, in a single scan, for substrates hyperpolarised by dissolution dynamic nuclear polarisation (D-DNP), which provides signal enhancements of several orders of magnitude. For this we use a convection-compensation pulse scheme, which we also analyse by numerical simulation. The proposed method further allows the acquisition of several consecutive DOSY spectra in a single D-DNP experiment.

Monday, September 11, 2017

Overhauser-enhanced magnetic resonance elastography


Salameh, N., et al., Overhauser-enhanced magnetic resonance elastography. NMR in Biomedicine, 2016. 29(5): p. 607-613.


Magnetic resonance elastography (MRE) is a powerful technique to assess the mechanical properties of living tissue. However, it suffers from reduced sensitivity in regions with short T2 and T2* such as in tissue with high concentrations of paramagnetic iron, or in regions surrounding implanted devices. In this work, we exploit the longer T2* attainable at ultra-low magnetic fields in combination with Overhauser dynamic nuclear polarization (DNP) to enable rapid MRE at 0.0065 T. A 3D balanced steady-state free precession based MRE sequence with undersampling and fractional encoding was implemented on a 0.0065 T MRI scanner. A custom-built RF coil for DNP and a programmable vibration system for elastography were developed. Displacement fields and stiffness maps were reconstructed from data recorded in a polyvinyl alcohol gel phantom loaded with stable nitroxide radicals. A DNP enhancement of 25 was achieved during the MRE sequence, allowing the acquisition of 3D Overhauser-enhanced MRE (OMRE) images with (1.5 × 2.7 × 9) mm3 resolution over eight temporal steps and 11 slices in 6 minutes. In conclusion, OMRE at ultra-low magnetic field can be used to detect mechanical waves over short acquisition times. This new modality shows promise to broaden the scope of conventional MRE applications, and may extend the utility of low-cost, portable MRI systems to detect elasticity changes in patients with implanted devices or iron overload. Copyright © 2016 John Wiley & Sons, Ltd.

[NMR] Faculty position at New York University

From the Ampere Magnetic Resonance List



Dear Colleagues,

The Department of Chemistry at New York University is soliciting applications for faculty positions in Chemistry. One of the emphasis areas is biophysical chemistry, which may include NMR or EPR. The deadline for the application is Sep 29, 2017. The full search advertisement is copied and pasted below, and can also be found via the link: http://as.nyu.edu/chemistry/recruitment.html


best wishes,
Nate


----

ASSISTANT PROFESSOR

Department of Chemistry
Arts and Science
New York University

The Department of Chemistry at New York University (NYU) invites applications for several tenure-track faculty positions in all areas of Chemistry and Biochemistry, subject to final administrative approval. Successful candidates must have a Ph.D in chemistry or related field and demonstrate the potential to do pioneering research and to teach effectively at the undergraduate and graduate levels. The positions are anticipated to be at the junior level, although exceptional senior level candidates will be considered. The Department of Chemistry is continuing a significant growth plan, including the creation of the Biomedical Chemistry Institute, the Molecular Design Institute, and the addition of numerous senior and junior faculty members. Interested faculty are able to participate in significant interdisciplinary programs within the Washington Square campus, as well as with NYU’s engineering and medical schools, and scholarly activities at its campuses in Shanghai and Abu Dhabi.

Candidates should submit a curriculum vitae, a detailed description of research plans and interests, and a statement of teaching experience and interests. The application should include three letters of recommendation. Review of complete applications will begin September 29, 2017. The anticipated start date is September 1, 2018. Please submit applications through our web portal using the following link: apply.interfolio.com/43972

The Faculty of Arts and Science at NYU is at the heart of a leading research university that spans the globe. We seek scholars of the highest caliber, who embody the diversity of the United States as well as the global society in which we live. We strongly encourage applications from women, racial and ethnic minorities, and other individuals who are under-represented in the profession, across color, creed, race, ethnic and national origin, physical ability, gender and sexual identity, or any other legally protected basis. NYU affirms the value of differing perspectives on the world as we strive to build the strongest possible university with the widest reach. To learn more about the FAS commitment to diversity, equality and inclusion, please read here.

EOE/Affirmative Action/Minorities/Females/Vet/Disabled/Sexual Orientation/Gender Identity

--

Nate Traaseth | Associate Professor of Chemistry, NYU | traaseth@nyu.edu | 212-992-9784

lab website | full contact info


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Friday, September 8, 2017

Near-unity nuclear polarization with an open-source 129Xe hyperpolarizer for NMR and MRI


Already a bit older this article, but still a good read.


Nikolaou, P., et al., Near-unity nuclear polarization with an open-source 129Xe hyperpolarizer for NMR and MRI. Proc. Nat. Aca. Sci. USA, 2013. 110(35): p. 14150-14155.


The exquisite NMR spectral sensitivity and negligible reactivity of hyperpolarized xenon-129 (HP129Xe) make it attractive for a number of magnetic resonance applications; moreover, HP129Xe embodies an alternative to rare and nonrenewable 3He. However, the ability to reliably and inexpensively produce large quantities of HP129Xe with sufficiently high 129Xe nuclear spin polarization (PXe) remains a significant challenge—particularly at high Xe densities. We present results from our “open-source” large-scale (∼1 L/h) 129Xe polarizer for clinical, preclinical, and materials NMR and MRI research. Automated and composed mostly of off-the-shelf components, this “hyperpolarizer” is designed to be readily implementable in other laboratories. The device runs with high resonant photon flux (up to 200 W at the Rb D1 line) in the xenon-rich regime (up to 1,800 torr Xe in 500 cc) in either single-batch or stopped-flow mode, negating in part the usual requirement of Xe cryocollection. Excellent agreement is observed among four independent methods used to measure spin polarization. In-cell PXe values of ∼90%, ∼57%, ∼50%, and ∼30% have been measured for Xe loadings of ∼300, ∼500, ∼760, and ∼1,570 torr, respectively. PXe values of ∼41% and ∼28% (with ∼760 and ∼1,545 torr Xe loadings) have been measured after transfer to Tedlar bags and transport to a clinical 3 T scanner for MR imaging, including demonstration of lung MRI with a healthy human subject. Long “in-bag” 129Xe polarization decay times have been measured (T1 ∼38 min and ∼5.9 h at ∼1.5 mT and 3 T, respectively)—more than sufficient for a variety of applications.

Thursday, September 7, 2017

PhD/Postdoc positions, available on DNP/MAS NMR and multi-frequency EPR

The original posting can be found here:



The University of Konstanz with its "Institutional Strategy to promote Top-Level Research" has been receiving continuous funding since 2007 within the framework of the Excellence Initiative by the German Federal and State Governments.

PhD/Postdoc positions available on DNP/MAS NMR and multi-frequency EPR (67 % EG 13 TV-L)

The positions are to be filled as soon as possible and initially limited for two years. 

We are a newly established research group in the Chemistry Department. Our research encompasses the development of magnetic resonance spectroscopy, particularly dynamic nuclear polarization (DNP) / magic-angle spinning (MAS) NMR and multi-frequency electron-paramagnetic resonance (EPR) and their application in structural biology, enzymology, and catalysis. 

Possible research projects are:

To investigate if and how the high polarization generated in the photo-excited triplet states of certain chro-mophores can be used for DNP/MAS NMR. 

The development of "DNP pulse sequences". This project has an experimental component, as well as a theoretical component. 

The application and development of multi-frequency EPR spectroscopy to study enzymatic reaction mechanisms.

The exact topic of the candidates research can be agreed on in consultation and will depend on the candidates background and interests. 

You have a strong interest in basic science, particularly in physical chemistry and spectroscopy. You are highly motivated and willing to work on solving complex, long-term problems. In your research, you are able to make the combination between theory and experiment. You have a MSc degree in Physics, Chemistry or a related field. For postdocs a PhD in MAS NMR is a plus. 

The University of Konstanz encourages disabled persons to apply. They will be given preference if appropriately qualified (contact + 49 (0) 7531 / 88 - 4016). 

The University of Konstanz is committed to further the compatibility of work and family life. 

The University of Konstanz is an equal opportunity employer that tries to increase the number of women in research and teaching. 

The University of Konstanz offers a ,,Dual Career Couples Program". Information can be obtained from: www.uni-konstanz.de/dcc

Applicants should send a cover letter, CV, and contact information of two references before Oct 15, 2017 to Dr. Guinevere Mathies. E-mail: guinevere.mathies [at] uni-konstanz[.]de. 
Visit also our website: http://chemie.uni.kn/mathies . 

Bewerbungsende: 15.10.2017

Wednesday, September 6, 2017

Frozen Acrylamide Gels as Dynamic Nuclear Polarization Matrices #DNPNMR


Viger-Gravel, J., et al., Frozen Acrylamide Gels as Dynamic Nuclear Polarization Matrices. Angewandte Chemie, 2017. 129(30): p. 8852-8856.


Aqueous acrylamide gels can be used to provide dynamic nuclear polarization (DNP) NMR signal enhancements of around 200 at 9.4 T and 100 K. The enhancements are shown to increase with crosslinker concentration and low concentrations of the AMUPol biradical. This DNP matrix can be used in situations where conventional incipient wetness methods fail, such as to obtain DNP surface enhanced NMR spectra from inorganic nanoparticles. In particular, we obtain 113Cd spectra from CdTe-COOH NPs in minutes. The spectra clearly indicate a highly disordered cadmium-rich surface.

Tuesday, September 5, 2017

[NMR] Postdoctoral position in chromatin structural biology at UC, San Diego

The Debelouchina lab at the University of California, San Diego is looking for a motivated postdoctoral researcher to join our growing team. Our work combines NMR spectroscopy tools with chemical and cell biology techniques to study chromatin and gene regulation. This position will provide the candidate with the opportunity to apply and/or learn solid-state and solution NMR methods, protein and peptide synthesis, protein biochemistry, as well as cell biology techniques. Candidates must hold a Ph.D. in chemistry, biochemistry, biophysics or a related discipline. Extensive background in biomolecular NMR or NMR method development is not required but will be particularly helpful.

The University of California, San Diego has outstanding resources for high-field NMR spectroscopy, including 900 MHz, 750 MHz, 700 MHz and 500 MHz solid-state NMR spectrometers equipped with MAS and static probes, as well as solution spectrometers operating at 800 MHz, 600 MHz and 500 MHz dedicated to biomolecular NMR applications. The large UCSD scientific community and several research institutes nearby (The Salk Institute for Biological Studies, the Scripps Research Institute and the Sanford Burnham Prebys Medical Discovery Institute) provide a vast network and potential for collaborations and scientific exchange. In addition to a vibrant scientific environment, San Diego also offers beautiful weather all year round and many opportunities for nature and ocean exploration.

For more information, interested candidates should contact Dr. Debelouchina directly at gdebelouchina@ucsd.edu.

Representative publications:

Debelouchina GT, Gerecht K, Muir TW (2017). Ubiquitin utilizes an acidic surface patch to alter chromatin structure. Nat. Chem. Biol. 13, 105-110.

Debelouchina GT and Muir TW (2017). A Molecular Engineering Toolbox for the Structural Biologist. Q. Rev. Biophys. 50, e7.

Debelouchina GT, Bayro MJ, Fitzpatrick AWP, Ladizhansky V, Colvin MT, Caporini MA, Jaroniec CP, Bajaj VS, Rosay M, MacPhee C, Vendruscolo M, Maas WE, Dobson CM, Griffin RG (2013). Higher Order Amyloid Fibril Structure by MAS NMR and DNP Spectroscopy. J. Am. Chem. Soc. 135, 19237-47. 

___________________________
Galia Debelouchina, Ph.D.
Assistant Professor
Department of Chemistry and Biochemistry
University of California, San Diego
9500 Gilman Drive
La Jolla, CA 92093

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Monday, September 4, 2017

Hyperpolarization of nitrogen-15 nuclei by cross polarization and dissolution dynamic nuclear polarization


Milani, J., et al., Hyperpolarization of nitrogen-15 nuclei by cross polarization and dissolution dynamic nuclear polarization. Review of Scientific Instruments, 2017. 88(1): p. 015109.


Dynamic Nuclear Polarization (DNP) is often achieved by the direct transfer of polarization from electrons to nuclei such as 13C, induced by microwavesaturation of the wings of narrow EPR lines of radicals like trityl. In the indirectapproach on the other hand, DNP is used to transfer the polarization from the electrons of radicals such as nitroxides that have broad EPR lines to nuclear spins I = 1H, followed by cross-polarization (CP) from I = 1H to S = 13C or other nuclei with low gyromagnetic ratios. This approach is particularly attractive for S = 15N, since direct DNP yields modest polarizations P(15N) < 4% with build-up times that can be as long as τDNP(15N) > 2 h. In this paper, we show that CP from 1H to 15N at 1.2 K can yield P(15N) = 25% with τCP-DNP(15N) = 10–15 min. After rapid dissolution and transfer to a solution-state NMR spectrometer, a polarizationP(15N) = 20% was observed at 300 K. The longitudinal relaxation times in solution can be as long as T1(15N) > 800 s in favorable cases.





Friday, September 1, 2017

Arbitrary waveform modulated pulse EPR at 200GHz


Kaminker, I., R. Barnes, and S. Han, Arbitrary waveform modulated pulse EPR at 200GHz. J Magn Reson, 2017. 279: p. 81-90.


We report here on the implementation of arbitrary waveform generation (AWG) capabilities at approximately 200GHz into an Electron Paramagnetic Resonance (EPR) and Dynamic Nuclear Polarization (DNP) instrument platform operating at 7T. This is achieved with the integration of a 1GHz, 2 channel, digital to analog converter (DAC) board that enables the generation of coherent arbitrary waveforms at Ku-band frequencies with 1ns resolution into an existing architecture of a solid state amplifier multiplier chain (AMC). This allows for the generation of arbitrary phase- and amplitude-modulated waveforms at 200GHz with >150mW power. We find that the non-linearity of the AMC poses significant difficulties in generating amplitude-modulated pulses at 200GHz. We demonstrate that in the power-limited regime of omega1<1MHz phase-modulated pulses were sufficient to achieve significant improvements in broadband (>10MHz) spin manipulation in incoherent (inversion), as well as coherent (echo formation) experiments. Highlights include the improvement by one order of magnitude in inversion bandwidth compared to that of conventional rectangular pulses, as well as a factor of two in improvement in the refocused echo intensity at 200GHz.