Friday, April 28, 2017

Delivering strong 1H nuclear hyperpolarization levels and long magnetic lifetimes through signal amplification by reversible exchange


Rayner, P.J., et al., Delivering strong 1H nuclear hyperpolarization levels and long magnetic lifetimes through signal amplification by reversible exchange. Proc Natl Acad Sci U S A, 2017. 114(16): p. E3188-E3194.


Hyperpolarization turns typically weak NMR and MRI responses into strong signals so that ordinarily impractical measurements become possible. The potential to revolutionize analytical NMR and clinical diagnosis through this approach reflect this area's most compelling outcomes. Methods to optimize the low-cost parahydrogen-based approach signal amplification by reversible exchange with studies on a series of biologically relevant nicotinamides and methyl nicotinates are detailed. These procedures involve specific 2H labeling in both the agent and catalyst and achieve polarization lifetimes of ca 2 min with 50% polarization in the case of methyl-4,6-d2 -nicotinate. Because a 1.5-T hospital scanner has an effective 1H polarization level of just 0.0005% this strategy should result in compressed detection times for chemically discerning measurements that probe disease. To demonstrate this technique's generality, we exemplify further studies on a range of pyridazine, pyrimidine, pyrazine, and isonicotinamide analogs that feature as building blocks in biochemistry and many disease-treating drugs.

Monday, April 24, 2017

Combining DNP NMR with segmental and specific labeling to study a yeast prion protein strain that is not parallel in-register #DNPNMR


Frederick, K.K., et al., Combining DNP NMR with segmental and specific labeling to study a yeast prion protein strain that is not parallel in-register. Proc. Nat. Aca. Sci. USA, 2017. 114(14): p. 3642-3647.


The yeast prion protein Sup35NM is a self-propagating amyloid. Despite intense study, there is no consensus on the organization of monomers within Sup35NM fibrils. Some studies point to a β-helical arrangement, whereas others suggest a parallel in-register organization. Intermolecular contacts are often determined by experiments that probe long-range heteronuclear contacts for fibrils templated from a 1:1 mixture of 13C- and 15N-labeled monomers. However, for Sup35NM, like many large proteins, chemical shift degeneracy limits the usefulness of this approach. Segmental and specific isotopic labeling reduce degeneracy, but experiments to measure long-range interactions are often too insensitive. To limit degeneracy and increase experimental sensitivity, we combined specific and segmental isotopic labeling schemes with dynamic nuclear polarization (DNP) NMR. Using this combination, we examined an amyloid form of Sup35NM that does not have a parallel in-register structure. The combination of a small number of specific labels with DNP NMR enables determination of architectural information about polymeric protein systems.

Friday, April 21, 2017

Extruded dielectric sample tubes of complex cross section for EPR signal enhancement of aqueous samples


Sidabras, J.W., R.R. Mett, and J.S. Hyde, Extruded dielectric sample tubes of complex cross section for EPR signal enhancement of aqueous samples. J Magn Reson, 2017. 277: p. 45-51.


This paper builds on the work of Mett and Hyde (2003) and Sidabras et al. (2005) where multiple flat aqueous sample cells placed perpendicular to electric fields in microwave cavities were used to reduce the RF losses and increase the EPR signal. In this work, we present three novel sample holders for loop-gap resonators (LGRs) and cylindrical cavity geometries. Two sample holders have been commissioned and built by polytetrafluoroethylene (PTFE) extrusion techniques: a 1mm O.D. capillary with a septum down the middle, named DoubleDee, and a 3.5mm O.D. star shaped sample holder, named AquaStar. Simulations and experimental results at X-band show that the EPR signal intensity increases by factors of 1.43 and 3.87 in the DoubleDee and AquaStar respectively, over the current TPX 0.9mm O.D. sample tube in a two-loop-one-gap LGR. Finally, combining the insight gained from the constructed sample holders and finite-element solutions, a third multi-lumen sample holder for a cylindrical TE011 cavity is optimized, named AquaSun, where simulations show an EPR signal intensity increase by a factor of 8.2 over a standard 1mm capillary.

Wednesday, April 19, 2017

EPR Imaging Spin Probe Trityl Radical OX063: A Method for Its Isolation from Animal Effluent, Redox Chemistry of Its Quinone Methide Oxidation Product, and in Vivo Application in a Mouse


Serda, M., et al., EPR Imaging Spin Probe Trityl Radical OX063: A Method for Its Isolation from Animal Effluent, Redox Chemistry of Its Quinone Methide Oxidation Product, and in Vivo Application in a Mouse. Chem Res Toxicol, 2016. 29(12): p. 2153-2156.


We report herein a method for the recovery, purification, and application of OX063, a costly, commercially available nontoxic spin probe widely used for electron paramagnetic resonance (EPR) imaging, as well as its corresponding quinone methide (QM) form. This precious probe can be successfully recovered after use in animal model experiments (25-47% recovery from crude lyophilizate with 98.5% purity), even from samples that are >2 years old. Significantly, the recovered trityl can be reused in further animal model EPR imaging experiments. The work also describes support for the observed formation of an air-sensitive radical derived from the QM under reducing conditions.

[NMR] Postdoc position in liquid-state NMR methodology and hyperpolarization, Nantes, France

From the Ampere Magnetic Resonance List



Subject: Hyperpolarized ultrafast 2D NMR for “omics” sciences

A two-year post-doctoral position in liquid-state NMR methodology is available in the group of Patrick Giraudeau at the University of Nantes, France, starting preferably in September 2017. It will involve a close collaboration with the group of Sami Jannin in Lyon, France, with frequent travel to Lyon for DNP experiments.

Project description: Dissolution Dynamic Nuclear Polarization (D-DNP) has been the focus of major developments and applications over the last decade; however its potential for the analysis of complex mixtures is largely underexploited. We recently showed the excellent analytical performance of D-DNP for the analysis of complex mixtures (Dumez et al. Analyst 2015, 140, 5860; Bornet et al. Anal. Chem. 2016, 88, 6179) and the promising perspectives arising from its combination with ultrafast 2D NMR. The goal of this project is to exploit further this complementarity by developing tailored ultrafast 2D NMR pulse sequences combined with D-DNP, and to evaluate the potential of this tool on a variety of samples and analytical situations. The subject will involve collaborations with various groups in the fields of metabolomics, fluxomics and isotopomics, as well as a collaboration with the group of Jean-Nicolas Dumez (Paris) for the development of spectral-spatial pulses. The D-DNP experiments will be carried out in the group of Sami Jannin (Lyon). 

Host laboratory: The CEISAM research institute at the University of Nantes has a strong expertise in the development of quantitative multi-dimensional methods applied to complex samples. In particular, the group of P. Giraudeau is well-known for its original research consisting in the association of innovative NMR methods with challenging applications such as isotopomics and metabolomics. The methodological developments will be performed on the CEISAM NMR platform, equipped with 5 state-of-the art liquid-state NMR spectrometers up to 700 MHz. The student will enjoy the excellent collaborative atmosphere of the lab and of the entire University, located in one of France’s most vibrant cities, widely recognized for its excellent quality of life. The project will also involve frequent mobility to the group of Sami Jannin (Lyon) where the candidate will spend approximately 20% of his working time (travelling expenses will be covered).

Candidates: We seek application from national and international students with a PhD in the field of Magnetic Resonance. Experience with pulse sequence development is required. The successful applicant will be given the opportunity to work in an exciting environment with national and international collaborations, and to present his/her work in international conferences. Excellent communication skills are necessary.

Contact: Applications (including CV, cover letter and two reference letters) should be sent to patrick.giraudeau@univ-nantes.fr

-- 
Dr. Patrick Giraudeau

Associate Professor (MCF HDR)
Junior Fellow of the Institut Universitaire de France
Vice-president of RFMF
Head of Associate Editorial Board, MRC

Faculté des Sciences et Techniques
CEISAM, Equipe EBSI - Bureau 120
BP 92208
2 Rue de la Houssinière
44322 Nantes Cedex 3
France

02 51 12 57 09 


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Monday, April 17, 2017

Low-cost, pseudo-Halbach dipole magnets for NMR


Tayler, M.C. and D. Sakellariou, Low-cost, pseudo-Halbach dipole magnets for NMR. J Magn Reson, 2017. 277: p. 143-148.


We present designs for compact, inexpensive and strong dipole permanent magnets aimed primarily at magnetic resonance applications where prepolarization and detection occur at different locations. Low-homogeneity magnets with a 7.5mm bore size and field up to nearly 2T are constructed using low-cost starting materials, standard workshop tools and only few hours of labor - an achievable project for a student or postdoc with spare time. As an application example we show how our magnet was used to polarize the nuclear spins in approximately 1mL of pure [13C]-methanol prior to detection of its high-resolution NMR spectrum at zero field (measurement field below 10-10T), where signals appear at multiples of the carbon-hydrogen spin-spin coupling frequency 1JCH=140.7(1)Hz.

Friday, April 14, 2017

Atomic-Level Structure Characterization of Biomass Pre- and Post-Lignin Treatment by Dynamic Nuclear Polarization-Enhanced Solid-State NMR #DNPNMR


Perras, F.A., et al., Atomic-Level Structure Characterization of Biomass Pre- and Post-Lignin Treatment by Dynamic Nuclear Polarization-Enhanced Solid-State NMR. The Journal of Physical Chemistry A, 2017. 121(3): p. 623-630.


Lignocellulosic biomass is a promising sustainable feedstock for the production of biofuels, biomaterials, and biospecialty chemicals. However, efficient utilization of biomass has been limited by our poor understanding of its molecular structure. Here, we report a dynamic nuclear polarization (DNP)-enhanced solid-state (SS)NMR study of the molecular structure of biomass, both pre- and postcatalytic treatment. This technique enables the measurement of 2D homonuclear 13C–13C correlation SSNMR spectra under natural abundance, yielding, for the first time, an atomic-level picture of the structure of raw and catalytically treated biomass samples. We foresee that further such experiments could be used to determine structure–function relationships and facilitate the development of more efficient, and chemically targeted, biomass-conversion technologies.

Wednesday, April 12, 2017

Surface-Sensitive NMR Detection of the Solid Electrolyte Interphase Layer on Reduced Graphene Oxide #DNPNMR


Leskes, M., et al., Surface-Sensitive NMR Detection of the Solid Electrolyte Interphase Layer on Reduced Graphene Oxide. The Journal of Physical Chemistry Letters, 2017. 8(5): p. 1078-1085.


Forming a stable solid electrolyte interphase (SEI) is critical for rechargeable batteries’ performance and lifetime. Understanding its formation requires analytical techniques that provide molecular-level insight. Here, dynamic nuclear polarization (DNP) is utilized for the first time to enhance the sensitivity of solid-state NMR (ssNMR) spectroscopy to the SEI. The approach is demonstrated on reduced graphene oxide (rGO) cycled in Li-ion cells in natural abundance and 13C-enriched electrolyte solvents. Our results indicate that DNP enhances the signal of outer SEI layers, enabling detection of natural abundance 13C spectra from this component of the SEI on reasonable time frames. Furthermore, 13C-enriched electrolyte measurements at 100 K provide ample sensitivity without DNP due to the vast amount of SEI filling the rGO pores, thereby allowing differentiation of the inner and outer SEI layer composition. Developing this approach further will benefit the study of many electrode materials, equipping ssNMR with the necessary sensitivity to probe the SEI efficiently.

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

From the Ampere Magnetic Resonance List



Project title: Development of high-field (DNP)-NMR methods for the observation of quadrupolar nuclei in hybrid materials

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

Project description: Hybrid materials are promising for numerous applications, such as catalysis, gas storage or drug delivery. Solid-state NMR provides unique information about the atomic-level structure of defects and surfaces in hybrid materials. Nevertheless, a major limitation is the lack of sensitivity of solid-state NMR, which limits the observation of defects and surfaces, particularly for insensitive isotopes with low gyromagnetic ratio, low natural abundance or subject to large quadrupolar interaction. Recent instrumental developments, such as high-magnetic field and Dynamic Nuclear Polarization (DNP), can boost the sensitivity of solid-state NMR. This project aims at developing and applying novel solid-state NMR methods to probe the local environment of quadrupolar nuclei in hybrid materials. The structural information obtained by solid-state NMR will be useful to improve the performances of hybrid materials.

Host and research infrastructure: Lille is a vibrant and handsome city, imbued with a rich history, located in the middle 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 hybrid materials. 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 national and international students who have graduated in physics or chemistry, preferably with a background in material sciences or NMR spectroscopy. 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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Monday, April 10, 2017

Field‐frequency locked X‐band Overhauser effect spectrometer #DNPNMR

This article is already a bit older. However, it nicely illustrates that DNP, specifically ODNP has been around for a while already, and gives some interesting specifics on the instrumentation that are still valid today.

Chandrakumar, N. and P.T. Narasimhan, Field‐frequency locked X‐band Overhauser effect spectrometer. Review of Scientific Instruments, 1981. 52(4): p. 533-538.


The design and construction of an Overhauser Effect Spectrometer operating at X band is described. The ESR section is a Varian V-4502 spectrometer equipped with a 9-in. electromagnet and a shim coil assembly. NMR detection is based on a broadband rf hybrid juction feeding a coil in an X-band quartz dielectric cavity. Signal processing is carried out at a constant intermediate frequency of 25.1 MHz with a Varian V -4311 fixed frequency rf unit. The mixing scheme employed to translate the NMR information to 25.1 MHz is described. Medium resolution performance (resolution _10-6 ) for the NMR is achieved under field-frequency locked conditions. The lock is based on a Super-Regenerative Oscillator (SRO) housing a control sample, and operating as a field-tracking frequency source. This SRO injects into an oscillator which excites the analytical sample resonance and also serves as a local oscillator, thereby making the locked spectrometer multinuclear in capability. Typical Overhauser effect recordings of protons and fluorines are presented.

Friday, April 7, 2017

Directly vs Indirectly Enhanced 13C in Dynamic Nuclear Polarization Magic Angle Spinning NMR Experiments of Nonionic Surfactant Systems


Hoffmann, M.M., et al., Directly vs Indirectly Enhanced 13C in Dynamic Nuclear Polarization Magic Angle Spinning NMR Experiments of Nonionic Surfactant Systems. The Journal of Physical Chemistry C, 2017. 121(4): p. 2418-2427.


A study of dynamic nuclear polarization (DNP) in polyethylene glycol and related nonionic surfactants is presented. In these experiments, we found the surprising result that DNP enhanced 13C magic angle spinning (MAS) spectra display two sets of resonances, one with broad and one with sharp spectral features that are 180° opposite in phase. These two sets indicate the presence of a direct polarization transfer channel as expected for 13C MAS experiments, and a second unexpected indirect polarization transfer channel. Plots of DNP enhancements as a function of applied magnetic field for the two resonances show a superposition of two DNP enhancement profiles for AMUpol in the nonionic surfactant C10E6. The indirect polarization channel can be suppressed by application of a string of 1H 180° pulses during 13C DNP buildup. The presence of direct and indirect polarization channels is observed in a total of four different nonionic surfactants and with three different radicals, showing that these concurring polarization mechanisms are of general nature. Therefore, the presented findings, including the demonstration of how the indirect polarization channel can be suppressed, are of high importance for all future applications of direct 13C MAS DNP.

Wednesday, April 5, 2017

Dynamic Nuclear Polarization Signal Amplification as a Sensitive Probe for Specific Functionalization of Complex Paper Substrates #DNPNMR


Gutmann, T., et al., Dynamic Nuclear Polarization Signal Amplification as a Sensitive Probe for Specific Functionalization of Complex Paper Substrates. The Journal of Physical Chemistry C, 2017. 121(7): p. 3896-3903.


In this work, it is shown how solid-state NMR combined with dynamic nuclear polarization (DNP) can be employed as a powerful tool to selectively enhance the spectral intensity of functional groups on the surface of cellulose fibers in paper materials. As a model system, a poly(benzyl methacrylate) (PBEMA)-functionalized paper material is chosen that contains hydrophobic and hydrophilic domains. Detailed analysis of the DNP NMR data and of T1ρ data suggests that inhomogeneous 1H–1H spin diffusion is responsible for the observed differences in signal enhancement. These findings are fundamental for structural understanding of complex paper substrates for fluid transport or sensor materials.

Monday, April 3, 2017

Dynamic Nuclear Polarization of β-Cyclodextrin Macromolecules #DNPNMR


Caracciolo, F., et al., Dynamic Nuclear Polarization of β-Cyclodextrin Macromolecules. The Journal of Physical Chemistry B, 2017.


1H dynamic nuclear polarization and nuclear spin-lattice relaxation rates have been studied in amorphous complexes of β-cyclodextrins doped with different concentrations of the TEMPO radical. Nuclear polarization increased up to 10% in the optimal case, with a behavior of the buildup rate (1/TPOL) and of the nuclear spin-lattice relaxation rate (1/T1n) consistent with a thermal mixing regime. The temperature dependence of 1/T1n and its increase with the radical concentration indicate a relaxation process arising from the modulation of the electron–nucleus coupling by the glassy dynamics. The high-temperature relaxation is driven by molecular motions, and 1/T1n was studied at room temperature in liquid solutions for dilution levels close to the ones typically used for in vivo studies.