Friday, December 14, 2018

Large-scale ab initio simulations of MAS DNP enhancements using a Monte Carlo optimization strategy #DNPNMR

Perras, Frédéric A., and Marek Pruski. “Large-Scale Ab Initio Simulations of MAS DNP Enhancements Using a Monte Carlo Optimization Strategy.” The Journal of Chemical Physics 149, no. 15 (October 21, 2018): 154202.


Magic-angle-spinning (MAS) dynamic nuclear polarization (DNP) has recently emerged as a powerful technology enabling otherwise unrealistic solid-state NMR experiments. The simulation of DNP processes which might, for example, aid in refining the experimental conditions or the design of better performing polarizing agents, is, however, plagued with significant challenges, often limiting the system size to only 3 spins. Here, we present the first approach to fully ab initio large-scale simulations of MAS DNP enhancements. The Landau-Zener equation is used to treat all interactions concerning electron spins, and the low-order correlations in the Liouville space method is used to accurately treat the spin diffusion, as well as its MAS speed dependence. As the propagator cannot be stored, a Monte Carlo optimization method is used to determine the steady-state enhancement factors. This new software is employed to investigate the MAS speed dependence of the enhancement factors in large spin systems where spin diffusion is of importance, as well as to investigate the impacts of solvent and polarizing agent deuteration on the performance of MAS DNP.

Wednesday, December 12, 2018

Conformation of Bis-nitroxide Polarizing Agents by Multi- frequency EPR Spectroscopy #DNPNMR

To optimize the DNP process it is crucial to understand the EPR properties of the polarizing agents. This article demonstrates the need of multi-frequency, high-field EPR spectroscopy to gain a deep understanding of all EPR parameters and how they influence the DNP process.


Soetbeer, Janne, Peter Gast, Joseph J Walish, Yanchuan Zhao, Christy George, Chen Yang, Timothy M Swager, Robert G Griffin, and Guinevere Mathies. “Conformation of Bis-Nitroxide Polarizing Agents by Multi- Frequency EPR Spectroscopy,”


The chemical structure of polarizing agents critically determines the efficiency of dynamic nuclear polarization (DNP). For cross-effect DNP, biradicals are the polarizing agents of choice and the interaction and relative orientation of the two unpaired electrons should be optimal. Both parameters are affected by the molecular structure of the biradical in the frozen glassy matrix that is typically used for DNP/MAS NMR and likely differs from the structure observed with X-ray crystallography. We have determined the conformations of six bis-nitroxide polarizing agents, including the highly efficient AMUPol, in their DNP matrix with EPR spectroscopy at 9.7 GHz, 140 GHz, and 275 GHz. The multi-frequency approach in combination with an advanced fitting routine allows us to reliably extract the interaction and relative orientation of the nitroxide moieties. We compare the structures of six bis-nitroxides to their DNP performance at 500 MHz/330 GHz.

Tuesday, December 11, 2018

[NMR] Postdoctoral position in NMR of polymer electrolytes for energy storage at UCSB (Santa Barbara, USA) #DNPNMR

Postdoctoral position in NMR of polymer ionic liquid electrolytes for energy storage at UCSB (Santa Barbara, USA)

The postdoctoral research position is based at the Materials Department, University of California Santa Barbara (UCSB), in the group of Prof. Raphaële Clément. The position is available from January, 1st, 2019, and comes with an initial one-year contract. 

Project Description

The research program focuses on the study of polymer ionic liquids (PILs), used as electrolytes in Li-ion rechargeable batteries, with solid-state NMR techniques. The postdoc will be working in close collaboration with the group of Prof. Segalman at UCSB, in charge of the synthesis of the PILs. 

Li-ion batteries are the technology of choice for numerous applications, yet the energy density and safety of commercial devices is often limited by using organic liquid electrolytes with high flammability and poor stability of electrode/electrolyte interfaces during operation. Ionic liquids are a class of functional liquid salts that address both voltage and thermal stability concerns [1]. Incorporation of ionic liquid moieties onto a polymer to form PILs synergistically combines the functionality of ionic liquids with the mechanical robustness of the polymer backbone, an important criterion for lithium metal batteries. Unfortunately, polymer electrolytes generally exhibit low ionic conductivity due to a fundamental trade-off between improved mechanical properties and ion mobility [2]. Thus, an understanding of promising systems that would enable a decoupling of polymer mechanics from ion transport would be beneficial towards the targeted design of novel polymer electrolytes with good mechanical properties and high ionic conductivity.

The postdoc will investigate the Li+ transport properties of several PIL compositions using 7Li pulsed field gradient (PFG) NMR to determine the Li self-diffusion coefficient on the macroscopic (1-2 mm) lengthscale, as well as NMR relaxometry to characterize ionic conductivity at the microscopic scale. In addition, NMR will be used to investigate Li-Li site exchange [3] and Li-ligand binding kinetics [4]. NMR measurements will be correlated with conductivity measurements obtained via AC impedance techniques.

Relevant publications 

[1] B. Garcia, S. Lavalle, G. Perron, C. Michot, and M. Armand, Room temperature molten salts as lithium battery electrolyte, Electrochim. Acta 49 (2004) 4583–4588. DOI: 10.1016/j.electacta.2004.04.041

[2] J. R. Sangoro, C. Iacob, A. L. Agapov, Y. Wang, S. Berdzinski, H. Rexhausen, V. Strehmel, C. Friedrich, A. P. Sokolov, and F. Kremer, Decoupling of ionic conductivity from structural dynamics in polymerized ionic liquids, Soft Matter 10 (2014) 3536–3540.

DOI: 10.1039/C3SM53202J

[3] M. N. d’Eurydice, E. T. Montrazi, C. A. Fortulan and T. J. Bonagamba, T2-tiltered T2-T2 Exchange NMR. J. Chem. Phys. 144 (2016) 204201. DOI: 10.1063/1.4951712

[4] Tan-Vu Huynh. NMR study of lithium mobility in polymer electrolytes. Ph.D. thesis. Université d’Orléans, 2015. English.

Requirements and Preferred Experience

The requirements for the position are a Ph.D. in Chemistry, Materials Science, Physics or Engineering, and experience with PFG-NMR and standard 2D solid-state NMR techniques. In addition to performing research, the postdoc will be expected to provide assistance with the training of graduate and undergraduate students in the group.


The Magnetic Resonance Facilities at UCSB

The spectroscopy facility of the Materials Research Laboratory at UCSB (see https://www.mrl.ucsb.edu/spectroscopy-facility/instruments) comprises several solid-state NMR spectrometers, including a 300 MHz system equipped with a MRI/diffusion probe, a 400 MHz DNP-NMR spectrometer, and 500 MHz and 800 MHz systems.

Additional Information

Interested candidates should send a cover letter, a résumé (including a list of publications), and the names and email addresses of at least two references to rclement@ucsb.edu.
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Raphaële Clément

Assistant Professor, Materials Department
Materials Research Laboratory, Room 3009
University of California, Santa Barbara, CA 93106-5121

Phone: 805-893-4294

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Monday, December 10, 2018

DNP NMR Studies of Crystalline Polymer Domains by Copolymerization with Nitroxide Radical Monomers #DNPNMR

Verde-Sesto, Ester, Nicolas Goujon, Haritz Sardon, Pauline Ruiz, Tan Vu Huynh, Fermin Elizalde, David Mecerreyes, Maria Forsyth, and Luke A. O’Dell. “DNP NMR Studies of Crystalline Polymer Domains by Copolymerization with Nitroxide Radical Monomers.” Macromolecules 51, no. 20 (October 23, 2018): 8046–53.


Dynamic nuclear polarization (DNP) nuclear magnetic resonance (NMR) spectroscopy is increasingly recognized as a powerful and versatile tool for the characterization of polymers and polymer-based materials. DNP requires the presence of unpaired electrons, usually mono- or biradicals, and the method of incorporation of these groups and their distribution within the structure is crucial. Methods for covalently binding the radicals to the polymer and controlling their location (e.g., exclusively within a specific phase or at an interface) can allow the selective enhancement of a particular region or the measurement of domain sizes. We have prepared a series of polyurethanes by copolymerization of a nitroxide radical monomer with poly(ethylene glycol) (PEO) and diisocyanate linkers. The PEO is shown to form crystalline domains with the radical monomers in a separate phase, providing DNP enhancements of around 10 and allowing the domain size and morphology to be probed with the aid of X-ray scattering data. Additionally, electron paramagnetic resonance is used to estimate the inter-radical distances and density functional theory calculations are used to refine the PEO crystal structure.

Saturday, December 8, 2018

[NMR] Post-doctoral position available #DNPNMR

A postdoctoral position is available to join the Emsley group at EPFL, Lausanne

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


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 developing experimental multi-dimensional nuclear magnetic resonance are a plus. 

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 at lyndon.emsley@epfl.ch



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Friday, December 7, 2018

Long-range heteronuclear J-coupling constants in esters: Implications for 13C metabolic MRI by side-arm parahydrogen-induced polarization

Stewart, Neil J., Hiroyuki Kumeta, Mitsushi Tomohiro, Takuya Hashimoto, Noriyuki Hatae, and Shingo Matsumoto. “Long-Range Heteronuclear J-Coupling Constants in Esters: Implications for 13C Metabolic MRI by Side-Arm Parahydrogen-Induced Polarization.” Journal of Magnetic Resonance 296 (November 2018): 85–92.


Side-arm parahydrogen induced polarization (PHIP-SAH) presents a cost-effective method for hyperpolarization of 13C metabolites (e.g. acetate, pyruvate) for metabolic MRI. The timing and efficiency of typical spin order transfer methods including magnetic field cycling and tailored RF pulse sequences crucially depends on the heteronuclear J coupling network between nascent parahydrogen protons and 13C, post-parahydrogenation of the target compound. In this work, heteronuclear nJHC (1<n≤5) couplings of acetate and pyruvate esters pertinent for PHIP-SAH were investigated experimentally using selective HSQMBC-based pulse sequences and numerically using DFT simulations. The CLIP-HSQMBC technique was used to quantify 2/3-bond JHC couplings, and 4/5-bond JHC ≲ 0.5 Hz were estimated by the sel-HSQMBC-TOCSY approach. Experimental and numerical (DFT-simulated) nJHC couplings were strongly correlated (P < 0.001). Implications for 13C hyperpolarization by magnetic field cycling, and PH-INEPT and ESOTHERIC type spin order transfer methods for PHIP-SAH were assessed, and the influence of direct nascent parahydrogen proton to 13C coupling when compared with indirect TOCSY-type transfer through intermediate (non-nascent parahydrogen) protons was studied by the density matrix approach.

Wednesday, December 5, 2018

Electron decoupling with cross polarization and dynamic nuclear polarization below 6 K #DNPNMR

Sesti, Erika L., Edward P. Saliba, Nicholas Alaniva, and Alexander B. Barnes. “Electron Decoupling with Cross Polarization and Dynamic Nuclear Polarization below 6 K.” Journal of Magnetic Resonance 295 (October 2018): 1–5.


Dynamic nuclear polarization (DNP) can improve nuclear magnetic resonance (NMR) sensitivity by orders of magnitude. Polarizing agents containing unpaired electrons required for DNP can broaden nuclear resonances in the presence of appreciable hyperfine couplings. Here we present the first cross polarization experiments implemented with electron decoupling, which attenuates detrimental hyperfine couplings. We also demonstrate magic angle spinning (MAS) DNP experiments below 6 K, producing unprecedented nuclear spin polarization in rotating solids. 13C correlation spectra were collected with MAS DNP below 6 K for the first time. Longitudinal magnetization recovery times with MAS DNP (T1DNP, 1H) of urea in a frozen glassy matrix below 6 K were measured for both the solid effect and the cross effect. Trityl radicals exhibit a T1DNP (1H) of 18.7 s and the T1DNP (1H) of samples doped with 20 mM AMUPol is only 1.3 s. MAS below 6 K with DNP and electron decoupling is an effective strategy to increase NMR signal-to-noise ratios per transient while retaining short recovery periods.