Category Archives: MAS-DNP

Balancing dipolar and exchange coupling in biradicals to maximize cross effect dynamic nuclear polarization #DNPNMR

Equbal, Asif, Kan Tagami, and Songi Han. “Balancing Dipolar and Exchange Coupling in Biradicals to Maximize Cross Effect Dynamic Nuclear Polarization.” Physical Chemistry Chemical Physics 22, no. 24 (2020): 13569–79.

https://doi.org/10.1039/D0CP02051F

Dynamic nuclear polarization (DNP) by the Cross Eect (CE) has become a game changer for solid-state nuclear magnetic resonance (NMR) spectroscopy. The eciency of CE-DNP depends on the strength of the electron-electron coupling in biradical polarizing agents. Hence, the focus lately has been on designing biradicals with a large net exchange (J) and dipolar (D) coupling. In this study, we reveal that the crucial factor for CE-DNP is not the sum, J+D, but rather the relative magnitude of J and D, expressed as the J/D ratio. We show that the mechanistic basis of this interference lies in the isotropic v.s. the anisotropic nature of the J and D couplings, respectively. This interference can lead to a small (eective) electron-electron coupling for many orientations even when J+D is large, resulting in non-adiabatic rotor-events. We find that when 0< jJ/Dj < 1 the CE-DNP eciency is attenuated for the majority of orientations, with greater attenuation observed at higher magnetic elds and faster Magic-Angle Spinning (MAS) frequency. The interference eect of J and D coupling introduced in this study can explain why many biradicals with high or comparable J + D still show signicantly divergent DNP performances. We debut J/D as a consequential criteria for designing ecient biradicals to robustly perform across a large range of B0 elds and MAS frequencies.

[NMR] MAS DNP | Educational Tutorial | Tuesday, September 15, 8:00am California #DNPNMR

Dear NMR Enthusiast,

The 14th Educational Tutorial will be given by Dr. Asif Equbal, Postdoc in Prof. Songi Han’s lab at University of California Santa Barbara, on the topic:

“Theoretical Understanding of MAS DNP”.

Abstract: The theoretical basics of MAS-DNP will be discussed. This will include essential Spin interactions and Landau-Zener formalism, to gain microscopic insights into the underlying mechanism. Using the theoretical basics, radical design for efficient DNP under fast MAS and high magnetic field will be discussed. 

Speaker’s biography:

2013-2016: PhD, Aarhus University, Denmark (Prof. Niels Chr. Nielsen)

2016: Postdoc, TIFR Hyderabad (Prof. P K Madhu)

2017-present: Postdoc, UC Santa Barbara, USA (Prof. Songi Han)

Webinar details:

Time: Tuesday, September 15, 2020, 08:00 AM California or 11:00 am Boston or 5:00 PM Paris or 8:30 PM Delhi

Join Meeting: https://ucsb.zoom.us/j/92480496788

Meeting ID: 924 8049 6788

Please note that the timing has changed.

Best regards,

Global NMR Discussion Meetings

[Organizers:

Adrian Draney (Guido Pintacuda Lab, CRMN lyon)

Amrit Venkatesh (Aaron Rossini Lab, Iowa)

Asif Equbal (Songi Han Lab, UCSB)

Blake Wilson (Robert Tycko Lab, NIH)

Michael Hope (Lyndon Emsley Lab, EPFL)

Mona Mohammadi (Alexej Jerschow, NYU)

PinelopiMoutzouri (Lyndon Emsley Lab, EPFL) ]

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[NMR] Solid-State NMR Postdoc Position at Ames Laboratory #DNPNMR

Dear Colleagues,

We are seeking a postdoctoral associate with a background in solid-state NMR spectroscopy. The postdoc will be responsible for conducting solid-state NMR investigations of heterogeneous catalysts, by conventional as well as dynamic nuclear polarization (DNP) enhanced solid-state NMR spectroscopy. A significant portion of the work will involve solid-state NMR methods development for instance through the development of novel data analysis tools, pulse sequence development, and the advancement and application of emerging technologies including ultra-fast (100 kHz+) magic-angle-spinning, dynamic nuclear polarization, and ultrahigh magnetic fields. The main focus of the work will be geared towards gaining a dynamic understanding of the structures of heterogeneous catalyst surfaces through multidimensional NMR spectroscopy.

Ames Laboratory is equipped with 9.4 and 14.1 T solid-state NMR spectrometers with MAS probes for rotor diameters ranging from 5 to 0.7-mm. Aside from these instruments, the lab is also equipped with a 9.4 T Bruker MAS-DNP NMR spectrometer with both 3.2 and 1.3-mm MAS-DNP probes. Access to computational resources and synthetic resources, if needed, will also be available.

Interested people are encouraged to apply for the position. More details can be found at this link:

https://isu.wd1.myworkdayjobs.com/en-US/IowaStateJobs/job/Ames-IA/Postdoctoral-Research-Associate—Ames-Laboratory_R2763

Best regards,

Frédéric Perras, PhD

Associate Scientist

Ames Laboratory

US Department of Energy

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Structural analysis of cross-linked poly(vinyl alcohol) using high-field DNP-NMR #DNPNMR

Kanda, Taiji, Mayuka Kitawaki, Toshiaki Arata, Yoh Matsuki, and Toshimichi Fujiwara. “Structural Analysis of Cross-Linked Poly(Vinyl Alcohol) Using High-Field DNP-NMR.” RSC Advances 10, no. 14 (2020): 8039–43.

https://doi.org/10.1039/D0RA00399A.

Poly(vinyl alcohol) (PVOH) is a water-soluble synthetic polymer, widely used in materials for functional films and moldings, fiber fabric sizing agents, paper coating resins, and adhesives. PVOH is mainly applied in the form of an aqueous solution, yet after its application, insolubility (water resistance) is required. To achieve this, additives are introduced. These additives used with PVOH are cross-linking agents which react with the hydroxyl groups and modified functional groups in PVOH. Because of the poor reactivity of unmodified PVOH, it does not react with cross-linking agents that have functional reactive groups. Therefore, modified PVOH that reacts with a cross-linking agent more successfully is required. These chemical bonding sites are so low in abundance that it is difficult to characterize the cross-linking structure. Solid-state 13C NMR is a powerful technique that can be used for the structural analysis of a polymer material. However, its sensitivity is low, hence it is difficult to determine crosslinking in a polymer, as it makes up only a small proportion of the product. Therefore, solid-state 13C NMR sensitivity can be enhanced by high-field dynamic nuclear polarization (DNP) using strong electron polarization. In this study, the reaction of acetoacetylated PVOH with a cross-linking agent, adipic dihydrazide, was analyzed. This crosslinked PVOH is the most popular vinyl alcohol polymer on the commercial market. The sensitivity enhanced 13C NMR spectra reveal that the carbonyl of the acetoacetyl group of PVOH crosslinks with adipic hydrazide by forming an imine bond (>CN–) this study also shows that the product has only seven crosslinking sites per molecular chain with a polymerization degree of 1000 and is water resistant.

Photocycle-dependent conformational changes in the proteorhodopsin cross-protomer Asp–His–Trp triad revealed by DNP-enhanced MAS-NMR #DNPNMR

Maciejko, Jakob, Jagdeep Kaur, Johanna Becker-Baldus, and Clemens Glaubitz. “Photocycle-Dependent Conformational Changes in the Proteorhodopsin Cross-Protomer Asp–His–Trp Triad Revealed by DNP-Enhanced MAS-NMR.” Proceedings of the National Academy of Sciences 116, no. 17 (April 23, 2019): 8342–49.

https://doi.org/10.1073/pnas.1817665116

Proteorhodopsin (PR) is a highly abundant, pentameric, light-driven proton pump. Proton transfer is linked to a canonical photocycle typical for microbial ion pumps. Although the PR monomer is able to undergo a full photocycle, the question arises whether the pentameric complex formed in the membrane via specific cross-protomer interactions plays a role in its functional mechanism. Here, we use dynamic nuclear polarization (DNP)-enhanced solid-state magic-angle spinning (MAS) NMR in combination with light-induced cryotrapping of photointermediates to address this topic. The highly conserved residue H75 is located at the protomer interface. We show that it switches from the (τ)- to the (π)-tautomer and changes its ring orientation in the M state. It couples to W34 across the oligomerization interface based on specific His/Trp ring orientations while stabilizing the pKa of the primary proton acceptor D97 within the same protomer. We further show that specific W34 mutations have a drastic effect on D97 and proton transfer mediated through H75. The residue H75 defines a cross-protomer Asp–His–Trp triad, which potentially serves as a pH-dependent regulator for proton transfer. Our data represent light-dependent, functionally relevant cross talk between protomers of a microbial rhodopsin homo-oligomer.

Recent Advances in Magic Angle Spinning‐Dynamic Nuclear Polarization Methodology #DNPNMR

Kaminker, Ilia. “Recent Advances in Magic Angle Spinning‐Dynamic Nuclear Polarization Methodology.” Israel Journal of Chemistry 59, no. 11–12 (November 2019): 990–1000.

https://doi.org/10.1002/ijch.201900092.

Dynamic nuclear polarization (DNP) is a method to boost the nuclear magnetic resonance (NMR) signal and thus alleviate the main limitation of NMR spectroscopy-its low sensitivity. One particularly successful methodology is the combination of DNP with magic angle spinning (MAS). MAS-DNP enables orders of magnitude signal enhancements in solid-state NMR experiments. The success of modern MAS-DNP stems from a combination of multiple developments in hardware, polarization agents design, sample preparation, theoretical understanding, and experimental methodology. Altogether these developments have allowed numerous breakthrough applications in biology and materials science. Despite its proven successes, ongoing research aims to further optimize hardware and polarization agent chemistry. Recent advances in MAS-DNP methodology that will allow unprecedented sensitivity in novel future applications are reviewed in this manuscript.

Complex Formation of the Tetracycline‐Binding Aptamer Investigated by Specific Cross‐Relaxation under DNP #DNPNMR

Aladin, Victoria, Marc Vogel, Robert Binder, Irene Burghardt, Beatrix Suess, and Björn Corzilius. “Complex Formation of the Tetracycline‐Binding Aptamer Investigated by Specific Cross‐Relaxation under DNP.” Angewandte Chemie 131, no. 15 (April 2019): 4917–22.

https://doi.org/10.1002/ange.201811941

While dynamic nuclear polarization (DNP) under magic-angle spinning (MAS) is generally a powerful method capable of greatly enhancing the sensitivity of solid-state NMR spectroscopy, hyperpolarization also gives rise to peculiar spin dynamics. Here, we elucidate how specific cross-relaxation enhancement by active motions under DNP (SCREAM-DNP) can be utilized to selectively obtain MAS-NMR spectra of an RNA aptamer in a tightly bound complex with a methylbearing ligand (tetracycline) due to the effective CH3-reorientation at an optimized sample temperature of approximately 160 K. SCREAM-DNP can spectrally isolate the complex from non-bound species in an RNA mixture. This selectivity allows for a competition assay between the aptamer and a mutant with compromised binding affinity. Variations in molecular structure and methyl dynamics, as observed by SCREAM-DNP, between free tetracycline and RNA-bound tetracycline are discussed.

19F Magic Angle Spinning Dynamic Nuclear Polarization Enhanced NMR Spectroscopy #DNPNMR

Viger-Gravel, Jasmine, Claudia E. Avalos, Dominik J. Kubicki, David Gajan, Moreno Lelli, Olivier Ouari, Anne Lesage, and Lyndon Emsley. “19F Magic Angle Spinning Dynamic Nuclear Polarization Enhanced NMR Spectroscopy.” Angewandte Chemie International Edition 58, no. 22 (May 27, 2019): 7249–53.

https://doi.org/10.1002/anie.201814416

The introduction of high frequency, high power microwave sources, tailored biradicals, and low-temperature magic- 30 angle spinning probes has led to a rapid development of hyperpolarization strategies for solids and frozen solutions, leading to large gains in NMR sensitivity. Here, we introduce a protocol for efficient hyperpolarization of 19F nuclei in MAS DNP enhanced NMR. We identify trifluoroethanol-d3 as a versatile glassy matrix and show that 12 mM AMUPol (with microcrystalline KBr) provides direct 19F DNP enhancements of over 100 at 9.4 T. We apply this protocol to 10 obtain DNP-enhanced 19F and 19F-13C cross-polarization (CP) spectra for an active pharmaceutical ingredient and a fluorinated mesostructured hybrid material, using incipient wetness 40 impregnation with enhancements of ~25 and ~10 in the bulk solid, respectively. This strategy is a general and straightforward method for obtaining enhanced 19F MAS spectra from fluorinated materials.

Dynamic Nuclear Polarization Magic-Angle Spinning Nuclear Magnetic Resonance Combined with Molecular Dynamics Simulations Permits Detection of Order and Disorder in Viral Assemblies #DNPNMR

Gupta, Rupal, Huilan Zhang, Manman Lu, Guangjin Hou, Marc Caporini, Melanie Rosay, Werner Maas, et al. “Dynamic Nuclear Polarization Magic-Angle Spinning Nuclear Magnetic Resonance Combined with Molecular Dynamics Simulations Permits Detection of Order and Disorder in Viral Assemblies.” The Journal of Physical Chemistry B 123, no. 24 (June 20, 2019): 5048–58.

https://doi.org/10.1021/acs.jpcb.9b02293

We report dynamic nuclear polarization (DNP) enhanced magic angle spinning (MAS) NMR spectroscopy in viral capsids from HIV-1 and bacteriophage AP205. Viruses regulate their lifecycles and infectivity through modulation of their structures and dynamics. While static structures of capsids from several viruses are now accessible with near-atomic level resolution, atomic-level understanding of functionally important motions in assembled capsids is lacking. We observed up to 64-fold signal enhancements by DNP, which permitted in-depth analysis of these assemblies. For the HIV-1 CA assemblies, remarkably high spectral resolution in the 3D and 2D heteronuclear datasets permitted the assignments of a significant fraction of backbone and side chain resonances. Using an integrated DNP MAS NMR and molecular dynamics simulations approach, the conformational space sampled by the assembled CA at cryogenic temperatures was mapped. Qualitatively, remarkable agreement was observed for the experimental 13C/15N chemical shift distributions and those calculated from substructures along the MD trajectory. Residues that are mobile at physiological temperatures are frozen out in multiple conformers at cryogenic conditions, resulting in broad experimental and calculated chemical shift distributions. Overall, our results suggest that DNP MAS NMR measurements in combination with MD simulations facilitate a thorough understanding of the dynamic signatures of viral capsids.

[NMR] Postdoctoral position in biomolecular MAS-DNP in Grenoble, France #DNPNMR

Post-doctoral position in MAS-DNP for the study of bacterial cell wall at CEA / Univ. Grenoble Alpes (France)

A post-doctoral position is available immediately for a period of 18 months to work with Sabine Hediger and Gaël De Paëpe on developing MAS-DNP for the study of bacterial cell wall. More information about our group at CEA Grenoble / Univ. Grenoble Alpes and a list of recent publications can be found here: www.dnpgrenoble.net.

Context of the project:

For over 50 years, peptidoglycan has played a pivotal role in the development of antibacterial chemotherapy. In the hunt for new drugs, the biosynthetic pathways of this ubiquitous cell wall polymer have been deciphered and essential peptidoglycan-synthesizing enzymes identified as antibacterial targets with high potential. Focusing on the L,D-transpeptidation, a key cell-wall synthesis and maturation reaction, we will first study purified enzymes in interaction with peptidoglycan fragments and then move on to the study of the complete cell-wall synthesis machinery in bacterial cells during the cell maturation.

Project :

In this context, innovative spectroscopic approaches including MAS-DNP will be conducted to provide new tools for the investigation of protein interaction with the bacterial cell wall. This project aims at developing the available MAS-DNP technique in order to provide best spectral sensitivity and resolution for the investigation of the bacterial cell wall itself in extracted and entire cells, as well as possible interactions with proteins involved in L,D-transpeptidation. These developments will make use of state-of-the-art DNP methods and polarizing agents developed or under development in the lab, which hosts two 400 MHz MAS-DNP spectrometers.

Requirements and application:

Applicants are expected to have a doctoral degree in liquid-state and/or solid-state biomolecular NMR spectroscopy. Knowledge about MAS-DNP will be considered as a plus. The successful candidate will be recruited for 18 months and will benefit from an ANR postdoctoral fellowship. Deadline for application is end of August. Interested candidates are welcomed to send an email to: sabine.hediger@cea.fr

Grenoble is one of the major cities in Europe for research with a large international scientific community. In addition, Grenoble has a large international student population, is a very pleasant city to live in, and is known as the “Capital of the Alps” with easy access to great skiing and hiking. It’s also only 2 hours’ drive to the Mediterranean Sea, Italy, or Switzerland. Grenoble, Lyon, and Geneva airports are nearby and permit straightforward international travel.

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