Category Archives: solid-state DNP

Surface-Only Spectroscopy for Diffusion-Limited Systems Using Ultra-Low-Temperature DNP MAS NMR at 16.4 T #DNPNMR

Matsuki, Yoh, Tomoaki Sugishita, and Toshimichi Fujiwara. “Surface-Only Spectroscopy for Diffusion-Limited Systems Using Ultra-Low-Temperature DNP MAS NMR at 16.4 T.” The Journal of Physical Chemistry C, August 12, 2020, acs.jpcc.0c04873.

https://doi.org/10.1021/acs.jpcc.0c04873

The conventional dynamic nuclear polarization (DNP) technique at T ∼ 100 K can enhance sensitivity of magic-angle spinning (MAS) NMR over 100-fold for standard samples containing urea/proline under high-field conditions, B0 = 9.4−16.4 T. In the scene of real applications, however, the achievable enhancement is often much lower than for urea/proline due to faster 1H relaxation (T1H) promoted by molecular segmental fluctuations and methyl group rotations active even at low temperatures, hindering efficient polarization diffusion within the system. Here, we show at 16.4 T that ultra-low temperature (T ≪ 100 K) provides a general way to improve the DNP efficiency for such diffusion-limited systems as we demonstrate on a microcrystalline sample of the tripeptide N-f-MLF-OH. In a further step, the hyperpolarization localized at the crystal surface enabled “surface-only” spectroscopy eliminating background signals from the crystal core. The surface-only data, rather than the currently popular surface-enhanced data, would prove to be useful in many applications in biological and materials sciences.

Heteronuclear cross-relaxation effect modulated by the dynamics of N-functional groups in the solid state under 15N DP-MAS DNP #DNPNMR

Park, Heeyong, Boran Uluca-Yazgi, Saskia Heumann, Robert Schlögl, Josef Granwehr, Henrike Heise, and P. Philipp M. Schleker. “Heteronuclear Cross-Relaxation Effect Modulated by the Dynamics of N-Functional Groups in the Solid State under 15N DP-MAS DNP.” Journal of Magnetic Resonance 312 (March 2020): 106688.

https://doi.org/10.1016/j.jmr.2020.106688

In a typical magic-angle spinning (MAS) dynamic nuclear polarization (DNP) nuclear magnetic resonance (NMR) experiment, several mechanisms are simultaneously involved when transferring much larger polarization of electron spins to NMR active nuclei of interest. Recently, specific cross-relaxation enhancement by active motions under DNP (SCREAM-DNP) [Daube et al. JACS 2016] has been reported as one of these mechanisms. Thereby 13C enhancement with inverted sign was observed in a direct polarization (DP) MAS DNP experiment, caused by reorientation dynamics of methyl that was not frozen out at 100 K. Here, we report on the spontaneous polarization transfer from hyperpolarized 1H to both primary amine and ammonium nitrogens, resulting in an additional positive signal enhancement in the 15N NMR spectra during 15N DP-MAS DNP. The cross-relaxation induced signal enhancement (CRE) for 15N is of opposite sign compared to that observed for 13C due to the negative sign of the gyromagnetic ratio of 15N. The influence on CRE efficiency caused by variation of the radical solution composition and by temperature was also investigated.

Slice selection in low-temperature, DNP-enhanced magnetic resonance imaging by Lee-Goldburg spin-locking and phase modulation #DNPNMR

Chen, Hsueh-Ying, and Robert Tycko. “Slice Selection in Low-Temperature, DNP-Enhanced Magnetic Resonance Imaging by Lee-Goldburg Spin-Locking and Phase Modulation.” Journal of Magnetic Resonance 313 (April 2020): 106715.

https://doi.org/10.1016/j.jmr.2020.106715

Large enhancements in nuclear magnetic resonance (NMR) signals provided by dynamic nuclear polarization (DNP) at low temperatures have the potential to enable inductively-detected 1H magnetic resonance imaging (MRI) with isotropic spatial resolution on the order of one micron, especially when low temperatures and DNP are combined with microcoils, three-dimensional (3D) phase encoding of image information, pulsed spin locking during NMR signal detection, and homonuclear dipolar decoupling by Lee-Goldburg (LG) irradiation or similar methods. However, the relatively slow build-up of nuclear magnetization under DNP leads to very long acquisition times for high-resolution 3D images unless the sample volume or field of view (FOV) is restricted. We have therefore developed a method for slice selection in low-temperature, DNP-enhanced MRI that limits the FOV to about 50 m in one or more dimensions. This method uses small-amplitude phase modulation of LG irradiation in the presence of a strong magnetic field gradient to invert spin-locked 1H magnetization in the selected slice. Experimental results are reported, including effects of radio-frequency field inhomogeneity, variations in the amplitude of phase modulation, and shaped phase modulation.

ssNMR/DNP ZOOMinar (4/29) : Matthias Ernst and Songi Han #DNPNMR

From the ssNMR mailing list

Date: Sun, 26 Apr 2020 15:10:25 +0000

From: Kong Ooi Tan <kongooi@mit.edu>

Subject: [ssNMR] ssNMR/DNP ZOOMinar (4/29) : Matthias Ernst and Songi Han

Hi all,

I would like to announce our second ZOOMinar session on 4/29, Wed 11 am Boston / 5 pm Zurich / 8 am California. Our speakers are Prof. Matthias Ernst (ETHZ) and Prof. Songi Han (UCSB), the details are:

Zoom link: https://mit.zoom.us/j/91253458660 <https://mit.zoom.us/j/91253458660>

Duration: 1 hr, i.e. 30 mins (23 mins talk + 7 mins Q&A) per speaker

1st speaker: Matthias Ernst, ?Residual Line Width in FSLG Decoupled Proton MAS Spectra?

Recorded (Yes/No): No

-PhD studies with Prof. Richard R. Ernst at ETHZ.

-Postdoc with Prof. Alex Pines at UC Berkeley for 2 years

-Staff scientist with Prof. Beat H. Meier at University of Nijmegen

-Joined ETHZ as a senior scientist in Beat?s group, and promoted to adjunct Professor in 2011.

2nd speaker: Songi Han, ?Asymmetry in Electron Spin Polarization and Coupling drives Cross-Effect and Thermal Mixing DNP?

Recorded (Yes/No): Yes

She received her Doctoral Degree from Aachen University of Technology (RWTH), Germany, in 2001. She pursued her postdoctoral studies at the Max-Planck Institute for Polymer Research, Mainz, and the University of California Berkeley. She joined the faculty at UCSB in 2004, and was promoted to full professor in 2012.

Regards,

Kong

Dr. Kong Ooi Tan

Postdoctoral Fellow

Francis Bitter Magnet Laboratory

Massachusetts Institute of Technology

77 Massachusetts Avenue, NW14-4112

Cambridge, MA 02139

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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.

Structure determination of supra-molecular assemblies by solid-state NMR: Practical considerations #DNPNMR

Demers, Jean-Philippe, Pascal Fricke, Chaowei Shi, Veniamin Chevelkov, and Adam Lange. “Structure Determination of Supra-Molecular Assemblies by Solid-State NMR: Practical Considerations.” Progress in Nuclear Magnetic Resonance Spectroscopy 109 (December 2018): 51–78.

https://doi.org/10.1016/j.pnmrs.2018.06.002

In the cellular environment, biomolecules assemble in large complexes which can act as molecular machines. Determining the structure of intact assemblies can reveal conformations and inter-molecular interactions that are only present in the context of the full assembly. Solid-state NMR (ssNMR) spectroscopy is a technique suitable for the study of samples with high molecular weight that allows the atomic structure determination of such large protein assemblies under nearly physiological conditions.

This review provides a practical guide for the first steps of studying biological supramolecular assemblies using ssNMR. The production of isotope-labeled samples is achievable via several means, which include recombinant expression, cell-free protein synthesis, extraction of assemblies directly from cells, or even the study of assemblies in whole cells in situ. Specialized isotope labeling schemes greatly facilitate the assignment of chemical shifts and the collection of structural data. Advanced strategies such as mixed, diluted, or segmental subunit labeling offer the possibility to study inter-molecular interfaces.

Detailed and practical considerations are presented with respect to first setting up magicangle spinning (MAS) ssNMR experiments, including the selection of the ssNMR rotor, different methods to best transfer the sample and prepare the rotor, as well as common and robust procedures for the calibration of the instrument. Diagnostic spectra to evaluate the resolution and sensitivity of the sample are presented. Possible improvements that can reduce sample heterogeneity and improve the quality of ssNMR spectra are reviewed.

Improved Structural Elucidation of Synthetic Polymers by Dynamic Nuclear Polarization Solid-State NMR Spectroscopy #DNPNMR

Ouari, Olivier, Trang Phan, Fabio Ziarelli, Gilles Casano, Fabien Aussenac, Pierre Thureau, Didier Gigmes, Paul Tordo, and Stéphane Viel. “Improved Structural Elucidation of Synthetic Polymers by Dynamic Nuclear Polarization Solid-State NMR Spectroscopy.” ACS Macro Letters 2, no. 8 (August 20, 2013): 715–19.

https://doi.org/10.1021/mz4003003

Dynamic nuclear polarization (DNP) is shown to greatly improve the solid-state nuclear magnetic resonance (SSNMR) analysis of synthetic polymers by allowing structural assignment of intrinsically diluted NMR signals, which are typically not detected in conventional SSNMR. Specifically, SSNMR and DNP SSNMR were comparatively used to study functional polymers for which precise structural elucidation of chain ends is essential to control their reactivity and to eventually obtain advanced polymeric materials of complex architecture. Results show that the polymer chain-end signals, while hardly observable in conventional SSNMR, could be clearly identified in the DNP SSNMR spectrum owing to the increase in sensitivity afforded by the DNP setup (a factor ∼10 was achieved here), hence providing access to detailed structural characterization within realistic experimental times. This sizable gain in sensitivity opens new avenues for the characterization of “smart” functional polymeric materials and new analytical perspectives in polymer science.

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.

DNP NMR spectroscopy reveals new structures, residues and interactions in wild spider silks #DNPNMR

Craig, Hamish C., Sean J. Blamires, Marc-Antoine Sani, Michael M. Kasumovic, Aditya Rawal, and James M. Hook. “DNP NMR Spectroscopy Reveals New Structures, Residues and Interactions in Wild Spider Silks.” Chemical Communications 55, no. 32 (2019): 4687–90.

https://doi.org/10.1039/C9CC01045A.

DNP solid state NMR spectroscopy allows non-targeted analysis of wild spider silk in unprecedented detail at natural abundance, revealing hitherto unreported features across several species. A >50-fold signal enhancement for each silk, enables the detection of novel H-bonding networks and arginine conformations, and the post-translational modified amino acid, hydroxyproline.

The effect of drug binding on specific sites in transmembrane helices 4 and 6 of the ABC exporter MsbA studied by DNP-enhanced solid-state NMR #DNPNMR

Spadaccini, Roberta, Hundeep Kaur, Johanna Becker-Baldus, and Clemens Glaubitz. “The Effect of Drug Binding on Specific Sites in Transmembrane Helices 4 and 6 of the ABC Exporter MsbA Studied by DNP-Enhanced Solid-State NMR.” Biochimica et Biophysica Acta (BBA) – Biomembranes 1860, no. 4 (April 2018): 833–40.

https://doi.org/10.1016/j.bbamem.2017.10.017.

MsbA, a homodimeric ABC exporter, translocates its native substrate lipid A as well as a range of smaller, amphiphilic substrates across the membrane. Magic angle sample spinning (MAS) NMR, in combination with dynamic nuclear polarization (DNP) for signal enhancement, has been used to probe two specific sites in transmembrane helices 4 and 6 of full length MsbA embedded in lipid bilayers. Significant chemical shift changes in both sites were observed in the vanadate-trapped state compared to apo state MsbA. The reduced spectral line width indicates a more confined conformational space upon trapping. In the presence of substrates Hoechst 33342 and daunorubicin, further chemical shift changes and line shape alterations mainly in TM6 in the vanadate trapped state were detected. These data illustrate the conformational response of MsbA towards the presence of drugs during the catalytic cycle.

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