Category Archives: DNP

Colloidal-ALD-Grown Core/Shell CdSe/CdS Nanoplatelets as Seen by DNP Enhanced PASS–PIETA NMR Spectroscopy #DNPNMR

Piveteau, Laura, Dmitry N. Dirin, Christopher P. Gordon, Brennan J. Walder, Ta-Chung Ong, Lyndon Emsley, Christophe Copéret, and Maksym V. Kovalenko. “Colloidal-ALD-Grown Core/Shell CdSe/CdS Nanoplatelets as Seen by DNP Enhanced PASS–PIETA NMR Spectroscopy.” Nano Letters 20, no. 5 (May 13, 2020): 3003–18.

https://doi.org/10.1021/acs.nanolett.9b04870

Ligand exchange and CdS shell growth onto colloidal CdSe nanoplatelets (NPLs) using colloidal atomic layer deposition (c-ALD) were investigated by solid-state nuclear magnetic resonance (NMR) experiments, in particular, dynamic nuclear polarization (DNP) enhanced phase adjusted spinning sidebands−phase incremented echo-train acquisition (PASS−PIETA). The improved sensitivity and resolution of DNP enhanced PASS−PIETA permits the identification and study of the core, shell, and surface species of CdSe and CdSe/CdS core/shell NPLs heterostructures at all stages of c-ALD. The cadmium chemical shielding was found to be proportionally dependent on the number and nature of coordinating chalcogen-based ligands. DFT calculations permitted the separation of the the 111/113Cd chemical shielding into its different components, revealing that the varying strength of paramagnetic and spin−orbit shielding contributions are responsible for the chemical shielding trend of cadmium chalcogenides. Overall, this study points to the roughening and increased chemical disorder at the surface during the shell growth process, which is not readily captured by the conventional characterization tools such as electron microscopy.

[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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http://www.drorlist.com/nmrlist.html

NMR web database:

http://www.drorlist.com/nmr.html

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.

Adiabatic Solid Effect

Tan, Kong Ooi, Ralph T. Weber, Thach V. Can, and Robert G. Griffin. “Adiabatic Solid Effect.” The Journal of Physical Chemistry Letters, April 20, 2020, 3416–21. 

https://doi.org/10.1021/acs.jpclett.0c00654

The solid effect (SE) is a two spin dynamic nuclear polarization (DNP) mechanism that enhances the sensitivity in NMR experiments by irradiation of the electron-nuclear spin transitions with continuous wave (CW) microwaves at 𝜔0S ± 𝜔0I, where 𝜔0S and 𝜔0I are electron and nuclear Larmor frequencies, respectively. Using trityl (OX063), dispersed in a 60/40 glycerol/water mixture at 80 K, as a polarizing agent, we show here that application of a chirped microwave pulse, with a bandwidth comparable to the EPR linewidth applied at the SE matching condition, improves the enhancement by a factor of 2.4 over the CW method. Furthermore, the chirped pulse yields an enhancement that is ~20 % larger than obtained with the ramped-amplitude NOVEL (RA-NOVEL), which to date has achieved the largest enhancements in time domain DNP experiments. Numerical simulations suggest that the spins follow an adiabatic trajectory during the polarization transfer; hence, we denote this sequence as an adiabatic solid effect (ASE). We foresee that ASE will be a practical pulsed DNP experiment to be implemented at higher static magnetic fields due to moderate power requirement. In particular, the ASE uses only 13 % of the maximum microwave power required for RA-NOVEL.

Colloidal-ALD-Grown Core/Shell CdSe/CdS Nanoplatelets as Seen by DNP Enhanced PASS–PIETA NMR Spectroscopy #DNPNMR

Piveteau, Laura, Dmitry N. Dirin, Christopher P. Gordon, Brennan J. Walder, Ta-Chung Ong, Lyndon Emsley, Christophe Copéret, and Maksym V. Kovalenko. “Colloidal-ALD-Grown Core/Shell CdSe/CdS Nanoplatelets as Seen by DNP Enhanced PASS–PIETA NMR Spectroscopy.” Nano Letters 20, no. 5 (May 13, 2020): 3003–18

https://doi.org/10.1021/acs.nanolett.9b04870

Ligand exchange and CdS shell growth onto colloidal CdSe nanoplatelets (NPLs) using colloidal atomic layer deposition (c-ALD) were investigated by solid-state nuclear magnetic resonance (NMR) experiments, in particular, dynamic nuclear polarization (DNP) enhanced phase adjusted spinning sidebands−phase incremented echo-train acquisition (PASS−PIETA). The improved sensitivity and resolution of DNP enhanced PASS−PIETA permits the identification and study of the core, shell, and surface species of CdSe and CdSe/CdS core/shell NPLs heterostructures at all stages of c-ALD. The cadmium chemical shielding was found to be proportionally dependent on the number and nature of coordinating chalcogen-based ligands. DFT calculations permitted the separation of the the 111/113Cd chemical shielding into its different components, revealing that the varying strength of paramagnetic and spin−orbit shielding contributions are responsible for the chemical shielding trend of cadmium chalcogenides. Overall, this study points to the roughening and increased chemical disorder at the surface during the shell growth process, which is not readily captured by the conventional characterization tools such as electron microscopy.

A prototype system for dynamically polarized neutron protein crystallography #DNPNMR

Pierce, J., L. Crow, M. Cuneo, M. Edwards, K.W. Herwig, A. Jennings, A. Jones, et al. “A Prototype System for Dynamically Polarized Neutron Protein Crystallography.” Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 940 (October 2019): 430–34.

https://doi.org/10.1016/j.nima.2019.06.023

The sensitivity of Neutron Macromolecular Crystallography to the presence of hydrogen makes it a powerful tool to complement X-ray crystallographic studies using protein crystals. The power of this technique is currently limited by the relative low neutron flux provided by even the most powerful neutron sources. The strong polarization dependence of the neutron scattering cross section of hydrogen will allow us to use Dynamic Nuclear Polarization to dramatically improve the signal to noise ratio of neutron diffraction data, delivering order of magnitude gains in performance, and enabling measurements of radically smaller crystals of larger protein systems than are possible today. We present a prototype frozen spin system, built at Oak Ridge National Laboratory to polarize single protein crystals on the IMAGINE beamline at the High Flux Isotope Reactor (HFIR). Details of the design and construction will be described, as will the performance of the system offline and during preliminary tests at HFIR.

Dynamic Nuclear Polarization Enhanced Neutron Crystallography: Amplifying Hydrogen in Biological Crystals #DNPNMR

Pierce, Joshua, Matthew J. Cuneo, Anna Jennings, Le Li, Flora Meilleur, Jinkui Zhao, and Dean A.A. Myles. “Dynamic Nuclear Polarization Enhanced Neutron Crystallography: Amplifying Hydrogen in Biological Crystals.” In Methods in Enzymology, 634:153–75. Elsevier, 2020. 

https://doi.org/10.1016/bs.mie.2019.11.018

Dynamic nuclear polarization (DNP) can provide a powerful means to amplify neutron diffraction from biological crystals by 10–100-fold, while simultaneously enhancing the visibility of hydrogen by an order of magnitude. Polarizing the neutron beam and aligning the proton spins in a polarized sample modulates the coherent and incoherent neutron scattering cross-sections of hydrogen, in ideal cases amplifying the coherent scattering by almost an order of magnitude and suppressing the incoherent background to zero. This chapter describes current efforts to develop and apply DNP techniques for spin polarized neutron protein crystallography, highlighting concepts, experimental design, labeling strategies and recent results, as well as considering new strategies for data collection and analysis that these techniques could enable.

Heteronuclear DNP of 1H and 19F nuclei using BDPA as a polarizing agent #DNPNMR

Gennaro, Antonio, Alexander Karabanov, Alexey Potapov, and Walter Köckenberger. “Heteronuclear DNP of 1H and 19F Nuclei Using BDPA as a Polarizing Agent.” Physical Chemistry Chemical Physics 22, no. 15 (2020): 7803–16.

https://doi.org/10.1039/D0CP00892C.

This work explores the dynamic nuclear polarization (DNP) of 1H and 19F nuclei in a sample of 25/75 (% v/v) fluorobenzene/toluene containing the radical 1,3-bisphenylene-2-phenylallyl radical (BDPA) as a polarizing agent. Previously, heteronuclear effects in DNP were studied by analysing the shapes of DNP spectra, or by observing cross-relaxation between nuclei of different types. In this work, we report a rather specific DNP spectrum, where 1H and 19F nuclei obtain polarizations of opposite signs upon microwave (MW) irradiation. In order to explain this observation, we introduce a novel mechanism called heteronuclear thermal mixing (hn-TM). Within this mechanism the spectra of opposite signs can then be explained due to the presence of four-spin systems, involving a pair of dipolar coupled electron spins and hyperfine coupled nuclear spins of 1H and 19F, such that a condition relating their Larmor frequencies |o1e o2e| E oH oF is satisfied. Under this condition, a strong mixing of electron and nuclear states takes place, enabling simultaneous four-spin flip-flops. Irradiation of electron spin transitions with MW followed by such four-spin flip-flops produces non-equilibrium populations of |aHbFi and |bHaFi states, thus leading to the enhancements of opposite signs for 1H and 19F. Signal enhancements, build-up times and DNP-spectra as a function of MW power and polarizing agent concentration, all provide additional support for assigning the observed DNP mechanism as hn-TM and distinguishing it from other possible mechanisms. We also develop a quantum mechanical model of hn-TM based on averaging of spin Hamiltonians. Simulations based on this model show very good qualitative agreement with experimental data. In addition, the system exhibits cross-relaxation between 1H and 19F induced by the presence of BDPA, which was detected by measuring the 19F signal build-up upon saturation of 1H nuclei with a train of radio-frequency pulses. We demonstrate that such cross-relaxation most likely originates due to the same electron and nuclear states mixing in the four-spin systems.

Aqueous aging of a silica coated TiO2UV filter used in sunscreens: investigations at the molecular scale with dynamic nuclear polarization NMR #DNPNMR

Slomberg, Danielle L., Riccardo Catalano, Fabio Ziarelli, Stéphane Viel, Vincent Bartolomei, Jérôme Labille, and Armand Masion. “Aqueous Aging of a Silica Coated TiO 2 UV Filter Used in Sunscreens: Investigations at the Molecular Scale with Dynamic Nuclear Polarization NMR.” RSC Advances 10, no. 14 (2020): 8266–74

https://doi.org/10.1039/D0RA00595A. , 

Short-term, aqueous aging of a commercial nanocomposite TiO2 UV filter with a protective SiO2 shell was examined in abiotic simulated fresh- and seawater. Under these conditions, the SiO2 layer was quantitatively removed (∼88–98%) within 96 hours, as determined using inductively coupled plasma-atomic emission spectroscopy (ICP-AES). While these bulk ICP-AES analyses suggested almost identical SiO2 shell degradation after aging in fresh- and seawater, surface sensitive 29Si dynamic nuclear polarization (DNP) solid-state nuclear magnetic resonance (SSNMR), with signal enhancements of 5–10× compared to standard SSNMR, was able to distinguish differences in the aged nanocomposites at the molecular level. DNP-SSNMR revealed that the attachment of the silica layer to the underlying TiO2 core rested on substantial Si–O–Ti bond formation, bonds which were preserved after freshwater aging, yet barely present after aging in seawater. The removal of the protective SiO2 layer is due to ionic strength accelerated dissolution, which could present significant consequences to aqueous environments when the photoactive TiO core becomes exposed. This work demonstrates the importance of characterizing aged nanocomposites not only on the bulk scale, but also on the molecular level by employing surface sensitive techniques, such as DNP-NMR. Molecular level details on surface transformation and elemental speciation will be crucial for improving the environmental safety of nanocomposites.

Dynamic nuclear polarization enhanced neutron crystallography: Amplifying hydrogen in biological crystals #DNPNMR

Pierce, Joshua, Matthew J. Cuneo, Anna Jennings, Le Li, Flora Meilleur, Jinkui Zhao, and Dean A. A. Myles. “Chapter Eight – Dynamic Nuclear Polarization Enhanced Neutron Crystallography: Amplifying Hydrogen in Biological Crystals.” In Methods in Enzymology, edited by Peter C. E. Moody, 634:153–75. Neutron Crystallography in Structural Biology. Academic Press, 2020.

https://doi.org/10.1016/bs.mie.2019.11.018

Dynamic nuclear polarization (DNP) can provide a powerful means to amplify neutron diffraction from biological crystals by 10–100-fold, while simultaneously enhancing the visibility of hydrogen by an order of magnitude. Polarizing the neutron beam and aligning the proton spins in a polarized sample modulates the coherent and incoherent neutron scattering cross-sections of hydrogen, in ideal cases amplifying the coherent scattering by almost an order of magnitude and suppressing the incoherent background to zero. This chapter describes current efforts to develop and apply DNP techniques for spin polarized neutron protein crystallography, highlighting concepts, experimental design, labeling strategies and recent results, as well as considering new strategies for data collection and analysis that these techniques could enable.

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