Category Archives: Research Article

Zero-field nuclear magnetic resonance of chemically exchanging systems

Barskiy, Danila A., Michael C. D. Tayler, Irene Marco-Rius, John Kurhanewicz, Daniel B. Vigneron, Sevil Cikrikci, Ayca Aydogdu, et al. “Zero-Field Nuclear Magnetic Resonance of Chemically Exchanging Systems.” Nature Communications 10, no. 1 (December 2019): 3002.

https://doi.org/10.1038/s41467-019-10787-9.

Zero- to ultralow-field (ZULF) nuclear magnetic resonance (NMR) is an emerging tool for precision chemical analysis. In this work, we study dynamic processes and investigate the influence of chemical exchange on ZULF NMR J-spectra. We develop a computational approach that allows quantitative calculation of J-spectra in the presence of chemical exchange and apply it to study aqueous solutions of [15N]ammonium (15NHfl4 ) as a model system. We show that pH-dependent chemical exchange substantially affects the J-spectra and, in some cases, can lead to degradation and complete disappearance of the spectral features. To demonstrate potential applications of ZULF NMR for chemistry and biomedicine, we show a ZULF NMR spectrum of [2-13C]pyruvic acid hyperpolarized via dissolution dynamic nuclear polarization (dDNP). We foresee applications of affordable and scalable ZULF NMR coupled with hyperpolarization to study chemical exchange phenomena in vivo and in situations where high-field NMR detection is not possible to implement.

Hyperpolarized relaxometry based nuclear T1 noise spectroscopy in diamond

Ajoy, A., B. Safvati, R. Nazaryan, J. T. Oon, B. Han, P. Raghavan, R. Nirodi, et al. “Hyperpolarized Relaxometry Based Nuclear T1 Noise Spectroscopy in Diamond.” Nature Communications 10, no. 1 (December 2019): 5160.

https://doi.org/10.1038/s41467-019-13042-3.

The origins of spin lifetimes in quantum systems is a matter of importance in several areas of quantum information. Spectrally mapping spin relaxation processes provides insight into their origin and motivates methods to mitigate them. In this paper, we map nuclear relaxation in a prototypical system of 13C nuclei in diamond coupled to Nitrogen Vacancy (NV) centers over a wide field range (1 mT-7 T). Nuclear hyperpolarization through optically pumped NV electrons allows signal measurement savings exceeding million-fold over conventional methods. Through a systematic study with varying substitutional electron (P1 center) and 13C concentrations, we identify the operational relaxation channels for the nuclei at different fields as well as the dominant role played by 13C coupling to the interacting P1 electronic spin bath. These results motivate quantum control techniques for dissipation engineering to boost spin lifetimes in diamond, with applications including engineered quantum memories and hyperpolarized 13C imaging.

Photochemically induced dynamic nuclear polarization NMR on photosystem II: donor cofactor observed in entire plant #CIDNP

Janssen, Geertje J., Pavlo Bielytskyi, Denis G. Artiukhin, Johannes Neugebauer, Huub J. M. de Groot, Jörg Matysik, and A. Alia. “Photochemically Induced Dynamic Nuclear Polarization NMR on Photosystem II: Donor Cofactor Observed in Entire Plant.” Scientific Reports 8, no. 1 (December 2018): 17853.

https://doi.org/10.1038/s41598-018-36074-z.

The solid-state photo-CIDNP (photochemically induced dynamic nuclear polarization) effect allows for increase of signal and sensitivity in magic-angle spinning (MAS) NMR experiments. The effect occurs in photosynthetic reaction centers (RC) proteins upon illumination and induction of cyclic electron transfer. Here we show that the strength of the effect allows for observation of the cofactors forming the spin-correlated radical pair (SCRP) in isolated proteins, in natural photosynthetic membranes as well as in entire plants. To this end, we measured entire selectively 13C isotope enriched duckweed plants (Spirodela oligorrhiza) directly in the MAS rotor. Comparison of 13C photo-CIDNP MAS NMR spectra of photosystem II (PS2) obtained from different levels of RC isolation, from entire plant to isolated RC complex, demonstrates the intactness of the photochemical machinery upon isolation. The SCRP in PS2 is structurally and functionally very similar in duckweed and spinach (Spinacia oleracea). The analysis of the photo-CIDNP MAS NMR spectra reveals a monomeric Chl a donor. There is an experimental evidence for matrix involvement, most likely due to the axial donor histidine, in the formation of the SCRP. Data do not suggest a chemical modification of C-131 carbonyl position of the donor cofactor.

Shedding light on the atomic-scale structure of amorphous silica–alumina and its Brønsted acid sites #DNPNMR

Perras, Frédéric A., Zichun Wang, Takeshi Kobayashi, Alfons Baiker, Jun Huang, and Marek Pruski. “Shedding Light on the Atomic-Scale Structure of Amorphous Silica–Alumina and Its Brønsted Acid Sites.” Physical Chemistry Chemical Physics 21, no. 35 (2019): 19529–37.

https://doi.org/10.1039/C9CP04099D

In spite of the widespread applications of amorphous silica–aluminas (ASAs) in many important industrial chemical processes, their high-resolution structures have remained largely elusive. Specifically, the lack of long-range ordering in ASA precludes the use of diffraction methods while NMR spectroscopy has been limited by low sensitivity. Here, we use conventional as well as DNP-enhanced 29Si–29Si, 27Al–27Al, and 29Si–27Al solid-state NMR experiments to shed light on the ordering of atoms in ASAs prepared by flame-spray-pyrolysis. These experiments, in conjunction with a novel Monte Carlo-based approach to simulating RESPDOR dephasing curves, revealed that ASA materials obey Loewenstein’s rule of aluminum avoidance. 3D 17O{1H} and 2D
17O{1H, 27Al} experiments were developed to measure site-specific O–H and HO–Al distances, and show that the Brønsted acid sites originate predominantly from the pseudo-bridging silanol groups.

Quantifying the effects of quadrupolar sinks via 15N relaxation dynamics in metronidazoles hyperpolarized via SABRE-SHEATH

Birchall, Jonathan R., Mohammad S. H. Kabir, Oleg G. Salnikov, Nikita V. Chukanov, Alexandra Svyatova, Kirill V. Kovtunov, Igor V. Koptyug, et al. “Quantifying the Effects of Quadrupolar Sinks via 15N Relaxation Dynamics in Metronidazoles Hyperpolarized via SABRE-SHEATH.” Chemical Communications 56, no. 64 (2020): 9098–9101.

https://doi.org/10.1039/D0CC03994B

15N spin–lattice relaxation dynamics in metronidazole-15N3 and metronidazole-15N2 isotopologues are studied for rational design of 15N-enriched biomolecules for signal amplification by reversible exchange in microtesla fields. 15N relaxation dynamics mapping reveals the deleterious effects of interactions with the polarization transfer catalyst and a quadrupolar 14N nucleus within the spin-relayed 15N–15N network.

Molecular Dynamics and Hyperpolarization Performance of Deuterated β-Cyclodextrins #DNP

Caracciolo, Filippo, Efstathios Charlaftis, Lucio Melone, and Pietro Carretta. “Molecular Dynamics and Hyperpolarization Performance of Deuterated β-Cyclodextrins.” The Journal of Physical Chemistry B 123, no. 17 (May 2, 2019): 3731–37.

https://doi.org/10.1021/acs.jpcb.9b01857.

We discuss the temperature dependence of the 1H and 13C nuclear spin−lattice relaxation rate 1/T1 and dynamic nuclear polarization (DNP) performance in β-cyclodextrins with deuterated methyl groups. It is shown that 13C DNP-enhanced polarization is raised up to 10%. The temperature dependence of the buildup rate for nuclear spin polarization and of 1/T1, below 4.2 K, is analyzed in the framework of the thermal mixing regime and the origin of the deviations from the theoretical behavior discussed. 13C 1/T1 is determined at low temperature by the glassy dynamics and at high temperature by the rotational molecular motions of the deuterated methyl groups. Thanks to deuteration, relaxation times approaching 30 s are achieved at room temperature, making this material interesting for molecular imaging applications. The effect of molecular dynamics on the line width of the NMR spectra is also discussed.

A method for fast field settling in cryogen-free superconducting magnets for NMR

Cryogen-free magnets are around for EPR spectroscopy for a while already, however, in recent years they also become more popular for NMR spectroscopy (solids and solutions). This article greatly demonstrate the potential of the technology.

Kryukov, Eugeny, Yury Bugoslavsky, Angel Joaquin Perez Linde, Thomas Holubar, Stephen Burgess, David Marlow, and Jeremy Good. “A Method for Fast Field Settling in Cryogen-Free Superconducting Magnets for NMR.” Solid State Nuclear Magnetic Resonance 109 (October 2020): 101684.

https://doi.org/10.1016/j.ssnmr.2020.101684.

We propose a fast algorithm to energise a cryogen free magnet to a highly persistent state. A decay rate as low as 0.021 ppm/h can be achieved in less than an hour after reaching the target field. The decay rate drops further to 0.0004 ppm/h in the following 48 h. This procedure can be applied at different values of target field, which makes it feasible to use a single magnet for study of various NMR lines at different fields. The mechanism of establishing a highly stable magnetic field can be understood on the basis of the magnetic properties of the superconducting wire, which were studied using a vibrating sample magnetometer. The results confirm the high quality of the superconducting wire and joints.

XeUS: A second-generation automated open-source batch-mode clinical-scale hyperpolarizer

Birchall, Jonathan R., Robert K. Irwin, Panayiotis Nikolaou, Aaron M. Coffey, Bryce E. Kidd, Megan Murphy, Michael Molway, et al. “XeUS: A Second-Generation Automated Open-Source Batch-Mode Clinical-Scale Hyperpolarizer.” Journal of Magnetic Resonance 319 (October 2020): 106813.

https://doi.org/10.1016/j.jmr.2020.106813.

We present a second-generation open-source automated batch-mode 129Xe hyperpolarizer (XeUS GEN2), designed for clinical-scale hyperpolarized (HP) 129Xe production via spin-exchange optical pumping (SEOP) in the regimes of high Xe density (0.66–2.5 atm partial pressure) and resonant photon flux (~170 W, Dk = 0.154 nm FWHM), without the need for cryo-collection typically employed by continuous-flow hyperpolarizers. An Arduino micro-controller was used for hyperpolarizer operation. Processing open-source software was employed to program a custom graphical user interface (GUI), capable of remote automation. The Arduino Integrated Development Environment (IDE) was used to design a variety of customized automation sequences such as temperature ramping, NMR signal acquisition, and SEOP cell refilling for increased reliability. A polycarbonate 3D-printed oven equipped with a thermoelectric cooler/heater provides thermal stability for SEOP for both binary (Xe/N2) and ternary (4He-containing) SEOP cell gas mixtures. Quantitative studies of the 129Xe hyperpolarization process demonstrate that near-unity polarization can be achieved in a 0.5 L SEOP cell. For example, %PXe of 93.2 ± 2.9% is achieved at 0.66 atm Xe pressure with polarization build-up rate constant cSEOP = 0.040 ± 0.005 minÀ1, giving a max dose equivalent % 0.11 L/h 100% hyperpolarized, 100% enriched 129Xe; %PXe of 72.6 ± 1.4% is achieved at 1.75 atm Xe pressure with cSEOP of 0.041 ± 0.001 minÀ1, yielding a corresponding max dose equivalent of 0.27 L/h. Quality assurance studies on this device have demonstrated the potential to refill SEOP cells hundreds of times without significant losses in performance, with average %PXe = 71.7%, (standard deviation rP = 1.52%) and mean polarization lifetime T1 = 90.5 min, (standard deviation rT = 10.3 min) over the first ~200 gas mixture refills, with sufficient performance maintained across a further ~700 refills. These findings highlight numerous technological developments and have significant translational relevance for efficient production of gaseous HP 129Xe contrast agents for use in clinical imaging and bio-sensing techniques.

Materials chemistry of triplet dynamic nuclear polarization #DNPNMR

Nishimura, Koki, Hironori Kouno, Yusuke Kawashima, Kana Orihashi, Saiya Fujiwara, Kenichiro Tateishi, Tomohiro Uesaka, Nobuo Kimizuka, and Nobuhiro Yanai. “Materials Chemistry of Triplet Dynamic Nuclear Polarization.” Chemical Communications 56, no. 53 (2020): 7217–32.

https://doi.org/10.1039/D0CC02258F

This Feature Article overviews the recently-emerged materials chemistry of triplet dynamic nuclear polarization (triplet-DNP) towards biological and medical applications.

Dynamic nuclear polarization with photo-excited triplet electrons (triplet-DNP) has the potential to enhance the sensitivity of nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) at a moderate temperature. While many efforts have been devoted to achieving a large nuclear polarization based on triplet-DNP, the application of triplet-DNP has been limited to nuclear physics experiments. The recent introduction of materials chemistry into the field of triplet-DNP has achieved air-stable and water-soluble polarizing agents as well as the hyperpolarization of nanomaterials with a large surface area such as nanoporous metal–organic frameworks (MOFs) and nanocrystal dispersion in water. This Feature Article overviews the recently-emerged materials chemistry of triplet-DNP that paves new paths towards unprecedented biological and medical applications.

Water-soluble BDPA radicals with improved persistence #DNPNMR

Mandal, Sucharita, and Snorri Th. Sigurdsson. “Water-Soluble BDPA Radicals with Improved Persistence.” Chemical Communications, 2020, 10.1039.D0CC04920D. 

https://doi.org/10.1039/D0CC04920D.

1,3-Bis(diphenylene)-2-phenylallyl (BDPA) radicals are promising polarizing agents for increasing the sensitivity of NMR spectroscopy through dynamic nuclear polarization (DNP), but have low persistence and solubility in aqueous media. New tetraalkyl/aryl-ammonium derivatives of BDPA are soluble in polar solvents and are highly persistent, with 5–20-fold lower initial rates of degradation than BDPA.

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