1
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Cheney DJ, Cerreia Vioglio P, Brookfield A, Blanc F. Optimisation of dynamic nuclear polarisation using "off-the-shelf" Gd(III)-based polarising agents. Phys Chem Chem Phys 2024. [PMID: 39258402 DOI: 10.1039/d4cp02924k] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/12/2024]
Abstract
Complexes of paramagnetic metal ions, in particular Gd3+, have been demonstrated as efficient polarising agents for magic-angle spinning (MAS) dynamic nuclear polarisation (DNP). We recently demonstrated that commercially available and inexpensive Gd(NO3)3 is suitable for use as an "off-the-shelf" MAS DNP polarising agent, providing promising sensitivity enhancements to 1H, 13C, and 15N NMR signals. Here we expand upon this approach by investigating the impact of the Gd(NO3)3 concentration and by exploring a larger range of readily available Gd3+ sources. We found that a Gd(NO3)3 concentration of 20 mM in the case of 1H and 13C, and 40 mM in the case of 15N, offers optimum signal enhancements and is rationalised as a trade-off between DNP enhancements, polarisation build-up times, and electron paramagnetic resonance (EPR) spin-spin relaxation times. We determined that a range of different gadolinium compounds (GdCl3, Gd2(SO4)3, GdBr3, and Gd(OAc)3) are also suitable for use as polarising agents and yield 1H, 13C, and 15N signal enhancements of variable values. Gd(OAc)3 yields lower signal enhancements, which is proposed to be the result of greater local asymmetry at the Gd3+ centre leading to EPR line broadening, and the methyl group in the acetate ion acting as a relaxation sink and limiting the nuclear polarisation available.
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Affiliation(s)
- Daniel J Cheney
- Department of Chemistry, University of Liverpool, Liverpool L69 7ZD, UK.
| | - Paolo Cerreia Vioglio
- DNP MAS NMR Facility, Sir Peter Mansfield Imaging Centre, University of Nottingham, Nottingham NG7 2RD, UK
| | - Adam Brookfield
- Department of Chemistry and Photon Science Institute, University of Manchester, Manchester M13 9PL, UK
| | - Frédéric Blanc
- Department of Chemistry, University of Liverpool, Liverpool L69 7ZD, UK.
- Leverhulme Research Centre for Functional Materials Design, Materials Innovation Factory, University of Liverpool, Liverpool, L69 7ZD, UK
- Stephenson Institute for Renewable Energy, University of Liverpool, Liverpool L69 7ZF, UK
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2
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Moroz IB, Feldman Y, Carmieli R, Liu X, Leskes M. Endogenous metal-ion dynamic nuclear polarization for NMR signal enhancement in metal organic frameworks. Chem Sci 2023; 15:336-348. [PMID: 38131097 PMCID: PMC10731914 DOI: 10.1039/d3sc03456a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2023] [Accepted: 11/23/2023] [Indexed: 12/23/2023] Open
Abstract
Rational design of metal-organic framework (MOF)-based materials for catalysis, gas capture and storage, requires deep understanding of the host-guest interactions between the MOF and the adsorbed molecules. Solid-State NMR spectroscopy is an established tool for obtaining such structural information, however its low sensitivity limits its application. This limitation can be overcome with dynamic nuclear polarization (DNP) which is based on polarization transfer from unpaired electrons to the nuclei of interest and, as a result, enhancement of the NMR signal. Typically, DNP is achieved by impregnating or wetting the MOF material with a solution of nitroxide biradicals, which prevents or interferes with the study of host-guest interactions. Here we demonstrate how Gd(iii) ions doped into the MOF structure, LaBTB (BTB = 4,4',4''-benzene-1,3,5-triyl-trisbenzoate), can be employed as an efficient polarization agent, yielding up to 30-fold 13C signal enhancement for the MOF linkers, while leaving the pores empty for potential guests. Furthermore, we demonstrate that ethylene glycol, loaded into the MOF as a guest, can also be polarized using our approach. We identify specific challenges in DNP studies of MOFs, associated with residual oxygen trapped within the MOF pores and the dynamics of the framework and its guests, even at cryogenic temperatures. To address these, we describe optimal conditions for carrying out and maximizing the enhancement achieved in DNP-NMR experiments. The approach presented here can be expanded to other porous materials which are currently the state-of-the-art in energy and sustainability research.
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Affiliation(s)
- Ilia B Moroz
- Department of Molecular Chemistry and Materials Science, Weizmann Institute of Science Rehovot 76100 Israel
| | - Yishay Feldman
- Department of Chemical Research Support, Weizmann Institute of Science Rehovot 76100 Israel
| | - Raanan Carmieli
- Department of Chemical Research Support, Weizmann Institute of Science Rehovot 76100 Israel
| | - Xinyu Liu
- Yusuf Hamied Department of Chemistry, University of Cambridge Lensfield Road Cambridge CB2 1EW UK
| | - Michal Leskes
- Department of Molecular Chemistry and Materials Science, Weizmann Institute of Science Rehovot 76100 Israel
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3
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Ossadnik D, Voss J, Godt A. Equipping 1,4,7-Triazacyclononane with Substituents via Solid-Phase Synthesis. J Org Chem 2023. [PMID: 38016917 DOI: 10.1021/acs.joc.3c01974] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2023]
Abstract
Metal ion complexes frequently show substituted 1,4,7-triazacyclononane (tacn) as the ligand. Besides providing donor atoms for complex formation, tacn serves as a scaffold for equipping the complex with further functional units that are needed for the complementation and electronic tuning of the metal ion coordination sphere and/or add other features, e.g., light-absorbing antennas and groups for bioconjugation. To exploit the full potential of substituted tacn, strategies for directed syntheses of NO(R1,R1,R2) and NO(R1,R2,R3), i.e., tacn with two and even three different substituents R, are needed. Herein, we report a strategy that takes advantage of solid-phase synthesis in the assembly of the precursors NO(R1,R1,H) and NO(R1,R2,H). The assembly of NO(R1,R2,H) is based on a highly selective formation of NO(Cbz,tfAc,H), with Cbz being the link between tacn and solid phase. For this, tacn was loaded onto (4-nitrophenyl carbonate)-resin, thereby forming resin-bound (rb)-tacn, which corresponds to NO(Cbz,H,H) bound to the solid phase. Treatment of rb-tacn with ethyl trifluoroacetate gave rb-NO(tfAc,H), which corresponds to NO(Cbz,tfAc,H). With rb-tacn and rb-NO(tfAc,H) in hand, a variety of NO(R1,R1,H) and NO(R1,R2,H) were prepared, showing the broad applicability of the strategy with respect to the type of substituents and of reactions (nucleophilic substitution, reductive amination, aza-Michael addition, addition to epoxides, acylation). The study also identified limitations and points for improvement.
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Affiliation(s)
- Daniel Ossadnik
- Faculty of Chemistry and Center for Molecular Materials (CM2), Bielefeld University, Universitätsstraße 25, 33615 Bielefeld, Germany
| | - Jona Voss
- Faculty of Chemistry and Center for Molecular Materials (CM2), Bielefeld University, Universitätsstraße 25, 33615 Bielefeld, Germany
| | - Adelheid Godt
- Faculty of Chemistry and Center for Molecular Materials (CM2), Bielefeld University, Universitätsstraße 25, 33615 Bielefeld, Germany
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4
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Hope MA, Zhang Y, Venkatesh A, Emsley L. Dynamic nuclear polarisation of 1H in Gd-doped In(OH) 3. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2023; 353:107509. [PMID: 37331306 DOI: 10.1016/j.jmr.2023.107509] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/09/2023] [Revised: 06/08/2023] [Accepted: 06/09/2023] [Indexed: 06/20/2023]
Abstract
Dynamic nuclear polarisation (DNP) of solids doped with high-spin metal ions, such as Gd3+, is a useful strategy to enhance the nuclear magnetic resonance (NMR) sensitivity for these samples. Spin diffusion can relay polarisation throughout a sample, which is most effective for dense 1H networks, while the efficiency of DNP using Gd3+ depends on the symmetry of the metal site. Here, we investigate cubic In(OH)3 as a high-symmetry, proton-containing material for endogenous Gd DNP. A 1H enhancement of up to 9 is demonstrated and harnessed to measure the 17O spectrum at natural abundance. The enhancement is interpreted in terms of clustering of the Gd3+ dopants and the local reduction in symmetry of the metal site induced by proton disorder, as demonstrated by quadrupolar 115In NMR. This is the first example of 1H DNP using Gd3+ dopants in an inorganic solid.
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Affiliation(s)
- Michael A Hope
- Institut des Sciences et Ingenierie Chimiques, École Polytechnique Fedérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland.
| | - Yuxuan Zhang
- Institut des Sciences et Ingenierie Chimiques, École Polytechnique Fedérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
| | - Amrit Venkatesh
- Institut des Sciences et Ingenierie Chimiques, École Polytechnique Fedérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
| | - Lyndon Emsley
- Institut des Sciences et Ingenierie Chimiques, École Polytechnique Fedérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland.
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Alnami B, Kragskow JGC, Staab JK, Skelton JM, Chilton NF. Structural Evolution of Paramagnetic Lanthanide Compounds in Solution Compared to Time- and Ensemble-Average Structures. J Am Chem Soc 2023; 145:13632-13639. [PMID: 37327086 PMCID: PMC10311533 DOI: 10.1021/jacs.3c01342] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2023] [Indexed: 06/18/2023]
Abstract
Anisotropy in the magnetic susceptibility strongly influences the paramagnetic shifts seen in nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) experiments. A previous study on a series of C3-symmetric prototype MRI contrast agents showed that their magnetic anisotropy was highly sensitive to changes in molecular geometry and concluded that changes in the average angle between the lanthanide-oxygen (Ln-O) bonds and the molecular C3 axis due to solvent interactions had a significant impact on the magnetic anisotropy and, consequently, the paramagnetic shift. However, this study, like many others, was predicated on an idealized C3-symmetric structural model, which may not be representative of the dynamic structure in solution at the single-molecule level. Here, we address this by using ab initio molecular dynamics simulations to simulate how the molecular geometry, in particular the angles between the Ln-O bonds and the pseudo-C3 axis, evolves over time in the solution, mimicking typical experimental conditions. We observe large-amplitude oscillations in the O-Ln-C̃3 angles, and complete active space self-consistent field spin-orbit calculations show that this leads to similarly large oscillations in the pseudocontact (dipolar) paramagnetic NMR shifts. The time-averaged shifts show good agreement with experimental measurements, while the large fluctuations suggest that an idealized structure provides an incomplete description of the solution dynamics. Our observations have significant implications for modeling the electronic and nuclear relaxation times in this and other systems where the magnetic susceptibility is exquisitely sensitive to the molecular structure.
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Affiliation(s)
- Barak Alnami
- Department of Chemistry, The University of Manchester, Manchester M13 9PL, U.K.
| | - Jon G. C. Kragskow
- Department of Chemistry, The University of Manchester, Manchester M13 9PL, U.K.
| | - Jakob K. Staab
- Department of Chemistry, The University of Manchester, Manchester M13 9PL, U.K.
| | - Jonathan M. Skelton
- Department of Chemistry, The University of Manchester, Manchester M13 9PL, U.K.
| | - Nicholas F. Chilton
- Department of Chemistry, The University of Manchester, Manchester M13 9PL, U.K.
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6
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Menzildjian G, Schlagnitweit J, Casano G, Ouari O, Gajan D, Lesage A. Polarizing agents for efficient high field DNP solid-state NMR spectroscopy under magic-angle spinning: from design principles to formulation strategies. Chem Sci 2023; 14:6120-6148. [PMID: 37325158 PMCID: PMC10266460 DOI: 10.1039/d3sc01079a] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2023] [Accepted: 05/09/2023] [Indexed: 06/17/2023] Open
Abstract
Dynamic Nuclear Polarization (DNP) has recently emerged as a cornerstone approach to enhance the sensitivity of solid-state NMR spectroscopy under Magic Angle Spinning (MAS), opening unprecedented analytical opportunities in chemistry and biology. DNP relies on a polarization transfer from unpaired electrons (present in endogenous or exogenous polarizing agents) to nearby nuclei. Developing and designing new polarizing sources for DNP solid-state NMR spectroscopy is currently an extremely active research field per se, that has recently led to significant breakthroughs and key achievements, in particular at high magnetic fields. This review describes recent developments in this area, highlighting key design principles that have been established over time and led to the introduction of increasingly more efficient polarizing sources. After a short introduction, Section 2 presents a brief history of solid-state DNP, highlighting the main polarization transfer schemes. The third section is devoted to the development of dinitroxide radicals, discussing the guidelines that were progressively established to design the fine-tuned molecular structures in use today. In Section 4, we describe recent efforts in developing hybrid radicals composed of a narrow EPR line radical covalently linked to a nitroxide, highlighting the parameters that modulate the DNP efficiency of these mixed structures. Section 5 reviews recent advances in the design of metal complexes suitable for DNP MAS NMR as exogenous electron sources. In parallel, current strategies that exploit metal ions as endogenous polarization sources are discussed. Section 6 briefly describes the recent introduction of mixed-valence radicals. In the last part, experimental aspects regarding sample formulation are reviewed to make best use of these polarizing agents in a broad panel of application fields.
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Affiliation(s)
- Georges Menzildjian
- Centre de RMN à, Très Hauts Champs, Université de Lyon (CNRS/ENS Lyon/UCB Lyon 1) 5 Rue de la doua 69100 Villeurbanne France
| | - Judith Schlagnitweit
- Centre de RMN à, Très Hauts Champs, Université de Lyon (CNRS/ENS Lyon/UCB Lyon 1) 5 Rue de la doua 69100 Villeurbanne France
| | - Gilles Casano
- Aix Marseille Univ., CNRS, Institut de Chimie Radicalaire, UMR 7273 Marseille France
| | - Olivier Ouari
- Aix Marseille Univ., CNRS, Institut de Chimie Radicalaire, UMR 7273 Marseille France
| | - David Gajan
- Centre de RMN à, Très Hauts Champs, Université de Lyon (CNRS/ENS Lyon/UCB Lyon 1) 5 Rue de la doua 69100 Villeurbanne France
| | - Anne Lesage
- Centre de RMN à, Très Hauts Champs, Université de Lyon (CNRS/ENS Lyon/UCB Lyon 1) 5 Rue de la doua 69100 Villeurbanne France
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7
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Ossadnik D, Kuzin S, Qi M, Yulikov M, Godt A. A Gd III-Based Spin Label at the Limits for Linewidth Reduction through Zero-Field Splitting Optimization. Inorg Chem 2023; 62:408-432. [PMID: 36525400 DOI: 10.1021/acs.inorgchem.2c03531] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
The remarkably narrow central line in the electron paramagnetic resonance spectrum and the very weak zero-field splitting (ZFS) make [GdIII(NO3Pic)] ([GdIII(TPATCN)]) an attractive starting point for the development of spin labels. For retaining the narrow line of this parent complex when modifying it with a substituent enabling bioconjugation, alkyl with a somehow remote functional group as a substituent at the picolinate moiety was found to be highly suitable because ZFS stayed weak, even if the threefold axial symmetry was broken. The ZFS is so weak that hyperfine coupling and/or g-value variations noticeably determine the linewidth in Q band and higher fields when the biomolecule is protonated, which is the standard situation, and in W band and higher fields for the protonated complex in a fully deuterated surrounding. Clearly, [NDSE-{GdIII(NO3Pic)}], a spin label targeting the cysteines in a peptide, is at a limit of linewidth narrowing through ZFS minimization. The labeling reaction is highly chemoselective and, applied to a polyproline with two cysteine units, it took no more than a minute at 7 °C and pH 7.8. Subsequent disulfide scrambling is very slow and can therefore be prevented. Double electron-electron resonance and relaxation-induced dipolar modulation enhancement applied to the spin-labeled polyproline proved the spin label useful for distance determination in peptides.
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Affiliation(s)
- Daniel Ossadnik
- Faculty of Chemistry and Center for Molecular Materials (CM2), Bielefeld University, Universitätsstraße 25, 33615Bielefeld, Germany
| | - Sergei Kuzin
- Laboratory of Physical Chemistry, Department of Chemistry and Applied Biosciences, ETH Zurich, Vladimir-Prelog-Weg 2, 8093Zurich, Switzerland
| | - Mian Qi
- Faculty of Chemistry and Center for Molecular Materials (CM2), Bielefeld University, Universitätsstraße 25, 33615Bielefeld, Germany
| | - Maxim Yulikov
- Laboratory of Physical Chemistry, Department of Chemistry and Applied Biosciences, ETH Zurich, Vladimir-Prelog-Weg 2, 8093Zurich, Switzerland
| | - Adelheid Godt
- Faculty of Chemistry and Center for Molecular Materials (CM2), Bielefeld University, Universitätsstraße 25, 33615Bielefeld, Germany
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Elliott SJ, Duff BB, Taylor-Hughes AR, Cheney DJ, Corley JP, Paul S, Brookfield A, Pawsey S, Gajan D, Aspinall HC, Lesage A, Blanc F. Off-the-Shelf Gd(NO 3) 3 as an Efficient High-Spin Metal Ion Polarizing Agent for Magic Angle Spinning Dynamic Nuclear Polarization. J Phys Chem B 2022; 126:6281-6289. [PMID: 35973071 PMCID: PMC9421651 DOI: 10.1021/acs.jpcb.2c04184] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Magic angle spinning nuclear magnetic resonance spectroscopy experiments are widely employed in the characterization of solid media. The approach is incredibly versatile but deleteriously suffers from low sensitivity, which may be alleviated by adopting dynamic nuclear polarization methods, resulting in large signal enhancements. Paramagnetic metal ions such as Gd3+ have recently shown promising results as polarizing agents for 1H, 13C, and 15N nuclear spins. We demonstrate that the widely available and inexpensive chemical agent Gd(NO3)3 achieves significant signal enhancements for the 13C and 15N nuclear sites of [2-13C,15N]glycine at 9.4 T and ∼105 K. Analysis of the signal enhancement profiles at two magnetic fields, in conjunction with electron paramagnetic resonance data, reveals the solid effect to be the dominant signal enhancement mechanism. The signal amplification obtained paves the way for efficient dynamic nuclear polarization without the need for challenging synthesis of Gd3+ polarizing agents.
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Affiliation(s)
- Stuart J Elliott
- Department of Chemistry, University of Liverpool, Liverpool L69 7ZD, United Kingdom
| | - Benjamin B Duff
- Department of Chemistry, University of Liverpool, Liverpool L69 7ZD, United Kingdom.,Stephenson Institute for Renewable Energy, University of Liverpool, Liverpool L69 7ZD, United Kingdom
| | | | - Daniel J Cheney
- Department of Chemistry, University of Liverpool, Liverpool L69 7ZD, United Kingdom
| | - John P Corley
- Department of Chemistry, University of Liverpool, Liverpool L69 7ZD, United Kingdom
| | - Subhradip Paul
- DNP MAS NMR Facility, Sir Peter Mansfield Imaging Centre, University of Nottingham, Nottingham NG7 3RD, United Kingdom
| | - Adam Brookfield
- Department of Chemistry and Photon Science Institute, University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom
| | - Shane Pawsey
- Bruker BioSpin Corporation, Billerica, Massachusetts 01821, United States
| | - David Gajan
- Université de Lyon, Centre de Résonance Magnétique Nucléaire à Très Hauts Champs (UMR 5082, CNRS/ENS Lyon/UCBL), 69100 Villeurbanne, France
| | - Helen C Aspinall
- Department of Chemistry, University of Liverpool, Liverpool L69 7ZD, United Kingdom
| | - Anne Lesage
- Université de Lyon, Centre de Résonance Magnétique Nucléaire à Très Hauts Champs (UMR 5082, CNRS/ENS Lyon/UCBL), 69100 Villeurbanne, France
| | - Frédéric Blanc
- Department of Chemistry, University of Liverpool, Liverpool L69 7ZD, United Kingdom.,Stephenson Institute for Renewable Energy, University of Liverpool, Liverpool L69 7ZD, United Kingdom
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