Dynamic Nuclear Polarization with Vanadium(IV) Metal Centers

Sheetal Kumar Jain; Chung Jui Yu; Christopher Blake Wilson; Tarnuma Tabassum; Danna E. Freedman; Songi Han

doi:10.1016/j.chempr.2020.10.021

Dynamic Nuclear Polarization with Vanadium(IV) Metal Centers

Sheetal Kumar Jain, Chung Jui Yu, Christopher Blake Wilson, Tarnuma Tabassum, Danna E. Freedman^*, Songi Han^*

^*Corresponding author for this work

Chemistry

Research output: Contribution to journal › Article › peer-review

22 Scopus citations

Abstract

Dynamic nuclear polarization (DNP) harnesses the large polarization of electron spins to dramatically increase nuclear magnetic resonance (NMR) sensitivity. This study expands the scope of DNP beyond its traditional focus on hyperpolarizing the solvent network using exogenous polarizing agents (PAs). We introduce ¹H DNP with endogenous V⁴⁺ centers positioned in a set of vanadyl complexes with tunable V⁴⁺-¹H distances. We traced the polarization transfer from V⁴⁺ to ¹H spins, specifically differentiating between direct V⁴⁺-¹Hs polarization transfer and the ¹H spin-diffusion-mediated bulk solvent ¹H polarization buildup and illuminated the effect of the V⁴⁺-¹H distance on these processes. These results deepen our understanding of polarization pathways and expand the catalog of PAs to broad-line transition metals. This study establishes crucial first steps toward employing strategically positioned endogenous paramagnetic metal centers for DNP and the conceptual framework of hyperfine DNP spectroscopy that merges both spatial and chemical diagnosis of target nuclear spins. Dynamic nuclear polarization (DNP) offers a strategy to amplify the inherently insensitive nuclear magnetic resonance (NMR) signal by orders of magnitude, dramatically enhancing the NMR studies of molecules and materials. To date, most DNP studies have relied on exogenous polarizing agents (PAs) with narrow electron paramagnetic resonance (EPR) lines. Expanding the catalog of PAs to paramagnetic centers at the core of active sites in enzymes and functional materials will offer the opportunity to illuminate the local structure around these metal centers during chemical transformations. This study is the first demonstration of DNP using V⁴⁺ centers with broad EPR lines as PAs to enhance and detect the NMR signal of ¹H nuclei at discrete distances from the V⁴⁺ center. These results pave the way toward endogenous DNP studies of active molecules and materials in which paramagnetic metals play key functional roles. We demonstrate dynamic nuclear polarization (DNP) with a set of complexes with controlled V⁴⁺-¹H distances and gain mechanistic insight into DNP. DNP from the paramagnetic V⁴⁺center directly polarized ¹H nuclei located 12.6 Å from the electronic spin. Critically, we find the buildup rate of polarization is dependent on the separation of the ¹H from the V⁴⁺center. These results lay the foundation for endogenous DNP studies of systems in which intrinsic paramagnetic metals serve as the polarizing agent.

Original language	English (US)
Pages (from-to)	421-435
Number of pages	15
Journal	Chem
Volume	7
Issue number	2
DOIs	https://doi.org/10.1016/j.chempr.2020.10.021
State	Published - Feb 11 2021

Funding

We thank Dr. Asif Equbal for performing the quantum mechanical simulations using SpinEvolution shown in Figure S10 . We are thankful to Dr. Ilia Kaminker for the fruitful discussions on the experimental data and manuscript. We thank M.J. Graham and K.A. Collins for experimental assistance. D.E.F. and C.-J.Y. acknowledge NSF CHE-1455017 for funding the synthetic component of this research. S.K.J., T.T., and S.H. acknowledge the NSF CHE-2004217 for DNP method development, and B.W. and S.H. acknowledge NSF MCB-1617025 for EPR studies at 240 GHz. Part of this work was performed at the ITST Terahertz Facilities at UCSB, which have been upgraded under NSF award no. DMR-1126894 . We thank Dr. Asif Equbal for performing the quantum mechanical simulations using SpinEvolution shown in Figure S10. We are thankful to Dr. Ilia Kaminker for the fruitful discussions on the experimental data and manuscript. We thank M.J. Graham and K.A. Collins for experimental assistance. D.E.F. and C.-J.Y. acknowledge NSF CHE-1455017 for funding the synthetic component of this research. S.K.J. T.T. and S.H. acknowledge the NSF CHE-2004217 for DNP method development, and B.W. and S.H. acknowledge NSF MCB-1617025 for EPR studies at 240 GHz. Part of this work was performed at the ITST Terahertz Facilities at UCSB, which have been upgraded under NSF award no. DMR-1126894. Conceptualization, S.K.J. C.-J.Y. D.E.F. and S.H.; Methodology, S.K.J. C.-J.Y. B.W. and T.T.; Writing-Original Draft S.K.J. C.-J.Y. D.E.F. and S.H.; Visualization S.K.J. and C.-J.Y.; Supervision D.E.F. and S.H.; Funding Acquisition D.E.F. and S.H. The authors declare no competing interests.

Keywords

SDG3: Good health and well-being
coordination chemistry
direct DNP
endogenous DNP
polarizing agent
spin decoherence
spin diffusion
spin diffusion barrier
spin dynamics
transition metal EPR
vanadium DNP

ASJC Scopus subject areas

General Chemistry
Biochemistry
Environmental Chemistry
General Chemical Engineering
Biochemistry, medical
Materials Chemistry

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10.1016/j.chempr.2020.10.021

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@article{a355bca3438c42efa7ad034a6b530317,

title = "Dynamic Nuclear Polarization with Vanadium(IV) Metal Centers",

abstract = "Dynamic nuclear polarization (DNP) harnesses the large polarization of electron spins to dramatically increase nuclear magnetic resonance (NMR) sensitivity. This study expands the scope of DNP beyond its traditional focus on hyperpolarizing the solvent network using exogenous polarizing agents (PAs). We introduce 1H DNP with endogenous V4+ centers positioned in a set of vanadyl complexes with tunable V4+-1H distances. We traced the polarization transfer from V4+ to 1H spins, specifically differentiating between direct V4+-1Hs polarization transfer and the 1H spin-diffusion-mediated bulk solvent 1H polarization buildup and illuminated the effect of the V4+-1H distance on these processes. These results deepen our understanding of polarization pathways and expand the catalog of PAs to broad-line transition metals. This study establishes crucial first steps toward employing strategically positioned endogenous paramagnetic metal centers for DNP and the conceptual framework of hyperfine DNP spectroscopy that merges both spatial and chemical diagnosis of target nuclear spins. Dynamic nuclear polarization (DNP) offers a strategy to amplify the inherently insensitive nuclear magnetic resonance (NMR) signal by orders of magnitude, dramatically enhancing the NMR studies of molecules and materials. To date, most DNP studies have relied on exogenous polarizing agents (PAs) with narrow electron paramagnetic resonance (EPR) lines. Expanding the catalog of PAs to paramagnetic centers at the core of active sites in enzymes and functional materials will offer the opportunity to illuminate the local structure around these metal centers during chemical transformations. This study is the first demonstration of DNP using V4+ centers with broad EPR lines as PAs to enhance and detect the NMR signal of 1H nuclei at discrete distances from the V4+ center. These results pave the way toward endogenous DNP studies of active molecules and materials in which paramagnetic metals play key functional roles. We demonstrate dynamic nuclear polarization (DNP) with a set of complexes with controlled V4+-1H distances and gain mechanistic insight into DNP. DNP from the paramagnetic V4+center directly polarized 1H nuclei located 12.6 {\AA} from the electronic spin. Critically, we find the buildup rate of polarization is dependent on the separation of the 1H from the V4+center. These results lay the foundation for endogenous DNP studies of systems in which intrinsic paramagnetic metals serve as the polarizing agent.",

keywords = "SDG3: Good health and well-being, coordination chemistry, direct DNP, endogenous DNP, polarizing agent, spin decoherence, spin diffusion, spin diffusion barrier, spin dynamics, transition metal EPR, vanadium DNP",

author = "Jain, {Sheetal Kumar} and Yu, {Chung Jui} and Wilson, {Christopher Blake} and Tarnuma Tabassum and Freedman, {Danna E.} and Songi Han",

note = "Funding Information: We thank Dr. Asif Equbal for performing the quantum mechanical simulations using SpinEvolution shown in Figure S10 . We are thankful to Dr. Ilia Kaminker for the fruitful discussions on the experimental data and manuscript. We thank M.J. Graham and K.A. Collins for experimental assistance. D.E.F. and C.-J.Y. acknowledge NSF CHE-1455017 for funding the synthetic component of this research. S.K.J., T.T., and S.H. acknowledge the NSF CHE-2004217 for DNP method development, and B.W. and S.H. acknowledge NSF MCB-1617025 for EPR studies at 240 GHz. Part of this work was performed at the ITST Terahertz Facilities at UCSB, which have been upgraded under NSF award no. DMR-1126894 . Funding Information: We thank Dr. Asif Equbal for performing the quantum mechanical simulations using SpinEvolution shown in Figure S10. We are thankful to Dr. Ilia Kaminker for the fruitful discussions on the experimental data and manuscript. We thank M.J. Graham and K.A. Collins for experimental assistance. D.E.F. and C.-J.Y. acknowledge NSF CHE-1455017 for funding the synthetic component of this research. S.K.J. T.T. and S.H. acknowledge the NSF CHE-2004217 for DNP method development, and B.W. and S.H. acknowledge NSF MCB-1617025 for EPR studies at 240 GHz. Part of this work was performed at the ITST Terahertz Facilities at UCSB, which have been upgraded under NSF award no. DMR-1126894. Conceptualization, S.K.J. C.-J.Y. D.E.F. and S.H.; Methodology, S.K.J. C.-J.Y. B.W. and T.T.; Writing-Original Draft S.K.J. C.-J.Y. D.E.F. and S.H.; Visualization S.K.J. and C.-J.Y.; Supervision D.E.F. and S.H.; Funding Acquisition D.E.F. and S.H. The authors declare no competing interests. Publisher Copyright: {\textcopyright} 2020 Elsevier Inc.",

year = "2021",

month = feb,

day = "11",

doi = "10.1016/j.chempr.2020.10.021",

language = "English (US)",

volume = "7",

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journal = "Chem",

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T1 - Dynamic Nuclear Polarization with Vanadium(IV) Metal Centers

AU - Jain, Sheetal Kumar

AU - Yu, Chung Jui

AU - Wilson, Christopher Blake

AU - Tabassum, Tarnuma

AU - Freedman, Danna E.

AU - Han, Songi

N1 - Funding Information: We thank Dr. Asif Equbal for performing the quantum mechanical simulations using SpinEvolution shown in Figure S10 . We are thankful to Dr. Ilia Kaminker for the fruitful discussions on the experimental data and manuscript. We thank M.J. Graham and K.A. Collins for experimental assistance. D.E.F. and C.-J.Y. acknowledge NSF CHE-1455017 for funding the synthetic component of this research. S.K.J., T.T., and S.H. acknowledge the NSF CHE-2004217 for DNP method development, and B.W. and S.H. acknowledge NSF MCB-1617025 for EPR studies at 240 GHz. Part of this work was performed at the ITST Terahertz Facilities at UCSB, which have been upgraded under NSF award no. DMR-1126894 . Funding Information: We thank Dr. Asif Equbal for performing the quantum mechanical simulations using SpinEvolution shown in Figure S10. We are thankful to Dr. Ilia Kaminker for the fruitful discussions on the experimental data and manuscript. We thank M.J. Graham and K.A. Collins for experimental assistance. D.E.F. and C.-J.Y. acknowledge NSF CHE-1455017 for funding the synthetic component of this research. S.K.J. T.T. and S.H. acknowledge the NSF CHE-2004217 for DNP method development, and B.W. and S.H. acknowledge NSF MCB-1617025 for EPR studies at 240 GHz. Part of this work was performed at the ITST Terahertz Facilities at UCSB, which have been upgraded under NSF award no. DMR-1126894. Conceptualization, S.K.J. C.-J.Y. D.E.F. and S.H.; Methodology, S.K.J. C.-J.Y. B.W. and T.T.; Writing-Original Draft S.K.J. C.-J.Y. D.E.F. and S.H.; Visualization S.K.J. and C.-J.Y.; Supervision D.E.F. and S.H.; Funding Acquisition D.E.F. and S.H. The authors declare no competing interests. Publisher Copyright: © 2020 Elsevier Inc.

PY - 2021/2/11

Y1 - 2021/2/11

N2 - Dynamic nuclear polarization (DNP) harnesses the large polarization of electron spins to dramatically increase nuclear magnetic resonance (NMR) sensitivity. This study expands the scope of DNP beyond its traditional focus on hyperpolarizing the solvent network using exogenous polarizing agents (PAs). We introduce 1H DNP with endogenous V4+ centers positioned in a set of vanadyl complexes with tunable V4+-1H distances. We traced the polarization transfer from V4+ to 1H spins, specifically differentiating between direct V4+-1Hs polarization transfer and the 1H spin-diffusion-mediated bulk solvent 1H polarization buildup and illuminated the effect of the V4+-1H distance on these processes. These results deepen our understanding of polarization pathways and expand the catalog of PAs to broad-line transition metals. This study establishes crucial first steps toward employing strategically positioned endogenous paramagnetic metal centers for DNP and the conceptual framework of hyperfine DNP spectroscopy that merges both spatial and chemical diagnosis of target nuclear spins. Dynamic nuclear polarization (DNP) offers a strategy to amplify the inherently insensitive nuclear magnetic resonance (NMR) signal by orders of magnitude, dramatically enhancing the NMR studies of molecules and materials. To date, most DNP studies have relied on exogenous polarizing agents (PAs) with narrow electron paramagnetic resonance (EPR) lines. Expanding the catalog of PAs to paramagnetic centers at the core of active sites in enzymes and functional materials will offer the opportunity to illuminate the local structure around these metal centers during chemical transformations. This study is the first demonstration of DNP using V4+ centers with broad EPR lines as PAs to enhance and detect the NMR signal of 1H nuclei at discrete distances from the V4+ center. These results pave the way toward endogenous DNP studies of active molecules and materials in which paramagnetic metals play key functional roles. We demonstrate dynamic nuclear polarization (DNP) with a set of complexes with controlled V4+-1H distances and gain mechanistic insight into DNP. DNP from the paramagnetic V4+center directly polarized 1H nuclei located 12.6 Å from the electronic spin. Critically, we find the buildup rate of polarization is dependent on the separation of the 1H from the V4+center. These results lay the foundation for endogenous DNP studies of systems in which intrinsic paramagnetic metals serve as the polarizing agent.

AB - Dynamic nuclear polarization (DNP) harnesses the large polarization of electron spins to dramatically increase nuclear magnetic resonance (NMR) sensitivity. This study expands the scope of DNP beyond its traditional focus on hyperpolarizing the solvent network using exogenous polarizing agents (PAs). We introduce 1H DNP with endogenous V4+ centers positioned in a set of vanadyl complexes with tunable V4+-1H distances. We traced the polarization transfer from V4+ to 1H spins, specifically differentiating between direct V4+-1Hs polarization transfer and the 1H spin-diffusion-mediated bulk solvent 1H polarization buildup and illuminated the effect of the V4+-1H distance on these processes. These results deepen our understanding of polarization pathways and expand the catalog of PAs to broad-line transition metals. This study establishes crucial first steps toward employing strategically positioned endogenous paramagnetic metal centers for DNP and the conceptual framework of hyperfine DNP spectroscopy that merges both spatial and chemical diagnosis of target nuclear spins. Dynamic nuclear polarization (DNP) offers a strategy to amplify the inherently insensitive nuclear magnetic resonance (NMR) signal by orders of magnitude, dramatically enhancing the NMR studies of molecules and materials. To date, most DNP studies have relied on exogenous polarizing agents (PAs) with narrow electron paramagnetic resonance (EPR) lines. Expanding the catalog of PAs to paramagnetic centers at the core of active sites in enzymes and functional materials will offer the opportunity to illuminate the local structure around these metal centers during chemical transformations. This study is the first demonstration of DNP using V4+ centers with broad EPR lines as PAs to enhance and detect the NMR signal of 1H nuclei at discrete distances from the V4+ center. These results pave the way toward endogenous DNP studies of active molecules and materials in which paramagnetic metals play key functional roles. We demonstrate dynamic nuclear polarization (DNP) with a set of complexes with controlled V4+-1H distances and gain mechanistic insight into DNP. DNP from the paramagnetic V4+center directly polarized 1H nuclei located 12.6 Å from the electronic spin. Critically, we find the buildup rate of polarization is dependent on the separation of the 1H from the V4+center. These results lay the foundation for endogenous DNP studies of systems in which intrinsic paramagnetic metals serve as the polarizing agent.

KW - SDG3: Good health and well-being

KW - coordination chemistry

KW - direct DNP

KW - endogenous DNP

KW - polarizing agent

KW - spin decoherence

KW - spin diffusion

KW - spin diffusion barrier

KW - spin dynamics

KW - transition metal EPR

KW - vanadium DNP

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DO - 10.1016/j.chempr.2020.10.021

M3 - Article

AN - SCOPUS:85096844793

SN - 2451-9308

VL - 7

SP - 421

EP - 435

JO - Chem

JF - Chem

IS - 2

ER -

Dynamic Nuclear Polarization with Vanadium(IV) Metal Centers

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