Abstract: We propose an explanation of the previously reported SABRE (Signal Amplification By Reversible Exchange) effect at high magnetic fields, observed in the absence of RF-excitation and relying only on “spontaneous” polarization transfer from parahydrogen (pH2, the H2 molecule in its nuclear singlet spin state) to a SABRE substrate. We propose a detailed mechanism for spontaneous polarization transfer and show that it is comprised of three steps: (i) Generation of the anti-phase I ̂ 1 z I ̂ 2 z spin order of catalyst-bound H2; (ii) spin order conversion I ̂ 1 z I ̂ 2 z → ( I ̂ 1 z + I ̂ 2 z ) due to cross-correlated relaxation, leading to net polarization of H2; (iii) polarization transfer to the SABRE substrate, occurring due to NOE. Formation of anti-phase polarization is due to singlet-to-T0 mixing in the catalyst-bound form of H2, while cross-correlated relaxation originates from fluctuations of dipole-dipole interactions and chemical shift anisotropy. The proposed mechanism is supported by a theoretical treatment, magnetic field-dependent studies and high-field NMR measurements with both pH2 and thermally polarized H2.

Cite: Knecht S. , Kiryutin A.S. , Yurkovskaya A.V. , Ivanov K.L.
Mechanism of spontaneous polarization transfer in high-field SABRE experiments
Journal of Magnetic Resonance. 2018. V.287. P.74-81. DOI: 10.1016/j.jmr.2017.12.018

Dates:

Submitted:	Nov 8, 2017
Accepted:	Dec 24, 2017
Published online:	Dec 26, 2017

Identifiers: No identifiers

Citing: Пока нет цитирований

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