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Abstract
Monodeuterated methyl groups may support a long-lived nuclear spin state, with a relaxation time exceeding the conventional spin-lattice relaxation time T1. Dissolution-DNP (dynamic nuclear polarization) may be used to hyperpolarize such a long-lived spin state. This is demonstrated for the CH2D groups of a piperidine derivative. The polarized sample is manipulated in the ambient magnetic field of the laboratory, without destruction of the hyperpolarized singlet order. Strongly enhanced CH2D signals are observed more than one minute after dissolution, even in the presence of paramagnetic radicals, by which time the NMR signal from the hyperpolarized proton magnetization has completely disappeared.
Highlights
Conventional nuclear magnetic resonance (NMR) experiments are limited by low sensitivity and weak signals
Enhanced CH2D signals are observed more than one minute after dissolution, even in the presence of paramagnetic radicals, by which time the NMR signal from the hyperpolarized proton magnetization has completely disappeared
This comparison gave the following estimate of the Zeeman polarization level in the solid-state, prior to dissolution: psZolid = À59 Æ 5%, see the Electronic supplementary information (ESI);† (ii) it was assumed that the Zeeman polarization is substantially preserved through the dissolution process, so that pZ(0) C psZolid, where pZ(0) is the Zeeman polarization immediately after dissolution; (iii) the thermal equilibrium Zeeman polarization for protons in a field of 11.7 Tesla and temperature of T = 300 Kelvin is governed by the Boltzmann distribution, and is given by peZq = hgB0/2kBT = 39.8 Â 10À6
Summary
Conventional nuclear magnetic resonance (NMR) experiments are limited by low sensitivity and weak signals. Hyperpolarization techniques such as dynamic nuclear polarization (DNP) enhance NMR signals by several orders of magnitude,[1,2,3,4,5] with applications to ligand-binding, drug transport and metabolic tracing.[6,7,8,9,10,11,12,13,14,15] applications of hyperpolarized NMR are strongly limited by the decay of polarization in solution, characterised by the spin– lattice relaxation time T1. Values of TS exceeding 1 hour in room temperature solution have been reported for 13C spin pairs.[29]
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