1 research outputs found
Long-Lived Nuclear Spin States in Methyl Groups and Quantum-Rotor-Induced Polarization
Substances containing rapidly rotating
methyl groups may exhibit
long-lived states (LLSs) in solution, with relaxation times substantially
longer than the conventional spin-lattice relaxation time <i>T</i><sub>1</sub>. The states become long-lived through rapid
internal rotation of the CH<sub>3</sub> group, which imposes an approximate
symmetry on the fluctuating nuclear spin interactions. In the case
of very low CH<sub>3</sub> rotational barriers, a hyperpolarized LLS
is populated by thermal equilibration at liquid helium temperature.
Following dissolution, cross-relaxation of the hyperpolarized LLS,
induced by heteronuclear dipolar couplings, generates strongly enhanced
antiphase NMR signals. This mechanism explains the NMR signal enhancements
observed for <sup>13</sup>C-γ-picoline (Icker, M.; Berger, S. <i>J. Magn. Reson.</i> <b>2012</b>, <i>219</i>,
1–3)