Long-Lived Nuclear Spin States in Methyl Groups and Quantum-Rotor-Induced Polarization

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• 作者：Benno Meier ; Jean-Nicolas Dumez ; Gabriele Stevanato ; Joseph T. Hill-Cousins ; Soumya Singha Roy ; P盲r H氓kansson ; Salvatore Mamone ; Richard C. D. Brown ; Giuseppe Pileio ; Malcolm H. Levitt
• 刊名：Journal of the American Chemical Society
• 出版年：2013
• 出版时间：December 18, 2013
• 年：2013
• 卷：135
• 期：50
• 页码：18746-18749
• 全文大小：257K
• 年卷期：v.135,no.50(December 18, 2013)
• ISSN：1520-5126

文摘

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 T₁. The states become long-lived through rapid internal rotation of the CH₃ group, which imposes an approximate symmetry on the fluctuating nuclear spin interactions. In the case of very low CH₃ 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 ¹³C-纬-picoline (Icker, M.; Berger, S. J. Magn. Reson. 2012, 219, 1鈥?).