Storage of nuclear magnetization as long-lived singlet order in low magnetic field
Pileio, Giuseppe, Carravetta, Marina and Levitt, Malcolm H. (2010) Storage of nuclear magnetization as long-lived singlet order in low magnetic field. Proceedings of the National Academy of Sciences, 107, (40), 17135-17139. (doi:10.1073/pnas.1010570107).
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Hyperpolarized nuclear states provide NMR signals enhanced by many orders of magnitude, with numerous potential applications to analytical NMR, in vivo NMR, and NMR imaging. However, the lifetime of hyperpolarized magnetization is normally limited by the relaxation time constant T1, which lies in the range of milliseconds to minutes, apart from in exceptional cases. In many cases, the lifetime of the hyperpolarized state may be enhanced by converting the magnetization into nuclear singlet order, where it is protected against many common relaxation mechanisms. However, all current methods for converting magnetization into singlet order require the use of a high-field, high-homogeneity NMR magnet, which is incompatible with most hyperpolarization procedures. We demonstrate a new method for converting magnetization into singlet order and back again. The new technique is suitable for magnetically inequivalent spin-pair systems in weak and inhomogeneous magnetic fields, and is compatible with known hyperpolarization technology. The method involves audio-frequency pulsed irradiation at the low-field nuclear Larmor frequency, employing coupling-synchronized trains of 180° pulses to induce singlet–triplet transitions. The echo trains are used as building blocks for a pulse sequence called M2S that transforms longitudinal magnetization into long-lived singlet order. The time-reverse of the pulse sequence, called S2M, converts singlet order back into longitudinal magnetization. The method is demonstrated on a solution of 15N-labeled nitrous oxide. The magnetization is stored in low magnetic field for over 30 min, even though the T1 is less than 3 min under the same conditions.
|Keywords:||long-lived spin states, low-field nmr, singlet states|
|Subjects:||Q Science > QC Physics
Q Science > QD Chemistry
|Divisions:||University Structure - Pre August 2011 > School of Chemistry
Faculty of Natural and Environmental Sciences > Chemistry > Magnetic Resonance
|Date Deposited:||24 Mar 2011 14:00|
|Last Modified:||28 Mar 2014 15:18|
Long-Lived Spin States in Nuclear Magnetic Resonance
Funded by: EPSRC (EP/D079209/1)
Led by: Malcolm Harris Levitt
1 May 2007 to 31 October 2010
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