Theory of long-lived nuclear spin states in methyl groups and quantum-rotor induced polarisation

Abstract

Long-lived nuclear spin states have a relaxation time much longer than the longitudinal relaxation time T1. Long-lived states extend significantly the time scales that may be probed with magnetic resonance, with possible applications to transport and binding studies, and to hyperpolarised imaging. Rapidly rotating methyl groups in solution may support a long-lived state, consisting of a population imbalance between states of different spin exchange symmetries. Here, we expand the formalism for describing the behaviour of long-lived nuclear spin states in methyl groups, with special attention to the hyperpolarisation effects observed in (13)CH3 groups upon rapidly converting a material with low-barrier methyl rotation from the cryogenic solid state to a room-temperature solution [M. Icker and S. Berger, J. Magn. Reson. 219, 1 (2012)]. We analyse the relaxation properties of methyl long-lived states using semi-classical relaxation theory. Numerical simulations are supplemented with a spherical-tensor analysis, which captures the essential properties of methyl long-lived states.

Symmetry constraints on spin dynamics: Application to hyperpolarized NMR

“…The transformation of total spin magnetization into singlet order, and back again, is an important manipulation in the NMR of long-lived states [13,14,15,16,17,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44] and in parahydrogen-enhanced NMR [18,19,20,21,22,45,46,47,48,49].…”

Long-lived nuclear spin states in rapidly rotating CH 2 D groups

“…We also assume that the overall correlation time τ C is short enough relative to the nuclear Larmor period to invoke the extreme narrowing approximation [40]. A model of this kind was used to treat methyl long-lived states and quantum-rotor-induced polarization in γ-picoline [41,42].…”

Singlet NMR methodology in two-spin-1/2 systems

“…Since its discovery in the Levitt group [24,25,26] a number of research groups have investigated the field of singlet NMR over the past 12 years with the purpose of defining and characterising singlet order relaxation properties [3,27,28,29,30], and the conditions for its existence [31,32,33,34], and of developing the methodology to access singlet order in different magnetic regimes [24,26,35,36,37,38,39,9,40,11,41,42,43] and to demonstrate the existence of long-lived singlet order in multiple-spin systems [44,45,46,47,48,49] and in heteronuclear systems [50]. Significant studies on the chemical requirements for obtaining long-lived spin order have been also conducted [17,51,52,53,54] with a record lifetime of 70 min for a 13 C-pair [54], 26 min for a 15 N-pair [51], and 10 min for a 1 H-pair [17] demonstrated.…”