Field-cycling long-lived-state NMR of ¹⁵N₂ spin pairs

Abstract

A range of nuclear magnetic resonance spectroscopy and imaging applications are limited by the short lifetimes of magnetization in solution. Long-lived states, which are slowly relaxing configurations of nuclear spins, have been shown to alleviate this limitation. Long-lived states have decay lifetimes T LLS significantly exceeding the longitudinal relaxation time T 1 , in some cases by an order of magnitude. Here we present an experimental case of a long-lived state for a 15 N labelled molecular system in solution. We observe a strongly biexponential decay for the long-lived state, with the lifetime of the slowly relaxing component exceeding 40 minutes, ∼21 times longer than the spin-lattice relaxation time T 1. The lifetime of the long-lived state was revealed by using a dedicated two-field NMR spectrometer capable of fast sample shuttling between high and low magnetic fields, and the application of a resonant radiofrequency field at low magnetic field. The relaxation characteristics of the long-lived state are examined.

Generating and sustaining long-lived spin states in 15N,15N′-azobenzene

“…Consequently, the singlet order lifetime, T S , can be much longer than the T 1 -relaxation time of the spin pair, which corresponds to the relaxation time of the longitudinal spin magnetization. Previous works report very large T S / T 1 ratios and T S relaxation times reaching minutes for 1 H spins 20,21 , tens of minutes 22,23 or even more than an hour 24 for pairs of 15 N or 13 C spins. All these examples of extremely long singlet state lifetimes have been found at low magnetic fields.…”

Hyperpolarization of cis‐15N2‐Azobenzene by Parahydrogen at Ultralow Magnetic Fields**

“…An alternative possibility is to store hyperpolarization in a so-called long-lived state (LLS), [9] a state that is immune to certain relaxation mechanisms. The longest relaxation times are observed for singlet order formed within pairs of 15 N spins [2,[10][11][12][13][14] or 13 C spins, [15] and nonequilibrium spin states can exist for up to tens of minutes in liquids at room temperature. The possibility to store hyperpolarization expands the field of applications and has intensified the development of SABRE experiments producing LLS.…”

Generalised magnetisation-to-singlet-order transfer in nuclear magnetic resonance

“…Eqn (9) shows that the mixing angle y ST is the important physical quantity and the effective frequency o e simply rescales the time axis. Define a basis B spanned by the following basis states…”

“…[1][2][3][4][5] In certain cases nuclear long-lived spin order may persist for tens of minutes. [6][7][8][9] The long-lived behaviour of such spin configurations has been integrated into a multitude of experimental protocols. [10][11][12] In the context of diffusion NMR long-lived spin states have enabled the study of previously inaccessible spatial and dynamical regimes.…”