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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 magnetisation 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 significantly exceeding the longitudinal relaxation time , in some cases by an order of magnitude. Here we present an experimental case of a long-lived state for a 15N 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 . 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. GRAPHICAL ABSTRACT