Mechanisms of coherent re-arrangement for long-lived spin order

Abstract

Abstract. Long-lived spin order-based approaches for magnetic resonance rely on the transition between two magnetic environments of different symmetry, one governed by the magnetic field of the spectrometer and the other where this strong magnetic field is inconsequential. Research on the excitation of magnetic-symmetry transitions in nuclear spins is a scientific field that debuted in Southampton in the years 2000. We advanced in this field carrying the baggage of pre-established directions in NMR spectroscopy. We propose to reveal in this text the part of discoveries that may have been obscured by our choice to only look at them through the experience of such pre-established directions, at the time. Focussing on potential applications, we may have insufficiently emphasised in the manuscripts the methodological developments that necessitated most scientific effort. Such methods developments foster most of the progress in NMR. Thus, we present the contributed mechanisms of translation between the symmetric and non-symmetric environments with respect to the main magnetic field B0, free of any utilitarian perspective. The concept of zero-quantum rotations in the starting blocks of long-lived state populations, magnetisation transfers between hyperpolarised heteronuclei and protons, and selective inversion for long-lived coherences are discussed, as well as hybrid 2D methods based on both insensitive nuclei excitation (“INEPT”) and long-lived spin order. We can see at this point that these magnetic wheels will take a longer time than we initially thought to set in motion new applications in studies of slow diffusion, angiography, or large-protein structure. However, these pulse sequences seed subsequent magnetic mechanisms that are sure to contribute to applications. For instance, some of the introduced coherence rotations were combined with classical pulse blocks to obtain 2D correlations between protons and heteronuclei. We hope the pulse sequence building blocks discussed herein open further perspectives for magnetic resonance experiments with long-lived spin order.