Multiple Quantum Coherences Hyperpolarized at Ultra-Low Fields

We used a home-made ultralow-field (ULF) NMR system for measuring multiple quantum coherences up to the third order via heteronuclear correlated spectroscopy (COSY). The multiple spin orders were generated using signal amplification by reversible exchange (SABE).

Hyperpolarized quantum coherences measured with the ULF COSY experiment (hyperpolarization field = 5.2 mT and static magnetic field = 91 μT): (a) experimental amplitude spectra of 3-Fluoro Pyridine.  is a symbol for QCs, where y is the order of the QC and x indicates the types of nuclei involved. (b) The zoomed out  and  QCs measured at 1H and 19F resonances are shown (indicated by the white rectangles). Red and white dashed lines mark the diagonal and off-diagonal peaks, respectively. Up to third-order coherences were observed. (c) Separation of QCs in the coherence selective ULF COSY experiment: experimental amplitude spectra obtained with four different phase alternating methods (here A – D corresponds to phase cycling schemes.

Modern hyperpolarization technologies, such as e.g. parahydrogen based hyperpolarization techniques, enabled several yet exotic NMR applications at low and ultra-low fields (ULF), where without hyperpolarization even the detection of a signal from analytes is a challenge. We developed a method for the simultaneous excitation and observation of homo- and heteronuclear multiple quantum coherences (from zero up to the third-order), which give an additional degree of freedom for ULF NMR experiments, where the chemical shift variation is negligible. The approach is based on heteronuclear correlated spectroscopy (COSY); its combination with a phasecycling scheme allows the selective observation of multiple quantum coherences (QC) of different orders. The nonequilibrium spin state and multiple spin orders are generated by signal amplification by reversible exchange (SABRE) and detected at ULF with a superconducting quantum interference device (SQUID)-based NMR system.

Buckenmaier K, Scheffler K, Plaumann M, Fehling P, Bernarding J, Rudolph M, Back C, Koelle D, Kleiner R, Hoevener J-B, Pravdivtsev A.:
Multiple quantum coherences hyperpolarized at ultra-low fields.
ChemPhysChem 2019;20:2823.
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