Fast 2D NMR and Hyperpolarization

Abstract

This chapter presents an overview of both the methodology and applications of fast two-dimensional (2D) NMR using nuclear spin hyperpolarization. Fast 2D NMR methods extend the information available from NMR experiments through spin correlations while allowing the utilization of large signals from hyperpolarized spins for the study of fast processes. Hyperpolarization methods typically provide orders of magnitude in NMR signal enhancement. In many cases, however, the mechanism of generating hyperpolarization imposes a technical limit on the number of repetitions of an experiment. Conventional multi-dimensional NMR methods, which rely on re-polarization of spins between each scan, are therefore not directly applicable. Two-dimensional or pseudo 2D NMR experiments can nevertheless be implemented using specific techniques such as ultrafast pulsed-field gradient encoding, sequential scanning with scan-to-scan preservation of spin polarization, or off-resonance decoupling. Intermolecular or intramolecular spin polarization transfer and the observation of correlations between reactants and products can be integrated into these experiments. These and other techniques can be used for the determination of mechanisms in fast chemical reactions or the elucidation of molecular interactions. Applications targeting small molecules, as well as biological macromolecules, protein structure, and protein folding, have been demonstrated.