Efficient Through-Bond Propagation of Nuclear-Spin Hyperpolarization via TOCSY-Enhanced LC-Photo-CIDNP

Nuclear magnetic resonance (NMR) spectroscopy provides atomic-resolution insights into biomolecular structure, dynamics and interactions under non-perturbative conditions. However, the widespread applicability of this technique continues to be limited by its intrinsically low sensitivity. This drawback is particularly severe in the case of concentration-limited samples. Low-concentration photochemically induced dynamic nuclear polarization (LC-photo-CIDNP) is an optically enhanced NMR hyperpolarization strategy capable of boosting NMR sensitivity in situ by several orders of magnitude under physiologically relevant environments. Yet, the inherent nature of the LC-photo-CIDNP phenomenon confines the achievable enhancements to only a subset of nuclei, thus limiting the extent of attainable residue-specific information. Here, we overcome this shortcoming by integrating LC-photo-CIDNP with Total Correlation Spectroscopy (TOCSY) to propagate initial hyperpolarization to other nuclei via scalar-coupled spin networks. First, we demonstrate efficient through-bond transfer of LC-photo-CIDNP enhanced signals throughout entire intramolecular atomic frameworks via 1D ¹ H- and ¹³ C-detected experiments. Second, we extend the approach to a model protein and demonstrate efficient polarization transfer via 1D and 2D ¹ H-detected ¹³ C-TOCSY LC-photo-CIDNP. Intrinsically photo-CIDNP-inactive nuclei can thus be visualized via ¹³ C- ¹ H correlations within minutes down to 10 μM concentration. In all, this work establishes a general strategy to achieve through-bond propagation of LC-photo-CIDNP hyperpolarization. This technology enables gaining residue-specific structural insights on amino acids and proteins at previously unattainable low concentrations.