H-1-Detected C-13 Photo-CIDNP as a Sensitivity Enhancement Tool in Solution NMR

NMR is a powerful yet intrinsically insensitive technique. The applicability of NMR to chemical and biological systems would be substantially extended by new approaches going beyond current signal-to-noise capabilities. Here, we exploit the large enhancements arising from C-13 photochemically induced dynamic nuclear polarization (C-13 photo-CIDNP) in solution to improve biomolecular NMR sensitivity in the context of heteronuclear correlation spectroscopy. The C-13-PRINT pulse sequence presented here involves an initial C-13 nuclear spin polarization via photo-CIDNP followed by conversion to anti-phase coherence and transfer to H-1 for detection. We observe substantial enhancements, up to >>200-fold, relative to the dark (laser off) experiment. Resonances of both side-chain and backbone CH pairs are enhanced for the three aromatic residues Trp, His, and Tyr, the sigma(32) peptide, and the drkN SH3 protein. The sensitivity of this experiment, defined as signal-to-noise per square root of unit time (S/N)(t), is unprecedented in the NMR polarization enhancement literature dealing with polypeptides in solution. Up to a 16-fold larger (S/N)(t) than for the H-1-C-13 SE-HSQC reference sequence is achieved, for the sigma(32) peptide. Data collection time is reduced up to 256-fold, highlighting the advantages of H-1-detected C-13 photo-CIDNP in solution NMR.