Higher resolution relaxometry with pure-shift NMR

High-resolution relaxometry (HRR) is an NMR method to investigate multiscale dynamics of chemical and biological systems, giving access to spin relaxation over orders of magnitude of magnetic field while maintaining the resolution and sensitivity of high-field NMR. We have recently shown that proton high-resolution relaxometry could identify transient interactions of small molecules with macromolecules in complex mixtures such as blood serum and recover atom-specific information. Yet, proton spectra of such mixtures can suffer from severe signal overlaps due to multiplet patterns from scalar couplings. Here, we introduce a pure shift-based experiment to measure site-specific longitudinal relaxation rates with enhanced resolution. We illustrate this pure-shift approach by detecting the differential binding of amino acids to a protein with a sample-shuttle system covering magnetic fields from 36 mT to 14.1 T installed on a conventional 600 MHz NMR spectrometer.