Capturing Excited States in the Fast-Intermediate Exchange Limit in Biological Systems Using 1 H NMR Spectroscopy.

Changes in molecular structure are essential for the function of biomolecules. Characterization of these structural fluctuations can illuminate alternative states and help in correlating structure to function. NMR relaxation dispersion (RD) is currently the only method for detecting these alternative, high-energy states. In this study, we present a versatile 1 H R1ρ RD experiment that not only extends the exchange timescales at least three times beyond the rate limits of 13 C/15 N R1ρ and ten times for CPMG experiments, but also makes use of easily accessible probes, thus allowing a general description of biologically important excited states. This technique can be used to extract chemical shifts for the structural characterization of excited states and to elucidate complex excited states.