Molecular dynamics monitored by cross-correlated cross relaxation of spins quantized along orthogonal axes

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Abstract
A new approach is proposed for the analysis of molecular dynamics on a wide range of time scales by the measurement of specific cross‐correlated nuclear magnetic resonance cross‐relaxation pathways of spins quantized along orthogonal spin‐lock axes. Cross‐correlated time modulation of (i) chemical shifts and J couplings, and of (ii) dipolar coupling and chemical shielding anisotropy, respectively, are determined using a sensitive technique, called o r t h o‐R O E S Y (orthogonal rotating frames Overhauser effect spectroscopy). The two processes (i) and (ii) can be separated experimentally by their distinct dependence on the spin‐lock radio frequency amplitude. The relaxation rate constant depends on the power spectral density sampled at a frequency close to zero. This renders the experiment attractive for investigations of slowly tumbling (bio)molecules.