Trajectory-Based Approach for the Analysis of CODEX Solid-State Exchange Experiments in the Slow and Intermediate Motion Regime: Comparison of Experiment, Simulation, and Analytical Treatment

We present an efficient approach to analyze CODEX-MAS exchange NMR data by comparing the experimental results with simulated data that are calculated from separately simulated motional trajectories rather than by application of the classic rate-equation approach. The trajectories can be calculated by random-walk simulations of dynamic processes of arbitrary motional geometries and distributions of exchange rates or taken from the result of MD simulations. The necessary computation time of this approach is independent of the complexity of the model and is particularly well-suited for the description of diffusive motions and/or complex models. It can also easily be expanded to intermediate motions. After comparison of trajectory and rate-equation approach, we discuss different dynamic models of discrete and diffusive motions and present applications to the model substance DMS and to scenarios that are applicable to polymeric or biological systems. As a proof of principle, we also calculate exchange-NMR data directly from a MD calculation of lipids; however, we adjusted its time scale to meet the dynamic range of the CODEX experiment.