Physical interpretation of residual dipolar couplings in neutral aligned media

A novel method is described for rapidly calculating alignment tensors from hydrodynamic shape, required for the prediction of residual dipolar couplings in neutral aligned media. Simulations of alignment were used to show that for steric restriction at a planar surface, the alignment process is dependent on linear hydrodynamic length. However, as discussed, previous methods are not in agreement with this observation. Therefore, the method presented here is the first to provide simple, accurate predictions of the alignment tensor for neutral and dilute media, while being consistent with simulations of alignment. It provides predictions in a fraction of the time of a simulation approach, while aiding physical intuition by providing a direct link between shape and alignment. Not only is this physically gratifying, but it also permits residual dipolar couplings to be applied in demanding situations where simulations of alignment are not desirable, such as in studies of molecular dynamics.