Dominant role of internal rotation in the dissociation of polyatomic ligands from the binding site. The case of opiates

Abstract

An analysis is presented of the dissociation of polyatomic ligands from the binding site, with the focus on the local bond breaking process. The approach is based on the dynamics of the ‘reaction coordinate’ for dissociation of the local bond which is defined on the grounds of previous studies of vibrational energy transfer in encounters of polyatomic molecules. The mass corresponding to the coordinate in question depends crucially on the properties of the internal rotation of the group involved in the local bond, as well as on the geometry of this bond. The model reproduces well the striking relative magnitudes of the experimental dissociation rates of several opiates.