The transition state in the isomerization of rhodopsin

We present an ab-initio molecular dynamics study of a model of the chromophore of rhodopsin. The 11-cis to all-trans ground-state isomerization of a retinylidene–ethylimine·HCl has been induced by applying an external classical force field to the C10–C11–C12–C13 dihedral angle, in addition to the ab-initio forces. By using this hybrid approach, we find that the transition state is characterized by a well-defined bond pattern along the chromophore and by a positive charge displacement. The relaxation of the chromophore is associated with propagation of a conjugation defect that transports the excess positive charge along the backbone.