Protein Induced Torsion of the Retinal Chromophore and How it Affects the Photochemistry of Rhopdopsin

The influence of protein induced chromophore deformations on reaction timescale and quantum yield is investigated using ab initio molecular dynamics in vacuo on four and five double bond models of the retinal chromophore. The opposite twist of the C11 = C12 and the C12-C13 bonds appears to be the prerequisite for the highly stereoselective and efficient cis-trans photodynamics of the retinal chromophore in the binding pocket of rhodopsin. The formation of the photoproduct is determined by the phase of the hydrogen out-of-plane mode of the 11-cis double bond