Physical Chemistry Seminar: Understanding Isomerization - Insight from hybrid QM/MM molecular dynamics simulations

Abstract:

The primary event of vision in the vertebrate eye is the highly selective and efficient photoisomerization of 11-cis-retinal protonated Schiff base (RPSB) bound to the visual protein rhodopsin (Rh). With a ~100% selectivity, ~65% quantum yield, and ~200 fs product appearance time, this isomerization is considered the archetype of a photochemical reaction optimized by nature to achieve a specific molecular response.

Recently, we have used a combination of a quantum chemical and a classical force field method (QM/MM) to resolve the isomerization mechanism for the RPSB chromophore in Rh[1]. Important stereoelectronic factors were found that determine the outcome of the photoisomerization. The same protocol was also applied to investigate the photochemical mechanism of the newly discovered Anabaena Sensory Rhodopsin[2] and of a biomimetic molecular switch that works in solution[3].

Using the same computational protocol we have also studied the ground state (thermal) isomerization.[4] The results of the simulations explain the molecular mechanism of thermal noise in rod photoreceptors and make a direct link to experimentally found correlations for night vision.