Relathionship Between the Excited State Relaxation Paths of Rhodopsin and Isorhodopsin
- STRAMBI A
- B. COTO P
- FRUTOS L. M
- FERRÉ N
- OLIVUCCI, MASSIMO
DOIAbstract
The pigment Isorhodopsin, an analogue of the visual pigment Rhodopsin, is investigated via quantum-mechanics/molecular-mechanics computations based on an ab initio multiconfigurational quantum chemical treatment. The limited <5 kcal mol-1 error found for the spectral parameters allows for a nearly quantitative analysis of the excited-state structure and reactivity of its 9-cis-retinal chromophore. We demonstrate that, similar to Rhodopsin, Isorhodopsin features a shallow photoisomerization path. However, the structure of the reaction coordinate appears to be reversed. In fact, while the coordinate still corresponds to an asynchronous crankshaft motion, the dominant isomerization component involves a counterclockwise, rather than clockwise, ...
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