10.1021/ja0749082.s002
Angela Strambi
Angela
Strambi
Pedro B. Coto
Pedro B.
Coto
Luis Manuel Frutos
Luis Manuel
Frutos
Nicolas Ferré
Nicolas
Ferré
Massimo Olivucci
Massimo
Olivucci
Relationship between the Excited State Relaxation Paths of
Rhodopsin and Isorhodopsin
American Chemical Society
2008
counterclockwise
energy valley
energy region
ab initio multiconfigurational quantum chemical treatment
pigments decay
IsorhodopsinThe pigment Isorhodopsin
isomerization component
asynchronous crankshaft motion
photoisomerization path
pigment Rhodopsin
conical intersection structures
Isorhodopsin features
intersection space
Excited State Relaxation Paths
bond
2008-03-19 00:00:00
Journal contribution
https://acs.figshare.com/articles/journal_contribution/Relationship_between_the_Excited_State_Relaxation_Paths_of_Rhodopsin_and_Isorhodopsin/2950624
The pigment Isorhodopsin, an analogue of the visual pigment Rhodopsin, is investigated via
quantum-mechanics/molecular-mechanics computations based on an <i>ab initio</i> multiconfigurational quantum
chemical treatment. The limited <5 kcal mol<sup>-1</sup> error found for the spectral parameters allows for a nearly
quantitative analysis of the excited-state structure and reactivity of its 9-<i>cis</i>-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, twisting of the 9-<i>cis</i> bond. Similarly, the minor component involves a clockwise,
rather than counterclockwise, twisting of the 11-<i>trans</i> bond. Ultimately, these results indicate that Rhodopsin
and Isorhodopsin relax along a common excited-state potential energy valley starting from opposite ends.
The fact that the central and lowest energy region of such valley runs along a segment of the intersection
space between the ground and excited states of the protein explains why the pigments decay at distinctive
conical intersection structures.