Relationship between the Excited State Relaxation Paths of Rhodopsin and Isorhodopsin

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• 作者：Angela Strambi ; Pedro B. Coto ; Luis Manuel Frutos ; Nicolas Ferr&eacute ; Massimo Olivucci
• 刊名：Journal of the American Chemical Society
• 出版年：2008
• 出版时间：March 19, 2008
• 年：2008
• 卷：130
• 期：11
• 页码：3382 - 3388
• 全文大小：300K
• 年卷期：v.130,no.11(March 19, 2008)
• ISSN：1520-5126

文摘

The pigment Isorhodopsin, an analogue of the visual pigment Rhodopsin, is investigated viaquantum-mechanics/molecular-mechanics computations based on an ab initio multiconfigurational quantumchemical treatment. The limited <5 kcal mol^-1 error found for the spectral parameters allows for a nearlyquantitative analysis of the excited-state structure and reactivity of its 9-cis-retinal chromophore. Wedemonstrate 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 correspondsto an asynchronous crankshaft motion, the dominant isomerization component involves a counterclockwise,rather than clockwise, twisting of the 9-cis bond. Similarly, the minor component involves a clockwise,rather than counterclockwise, twisting of the 11-trans bond. Ultimately, these results indicate that Rhodopsinand 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 intersectionspace between the ground and excited states of the protein explains why the pigments decay at distinctiveconical intersection structures.