TCB Publications - Abstract

Michal Ben-Nun, Ferenc Molnar, Hui Lu, James C. Phillips, Todd J. Martínez, and Klaus Schulten. Quantum dynamics of retinal's femtosecond photoisomerization in bacteriorhodopsin. In Faraday Discussions, No. 110, pp. 447-462. Faraday Publications, 1998.

BENN98 The membrane protein bacteriorhodopsin contains all-$trans$ retinal in a binding site lined by amino acid side groups and water molecules that guide retinal's photodynamics. Upon absorption of light, retinal undergoes a sub-picosecond all- $trans\rightarrow$ 13-$cis$ phototransformation involving torsion around a double bond. The main reaction product triggers later events in the protein that induce pumping of a proton through bacteriorhodopsin. Quantum-chemical calculations suggest that three coupled electronic states, the ground state and two closely lying excited states, are involved in the motion along the torsional reaction coordinate $\phi$. The evolution of the protein-retinal system on these three electronic surfaces has been modeled using the multiple spawning method for non-adiabatic dynamics. We find that although most of the population transfer occurs on a time scale of 300 fs, some population transfer occurs on a longer time scale, occasionally extending well beyond 1 ps. The simulations predict that the photoisomerization quantum yield is 48%, in reasonable accord with experimental observation.

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