engleski

Solvent dependent dynamics of the retinal chromophore

The all-trans protonated Schiff base of retinal (at-PSBR) is the chromophore of bacteriorhodopsin. The light triggered isomerization of the chromophore in the protein pocket is ultrafast (~500 fs), occurs with high quantum yield (0.64) and is highly specific (13-cis PSBR is the main photoproduct). In the solution, the quantum yield is lower (0.27 and 0.17 in CH3CN and CH2Cl2 (DCM), respectively), the isomerization dynamics is slower (~4 ps) and less specific (11-cis PSBR is dominant product). Recent pump-dump-probe experiments have demonstrated that the initially excited S1 state of PSBR relaxes to the ground state via one reactive and one or two nonreactive channels depending on the solvent. Ground state molecular dynamics simulations, multidimensional anharmonic frequency calculations and IR titration experiments have shown that the all-trans Schiff base of retinal (nSBR) and the trifluoroacetic acid (TFA) form ion pairs in DCM. TDDFT based QM/MM nonadiabatic dynamics simulations of at-PSBR with explicit TFA- counter-ions in DCM revealed the origin of the fast non-reactive channel as charge transfer from the hydrogen bonded TFA- to the chromophore backbone. The analysis of nonadiabatic dynamics trajectories indicate that the rotation of the β-ionone ring and concomitant dynamics of a n-butyl tail might be responsible for the slow nonreactive relaxation.

protonated Schiff base of retinal; nonadiabatic dynamics

http://chemie.uni-erlangen.de/stc2013/