Analysis of the mode-specific excited-state energy distribution and wavelength-dependent photoreaction quantum yield in rhodopsin.
The photoreaction quantum yield of rhodopsin is wavelength dependent: phi(lambda) is reduced by up to 5% at wavelengths to the red of 500 nm but is invariant (phi = 0.65 +/- 0.01) between 450 and 500 nm (Kim et al., 2001). To understand this nonstatistical internal conversion process, these results are compared with predictions of a Landau-Zener model for dynamic curve crossing. The initial distribution of excess photon energy in the 28 Franck-Condon active vibrational modes of rhodopsin is defined by a fully thermalized sum-over-states vibronic calculation. This calculation reveals that absorption by high-frequency unreactive modes (e.g., C[double bond]C stretches) increases as the excitation wavelength is shifted from 570 to 450 nm whereas relatively less energy is deposited into reactive low-frequency modes. This result qualitatively explains the experimentally observed wavelength dependence of phi(lambda) for rhodopsin and reveals the importance of delocalized, torsional modes in the reactive pathway.
Kim
Judy E
JE
Department of Chemistry, University of California at Berkeley, Berkeley, California 94720 USA.
Tauber
Michael J
MJ
Mathies
Richard A
RA
D003198:Computer Simulation; D004307:Dose-Response Relationship, Radiation; D004735:Energy Transfer; D008027:Light; D008958:Models, Molecular; D012243:Rhodopsin / Q000737:chemistry* / Q000528:radiation effects*
D012243:Rhodopsin