Picosecond Time-Resolved Resonance Raman Spectroscopy of Bacteriorhodopsin Intermediates

The time-resolved resonance Raman (TR 3 ) spectra of structural and conformational intermediates of retinal formed within the first 40 ps after the bacteriorhodopsin (BR) photocycle is initiated are presented. The assignment of the carbon-carbon single bond stretching (fingerprint) and hydrogen-out-of plane (HOOP) regions of these TR 3 spectra have shown that the C7 - C 15 hydrocarbon chain is twisted within 10 ps and that isomerization around the C 13 = C 14 bond to form 13-cis retinal occurs over a period as long as 40 ps. Single laser picosecond TR 3 (PTR 3 ) spectroscopy was used to examine these intermediates as a function of laser intensity while two laser PTR 3 spectroscopy characterized the BR intermediates with respect to reaction time.