title: Femtosecond coherent transient infrared spectroscopy of reaction centers from Rhodobacter sphaeroides.
abstract: Protein and cofactor vibrational dynamics associated with photoexcitation and charge separation in the photosynthetic reaction center were investigated with femto-second (300-400 fs) time-resolved infrared (1560-1960 cm-1) spectroscopy. The experiments are in the coherent transient limit where the quantum uncertainty principle governs the evolution of the protein vibrational changes. No significant protein relaxation accompanies charge separation, although the electric field resulting from charge separation modifies the polypeptide carbonyl spectra. The potential energy surfaces of the "special pair" P and the photoexcited singlet state P* and environmental perturbations on them are similar as judged from coherence transfer measurements. The vibrational dephasing time of P* modes in this region is 600 fs. A subpicosecond transient at 1665 cm-1 was found to have the kinetics expected for a sequential electron transfer process. Kinetic signatures of all other transient intermediates, P, P*, and P+, participating in the primary steps of photosynthesis were identified in the difference infrared spectra.
authors.affiliation: Department of Chemistry, University of Pennsylvania, Philadelphia 19104.
authors.forename: S
authors.initials: S
authors.lastname: Maiti
authors.forename: G C
authors.initials: GC
authors.lastname: Walker
authors.forename: B R
authors.initials: BR
authors.lastname: Cowen
authors.forename: R
authors.initials: R
authors.lastname: Pippenger
authors.forename: C C
authors.initials: CC
authors.lastname: Moser
authors.forename: P L
authors.initials: PL
authors.lastname: Dutton
authors.forename: R M
authors.initials: RM
authors.lastname: Hochstrasser
mesh_terms: D007700:Kinetics; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000378:metabolism; D012242:Rhodobacter sphaeroides / Q000378:metabolism*; D013055:Spectrophotometry, Infrared; D013997:Time Factors; D014732:Vibration
chemical_list: D045322:Photosynthetic Reaction Center Complex Proteins