title: Investigating excited state dynamics of salinixanthin and xanthorhodopsin in the near-infrared.
abstract: Excited state dynamics of native Xanthorhodopsin (XR), of an XR sample with a reduced prosthetic group, and of the associated Carotenoid (CAR) salinixanthin (SX) in ethanol were investigated by hyperspectral Near Infrared (NIR) probing. Global kinetic analysis shows that: (1) unlike the transient spectra recorded in the visible, fitting of the NIR data requires only two phases of exponential spectral evolution, assigned to internal conversion from S(2) → S(1) and from S(1) → S(0) of the carotene. (2) The rate of the internal conversion from S(2) → S(1) in the reduced sample is well fit with a decay time of 130 fs, significantly longer than in XR and in SX, both of which are well fit with τ ≈ 100 fs. This increased lifetime is consistent with a ∼30% efficiency of ET from SX to retinal in XR. (3) S(1) of salinixanthin is verified to lie ∼12,700 cm(-1) above the ground electronic surface, excluding its involvement in the retinal sensitization in XR. (4) The oscillator strength of the S(1) → S(2) transition is determined to be no more than 0.16, despite its symmetry allowedness. (5) No long lived NIR absorbance decay assignable to the carotenoid S* state was detected in any of the samples. Inconsistencies concerning previously determined S(2) lifetimes and kinetic schemes used to model these data are discussed.
authors.affiliation: Institute of Chemistry and The Farkas Center for Light Induced Processes, The Hebrew University, Jerusalem 91904, Israel.
authors.forename: Itay
authors.initials: I
authors.lastname: Gdor
authors.forename: Jingyi
authors.initials: J
authors.lastname: Zhu
authors.forename: Boris
authors.initials: B
authors.lastname: Loevsky
authors.forename: Elena
authors.initials: E
authors.lastname: Smolensky
authors.forename: Noga
authors.initials: N
authors.lastname: Friedman
authors.forename: Mordechai
authors.initials: M
authors.lastname: Sheves
authors.forename: Sanford
authors.initials: S
authors.lastname: Ruhman
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry*; D002338:Carotenoids / Q000737:chemistry*; D002942:Circular Dichroism; D000431:Ethanol / Q000737:chemistry; D006027:Glycosides / Q000737:chemistry*; D007700:Kinetics; D025604:Rhodopsins, Microbial / Q000737:chemistry*; D019265:Spectroscopy, Near-Infrared
chemical_list: D001426:Bacterial Proteins; D006027:Glycosides; D025604:Rhodopsins, Microbial; C470489:salinixanthin; C519152:xanthorhodopsin, Salinibacter; D002338:Carotenoids; D000431:Ethanol