Issue 9, 2011

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 S2 → S1 and from S1 → S0 of the carotene. (2) The rate of the internal conversion from S2 → S1 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) S1 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 S1 → S2 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 S2 lifetimes and kinetic schemes used to model these data are discussed.

Graphical abstract: Investigating excited state dynamics of salinixanthin and xanthorhodopsin in the near-infrared

Article information

Article type
Paper
Submitted
06 Sep 2010
Accepted
30 Nov 2010
First published
24 Dec 2010

Phys. Chem. Chem. Phys., 2011,13, 3782-3787

Investigating excited state dynamics of salinixanthin and xanthorhodopsin in the near-infrared

I. Gdor, J. Zhu, B. Loevsky, E. Smolensky, N. Friedman, M. Sheves and S. Ruhman, Phys. Chem. Chem. Phys., 2011, 13, 3782 DOI: 10.1039/C0CP01734E

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