TY - JOUR
T1 - Photoselective ultrafast investigation of xanthorhodopsin and Its carotenoid antenna salinixanthin
AU - Zhu, Jingyi
AU - Gdor, Itay
AU - Smolensky, Elena
AU - Friedman, Noga
AU - Sheves, Mordechai
AU - Ruhman, Sanford
PY - 2010/3/4
Y1 - 2010/3/4
N2 - Excited-state dynamics of xanthorhodopsin (XR) and of salinixanthin (SX) in ethanol were investigated by ultrafast pump-hyperspectral probe spectroscopy. Following excitation to the strongly allowed S2 state of the SX chromophore, transient spectra were recorded photoselectively in the range 430-850 nm. Global kinetic analysis of these data shows the following. (1) Efficient energy transfer from S2 of the SX in XR to its retinal moiety is verified here. The lifetime of S2 in SX is, however, determined to be ∼20 fs, much shorter than previously reported. (2) Branching ratios of excitation transfer from S2 to Si, to S*, and to retinal in XR are measured leading to species associated difference spectra (SADS) for all the states involved. Strong protein effects are detected on these branching probabilities. (3) Si and S* absorption bands in both systems exhibit anisotropy well below the expected r = 0.4, indicating an angle of ∼25° between the S0 → S2 and S1 →- Sn/S* → Sn transition dipoles. The latter allows confident assignment of the debated S* absorption band to an excited state of SX, and not to "hot" S0. In light of the extremely fast IC from S2 to lower excited singlets, possible involvement of ballistic IC in SX, and of coherent energy transfer in XR, are discussed.
AB - Excited-state dynamics of xanthorhodopsin (XR) and of salinixanthin (SX) in ethanol were investigated by ultrafast pump-hyperspectral probe spectroscopy. Following excitation to the strongly allowed S2 state of the SX chromophore, transient spectra were recorded photoselectively in the range 430-850 nm. Global kinetic analysis of these data shows the following. (1) Efficient energy transfer from S2 of the SX in XR to its retinal moiety is verified here. The lifetime of S2 in SX is, however, determined to be ∼20 fs, much shorter than previously reported. (2) Branching ratios of excitation transfer from S2 to Si, to S*, and to retinal in XR are measured leading to species associated difference spectra (SADS) for all the states involved. Strong protein effects are detected on these branching probabilities. (3) Si and S* absorption bands in both systems exhibit anisotropy well below the expected r = 0.4, indicating an angle of ∼25° between the S0 → S2 and S1 →- Sn/S* → Sn transition dipoles. The latter allows confident assignment of the debated S* absorption band to an excited state of SX, and not to "hot" S0. In light of the extremely fast IC from S2 to lower excited singlets, possible involvement of ballistic IC in SX, and of coherent energy transfer in XR, are discussed.
UR - http://www.scopus.com/inward/record.url?scp=77749305134&partnerID=8YFLogxK
U2 - 10.1021/jp910845h
DO - 10.1021/jp910845h
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AN - SCOPUS:77749305134
SN - 1520-6106
VL - 114
SP - 3038
EP - 3045
JO - Journal of Physical Chemistry B
JF - Journal of Physical Chemistry B
IS - 8
ER -