Nonconjugated Acyloxy Group Deactivates the Intramolecular Charge-Transfer State in the Carotenoid Fucoxanthin

0490023 - MBÚ 2019 RIV US eng J - Článek v odborném periodiku
Staleva-Musto, H. - Kuznetsova, V. - West, R.G. - Kesan, G. - Minofar, Babak - Fuciman, M. - Bína, David - Litvín, Radek - Polívka, Tomáš
Nonconjugated Acyloxy Group Deactivates the Intramolecular Charge-Transfer State in the Carotenoid Fucoxanthin.
Journal of Physical Chemistry B. Roč. 122, č. 11 (2018), s. 2922-2930. ISSN 1520-6106. E-ISSN 1520-5207
Grant CEP: GA ČR(CZ) GA16-10417S; GA MŠMT(CZ) LM2015055
Grant ostatní: GA MŠk(CZ) LM2015042
Institucionální podpora: RVO:61388971 ; RVO:60077344
Klíčová slova: EXCITATION-ENERGY TRANSFER * TRANSIENT ABSORPTION-SPECTROSCOPY * NANNOCHLOROPSIS-OCEANICA
Obor OECD: Microbiology; Biophysics (BC-A)
Impakt faktor: 2.923, rok: 2018

We used ultrafast transient absorption spectroscopy to study excited-state dynamics of the keto-carotenoid fucoxanthin (Fx) and its two derivatives: 19'-butanoyloxyfucoxanthin (bFx) and 19'-hexanoyloxyfucoxanthin (hFx). These derivatives occur in some light harvesting systems of photosynthetic microorganisms, and their presence is typically related to stress conditions. Even though the hexanoyl (butanoyl) moiety is not a part of the conjugated system of hFx (bFx), their absorption spectra in polar solvents exhibit more pronounced vibrational bands of the S-2 state than for Fx. The effect of the nonconjugated acyloxy moiety is further observed in transient absorption spectra, which for Fx exhibit characteristic features of an intramolecular charge transfer (ICT) state in all polar solvents. For bFx and hFx, however, much weaker ICT features are detected in methanol, and the spectral markers of the ICT state disappear completely in polar, but aprotic acetonitrile. The presence of the acyloxy moiety also alters the lifetimes of the S-1/ICT state. For Fx, the lifetimes are 60, 30, and 20 ps in n-hexane, acetonitrile, and methanol, whereas for bFx and hFx, these lifetimes yield 60, 60, and 40 ps, respectively. Testing the S-1/ICT state lifetimes of hFx in other solvents revealed that some ICT features can be induced only in polar, protic solvents (methanol, ethanol, and ethylene glycol). Thus, bFx and hFx represent a rather rare example of a system in which a nonconjugated functional group significantly alters excited-state dynamics. By comparison with other carotenoids, we show that a keto group at the acyloxy tail, even though it is not in conjugation, affects the electron distribution along the conjugated backbone, resulting in the observed decrease of the ICT character of the S-1/ICT state of bFx and hFx.
Trvalý link: http://hdl.handle.net/11104/0284332