Staleva-Musto H, Kuznetsova V, Bína D, Litvín R, Polívka T. Intramolecular charge-transfer state of carotenoids siphonaxanthin and siphonein: function of non-conjugated acyl-oxy group.
PHOTOSYNTHESIS RESEARCH 2020;
144:127-135. [PMID:
31802367 DOI:
10.1007/s11120-019-00694-x]
[Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/05/2019] [Accepted: 11/22/2019] [Indexed: 06/10/2023]
Abstract
We used ultrafast transient absorption spectroscopy to study excited-state dynamics of two keto-carotenoids, siphonaxanthin and siphonein. These two carotenoids differ in the presence of dodecanoyl-oxy group in siphonein, which is attached to the C19 carbon on the same side of the molecule as the conjugated keto group. We show that this dodecanoyl-oxy group, though not in conjugation, is still capable of modifying excited state properties. While spectroscopic properties of siphonein and siphonaxanthin are nearly identical in a non-polar solvent, they become markedly different in polar solvents. In a polar solvent, siphonein, having the dodecanoyl-oxy moiety, exhibits less pronounced vibrational bands in the absorption spectrum and has significantly enhanced characteristic features of an intramolecular charge-transfer (ICT) state in transient absorption spectra compared to siphonaxanthin. The presence of the dodecanoyl-oxy moiety also alters the lifetimes of the S1/ICT state. For siphonaxanthin, the lifetimes are 60, 20, and 14 ps in n-hexane, acetonitrile, and methanol, whereas for siphonein these lifetimes yield 60, 11, and 10 ps. Thus, we show that even a non-conjugated functional group can affect the charge-transfer character of the S1/ICT state. By comparison with fucoxanthin acyl-oxy derivatives, we show that position of the acyl-oxy group in respect to the conjugated keto group is the key feature determining whether the polarity-dependent behavior is enhanced or suppressed.
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