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Arch Biochem Biophys. 2013 Nov 15;539(2):142-55. doi: 10.1016/j.abb.2013.09.009. Epub 2013 Sep 19.

Vibrational and electronic spectroscopy of the retro-carotenoid rhodoxanthin in avian plumage, solid-state films, and solution.

Author information

1
Department of Chemistry and Biochemistry, University of California at San Diego, 9500 Gilman Drive MC 0314, La Jolla, CA 92093, USA.

Abstract

Rhodoxanthin is one of few retro-carotenoids in nature. These chromophores are defined by a pattern of single and double bond alternation that is reversed relative to most carotenoids. Rhodoxanthin is found in the plumage of several families of birds, including fruit doves (Ptilinopus, Columbidae) and the red cotingas (Phoenicircus, Cotingidae). The coloration associated with the rhodoxanthin-containing plumage of these fruit dove and cotinga species ranges from brilliant red to magenta or purple. In the present study, rhodoxanthin is characterized in situ by UV-Vis reflectance and resonance Raman spectroscopy to gain insights into the mechanisms of color-tuning. The spectra are compared with those of the isolated pigment in solution and in thin solid films. Key vibrational signatures are identified for three isomers of rhodoxanthin, primarily in the fingerprint region. Electronic structure (DFT) calculations are employed to describe the normal modes of vibration, and determine characteristic modes of retro-carotenoids. These results are discussed in the context of various mechanisms that change the electronic absorption, including structural distortion of the chromophore or enhanced delocalization of π-electrons in the ground-state. From the spectroscopic evidence, we suggest that the shift in absorption is likely a consequence of perturbations that primarily affect the excited state of the chromophore.

KEYWORDS:

Avian plumage; Bird feathers; Carotenoid; Resonance Raman spectroscopy; Retro-carotenoid; Rhodoxanthin

PMID:
24055537
DOI:
10.1016/j.abb.2013.09.009
[Indexed for MEDLINE]

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