title: Fermi resonance as a tool for probing peridinin environment.
abstract: In the present paper, we provide an extended study of the vibrational signature of a butenolide carotenoid, peridinin, in various solvents by combining resonance Raman spectroscopy (RRS) with theoretical calculations. The presence of a Fermi resonance due to coupling between the lactonic C═O stretching and the overtone of the wagging of the C-H in the lactonic ring provides a spectroscopic way of differentiating between peridinins lying in different environments. This is a significant achievement, given that simultaneous presence of several peridinins (each with a peculiar photophysical role) in different environments occurs in the most important peridinin containing proteins, the peridinin-chlorophyll proteins (PCPs) and the Chl a-c2-peridinin binding proteins. In RRS, small modifications of solvent polarity can give rise to large differences in the intensity and splitting between the two bands, resulting from the Fermi resonance. By changing the polarity, we can tune the frequency of stretching of the C═O and, while the C-H wagging frequency is almost always constant in different solvents, move the system from a perfect resonance condition to off-resonance ones. We have corroborated our spectroscopic findings with a quasi-classical dynamical model of two coupled oscillators, and DFT calculations on peridinin in different solvents; we have also used calculations to complete the peridinin vibrational mode assignments in the 800-1600 cm(-1) region of RRS spectra, corresponding to polyene chain motion. Finally, the presence of Fermi resonance has been used to reinterpret previous vibrational spectroscopic experiments in PCPs.
authors.affiliation: Institut de Biologie et de Technologie de Saclay, CEA, and UMR 8221, CNRS , Bat 532, CEA Saclay, 91191 Gif/Yvette, France.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Kish
authors.forename: Maria Manuela
authors.initials: MM
authors.lastname: Mendes Pinto
authors.forename: Daniele
authors.initials: D
authors.lastname: Bovi
authors.forename: Marie
authors.initials: M
authors.lastname: Basire
authors.forename: Leonardo
authors.initials: L
authors.lastname: Guidoni
authors.forename: Rodolphe
authors.initials: R
authors.lastname: Vuilleumier
authors.forename: Bruno
authors.initials: B
authors.lastname: Robert
authors.forename: Riccardo
authors.initials: R
authors.lastname: Spezia
authors.forename: Alberto
authors.initials: A
authors.lastname: Mezzetti
mesh_terms: D002338:Carotenoids / Q000737:chemistry* / Q000302:isolation & purification; D004141:Dinoflagellida / Q000737:chemistry*; D011789:Quantum Theory; D012997:Solvents; D013059:Spectrum Analysis, Raman / Q000379:methods*
chemical_list: D012997:Solvents; C016040:peridinin; D002338:Carotenoids