Optical Absorption Spectra of Dications of Carotenoids

Abstract

Quantitative optical absorption spectra of the cation radicals and the dications of canthaxanthin (I), -carotene (II), 7′-cyano-7′-ethoxycarbonyl-7′-apo--carotene (III), and 7′,7′-dimethyl-7′-apo--carotene (IV) in dichloromethane solution are reported. Exclusive formation of dications occurs when the carotenoids are oxidized with ferric chloride. Addition of neutral carotenoid to the dications results in equilibrium formation of cation radicals. Oxidation with iodine in dichloromethane affords only cation radicals; electrochemical oxidation under suitable conditions yields both dications and cation radicals. Values of the optical parameters depend on the nature of the oxidative medium. The oscillator strengths calculated for gas phase cation radicals and dications of I-IV using the INDO/S method show the same trend as the experimental values.

Snapshot Transient Absorption Spectroscopy of Carotenoid Radical Cations in High-Light-Acclimating Thylakoid Membranes

“…22−25 Because we do not know the role of any protein-induced conformational changes on the ε, we decided to use a range of values for ε (53 000−73 000 L mol −1 cm −1 ), centered around ε for β-carotene cation absorption at 970 nm (63 000 L mol −1 cm −1 ) to quantify the Zea •+ represented in our TA data. 23 On the basis of these values of ε, we were able to estimate that after 1 min of light acclimation (maximum Zea •+ signal) only a small portion (≤0.6%) of the Zea pool at that time was observed as the Zea •+ species in the snapshot TA signal. This is approximately equivalent to a Zea •+ in 5−7% of PSII supercomplexes (see the Supporting Information for values used in the calculation).…”

Charge Manipulation in Molecules Encapsulated Inside Single-Wall Carbon Nanotubes

“…S1 of the Supplemental Material [11]. In the case of Car, Car can be oxidized when the potential is positive, and the dications and cation radicals of Car are formed by the oxidation [12,13]. The optical absorption of neutral Car disappeared during the oxidation (Fig.…”

Synthesis of a Highly Unsaturated, Stable Hydroxy Peroxide: A Yellow [lrarr2] Blue Color‐Changing Carotenoid Oxidation Product with Leuco Dye Properties

“…[3] Car ·+ could as well transfer an electron to FeCl 3 yielding Car 2+ , whose λ max appears around 670 nm, just as observed for CarO 2 ·+ and CarO 2 + . However, Car 2+ is unstable at room temperature, [17] has been excluded as precursor for CarO 2 [4] and is hardly conceivable with the observed color inversion properties. As demonstrated earlier with carotenoid cations, CarO 2 + could be the target for nucleophiles other than H 2 O.…”