Radical Cation Generation from Singlet and Triplet Excited States of All‐trans‐Lycopene in Chloroform^¶

Abstract

On direct photoexcitation, subpicosecond time‐resolved absorption spectroscopy revealed that the 1Bu‐type singlet excited state of all‐trans‐lycopene in chloroform was about seven times more efficient than all‐trans‐β‐carotene in generating the radical cation. The time constant of radical cation generation from the 1Bu‐type state was found to be ∼0.14 ps, a value that was comparable for the two carotenoids. On anthracene‐sensitized triplet excitation, radical cation generation was found to be much less efficient for lycopene than for β‐carotene. A slow rising phase (20‐30 μs) in the bleaching of ground‐state absorption was common for both lycopene and β‐carotene in chloroform and was ascribed to an efficient secondary reaction with a solvent radical leading to the formation of carotenoid radical cations. The reverse ordering in the tendency of the excited states of different multiplicities for the two carotenoids to generate radical cations is discussed in relation to the two carotenoids as scavengers of free radicals.

Ultrafast Carotenoid-to-Chlorophyll Singlet Energy Transfer in the Cytochrome b6f Complex from Bryopsis corticulans

“…In the visible region and immediately after the pulsed excitation (Fig. 2 a, 0.0 ; 0.1 ps), a sharp negative feature appears at slightly longer wavelengths (;478 nm) to the 0 ) 0 transition in the ground state absorption (473 nm); this negative feature is due to the S 2 (1B u 1 ) / S 0 (1A g ÿ ) stimulated emission (SE) as previously reported for lycopene and b-carotene (49,39). The SE evolves from 0.2 ps through 0.5 ps and eventually transforms into the bleach of ground state absorption (BLC).…”

“…The femtosecond time-resolved absorption spectrometer has been described in detail elsewhere (39). Briefly, the output pulses (800 nm, 120 fs, 800 mJ/pulse) from a regenerative amplifier (Spitfire, Spectra Physics, Mountain View, CA) seeded with a mode-locked Ti:sapphire laser (Tsunami, Spectra Physics) were split into two components by the use of a 9:1 beam splitter.…”

Revisiting the Role of Xanthophylls in Nonphotochemical Quenching

“…It seems plausible that additional Xan •+ may form via S–T annihilation, which occurs when triplet states accumulate at high laser repetition rates (Table and Supporting Information Table 2). In solvents, the lowest-energy Xan triplets act as precursors for Xan •+ . − The higher-energy Xan triplet states formed by S–T annihilation may be even stronger electron donors. Indeed, in LHCII aggregates, strong laser pulses create long-living quenchers, probably Chl cations or other radicals, with triplet states as precursors .…”

Carotenoid feed supplementation in Argentine penaeoid shrimp broodstock

“…Antioxidant protective capacity was observed in shrimp under all treatments without significant differences among them; nevertheless, there were differences with initial individuals. The efficiency of carotenoids as antioxidants does not follow their capability as radical scavengers or the order of their oxidation potential (Han et al, 2006). The long-standing controversy of carotenoids' function as antioxidants may be related to extrapolation of properties determined in homogenous solutions to more complex biological systems, where other factors such as spatial organization and interaction between antioxidants become important (Liang et al, 2009).…”