TY - JOUR
T1 - Laser flash photolytic generation of radical ions of carotenoids in organic solvents. Studies of their subsequent fates, including formation of stable carotenoid sigma dimer radical anion (CAR)2[rad]–
AU - El-Agamey, Ali
AU - Melø, Thor B.
AU - Razi Naqvi, K.
AU - El-Hagrasy, Maha A.
AU - Ohkubo, Kei
AU - Fukuzumi, Shunichi
N1 - Publisher Copyright:
© 2021
PY - 2022/3/1
Y1 - 2022/3/1
N2 - In this study, time-resolved laser flash photolysis technique (LFP) was used to generate and study extraordinary stable transients formed following the decay of radical anions of canthaxanthin (CAN) and astaxanthin (ASTA). The radical anions were obtained via one-electron reduction of CAN and ASTA by acetone ketyl radical (AC[rad]−) in various solvents. At room temperature, the decay of CAN[rad]− (λmax = 870 nm) and ASTA[rad]− (λmax = 1000 nm), in acetonitrile (ACN), led to the formation of indefinitely stable colored transients (blue-green for CAN and navy blue for ASTA) absorbing at shorter wavelengths (λmax = 690 nm and 720 nm, respectively) relative to their corresponding radical anions. Rapid quenching by oxygen was observed indicating the radical nature of these transients, which was further confirmed by EPR spectroscopy. By employing EPR spectroscopy, LFP technique, and UV–visible absorption measurements, these extraordinary stable transients were identified as sigma-dimer radical anions ((CAR)2[rad]−) formed via the dimerization of the parent carotenoid (CAR) with its radical anion (CAR[rad]−). The suggested structures of these dimers were postulated using DFT calculations, which indicated that the unpaired electron is delocalized over the entire molecule. This result is extremely important because of the paucity of reports on dimer radical anions in solution.
AB - In this study, time-resolved laser flash photolysis technique (LFP) was used to generate and study extraordinary stable transients formed following the decay of radical anions of canthaxanthin (CAN) and astaxanthin (ASTA). The radical anions were obtained via one-electron reduction of CAN and ASTA by acetone ketyl radical (AC[rad]−) in various solvents. At room temperature, the decay of CAN[rad]− (λmax = 870 nm) and ASTA[rad]− (λmax = 1000 nm), in acetonitrile (ACN), led to the formation of indefinitely stable colored transients (blue-green for CAN and navy blue for ASTA) absorbing at shorter wavelengths (λmax = 690 nm and 720 nm, respectively) relative to their corresponding radical anions. Rapid quenching by oxygen was observed indicating the radical nature of these transients, which was further confirmed by EPR spectroscopy. By employing EPR spectroscopy, LFP technique, and UV–visible absorption measurements, these extraordinary stable transients were identified as sigma-dimer radical anions ((CAR)2[rad]−) formed via the dimerization of the parent carotenoid (CAR) with its radical anion (CAR[rad]−). The suggested structures of these dimers were postulated using DFT calculations, which indicated that the unpaired electron is delocalized over the entire molecule. This result is extremely important because of the paucity of reports on dimer radical anions in solution.
KW - Acetonitrile
KW - DFT calculations
KW - EPR spectroscopy
KW - Extraordinary stability
KW - Laser flash photolysis
KW - Sigma-dimer radical anions
UR - http://www.scopus.com/inward/record.url?scp=85121345348&partnerID=8YFLogxK
U2 - 10.1016/j.jphotochem.2021.113707
DO - 10.1016/j.jphotochem.2021.113707
M3 - Article
AN - SCOPUS:85121345348
SN - 1010-6030
VL - 425
JO - Journal of Photochemistry and Photobiology A: Chemistry
JF - Journal of Photochemistry and Photobiology A: Chemistry
M1 - 113707
ER -