Mechanistic Investigation of the Antioxidant Properties of Crocin by Radiolysis and Molecular Simulations
Résumé
Crocin is the gentiobiose ester of crocetin, its radiolytic oxidation by the OH radical has been
studied in the past [1] and recently revisited with pulse and γ radiolysis. [2] Pulse radiolysis
shows that at short times the oxidation product displays a typical absorption band at 670 nm
We have applied quantum chemistry [3] and our Monte-Carlo molecular simulation method
[4,5] to the methanol ester of crocetin (Figure 1, middle), a simpler molecule with the same
polyen chain. The computations show that:
1. The methyl groups -CaH3 and -CbH3 of the polyen chain are oxidable by the OH
radical without barrier, the other CH groups are also oxidable, but with a positive (0.1
eV) potential barrier.
2. Molecular simulations of the corresponding -CaH2 and -CbH2 radicals, with the lc-
ωPBE functional and the SMD simulation of the water solvent [3] give a low energy
absorption band at 642 nm, in good agreement with the measurement.
Our calculations also suggest that the products observed in pulse radiolysis at long times are
due to dimerization of these radicals and that the products observed in γ radiolysis are due to
dismutation of the same radicals, yielding closed shell cyclic molecules.
References
[1] W. Bors et al., Int. J. Radiat. Biol., 1982, 41(5), 493.
[2] S. Al Gharib et al., to be submitted 2023.
[3] Gaussian 16, Rev B01, Gaussian Inc.
[4] P. Ungerer et al. Technip Ed. Paris 2005
[5] P. Archirel et al., J. Phys. Chem. B, 2019, 123, 9087
Domaines
Chimie
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Licence : Domaine public