Regeneration of β-Carotene from Radical Cation by Eugenol, Isoeugenol, and Clove Oil in the Marcus Theory Inverted Region for Electron Transfer

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• 作者：Hui-Ting Chang ; Hong Cheng ; Rui-Min Han ; Peng Wang ; Jian-Ping Zhang ; Leif H. Skibsted
• 刊名：Journal of Agricultural and Food Chemistry
• 出版年：2017
• 出版时间：February 1, 2017
• 年：2017
• 卷：65
• 期：4
• 页码：908-912
• 全文大小：357K
• ISSN：1520-5118

文摘

The rate of regeneration of β-carotene by eugenol from the β-carotene radical cation, an initial bleaching product of β-carotene, was found by laser flash photolysis and transient absorption spectroscopy to be close to the diffusion limit in chloroform/methanol (9:1, v/v), with a second-order rate constant (k₂) of 4.3 × 10⁹ L mol^–1 s^–1 at 23 °C. Isoeugenol, more reducing with a standard reduction potential of 100 mV lower than eugenol, was slower, with k₂ = 7.2 × 10⁸ L mol^–1 s^–1. Regeneration of β-carotene following photobleaching was found 50% more efficient by eugenol, indicating that, for the more reducing isoeugenol, the driving force exceeds the reorganization energy for electron transfer significantly in the Marcus theory inverted region. For eugenol/isoeugenol mixtures and clove oil, kinetic control by the faster eugenol determines the regeneration, with a thermodynamic backup of reduction equivalent through eugenol regeneration by the more reducing isoeugenol for the mixture. Clove oil, accordingly, is a potential protector of provitamin A for use in red palm oils.