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Issue 5, 2011
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Kinetic studies of retinol addition radicals

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Abstract

Retinol neutral radicals (RS-retinol˙), generated from the reaction of retinol with 4-pyridylthiyl and 2-pyridylthiyl radicals in argon-saturated methanol, undergo β-elimination, which can be monitored via the slow secondary absorption rise at 380 nm attributed to the rearrangement of the unstable retinol neutral addition radicals to the more stable addition radicals. Rate constants for the β-elimination reactions (kβ) of 4-PyrS-retinol˙ were measured at different temperatures and the Arrhenius equation for the reaction is described by log (kβ/s−1) = (12.7 ± 0.2) − (54.3 ± 1.3)/θ, where θ = 2.3RT kJ mol−1. The reactivities of retinol addition radicals (RS-retinol˙), generated from the reaction of retinol with various thiyl radicals, towards oxygen have also been investigated in methanol. In the presence of oxygen, the decay of RS-retinol˙ fits to biexponential kinetics and both observed rate constants for the RS-retinol˙ decay are oxygen-concentration dependent. This suggests that at least two thiyl addition radicals, formed from the reaction of RS˙ with retinol, undergo oxygen addition reactions. In light of the estimated rate constants for oxygen addition to RS-retinol˙ and RS-CAR˙ (CAR: carotenoid), the antioxidant-prooxidant properties of retinol are discussed.

Graphical abstract: Kinetic studies of retinol addition radicals

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Publication details

The article was received on 29 Sep 2010, accepted on 22 Nov 2010 and first published on 11 Jan 2011


Article type: Paper
DOI: 10.1039/C0OB00799D
Org. Biomol. Chem., 2011,9, 1459-1465

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    Kinetic studies of retinol addition radicals

    A. El-Agamey, S. Fukuzumi, K. R. Naqvi and D. J. McGarvey, Org. Biomol. Chem., 2011, 9, 1459
    DOI: 10.1039/C0OB00799D

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