Abstract
This paper reports the results of comprehensive mechanistic investigations of the hydrogen atom transfer (HAT), radical adduct formation (RAF), single electron transfer – proton transfer (SET-PT), and sequential proton loss electron transfer (SPLET) mechanisms of caffeic acid (CA). The goals of the work were achieved by simulating the reactions of CA with hydroxyl radical in benzene and water solutions. It was found that SET-PT is not a favourable antioxidative mechanism of CA. On the other hand, HAT and RAF are competitive, because HAT pathways yield thermodynamically more stable radical products, and RAF pathways require smaller activation barriers. In polar basic environment SPLET is a probable antioxidative mechanism of CA, with exceptionally large rate.
Highlights
Phenolic compounds are well-known for their antioxidative action that can be realized via several mechanisms (TRUHLAR et al, 1983; GALANO et al, 2006; KLEIN et al, 2007; LITWINIENKO and INGOLD, 2007: GALANO and ALVAREZ-IDABOY, 2013)
The aim of the present paper is to contribute to the explanation of antioxidative activity of caffeic acid (CA) by examining its hydrogen atom transfer (HAT), radical adduct formation (RAF), sequential proton loss electron transfer (SPLET), and single electron transfer – proton transfer (SET-PT) reaction pathways in the presence of hydroxyl radical
The HAT mechanism is regarded as direct hydrogen atom transfer from phenolic groups of CA to HO
Summary
Phenolic compounds are well-known for their antioxidative action that can be realized via several mechanisms (TRUHLAR et al, 1983; GALANO et al, 2006; KLEIN et al, 2007; LITWINIENKO and INGOLD, 2007: GALANO and ALVAREZ-IDABOY, 2013). B− in Eq (5) denotes a base whose presence is necessary for heterolytic cleavage of the O–H bonds to occur
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