Abstract
Antioxidant capacity (AOC) against peroxyl radical and 2,2'-azino-bis-(3-ethylbenzothiazoline-6-sulphonic acid) diammonium salt (ABTS) radical cation was measured for a series of p-hydroxybenzoic (HB) and p-hydroxycinnamic (HC) acids at different pH. Quantum-chemical computation was performed using Gaussian 3.0 software package to calculate the geometry and energy parameters of the same compounds. Significant correlations were revealed between AOC and a number of calculated parameters. The most significant AOC descriptors for the studied compounds against peroxyl radical were found to be HOMO energy, rigidity (η) and Mulliken charge on the carbon atom in m-position to the phenolic hydroxyl. The most significant descriptor of the antioxidant properties against the ABTS radical cation at pH 7.40 is electron transfer enthalpy from the phenolate ion. The mechanism of AOC realization has been proposed for HB and HC acids against both radicals.
Highlights
Oxidative stress is one of the general-purpose forms of the body’s response to the exogenic and endogenic factors and plays the significant role in the pathogenesis of inflammatory and dystrophic, neurodegenerative, cardiovascular, oncological diseases and in acceleration of the individual ageing [1,2,3,4,5,6].Oxidative stress is caused by overproduction of reactive oxygen species (ROS)
The antioxidant effects of most compounds are realized through a mixed mechanism: either single electron transfer followed by proton transfer (SET–PT), or sequential proton loss and electron transfer (SPLET) [8,9,10,11,12,13,14,15,16,17,18,19,20]
The quantum-chemical computing methods are an effective tool for examination of the mechanisms of interaction between antioxidants and free radicals and can identify molecular and electronic descriptors that define the antioxidant properties of different classes of compounds
Summary
Oxidative stress is one of the general-purpose forms of the body’s response to the exogenic and endogenic factors and plays the significant role in the pathogenesis of inflammatory and dystrophic, neurodegenerative, cardiovascular, oncological diseases and in acceleration of the individual ageing [1,2,3,4,5,6]. The quantum-chemical computing methods are an effective tool for examination of the mechanisms of interaction between antioxidants and free radicals and can identify molecular (structural) and electronic descriptors that define the antioxidant properties of different classes of compounds. Over 40 different methods for testing antioxidants in vitro are described [23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38] Their classification is based on a key mechanism of the interaction of various radicals with tested antioxidants. The present paper’s general aim is the structural–functional analysis of the phenolic acids in relation to their antioxidant properties, including the investigation of molecular geometry and electronic descriptors for different states of ionization. The mechanism of antioxidant action against the ABTS radical cation and peroxyl radical has been proposed for phenyl carbonic acids at different pH
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