Quantitative study of antioxidant properties of phenolcarboxylic acids from Larix sibirica bark

Abstract

Antioxidant properties of caffeic, ferulic, vanillic, and 4-hydroxybenzoic acids isolated from Larix sibirica Ledeb. bark were studied using model radical-chain reactions for oxidation of propan-2-ol and 1,4-dioxane under kinetic control. Quantitative characteristics of the antioxidant activities were determined as effective rate constants fk In for oxidation chain termination of the phenolcarboxylic acids. It was found that caffeic acid had the highest antioxidant activity among the investigated natural compounds.Phenolcarboxylic acids possess a broad spectrum of biological activity and are promising sources for fabricating phytopreparations and parapharmaceuticals [1]. Adding these compounds to technical and food products and medical preparations can increase their shelf-life [2][3][4][5]. It has been proved that representatives of this class of compounds must be applied for nonspecific therapy of many diseases connected with advanced peroxide lipid oxidation [1, 6]. Thus, cinnamic and ferulic acids are found in agents intended to decrease the toxic effects of chemotherapy [5]. p-Coumaric, ferulic, and caffeic acids exhhibit antibacterial activity. Derivatives of cinnamic acid are widely used to fabricate photo-protective additives for cosmetics [2,7]. Addition of ferulic acid to food products protects an organism from the toxic action of nitroso compounds in them [2]. Caffeic and ferulic acids decrease the oxidation rate of lard, isopropylbenzene, and ethylbenzene [8]. However, primarily semi-quantitative data on the antioxidant action of phenolcarboxylic acids have been reported. This does not enable an objective conclusion about their antioxidant properties to be made. Therefore, the goal of our work was to study quantitatively the antioxidant properties of caffeic (CA), ferulic (FA), vanillic (VA), and 4-hydroxybenzoic (4-HA) acids using manometry and atmospheric oxygen absorption.The model reaction for studying the antioxidant activity (AOA) of the studied compounds was radical-chain oxidation of propan-2-ol and 1,4-dioxane (348 K, azodiisobutyronitrile initiator, V i = 1·10 -7 mol/L·s initiation rate). The inhibition effectiveness of compounds was estimated from the decrease in the initial rate of oxygen absorption upon oxidation of the model substrates. The experimental methods of the kinetics studies have been described in detail [9]. The rate constant of oxidation chain termination fk In , where f is the radical capacity of the antioxidant (AO) that indicates the number of radical intermediates consumed per single AO molecule during chain termination, was used as the quantitative characteristic of the AOA [10]. The ionol equivalent (IE), a quantity estimated by comparing experimental fk In values for the studied compounds with that for ionol, was used as a characteristic for the AOA of the studied compounds.We studied quantitatively the AOA of the four phenolcarboxylic acids CA, FA, VA, and 4-HA using initiated oxidation of propan-2-ol and 1,4-dioxane as model reactions. Initiated oxidation of the mode...