Application of a Potentiometric System with Data-Analysis Computer Programs to the Quantification of Metal-Chelating Activity of Two Natural Antioxidants:Caffeic Acid and Ferulic Acid
TL;DR: In this paper, the metal-chelating activity of caffeic and ferulic acids was successfully performed by using a potentiometric system with data-analysis computer programs, which was applied to two phenolic models, which have been systematically reported as antioxidants.
Abstract: The quantification of metal-chelating activity of caffeic and ferulic acids( 1 and 2, resp.) was successfully performed by using a potentiometric system with data-analysis computer programs. The method was applied to two phenolic models, which have been systematically reported as antioxidants. Although a chain-breaking mechanism was proposed, several studies pointed out the possibility of complexation of transition metals that can participate in single-electron reactions and mediate the formation of oxygen-derived free radicals. In this work, the complexation propertiestowardsCu II were investigated by potentiometry with a glass electrode. Acidity constants of the ligands (phenolic acids) and the formation constants of the ligandmetal complexes were evaluated by potentiometry. The modeling of the titration curvesand the data treatment were performed with the computer programsSuperquad and Bes t. A detailed quantitative examination of the complexation species formed in the Cu II /caffeic acid (1) and Cu II /ferulic acid (2) systems is presented together with the formation constants (log ). Results have shown that the complexation properties of the two phenolic acids towardsthe trans ition metal are quite different: the activity of caffeic acid ( 1) wasfound higher than that of ferulic acid (2). The data are important to get insight into the mechanism of action of antioxidants, and, in this case, could partially explain the efficacy of caffeic acid in the protection of LDL oxidative damage. In addition, the analytical method developed could be applied to quantify the chelating activity of important biological compounds, such as allopurinol, uric acid, cinnamic acids, flavonoids, and anthocianins, and, in that way, could be a valuable tool to understand the mechanisms underlying their protective effects.
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TL;DR: In this article, the acidity constants of catechin and taxifolin, as well as the formation constants of corresponding copper (II) complexes, were investigated by potentiometry and/or spectrophotometry.
Abstract: The screening of natural flavonoids for their bioactivity as antioxidants is usually carried out by determinination of their profile as chain-breaking antioxidants, by the evaluation of their direct free radical-scavenging activity as hydrogen- or electron-donating compounds. Since this may not be the only mechanism underlying the antioxidant activity it is important to check the ability of these compounds to act as chelators of transition metal ions. Accordingly, in the present study the acidity constants of catechin and taxifolin, as well as the formation constants of the corresponding copper (II) complexes, were investigated by potentiometry and/or spectrophotometry. Moreover, a detailed quantitative examination of the coordination species formed is presented. In addition, the partition coefficients of both catechin and taxifolin in a biomimetic system (micelles) were determined, since these properties may also contribute to the antioxidant behavior of this type of compound. The log P values determined depend on the electrostatic interactions of the compounds with the differently charged micelles (the highest values were obtained for zwitterionic and cationic micelles). The prooxidant behavior of the compounds was assessed through the oxidation of 2'-deoxyguanosine, induced by a Fenton reaction, catalyzed by copper. The data obtained reveal that the flavonoids under study did not present prooxidant activity, in this particular system. The results obtained are evidence of a clear difference among the pKa, the complexation properties, and the lipophilicity of the flavonoids studied, which can partially explain their distinct antioxidant activity. The most stable geometries of the free compounds were determined by theoretical (ab initio) methods, in order to properly account for the electron correlation effects which occur in these systems, thus allowing a better interpretation of the experimental data.
162 citations
TL;DR: The anti-apoptotic effect of EA, CA and FA in PBMCs seems to be through the Bcl-2 independent mechanism, and peripheral blood mononuclear cells pretreated with phenolics could resist H2O2-induced apoptotic damage.
Abstract: Polyphenols have been shown to induce apoptosis in a variety of tumor cells including leukemia both in vitro and in vivo. However, their action on normal human peripheral blood mononuclear cells (PBMCs) during oxidative stress remains to be explored. In this study, we have evaluated the anti-apoptotic and radical scavenging activities of dietary phenolics, namely caffeic acid (CA), ellagic acid (EA) and ferulic acid (FA). H2O2-induced apoptosis in normal human PBMCs was assayed by phosphotidylserine externalization, nucleosomal damage and DNA fragmentation. Incubation of PBMCs with 5 mM H2O2 led to increased Annexin-V binding to externalized phosphatidyl serine (PS), an event of pre-apoptotic stage of the cell. Peripheral blood mononuclear cells pretreated with phenolics could resist H2O2-induced apoptotic damage. Caffeic acid (60 and 120 microM) and EA (100 and 200 microM) caused no change in externalization of PS, whereas FA (100 and 200 microM) increased externalization of PS in PBMCs treated with H2O2. The effects of phenolics were abolished to a large extent by culturing the PBMCs for 24 h after washing the phenolics from the medium. Inhibitory activities of these phenolics on lipid peroxidation were in the order of EA
120 citations
TL;DR: The results gathered allow concluding that the redox potentials could contribute to the understanding of the antioxidants activity and that the presence of an electron withdrawing group of halogen type in an ortho position to a phenolic group of the cinnamic scaffold does not influence the antioxidant activity.
Abstract: An interdisciplinary research project was developed combining the synthesis of a series of hydroxycinnamic acid derivatives and the evaluation of their physicochemical parameters (namely redox potentials and partition coefficients), along with the corresponding antioxidant activity. A structure-property-activity relationship (SPAR) approach was then applied aiming at establishing a putative relation between the physicochemical parameters of the compounds under study and their antioxidant activity. The results gathered allow concluding that the redox potentials could contribute to the understanding of the antioxidant activity and that the presence of an electron withdrawing group (EWG) of halogen type, namely a bromo atom, in an ortho position to a phenolic group of the cinnamic scaffold does not influence the antioxidant activity. On the other hand after the introduction of this type of substituent a significant increase on the lipophilicity of cinnamic derivatives was observed, which is a feature of extreme importance in the development of novel lipophilic antioxidants. The SPAR results revealed a relation between the redox potentials and the antioxidant activity of hydroxycinnamic acids and derivatives. The data obtained operate as a positive reinforce of the tendency to use redox properties as a guideline of the rational design of this type of compounds.
73 citations
TL;DR: An electronic tongue based on potentiometric chemical sensors was assessed as a rapid tool for the quantification of bitterness in red wines and found that bitter-tasting wines had higher concentrations of phenolic compounds than non-bitter wines.
Abstract: An electronic tongue (ET) based on potentiometric chemical sensors was assessed as a rapid tool for the quantification of bitterness in red wines A set of 39 single cultivar Pinotage wines comprising 13 samples with medium to high bitterness was obtained from the producers in West Cape, South Africa Samples were analysed with respect to a set of routine wine parameters and major phenolic compounds using Fourier transform infrared-multiple internal reflection spectroscopy (WineScan) and high-performance liquid chromatography, respectively A trained sensory panel assessed the bitterness intensity of 15 wines, 13 of which had a bitter taste of medium to high intensity Thirty-one wine samples including seven bitter-tasting ones were measured by the ET Influence of the chemical composition of wine on the occurrence of the bitter taste was evaluated using one-way analysis of variance It was found that bitter-tasting wines had higher concentrations of phenolic compounds (catechin, epicatechin, gallic and caffeic acids and quercetin) than non-bitter wines Sensitivity of the sensors of the array to the phenolic compounds related to the bitterness was studied at different pH levels Sensors displayed sensitivity to all studied compounds at pH 7, but only to quercetin at pH 35 Based on these findings, the pH of wine was adjusted to 7 prior to measurements Calibration models for classification of wine samples according to the presence of the bitter taste and quantification of the bitterness intensity were calculated by partial least squares-discriminant analysis (PLS-DA) regression Statistical significance of the classification results was confirmed by the permutation test Both ET and chemical analysis data could discriminate between bitter and control wines with the correct classification rates of 94% and 91%, respectively Prediction of the bitterness intensity with good accuracy (root mean square error of 2 and mean relative error of 6% in validation) was possible only using ET data
50 citations
TL;DR: The galloyl-cinnamic acid hybrid stands out as the best antioxidant supplementing the effect of a blend of gallic acid plus caffeic acid endorsing the hypothesis that the whole is greater than the sum of the parts.
Abstract: Phenolic acids are ubiquitous antioxidants accounting for approximately one third of the phenolic compounds in our diet. Their importance was supported by epidemiological studies that suggest an inverse relationship between dietary intake of phenolic antioxidants and the occurrence of diseases, such as cancer and neurodegenerative disorders. However, until now, most of natural antioxidants have limited therapeutic success a fact that could be related with their limited distribution throughout the body and with the inherent difficulties to attain the target sites. The development of phenolic antioxidants based on a hybrid concept and structurally based on natural hydroxybenzoic (gallic acid) and hydroxycinnamic (caffeic acid) scaffolds seems to be a suitable solution to surpass the mentioned drawbacks. Galloyl-cinnamic hybrids were synthesized and their antioxidant activity as well as partition coefficients and redox potentials evaluated. The structure-property-activity relationship (SPAR) study revealed the existence of a correlation between the redox potentials and antioxidant activity. The galloyl-cinnamic acid hybrid stands out as the best antioxidant supplementing the effect of a blend of gallic acid plus caffeic acid endorsing the hypothesis that the whole is greater than the sum of the parts. In addition, some hybrid compounds possess an appropriate lipophilicity allowing their application as chain-breaking antioxidant in biomembranes or other type of lipidic systems. Their predicted ADME properties are also in accordance with the general requirements for drug-like compounds. Accordingly, these phenolic hybrids can be seen as potential antioxidants for tackling the oxidative status linked to the neurodegenerative, inflammatory or cancer processes.
49 citations
References
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13 Jun 1985
TL;DR: 1. Oxygen is a toxic gas - an introduction to oxygen toxicity and reactive species, and the chemistry of free radicals and related 'reactive species'
Abstract: 1. Oxygen is a toxic gas - an introductionto oxygen toxicity and reactive species 2. The chemistry of free radicals and related 'reactive species' 3. Antioxidant defences Endogenous and Diet Derived 4. Cellular responses to oxidative stress: adaptation, damage, repair, senescence and death 5. Measurement of reactive species 6. Reactive species can pose special problems needing special solutions. Some examples. 7. Reactive species can be useful some more examples 8. Reactive species can be poisonous: their role in toxicology 9. Reactive species and disease: fact, fiction or filibuster? 10. Ageing, nutrition, disease, and therapy: A role for antioxidants?
21,528 citations
"Application of a Potentiometric Sys..." refers background in this paper
...There is great interest in the possibility that diets rich in antioxidants may retard the development of atherosclerotic complications such as coronary heart diseases [3] [5]....
[...]
...It is currently assumed that the oxidative modification of low-density lipoproteins (LDL) by inducers such as CuII ions and oxygen radical species could be related to cardiovascular diseases [3] [4]....
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Book•
01 Jan 1992
TL;DR: In this article, the authors present a complete metal complex data base with linear stability constants and species concentrations of complex systems, including a mixed-ligand binuclear dioxygen system nonaqueous solvents complex multicomponent systems equilibrium with solid phases equilibrium involving hydrolytic species species distributions of hydroxo and fluoro complexes of AI(III).
Abstract: Part 1 Introduction: stability constants - early work recent developments historical evolution of computational methods purpose of this book. Part 2 Equilibrium constants, protonation constants, formation constants: concentration constants and activity constants conventions employment for expressing equilibrium constants equilibrium constants and stability constants for EDTA species distribution curves. Part 3 Experimental methods for measuring equilibrium constants: methods available potentiometric pH measurements displacement methods pH and p[H]measurement of metal complex equilibria: materials, the reaction mixture calibration of the potentiometric apparatus the experimental runs computation of stability constants.Part 4 Common errors and their elimination or minimization: measurements errors calibration and electrode care reagents equilibrium measurements calculations selection of the model. Part 5 Examples of stability constant determination: iminodiacetic acid (IDA) procedure for IDA C-BISTREN procedure for C-BISTREN. Part 6 Macroscopic and microscopic constants: some definitions and concepts ionization of tyrosine microscopic protonation equilibria of DOPA general comments and conclusions. Determination of stability constants and species concentrations of complex systems: a mixed-ligand binuclear dioxygen system non-aqueous solvents complex multicomponent systems equilibrium with solid phases equilibrium involving hydrolytic species species distributions of hydroxo and fluoro complexes of AI(III). Part 7 Critical stability constants and their selection: general criteria examples of critical data selection need for additional critical constants. Part 8 Development of a complete metal complex data base: introduction linear stability. constant correlations estimation of estability constants not measured experimentally metal speciation in sea water with and without added ligands.
962 citations
20 May 2003
TL;DR: In Vivo effects: anti-cancer properties of flavonoids, with emphasis on citrus flavonoid quercetin in foods, cardiovascular disease, and cancer absorption, metabolism, and bioavailability of Flavonoids flav onoids and coronary heart disease-dietary perspectives.
Abstract: Occurrence and analysis: analysis and identification of flavonoids in practice phenolic acids in fruits flavonoids in medical plants. Chemical and biochemical properties: chemistry of flavonoids antioxidant properties of flavonoids, reduction potentials, and electron transfer reactions of flavonoid radicals flavonoid and metal interactions in biological systems inhibition of mitochondrial function by flavonoids. Antioxidant activities: structure-antioxidant activity relationships of flavonoids and isoflavonoids structural aspects of antioxidant activity of flavonoids effects of flavonoids on the oxidation of low density lipoprotein flavonoids as inhibitors of lipid peroxidation in membranes isoflavonoids as inhibitors of lipid peroxidation and quenchers of singlet oxygen. Nutritional studies: ginkgo biloba extract EG6 761 - biological actions, antioxidant activity, and regulation of nitric oxide synthase nutritional studies of flavonoids in wine nutrition of grape phenolics flavonoids and phenylpropanoids as contributors to the antioxidant activity of fruit juices pycnogenol. In Vivo effects: anti-cancer properties of flavonoids, with emphasis on citrus flavonoids quercetin in foods, cardiovascular disease, and cancer absorption, metabolism, and bioavailability of flavonoids flavonoids and coronary heart disease-dietary perspectives.
686 citations
"Application of a Potentiometric Sys..." refers background in this paper
...There is great interest in the possibility that diets rich in antioxidants may retard the development of atherosclerotic complications such as coronary heart diseases [3] [5]....
[...]
01 Oct 1992
413 citations
"Application of a Potentiometric Sys..." refers background in this paper
...This type of compounds has been nowadays an important tool in the research on new effective antioxidants because of their role as inhibitors of deleterious oxidative processes [1] [2]....
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01 Jan 1993
TL;DR: The results show that catechins and ferulic acid possess antioxidant properties, which may become important given the current search for "natural" replacements for synthetic antioxidant food additives.
Abstract: We have evaluated the abilities of ferulic acid, (+/-) catechin, (+) catechin and (-) epicatechin to scavenge the reactive oxygen species hydroxyl radical (OH.), hypochlorous acid (HOCl) and peroxyl radicals (RO2.). Ferulic acid tested at concentrations up to 5 mM inhibited the peroxidation of phospholipid liposomes. Both (+/-) and (+) catechin and (-) epicatechin were much more effective. All the compounds tested reacted with trichloromethyl peroxyl radical (CCl3 O2.) with rate constants > 1 x 10(6) M-1 s-1. A mixture of FeCl3-EDTA, hydrogen peroxide (H2O2) and ascorbic acid at pH 7.4, has often been used to generate hydroxyl radicals (OH.) which are detected by their ability to cause damage to the sugar deoxyribose. Ferulic acid, (+) and (+/-) catechin and (-) epicatechin inhibited deoxyribose damage by reacting with OH. with rate constants of 4.5 x 10(9)M-1 s-1, 3.65 x 10(9) M-1 s-1, 2.36 x 10(9) M-1 s-1 and 2.84 x 10(9) M-1 s-1 respectively. (-) Epicatechin, ferulic acid and the (+) and (+/-) catechins exerted pro-oxidant action, accelerating damage to DNA in the presence of a bleomycin-iron complex. On a molar basis, ferulic acid was less effective in causing damage to DNA compared with the catechins. A mixture of hypoxanthine and xanthine oxidase generates O2-. which reduces cytochrome c to ferrocytochrome c. (+) Catechin and (-) epicatechin inhibited the reduction of cytochrome c in a concentration dependent manner. Ferulic acid and (+/-) catechin had only weak effects. All the compounds tested were able to scavenge hypochlorous acid at a rate sufficient to protect alpha-1-antiproteinase against inactivation. Our results show that catechins and ferulic acid possess antioxidant properties. This may become important given the current search for "natural" replacements for synthetic antioxidant food additives.
246 citations