pH-dependent redox mechanism and evaluation of kinetic and thermodynamic parameters of a novel anthraquinone (original) (raw)
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Electrochimica Acta, 2000
One-electron reduction of dihydroxyanthraquinone derivatives was studied in dimethylsulfoxide solution by means of electrochemical and spectrophotometric methods. It was found that dihydroxyanthraquinone reduction in the presence of oxygen occurs according to an EC mechanism, the second step being oxygen reaction with semiquinone anion radical. This mechanism was confirmed by the dependence of CV curves on dihydroxyanthraquinone and oxygen concentration. Supplementary spectrophotometric and electrochemical studies of the dihydroxyanthraquinone-potassium superoxide system have shown that no covalent compound is formed between seminquinone anion radical and molecular oxygen and therefore the reaction following dihydroxyanthraquinone reduction involves electron and proton transfer from semiquinone anion radical to molecular oxygen to form hydroperoxyl radical and deprotonated dihydroxyanthraquinone. The rate constants of the electron-transfer reactions from semiquinone anion radical to moleculax oxygen were determined from the dependence of anthraquinone cathodic reduction peak potential and the corresponding anodic peak current on oxygen concentration. It was found that the rate constants increase with decreasing pK a of the hydroxyanthraquinones, which confirms the postulated mechanism.
DOAJ (DOAJ: Directory of Open Access Journals), 2001
The aqueous electrochemistry of a number of anthraquinone derivatives was studied by using cyclic voltammetry at the surface of carbon paste electrode (CPE). From measurements of the half-wave potential as a function of pH, the potential-pH diagrams were constructed for each compound. The values of formal potentia Is and the pK' a of some different redox and acid-base couples involved in each compound at various pHs were obtained.
Electrochemical investigations of unexplored anthraquinones and their DNA binding
Journal of Electrochemical Science and Engineering, 2013
The redox behaviour of two potential anticancer anthraquinones, 9,10-anthraquinone and 2-chloromethyl-9,10-anthraquinone was investigated in a wide pH range. Cyclic voltammetry based assay was developed for the assessment of the effect of medium, substituents, potential scan rate and number of scans on the voltammetric response of anthraquinones. The electrode reaction mechanism was suggested on the basis of cyclic and differential pulse voltammetric results. The effect of DNA on anthraquinones was also probed at physiological pH which could lead to further investigation of possible citotoxic activity in vitro. The results revealed that anthraquinones interact with DNA more strongly than the clinically used anticancer drug, epirubicin.
Cyclic voltammetric study of anthraquinone-2-sulfonate in the presence of Acid Yellow 9
Electrochimica Acta, 1997
The electrochemical reduction of anthraquinone-2-sulfonate (AQS) has been examined in the presence of an azoic dyestuff (Acid Yellow 9, 4-amino-l,l'-azobenzene-3,4'-disulfonic acid, sodium salt) in alkaline solution. The dianion of the anthrahydroquinone-2-sulfonate (AQS*-) formed by cathodic reduction reacts with Acid Yellow 9 to regenerate AQS and yields the reduced dyestuff. The catalytic currents generated due to the chemical reaction between the AQS*-and the dyestuff have been used to estimate the rate constant of the reaction. 0 1997 Elsevier Science Ltd
Journal of Chemical & Engineering Data, 1997
Dissociation equilibria of 4-(2-pyridylazo) resorcinol (PAR) in aqueous micellar solutions were determined spectrophotometrically at 25°C and at the constant ionic strength I = 0.1 M KNO 3 . For this purpose, the effect of nonionic (Brij-35, Triton X-100, Triton X-114, Triton X-405), and anionic (SDS) surfactants on the absorption spectra of PAR at different pH values was studied. Results show that the pK a values and pure spectra of each species of PAR are influenced by percentages of a neutral and an anionic surfactant such as Brij-35, Triton X-100, Triton X-114, Triton X-405 and SDS, respectively, added to the solution of this reagent. Ghasemi et al. . The pure spectra of different forms of PAR in (a) pure water, (b) 0.05% (w/v) Brij-35 to water, (c) 0.05% (w/v) Triton X-100 to water, (d) 0.05% (w/v) Triton X-114 to water, (e) 0.05% (w/v) Triton X-405 to water and (f) 0.05% (w/v) SDS to water.
Electroanalysis, 2003
Three newly synthesized polyanthraquinone derivatives: 7,13-bis(9,10-dioxo-1-anthryl)-1,4,10-trioxa-7,13-diazacyclopentadecane, (AQ)A 2 15C5, 7,16-bis(9,10-dioxo-1-anthryl)-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane, (AQ)A 2 18C6, and tris[(9,10-diokso-1-antryl)-aminoethyl]amine, (AQNet) 3 N, were examined by cyclic and normal pulse voltammetry. All anthraquinone groups in these compounds were electroactive and formed the radicals and dianions similarly to simple anthraquinone. The differences between the voltammograms obtained in the absence and presence of supporting electrolyte are discussed, and the diffusion coefficients of the compounds and the rates of the chemical reactions following the first reduction step were evaluated. (AQNet) 3 N appears to be a good model compound for multi electron transfers in aprotic solvents. It offers two consecutive nearly reversible 3-electron redox systems: 0/À 3 and À 3/À 6. The interactions of the radicals and dianions of the above compounds with alkali metal cations were examined.
Study of natural anthraquinone colorants by EPR and UV/vis spectroscopy
The spectroscopic study was performed on 9,10-anthraquinone derivatives (purpurin, alizarin, carminic acid, and 2-(hydroxymethyl)-9,10-anthraquinone) in dimethylsulfoxide in the presence of triethylamine to bring information on their protonation/deprotonation equilibria in aprotic solvent. An interesting deprotonation effect of 5,5-dimethyl-1-pyrroline N-oxide (a spin trapping agent used in the EPR experiments) was revealed. The quantum chemical calculations enabled the identification of the individual protonated/deprotonated tautomeric forms present in the experimental systems. The UV photoexcitation of hydroxyanthraquinones (HAQ) led to the generation of reactive radical species and singlet oxygen, detected by in situ EPR spectroscopy (spin trapping, nitroxide radical elimination, oxidation of sterically hindered amines). The changes in the electronic absorption spectra upon photoexcitation, linked with the ability of the studied HAQ to generate reactive oxygen species upon exposure, confirm a substantial effect of the substituent character and position on the overall photochemical behavior of the HAQ, significantly influenced by the actual experimental conditions (solvent, pH).
Structural Chemistry, 2013
1-Amino-, 1-ethylamino-, and 1-(diethylamino)anthraquinone were characterized by UV-Vis spectroscopy, acid-base titration, electrochemical methods, and quantumchemical (QM) calculations at the B3LYP/6-31 ??G ** level. Acid-base titration and the relative differences between the free energies of the basic and acidic forms of the studied species show that 1-(diethylamino)anthraquinone is the strongest base in an acetonitrile solution. Moreover, the structural differences between the B3LYP-optimized neutral and protonated anthraquinones, notably the presence or the absence of internal hydrogen bonds, account well for the sequence of the measured/calculated basicity. The basicity of the investigated compounds strongly influences their electrochemical properties in acetonitrile. Indeed, the cyclic voltammograms of 1-aminoanthraquinone and 1-(ethylamino)anthraquinone display two well-resolved reduction waves that indicate a two-step reduction process (EE mechanism). On the other hand, the electroreduction of 1-(diethylamino)anthraquinone becomes complicated by the interaction of its reduced forms with traces of water present in an acetonitrile solution (ECE mechanism). The mechanism of this reaction is proposed, and its possibility to occur is examined based on QM calculations.
2009
This research presents calculations and computation of Anthraquinone-2-sulfonic acid (AQS) electrode potentials in water. For this purpose, the DFT and HF calculation with the 6-31G basis set were utilized. The calculated values were compared with the experimental values obtained by linear sweep voltammetry. The resulting data illustrated that the method was likely to be useful for the prediction of biomolecules electrode potentials in different aprotic solvents.