scholarly journals Probing of the pH-Dependent Redox Mechanism of a Biologically Active Compound, 5,8-Dihydroxynaphthalene-1,4-dione

2014 ◽  
Vol 67 (2) ◽  
pp. 206 ◽  
Author(s):  
Shamsa Munir ◽  
Afzal Shah ◽  
Usman Ali Rana ◽  
Imran Shakir ◽  
Zia-ur-Rehman ◽  
...  
Keyword(s):  
Square Wave Voltammetry ◽  
Reduction Process ◽  
Electrode Reaction ◽  
Biologically Active ◽  
Hydroxyl Group ◽  
General Mechanism ◽  
Semiquinone Radical ◽  
Square Wave ◽  
Wave Voltammetry ◽  
Ph Dependent

The redox behaviour of a potential anticancer organic compound, 5,8-dihydroxynaphthalene-1,4-dione (DND), was investigated in 1 : 1 buffered aqueous ethanol using cyclic, differential pulse, and square wave voltammetry. The redox processes were found to occur in a pH-dependent diffusion-controlled manner. Presence of an α-hydroxyl group stabilised semiquinone radical of DND, formed by the gain of 1 e– and 1 H+, prevented the second step reduction, which is in contrast to the general mechanism previously reported for quinines in protic and aprotic media. In addition, our results supported an independent oxidation and reduction process. Square wave voltammetry provided evidence about the reversible and quasi-reversible nature of oxidation and reduction peaks. Based on the voltammetric results, the electrode reaction mechanism of DND was proposed. Parameters including pKa, transfer coefficient, diffusion coefficient, and electron transfer rate constant were evaluated. The values of pKa obtained from cyclic voltammetry and ultraviolet-visible spectroscopy not only agreed with each other, but also with reported values of structurally related compounds evaluated by other techniques.

Isopotential points in square-wave voltammetry of reversible electrode reactions

2009 ◽  
Vol 74 (10) ◽  
pp. 1489-1501 ◽  
Author(s):  
Marina Zelić ◽  
Milivoj Lovrić
Keyword(s):  
Square Wave Voltammetry ◽  
Electrode Reaction ◽  
Time Model ◽  
Model Calculations ◽  
Square Wave ◽  
Electrode Reactions ◽  
Wave Voltammetry ◽  
Electron Transfer Processes ◽  
Diagnostic Criterion ◽  
First Time

Isopotential points in square-wave voltammetry are described for the first time. Model calculations and real measurements (performed with UO22+ and Eu3+ in perchlorate and bromide solutions, respectively) indicate that such an intersection could be observed when backward components of the net response, resulting from an increase in frequency or reactant concentration, are presented together. The electrode reaction should be fully reversible because quasireversible or slower electron transfer processes give the isopoints only at increasing reactant concentrations but not at increasing square-wave frequencies. The effect could be used as an additional diagnostic criterion for recognition of reversible electrode reactions where products remain dissolved in the electrolyte solution.

scholarly journals Theory of reverse scan square-wave voltammetry influenced by the kinetics of reactant adsorption

2010 ◽  
Vol 8 (3) ◽  
pp. 513-518 ◽  
Author(s):  
Milivoj Lovrić ◽  
Šebojka Komorsky-Lovrić
Keyword(s):  
Rate Constant ◽  
Square Wave Voltammetry ◽  
Electrode Reaction ◽  
Peak Current ◽  
Kinetics Of Adsorption ◽  
Square Wave ◽  
Wave Voltammetry ◽  
Reverse Scan ◽  
The Relationship ◽  
Kinetics Of

AbstractA model of electrode reaction complicated by slow adsorption of the reactant is developed for square-wave voltammetry with inverse scan direction. The relationship between the dimensionless net peak current and the logarithm of dimensionless rate constant of adsorption is a curve with a minimum and a maximum. For this reason the ratio of real net peak current and the square-root of frequency is a non-linear function of the logarithm of frequency and exhibits either a maximum or a minimum. The frequency of extreme serves for the estimation of the rate constant: log(k ads /D 1/2 ) = log(k*ads )crit + 0.5 log f crit , where (k*ads )crit is a critical dimensionless rate constant of adsorption. Square-wave voltammetry is sensitive to the kinetics of adsorption if k ads 2 cm s−1

scholarly journals Theory of Square-Wave Voltammetry of Two-Electron Reduction with the Adsorption of Intermediate

2012 ◽  
Vol 2012 ◽  
pp. 1-7 ◽  
Author(s):  
Milivoj Lovrić ◽  
Šebojka Komorsky-Lovrić
Keyword(s):  
Reaction Mechanism ◽  
Electrode Surface ◽  
Square Wave Voltammetry ◽  
Electrode Reaction ◽  
Square Wave ◽  
Wave Voltammetry ◽  
Adsorbed Intermediate ◽  
The Difference ◽  
Electron Reduction ◽  
Unstable Intermediate

Thermodynamically unstable intermediate of fast and reversible two-electron electrode reaction can be stabilized by the adsorption to the electrode surface. In square-wave voltammetry of this reaction mechanism, the split response may appear if the electrode surface is not completely covered by the adsorbed intermediate. The dependence of the difference between the net peak potentials of the prepeak and postpeak on the square-wave frequency is analyzed theoretically. This relationship can be used for the estimation of adsorption constant.

scholarly journals Theory of Square-Wave Voltammetry of Two-Step Electrode Reaction Using an Inverse Scan Direction

2011 ◽  
Vol 2011 ◽  
pp. 1-6 ◽  
Author(s):  
Milivoj Lovrić ◽  
Šebojka Komorsky-Lovrić
Keyword(s):  
Square Wave Voltammetry ◽  
Electrode Reaction ◽  
Reaction Step ◽  
Square Wave ◽  
Wave Voltammetry ◽  
Kinetically Controlled ◽  
Two Peaks ◽  
Electron Transfers ◽  
Special Case ◽  
Unstable Intermediate

A theory of square-wave voltammetry of two-step electrode reaction with kinetically controlled electron transfers is developed, and a special case of thermodynamically unstable intermediate is analyzed. If the first reaction step is reversible and the second one is quasireversible, the response splits into two peaks if the scan direction is inverted. The separation of these peaks increases with frequency.

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