The Effects of the pH and the Temperature on the Oxidation-reduction Properties of Adriamycin Adsorbed on a Mercury Electrode Surface

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Abstract
The effects of the pH and the temperature on the oxidation-reduction properties of the quinone moiety in adriamycin adsorbed on a mercury electrode surface have been investigated by means of cyclic d.c. voltammetry. The quinone waves have been fundamentally interpreted in terms of a two-step one-electron surface-redox reaction, even in a neutral or an alkaline solution, where the reduced product is liable to cause the following chemical reaction. The pH dependences of the standard surface-redox potential of the adsorbed adriamycin are −60 mV/pH (pH 2–6), −30 mV/pH (pH 7–8), and −60 mV/pH (pH 9–12). The semiquinone formation constant is 0.15 at pH 2–6 and 5 at pH 9–12. These results can be well explained by considering the protolytic equilibria of the phenolic hydroxyl groups among the oxidized, semiquinone, and reduced forms of adriamycin, the pKa’s of which are 8.53, 6.93, and 6.83 respectively. The thermodynamic constants of the semiquinone formation reaction at pH 4.5 have been determined to be ΔH=−24.6 kJ mol−1 and ΔS=−99.7 J K−1 mol−1.