| Abstrakt: |
Arrhenius parameters for the reactions of oxidizing hydroxyl radicals and reducing hydrated electrons with cisplatin, transplatin and carboplatin in aqueous solution have been determined using pulsed electron radiolysis and absorption spectroscopy techniques. Under physiological pH and chloride concentration conditions, hydroxyl radical reaction rate constants of (9.99 +/- 0.20) x 10(9), (8.38 +/- 0.55) x 10(9), and (6.03 +/- 0.08) x 10(9) M(-1) s(-1) at 24.0, 20.7 and 24.0 degrees C, respectively, with corresponding activation energies of 12.79 +/- 0.57, 13.88 +/- 1.14, and 14.35 +/- 0.56 kJ mol(-1) for these three reactions, were determined. These oxidations of cisplatin and transplatin to form a Pt(III) transient are significantly faster than reported previously at room temperature. The lower rate constant for carboplatin is consistent with hydroxyl radical reaction partitioning between reaction at the platinum center and the cyclobutanedicarboxylate ligand. The equivalent reductive hydrated electron reaction rate constants measured were (1.99 +/- 0.04) x 10(10) (24.0 degrees C), (1.77 +/- 0.08) x 10(10) (22.0 degrees C), and (8.92 +/- 0.06) x 10(9) M(-1) s(-1) (24.0 degrees C), with corresponding activation energies of 15.75 +/- 1.00, 19.74 +/- 1.82, and 19.99 +/- 0.34 kJ mol(-1). Again, the values determined for cisplatin and transplatin are faster than reported; however, all three values are consistent with direct reduction of the platinum center to form a Pt(I) moiety. |
