COMPLEX-FORMATION BETWEEN GALLIUM(III) AND ADRIAMYCIN IN AQUEOUS-SOLUTIONS

The complex formation between gallium(III) and adriamycin (ADR) was investigated in 0.1m KN03 at 25 °C. With excess concentration of Ga(III) compared to ADR, Ga(III) was found to be coordinated with ADR in the low pH region below about 4.0. The spectrophotometric titration data supported the hypothesis that one proton is released as a result of complexation between Ga(III) and ADR via a 1:1 stoichiometry, and a phenolic oxygen on the ADR is involved. The stability constant of the complex was obtained by two different spectrophotometric methods. First, the absorbance development and pH changes reflecting the release of a proton due to complexation were monitored and the stability constant was estimated using the method of Hildebrand-Reilley. Secondly, ADR was titrated with increasing Ga(III) at constant pH 3.0 and analyzed by the Benesi-Hildebrand method. We took into consideration gallium hydrolysis in the calculation. The stability constants, 1.24 × 108 and 3.06 × 108M−1 obtained by the two different methods, showed good agreement within an order-of-magnitude range. © 1990, The Pharmaceutical Society of Japan. All rights reserved.