Lanthanide complexes of adriamycin

We investigated the interactions of the trivalent lanthanides with adriamycin in aqueous solution. In all the cases studied, the complexes were found to have a 1:1 stoichiometry. The complex formation process was found to be pH dependent with a pK_a of about 8.2 which is the pK_a of the amino group of the daunosamine. We also found that self-association of the adriamycin is important in aqueous solution. We analysed all our binding data to take this interaction into account. From an analysis of the temperature dependence of the binding constant we find that the enthalpy for the binding process is near zero while the entropy is about 25 cal K^-1 mol^-1. This result is consistent with the idea that the complex formation results in desolvation of the lanthanide ion.