A proton NMR study of heteroassociation between daunomycin and ethidium bromide in aqueous solution

Heteroassociation between anthracycline antibiotic daunomycin (D) and phena nthridine dye ethidium bromide (E) in aqueous solutions was studied by one- and two-dimensional H-1 NMR spectroscopy (500 MHz). The experimental data were analyzed in terms of a modified statistical-thermodynamic heteroassoci ation model. The model differed from that described earlier by the absence of limitations on the self-association constants of interacting molecules i n a mixed solution. Analytic expressions for determining the NMR parameters of each of the molecular components in a mixed solution were obtained. The equilibrium E-D heteroassociation constant was found to substantially exce ed the homoassociation constants of E and D. The structural and thermodynam ic data showed that the heterocomplex between E and D was largely stabilize d by van der Waals interactions and Ii-bonding between the 3-amino group in E and the 9-MeCO group in D.