The addition of Ga(III) to an aqueous solution of bleomycin results in the observation of several new peaks in the 1H NMR spectrum, concomitant with the reduction in intensity of several of the peaks of the antibiotic. By measuring the relative intensity of the resonance of the C4 proton of the imidazole at various Ga(III) concentrations, we have found that the Ga(III)- bleomycin complex has a 1:1 stoichoimetry. The lifetime of the Ga(III)-bleomycin complex was found to be ca. 15 s at 343 K (70 °C) from NMR transfer of magnetization and spin-lattice relaxation time measurements. On the basis of a combination of fluorescence binding studies and proton-displacement experiments, we conclude that the binding of Ga(lll) to the bleomycins (As and Bs) displaces a single proton from the -amino group of the diaminopropionamide moiety of the drugs. This evidence implicates this portion of the molecule directly in metal binding.
ASJC Scopus subject areas
- Colloid and Surface Chemistry