Spectroscopic studies on the anticancer antibiotic Altromycin H and the interaction with copper(II) ions

The antitumor antibiotic Altromycin H was studied using electronic absorption (UV–Vis.) and circular dichroism (CD) spectroscopy. The dissociation constants of the phenolic groups on C(5) and C(11) were estimated as p K 1 = 6.7 and p K 2 = 11.8 at 25 °C, respectively, and a complete assignment of the CD and UV–Vis. bands is proposed. The interaction of Cu(II) ions with the Altromycin H has been also investigated by UV–Vis., CD and electron paramagnetic resonance (EPR) spectroscopy. A pH depended stepwise complex formation was observed. At pH < 4 no copper–Altromycin H interactions were detected. At the 4 < pH < 8 the Cu(II) ions coordinate to Altromycin H via the C(4) O and C(5)OH groups atoms of the chromophore ring and the [Cu(AltroH) 2] complex (formation constant, K f, 4.00 ± 0.9 × 10 11 M −2 at 25 °C) is the predominant species. In alkaline solution the hydroxo-bridged complex, [Cu(OH)(AltroH)] 2, is proposed to be as the unique present species.