STUDIA UBB CHEMIA, LVII, 1, 2012 (p. 213 - 217) DFT VIBRATIONAL ANALYSIS OF METAL-HYDROPEROXO BLEOMYCIN COMPLEXES RADU SILAGHI-DUMITRESCU  ABSTRACT. As part of our current efforts to understand the mechanisms of oxygen-oxygen bond cleavage in biological metal complexes, density functional theory (DFT) calculations are employed to calculate the vibrational spectra of the Fe(III)-hydroperoxo adduct of bleomycin and of its more stable cognate Co(III)-hydroperoxo, as models for the ABLM form of bleomycin thought to be key in its biological activity. In addition to bleomycin, we examine another Fe(III)-hydroperoxo complex, [Fe(III)(N4Py)(OOH)] 2+ . The theoretical predictions show errors of 20-100 cm -1 with respect to experiment, and reproduce some of the experimental trends, with the important observation that the vibrational modes are far more complex than usually assumed. Key words: bleomycin, cobalt, iron, DFT, vibrational spectrum INTRODUCTION Bleomycin is a drug whose action involves chelating a metal center and then damaging DNA within living cells. A key intermediate in bleomycin’s anti-DNA action is a species known as activated bleomycin, ABLM, which, on the basis of spectroscopic and theoretical studies, appears well described as a bleomycin-ferric-hydroperoxo adduct (cf. Figure 1). ABLM’s instability has to some extent precluded detailed structural characterization.[1-3] A somewhat more stable cognate, the Co(III)-hydroperoxo bleomycin adduct, has been characterized spectroscopically, and its inferred structural features appear very similar to those of ABLM.[4-12] The reactivity of the Fe-O-OH moiety is central to bleomycin’s therapeutic activity. Arguably, the most direct spectroscopic probe available to date for bonding in metal-hydroperoxo bleomycin adducts is vibrational spectroscopy. Although vibrational data is not available for the Fe-O-OH modes in ABLM, a detailed vibrational analysis of Co(III)-hydroperoxo bleomycin has recently been reported.[5,6] Here, we attempt to employ density functional (DFT) calculations to calculate the vibrational spectra of Fe(III)-hydroperoxo and Co(III)-hydroperoxo bleomycin. In addition to bleomycin, we examine an  Department of Chemistry, “Babes ,-Bolyai” University, Cluj-Napoca RO-400028, Romania, rsilaghi@chem.ubbcluj.ro