Formation of Cu(II)–brazilin complex in the presence of DNA and its activities as chemical nuclease

Brazilin, a traditional medicine for the treatment of pain and inflammation, forms a complex with Cu(II) in the presence as well as the absence of DNA. The Cu(II)–brazilin complex exhibited the strand cleavage activity for the pBR322 supercoiled DNA, converting supercoiled form to nicked form. The presence of various scavengers for the oxygen species suppresses or reduces the cleavage activity of the complex, indicating that the DNA cleavage is oxidative. The binding mode of the Cu(II)–brazilin complex was studied by absorption and CD spectroscopy. While a large metal-to-ligand charge transfer (MLCT) band was apparent when Cu(II) and brazilin was mixed in the presence and absence of DNA, the CD did not show any signal in the same region in the presence of DNA, suggesting a weak interaction between the Cu(II)–brazilin complex and DNA bases.