The antioxidant properties of flavonoids are mediated by their functional hydroxyl groups, which are capable of both chelating redox active metals such as iron, copper and scavenging free radicals. In this paper, the antioxidant vs. prooxidant and DNA protecting properties of baicalein and Cu(II)-baicalein complexes were studied under the conditions of the Copper-Fenton reaction and of the Copper-Ascorbate system. From the relevant EPR spectra, the interaction of baicalein with Cu(II) ions was confirmed, while UV-vis spectroscopy demonstrated a greater stability over time of Cu(II)-baicalein complexes in DMSO than in methanol and PBS and Phosphate buffers. An ABTS study confirmed a moderate ROS scavenging efficiency, at around 37%, for both free baicalein and Cu(II)-baicalein complexes (in the ratios 1:1 and 1:2). The results from absorption titrations are in agreement with those from viscometric studies and confirmed that the binding mode between DNA and both free baicalein and Cu-baicalein complexes, involves hydrogen bonds and van der Waals interactions. The DNA protective effect of baicalein has been investigated by means of gel electrophoresis under the conditions of the Cu-catalyzed Fenton reaction and of the Cu-Ascorbate system. In both cases, it was found that, at sufficiently high concentrations, baicalein offers some protection to cells from DNA damage caused by ROS (singlet oxygen, hydroxyl radicals and superoxide radical anions). Accordingly, baicalein may be useful as a therapeutic agent in diseases with a disturbed metabolism of redox metals such as copper, for example Alzheimer's disease, Wilson's disease and various cancers. While therapeutically sufficient concentrations of baicalein may protect neuronal cells from Cu-Fenton-induced DNA damage in regard to neurological conditions, conversely, in the case of cancers, low concentrations of baicalein do not inhibit the pro-oxidant effect of copper ions and ascorbate, which can, in turn, deliver an effective damage to DNA in tumour cells.

Department of Chemistry Faculty of Natural Sciences Constantine The Philosopher University in Nitra Nitra 949 74 Slovakia

Department of Chemistry Faculty of Sciences University of Hradec Kralove 50005 Hradec Kralove Czech Republic

Department of Chemistry Faculty of Sciences University of Hradec Kralove 50005 Hradec Kralove Czech Republic; Biomedical Research Centre University Hospital in Hradec Kralove Sokolska 581 50005 Hradec Kralove Czech Republic

Department of Condensed Matter Physics Faculty of Science University of P J Safarik Park Angelinum 9 Kosice 040 01 Slovakia

Faculty of Chemical and Food Technology Slovak University of Technology Bratislava 812 37 Slovakia; King Saud University Zoology Department College of Science Riyadh 11451 Saudi Arabia

Fresh Lands Environmental Actions Reading Berkshire RG4 5BE UK

King Saud University Zoology Department College of Science Riyadh 11451 Saudi Arabia

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