Synthesis and DNA binding studies by spectroscopic and PARAFAC methods of a ternary copper(II) complex

A new ternary copper(II) complex, [CU2(DL-Asp)(phen)(3)]SO4 center dot 4H(2)O (Phen = 1,10-phenanthroline, DL-Asp=DL-aspartic acid), has been synthesized and characterized by element analysis, infrared spectra and thermal analysis. Spectroscopic studies, including electronic absorption and fluorescence spectra, and parallel factor analysis (PARAFAC) of fluorescence excitation-emission three-way data array were carried out on the DNA binding modes of the complex. The results suggest that at low molar ratio of the complex to DNA (0.25 at most), the end of four-coordinated Cu(II) of the complex binds to DNA by hydrogen bond, which induces the breakage of the secondary structure of DNA. Otherwise, the six-coordinated Cu(II) end of the complex intercalates into the base pair of DNA. Electrostatic effect also takes place between the complex cation and the phosphate group of DNA. Additionally, the equilibrium concentrations of EB-DNA and EB (EB = ethidium bromide) could be directly obtained by PARAFAC algorithm. The results of PARAFAC also indicate that, the conformation of the DNA is changed from B form to BZ mixed form by the interaction with the complex; EB may interact with BZ-DNA by cooperative binding which has a higher affinity than by intercalation with B-DNA. The PARAFAC algorithm is proved a convincing method for studying the interaction of complexes with DNA. (c) 2006 Elsevier B.V. All rights reserved.