[Research on the interaction of Cr(III) complex of genistein with DNA]

The interaction of the Cr(III) complex of genistein (GEN-Cr) with calf thymus DNA (ctDNA) in Tris (pH 7.2) buffer was investigated using UV spectra, DNA melting, fluorescence spectra and viscosity. From the absorption titration experiment, no obvious red shift was found, but the notable hypochromicities were observed. When C(DNA)/C(GEN-Cr) = 3, the pi-pi* transitions of the complex at 272 nm showed a decrease in intensity of 29.1%, which indicated that there was remarkable intercalation between complex and DNA base pairs, involving a strong pi-stacking interacting between them. The binding constant for the complex was K = 1.9 x 10(5) mol x L(-1). From the melting curves of ctDNA in the absence and presence of the complex, the melting temperature of ctDNA was found to increase by 5.5 degrees C from 74 to 79.5 degrees C, owing to the increased stability of the helix in the presence of the complex that was intercalated into the double helix. The complex could emit weak luminescence in Tris buffer. The emission intensity of the complex at 340 nm increased steadily with the addition of ctDNA. The result suggested that the complex got into a hydrophobic environment inside the DNA and avoided the effect of solvent water molecules. The strong interaction of the complex and ctDNA also resulted in greatly enhanced intensity of the resonance light scattering spectra. The emission intensity of DNA-EB system at 600 nm decreased remarkably with increasing the complex concentration, which indicated that the complex could be intercalated into DNA and replace EB from the DNA-EB system. According to the classical Stern-Volmer equation, the quenching plots at 25 and 37 degrees C both appeared approximately linear. These results showed that there was one predominant quenching style in this process. Viscosity experiments were carried out by an Ubbelodhe viscometer at 20.0 (+/- 0.1) degrees C. The relative viscosity of ctDNA increased steadily with the increased in the complex. The result clearly showed that the complex could be intercalated between DNA base pairs, causing an extension of the helix, and thus increased the viscosity of DNA. The results above indicated that there is a relatively strong interaction between the GEN-Cr complex and ctDNA, and the complex could bind ctDNA mainly by intercalation. The research suggested that the GEN-Cr complex may be a promising candidate for anticancer, which deserves further research.