Interaction of the La3+-morin complex with DNA

The interaction of the La3+-morin complex with DNA has been examined using fluorescence and absorption spectroscopic as well as viscosity measurement methods. The fluorescence intensity of La3+-morin complex could be highly enhanced by DNA. In the presence of DNA the absorption wavelength or fluorescence excitation wavelength showed a red shift of 43-45 nm, while the emission wavelength remained unchanged, consistent with groove binding of fluorescent dye with DNA. In contrast to intercalators, the complex showed an enhanced stacking effect, based on a viscometer measurement, on base pairs of DNA. The presence of both NaCl and phosphate showed a strong quenching effect on the fluorescence of the ternary system. This is also in favor of groove binding. Thus, groove binding rather than intercalation of the complex to DNA was suggested. Binding of the complex into a DNA narrow minor groove imposed constrains on free motion of the complex. Therefore, the non-radioactive deactivation of the excited state of the complex was inhibited and fluorescence enhancement was observed. The enhancement effect of DNA on the fluorescence of La3+-morin complex was used for a quantitative and selective determination of double-stranded DNA. The detction limit was 20 ng/ml.