Interaction of DNA with [Cr(Schiff base)(H<SUB>2</SUB>O)<SUB>2</SUB>]ClO<SUB>4</SUB>

The binding of Schiff base complexes of chromium(III) of the type [Cr(salen)(H<SUB>2</SUB>O)<SUB>2</SUB>]<SUP>+</SUP> and [Cr(salprn)(H<SUB>2</SUB>O)<SUB>2</SUB>]<SUP>+</SUP>, where salen denotes 1,2-bis(salicylideneamino)ethane and salprn denotes 1,3-bis(salicylideneamino)propane to calf thymus DNA has been investigated by absorption, emission, circular dichroism, melting temperature and viscosity measurements. These chromium(III) complexes showed absorption hyperchromicity accompanied by red shift in charge transfer band, fluorescence enhancement, increase in melting temperature, some structural changes in CD spectra and changes in specific viscosity when bound to calf thymus DNA. The binding constant K<SUB>b</SUB> has been determined from absorption measurements for both the complexes and found to be (2.5±0.4)×10<SUP>3</SUP> M<SUP>-1</SUP> for [Cr(salen)(H<SUB>2</SUB>)<SUB>2</SUB>]<SUP>+</SUP> and (1.7±0.3)×10<SUP>4</SUP> M<SUP>-1</SUP> for [Cr(salprn)(H<SUB>2</SUB>O)<SUB>2</SUB>]<SUP>+</SUP>. From the binding stoichiometry of DNA-[Cr(salprn)(H<SUB>2</SUB>O)<SUB>2</SUB>]<SUP>+</SUP>, the number of binding site size has been determined and found to be ten base pairs per bound complex molecule. The chromium(III) complexes also bring about single strand cleavage in plasmid DNA. The experimental results show that the chromium(III) complexes bind to DNA by non-intercalative mode. Major groove binding is the preferred mode of interaction for these Schiff base complexes of chromium(III)