Spectral and fluorescent study of the interaction of cyanine dyes Cyan 2 and Cyan 45 with DNA

The noncovalent interaction of the cyanine dyes Cyan 2 and Cyan 45 with DNA (in a pH 7 phosphate buffer) was studied by spectral and fluorescent methods. Upon titration of dye solutions with a concentrated DNA solution, a drop in the absorption band of the initial dye, a long-wavelength shift, and a rise of the absorption of the dye bound to DNA occur. Simultaneously, a growth of dye fluorescence is observed. Mathematical modeling of the fluorescence growth has been performed on the basis of the formation of one or two types of dye complexes with DNA. The experimental results are adequately described by the model involving one type of the dye-DNA complex. It is shown that Cyan 2 binds to DNA probably as the cis-isomer, whereas Cyan 45 as the trans-isomer.