SPECTROSCOPIC AND BINDING-PROPERTIES OF NEAR-INFRARED TRICARBOCYANINEDYES TO DOUBLE-STRANDED DNA

The noncovalent binding and spectroscopic properties of several near-i nfrared tricarbocyanine dyes with respect to sonicated calf-thymus DNA are reported. The dyes investigated were diethylthiatricarbocyanine i odide (DTTCI), diethyloxatricarbocyanine iodide (DOTCI), and 1,1',3,3, 3',3'-hexamethylindotricarbocyanine iodide (HITCI), which are cationic and possess absorption maxima at 772, 695, and 750 nm, respectively, in DMSO. In buffered aqueous solutions, these dyes demonstrated extens ive ground-state aggregation in aqueous solvents when compared to DMSO . In the presence of double-stranded DNA (dsDNA), the fluorescence emi ssion spectra revealed enhancement ratios of bound-to-free dye ranging from 4.5 for DOTCI to 128 for DTTCI. Spectrophotometric titrations an d Scatchard analyses of the dye-dsDNA complexes yielded nonlinear plot s, suggestive of possible multiple binding sites on the DNA. Viscometr ic titrations of the complexes showed increased solution viscosities f or DTTCI, consistent with an unraveling and lengthening of the dsDNA u pon complexation. Fluorescence lifetime data of the dye-dsDNA complexe s showed longer lifetimes exhibited by these dyes in the presence of t he dsDNA compared with those in solutions with no DNA.