Cyanine Dyes as Intercalating Agents: Kinetic and Thermodynamic Studies on the DNA/Cyan40 and DNA/CCyan2 Systems

Abstract

The interaction of cyanines with nucleic acids is accompanied by intense changes of their optical properties. Consequently these molecules find numerous applications in biology and medicine. Since no detailed information on the binding mechanism of DNA/cyanine systems is available, a T-jump investigation of the kinetics and equilibria of binding of the cyanines Cyan40 [3-methyl-2-(1,2,6-trimethyl-4(1H)pyridinylidenmethyl)-benzothiazolium ion] and CCyan2 [3-methyl-2-[2-methyl-3-(3-methyl-2(3H)-benzothiazolylidene)-1-propenyl]-benzothiazolium ion] with CT-DNA is performed at 25 degrees C, pH 7 and various ionic strengths. Bathochromic shifts of the dye absorption band upon DNA addition, polymer melting point displacement (DeltaT = 8-10 degrees C), site size determination (n = 2), and stepwise kinetics concur in suggesting that the investigated cyanines bind to CT-DNA primary by intercalation. Measurements with poly(dA-dT).poly(dA-dT) and poly(dG-dC).poly(dG-dC) reveal fair selectivity of CCyan2 toward G-C basepairs. T-jump experiments show two kinetic effects for both systems. The binding process is discussed in terms of the sequence D + S left arrow over right arrow D,S left arrow over right arrow DS(I) left arrow over right arrow DS(II), which leads first to fast formation of an external complex D,S and then to a partially intercalated complex DS(I) which, in turn, converts to DS(II), a more stable intercalate. Absorption spectra reveal that both dyes tend to self-aggregate; the kinetics of CCyan2 self-aggregation is studied by T-jump relaxation and the results are interpreted in terms of dimer formation.

DNA Binding by a New Metallointercalator that Contains a Proflavine Group Bearing a Hanging Chelating Unit

“…This behaviour indicates that D is not able to push the intercalated dye out of the nucleotide cavities, otherwise a fluorescence increase would be observed at the wavelength of 500 nm at which only the D-DNA complex, which is formed according to binding mode 2, is fluorescent. Because it is demonstrated that Cyan40 is intercalated between the base pairs of DNA, [45] the binding mode 2 necessarily should correspond to an intercalative process. This hypothesis was confirmed by the unwinding assay as well as by CD experiments.…”

Complexation of heterocyclic ligands with DNA in aqueous solution

“…The fact that ligand-DNA complexes are formed is detected from the changes in the absorption spectra of the ligand, due to addition of the biopolymer to the ligand solution [8][9][10][11]14]. The nature of the changes occurring in this case is shown in Fig.…”

Repurposing of Anthelminthics as Anticancer Drugs

“…Pyrvinium exhibits a dark-red fluorescent color which yields a higher signal upon interaction with DNA [82,83]. This "light up" effect, the increase of fluorescence intensity upon intracellular binding, is a typical property of DNA intercalators [84,85].…”