Spectral-fluorescent properties of new cationic thiacarbocyanine dyes - 3,3'-dimethyl-9-phenylthiacarbocyanine iodide (DPTC) and its analogue, 3,3'-diethyl-9-(2-hydroxy-4-methoxyphenyl)thiacarbocyanine iodide (DMPTC), have been studied. Despite the presence of bulky substituents in the meso -position of the polymethine chain, these dyes in solutions are in the forms of trans- isomers regardless of the solvent polarity. In a phosphate buffer solution, these dyes form noncovalent complexes with DNA. The interaction with DNA proceeds with the formation of dye complexes in both monomeric and aggregated forms and is accompanied by changes in the spectral-fluorescent properties of the dyes. The interaction of monomeric molecules of DPTC and DMPTC with DNA does not lead to a shift of the isomeric equilibrium toward the cis- isomer and proceeds mainly through the trans- isomer. The triplet state of dye molecules bound in a complex with DNA has been studied by flash photolysis. An increase in the melting temperature of DNA indicates the formation of intercalation complexes by the dyes.
thiacarbocyanine dyes, DNA, noncovalent complex, spectral-fluorescent probes, flash photolysis, intercalation
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