title: 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.
authors.affiliation: Dipartimento di Chimica e Chimica Industriale, Università di Pisa, Pisa, Italy.
authors.forename: Tarita
authors.initials: T
authors.lastname: Biver
authors.forename: Angela
authors.initials: A
authors.lastname: De Biasi
authors.forename: Fernando
authors.initials: F
authors.lastname: Secco
authors.forename: Marcella
authors.initials: M
authors.lastname: Venturini
authors.forename: Sergiy
authors.initials: S
authors.lastname: Yarmoluk
mesh_terms: D000818:Animals; D002232:Carbocyanines / Q000737:chemistry* / Q000494:pharmacology*; D002417:Cattle; D004247:DNA / Q000737:chemistry / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005456:Fluorescent Dyes / Q000494:pharmacology*; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D007364:Intercalating Agents / Q000494:pharmacology*; D007477:Ions; D007700:Kinetics; D008956:Models, Chemical; D009711:Nucleotides / Q000737:chemistry; D011108:Polymers / Q000737:chemistry; D012492:Salts / Q000494:pharmacology; D013050:Spectrometry, Fluorescence; D013696:Temperature; D013816:Thermodynamics; D013950:Thymus Gland / Q000378:metabolism; D013997:Time Factors
chemical_list: D002232:Carbocyanines; C467363:Cyan 40; D005456:Fluorescent Dyes; D007364:Intercalating Agents; D007477:Ions; D009711:Nucleotides; D011108:Polymers; D012492:Salts; D004247:DNA