Article ID Journal Published Year Pages File Type
1927044 Archives of Biochemistry and Biophysics 2007 11 Pages PDF
Abstract

Kinetics and equilibria of cyanine dyes thiazole orange (TO) and benzothiazole orange (BO) self-aggregation and binding to CT-DNA are investigated in aqueous solution at 25 °C and pH 7. Absorbance spectra and T-jump experiments reveal that BO forms J-aggregates while TO forms more stable H-aggregates. Fluorescence and absorbance titrations show that TO binds to DNA more tightly than BO. TO stacks externally to DNA for low polymer-to-dye concentration ratios (CP/CD) while dye intercalation occurs for high values of CP/CD. T-jump and stopped-flow experiments performed at high CP/CD agree with reaction scheme D + S ⇆ D,S ⇆ DSI ⇆ DSII where the precursor complex D,S evolves to a partially intercalated complex DSI which converts to the more stable intercalate DSII. Non-electrostatic forces play a major role in D,S stabilization. Last step is similar for both dyes suggesting accommodation of the common benzothiazole residue between base pairs. Experiments using poly(dA-dT)·poly(dA-dT) and poly(dG-dC)·poly(dG-dC) confirm base pair preference for TO.

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